Quantum Physics
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Showing new listings for Thursday, 21 November 2024
- [1] arXiv:2411.12782 [pdf, html, other]
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Title: Multiplexed readout of ultrasensitive bolometersPriyank Singh, András Gunyhó, Heikki Suominen, Giacomo Catto, Florian Blanchet, Qi-Ming Chen, Arman Alizadeh, Aarne Keränen, Jian Ma, Timm Mörstedt, Wei Liu, Mikko MöttonenComments: 7 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Recently, ultrasensitive calorimeters have been proposed as a resource-efficient solution for multiplexed qubit readout in superconducting large-scale quantum processors. However, experiments demonstrating frequency multiplexing of these superconductor-normal conductor-superconductor (SNS) sensors are coarse. To this end, we present the design, fabrication, and operation of three SNS sensors with frequency-multiplexed input and probe circuits, all on a single chip. These devices have their probe frequencies in the range \SI{150}{\mega\hertz} -- \SI{200}{\mega\hertz}, which is well detuned from the heater frequencies of \SI{4.4}{\giga\hertz} -- \SI{7.6}{\giga\hertz} compatible with typical readout frequencies of superconducting qubits. Importantly, we show on-demand triggering of both individual and multiple low-noise SNS bolometers with very low cross talk. These experiments pave the way for multiplexed bolometric characterization and calorimetric readout of multiple qubits, a promising step in minimizing related resources such as the number of readout lines and microwave isolators in large-scale superconducting quantum computers.
- [2] arXiv:2411.12794 [pdf, html, other]
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Title: A Universal Protocol for Quantum-Enhanced Sensing via Information ScramblingBryce Kobrin, Thomas Schuster, Maxwell Block, Weijie Wu, Bradley Mitchell, Emily Davis, Norman Y. YaoSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph)
We introduce a novel protocol, which enables Heisenberg-limited quantum-enhanced sensing using the dynamics of any interacting many-body Hamiltonian. Our approach - dubbed butterfly metrology - utilizes a single application of forward and reverse time evolution to produce a coherent superposition of a "scrambled" and "unscrambled" quantum state. In this way, we create metrologically-useful long-range entanglement from generic local quantum interactions. The sensitivity of butterfly metrology is given by a sum of local out-of-time-order correlators (OTOCs) - the prototypical diagnostic of quantum information scrambling. Our approach broadens the landscape of platforms capable of performing quantum-enhanced metrology; as an example, we provide detailed blueprints and numerical studies demonstrating a route to scalable quantum-enhanced sensing in ensembles of solid-state spin defects.
- [3] arXiv:2411.12797 [pdf, html, other]
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Title: Stabilizer ScarsComments: 17 pages, 12 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat)
Quantum many-body scars are eigenstates in non-integrable isolated quantum systems that defy typical thermalization paradigms, violating the eigenstate thermalization hypothesis and quantum ergodicity. We identify exact analytic scar solutions in a 2 + 1 dimensional lattice gauge theory in a quasi-1d limit as zero-magic stabilizer states. We propose a protocol for their experimental preparation, presenting an opportunity to demonstrate a quantum over classical advantage via simulating the non-equilibrium dynamics of a strongly coupled system. Our results also highlight the importance of magic for gauge theory thermalization, revealing a connection between computational complexity and quantum ergodicity.
- [4] arXiv:2411.12805 [pdf, html, other]
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Title: Thermodynamic limitations on fault-tolerant quantum computingComments: 8 pages, 7 figuresSubjects: Quantum Physics (quant-ph)
We investigate the thermodynamic limits on scaling fault-tolerant quantum computers due to heating from quantum error correction (QEC). Quantum computers require error correction, which accounts for 99.9% of the qubit demand and generates heat through information-erasing processes. This heating increases the error rate, necessitating more rounds of error correction. We introduce a dynamical model that characterizes heat generation and dissipation for arrays of qubits weakly coupled to a refrigerator and identify a dynamical phase transition between two operational regimes: a bounded-error phase, where temperature stabilizes and error rates remain below fault-tolerance thresholds, and an unbounded-error phase, where rising temperatures drive error rates beyond sustainable levels, making fault tolerance infeasible. Applying our model to a superconducting qubit system performing Shor's algorithm to factor 2048-bit RSA integers, we find that current experimental parameters place the system in the bounded-error phase. Our results indicate that, while inherent heating can become significant, this thermodynamic constraint should not limit scalable fault tolerance if current hardware capabilities are maintained as systems scale.
- [5] arXiv:2411.12813 [pdf, html, other]
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Title: Quantum Prometheus: Defying Overhead with Recycled Ancillas in Quantum Error CorrectionComments: 7 pages, 4 figures, 3 tablesSubjects: Quantum Physics (quant-ph)
Quantum error correction (QEC) is crucial for ensuring the reliability of quantum computers. However, implementing QEC often requires a significant number of qubits, leading to substantial overhead. One of the major challenges in quantum computing is reducing this overhead, especially since QEC codes depend heavily on ancilla qubits for stabilizer measurements. In this work, we propose reducing the number of ancilla qubits by reusing the same ancilla qubits for both X- and Z-type stabilizers. This is achieved by alternating between X and Z stabilizer measurements during each half-round, cutting the number of required ancilla qubits in half. This technique can be applied broadly across various QEC codes, we focus on rotated surface codes only and achieve nearly \(25\%\) reduction in total qubit overhead. We also present a few use cases where the proposed idea enables the usage of higher-distance surface codes at a relatively lesser qubit count. Our analysis shows that the modified approach enables users to achieve similar or better error correction with fewer qubits, especially for higher distances (\(d \geq 13\)). Additionally, we identify conditions where the modified code allows for extended distances (\(d + k\)) while using the same or fewer resources as the original, offering a scalable and practical solution for quantum error correction. These findings emphasize the modified surface code's potential to optimize qubit usage in resource-constrained quantum systems.
- [6] arXiv:2411.12835 [pdf, html, other]
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Title: Measuring photon correlation using imperfect detectorsRachel N. Clark, Sam G. Bishop, Joseph K. Cannon, John P. Hadden, Philip R. Dolan, Alastair G. Sinclair, Anthony J. BennettComments: 8 pages, 6 figures including appendixSubjects: Quantum Physics (quant-ph)
Single-photon detectors are ``blind" after the detection of a photon, and thereafter display a characteristic recovery in efficiency, during which the number of undetected photons depends on the statistics of the incident light. We show how the efficiency-recovery, photon statistics and intensity have an interdependent relationship which suppresses a detector's ability to count photons and measure correlations. We also demonstrate this effect with an experiment using $n$ such detectors to determine the $n^{\mathrm{th}}$ order correlation function with pseudothermal light.
- [7] arXiv:2411.12870 [pdf, html, other]
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Title: Enhancement of Microwave to Optical Spin-Based Quantum Transduction via a Magnon ModeComments: 3 figures, 12 pages including supplementary materialSubjects: Quantum Physics (quant-ph)
We propose a new method for converting single microwave photons to single optical sideband photons based on spinful impurities in magnetic materials. This hybrid system is advantageous over previous proposals because (i) the implementation allows much higher transduction rates ($10^{3}$ times faster at the same optical pump Rabi frequency) than state-of the art devices, (ii) high-efficiency transduction is found to happen in a significantly larger space of device parameters (in particular, over $1$ GHz microwave detuning), and (iii) it does not require mode volume matching between optical and microwave resonators. We identify the needed magnetic interactions as well as potential materials systems to enable this speed-up using erbium dopants for telecom compatibility. This is an important step towards realizing high-fidelity entangling operations between remote qubits and will provide additional control of the transduction through perturbation of the magnet.
- [8] arXiv:2411.12894 [pdf, html, other]
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Title: The time-dependent quantum harmonic oscillator: a pedagogical approach via the Lewis-Riesenfeld dynamical invariant methodComments: 19 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Physics Education (physics.ed-ph)
In quantum mechanics courses, students often solve the Schrödinger equation for the harmonic oscillator with time-independent parameters. However, time-dependent quantum harmonic oscillators (TDHOs) are relevant in modeling several problems as, for instance, the description of quantum motion of particles in traps, in shortcuts to adiabaticity, as well as in quantum scalar fields evolving in expanding universes. In the present paper, we discuss, with a pedagogical approach, the TDHO with time-dependent frequency via the Lewis-Riesenfeld dynamical invariant method, revisiting the main steps to obtain the wave function associated with this model, and briefly discussing the relationship between this oscillator and the generation of squeezed states. As examples of pedagogical applications of TDHOs and the Lewis-Riesenfeld method in quantum mechanics courses, we solve the following problems: the calculation of the transition probability associated with a TDHO which undergoes jumps in its frequency, and the analysis of the dynamics of a quantum particle in a Paul trap.
- [9] arXiv:2411.12904 [pdf, html, other]
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Title: Quantum Teleportation with Telecom Photons from Remote Quantum EmittersTim Strobel, Michal Vyvlecka, Ilenia Neureuther, Tobias Bauer, Marlon Schäfer, Stefan Kazmaier, Nand Lal Sharma, Raphael Joos, Jonas H. Weber, Cornelius Nawrath, Weijie Nie, Ghata Bhayani, Caspar Hopfmann, Christoph Becher, Peter Michler, Simone Luca PortalupiSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
The quest for a global quantum internet is based on the realization of a scalable network which requires quantum hardware with exceptional performance. Among them are quantum light sources providing deterministic, high brightness, high-fidelity entangled photons and quantum memories with coherence times in the millisecond range and above. To operate the network on a global scale, the quantum light source should emit at telecommunication wavelengths with minimum propagation losses. A cornerstone for the operation of such a quantum network is the demonstration of quantum teleportation. Here we realize full-photonic quantum teleportation employing one of the most promising platforms, i.e. semiconductor quantum dots, which can fulfill all the aforementioned requirements. Two remote quantum dots are used, one as a source of entangled photon pairs and the other as a single-photon source. The frequency mismatch between the triggered sources is erased using two polarization-preserving quantum frequency converters, enabling a Bell state measurement at telecommunication wavelengths. A post-selected teleportation fidelity of up to 0.721(33) is achieved, significantly above the classical limit, demonstrating successful quantum teleportation between light generated by distinct sources. These results mark a major advance for the semiconductor platform as a source of quantum light fulfilling a key requirement for a scalable quantum network. This becomes particularly relevant after the seminal breakthrough of addressing a nuclear spin in semiconductor quantum dots demonstrating long coherence times, thus fulfilling another crucial step towards a scalable quantum network.
- [10] arXiv:2411.12920 [pdf, html, other]
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Title: Quantum Mini-Apps for Engineering Applications: A Case StudyHoria Mărgărit, Amanda Bowman, Krishnageetha Karuppasamy, Alberto Maldonado-Romo, Vardaan Sahgal, Brian J. McDermottComments: 8 pages, 6 figures, submitted on 2024-10-10 to IEEE Quantum Software and its EngineeringSubjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET)
In this work, we present a case study in implementing a variational quantum algorithm for solving the Poisson equation, which is a commonly encountered partial differential equation in science and engineering. We highlight the practical challenges encountered in mapping the algorithm to physical hardware, and the software engineering considerations needed to achieve realistic results on today's non-fault-tolerant systems.
- [11] arXiv:2411.12942 [pdf, html, other]
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Title: The Influence of Thermal Fluctuations on Bosonic Correlations and the AC Stark Effect in Two-Level Atoms: A Superstatistical PerspectiveComments: 16 pages, 6 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Optics (physics.optics)
We study the influence of thermal fluctuations on the two-time correlation functions of bosonic baths within a superstatistics framework by assuming that fluctuations follow the gamma distribution. We further establish a connection between superstatistics and Tsallis non-additive thermodynamics by introducing a temperature-renormalizing parameter. Our results show that, for an Ohmic model, the system's correlation functions exhibit diverse time-dependent behaviors, with the real and imaginary parts displaying enhancement or suppression depending on temperature and fluctuation strength. Additionally, we analyze the impact of these fluctuations on the quantum master equation of a damped two-level atom coupled to an out-of-equilibrium radiation bath. We demonstrate that while the equation's algebraic structure remains intact, the coupling constants are modified by the fluctuation parameters and cavity volume. Specifically, we observe that the AC Stark effect undergoes significant modifications, with fluctuations influencing the transition between repulsive and attractive energy levels.
- [12] arXiv:2411.12952 [pdf, html, other]
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Title: Optimized four-qubit quantum error correcting code for amplitude damping channelSubjects: Quantum Physics (quant-ph)
Quantum error correction (QEC) is essential for reliable quantum information processing. Targeting a particular error channel, both the encoding and the recovery channel can be optimized through a biconvex optimization to give a high-performance, noise-adapted QEC scheme. We solve the biconvex optimization by the technique of alternating semi-definite programming and identify a new four-qubit code for amplitude damping channel, one major noise in superconducting circuits and a good model for spontaneous emission and energy dissipation. We also construct analytical encoding and recovery channels that are close to the numerically optimized ones. We show that the new code notably outperforms the Leung-Nielsen-Chuang-Yamamoto four-qubit code in terms of the entanglement fidelity over an amplitude damping channel.
- [13] arXiv:2411.13037 [pdf, html, other]
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Title: Machine Learning for Arbitrary Single-Qubit Rotations on an Embedded DeviceMadhav Narayan Bhat, Marco Russo, Luca P. Carloni, Giuseppe Di Guglielmo, Farah Fahim, Andy C. Y. Li, Gabriel N. PerdueSubjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET)
Here we present a technique for using machine learning (ML) for single-qubit gate synthesis on field programmable logic for a superconducting transmon-based quantum computer based on simulated studies. Our approach is multi-stage. We first bootstrap a model based on simulation with access to the full statevector for measuring gate fidelity. We next present an algorithm, named adapted randomized benchmarking (ARB), for fine-tuning the gate on hardware based on measurements of the devices. We also present techniques for deploying the model on programmable devices with care to reduce the required resources. While the techniques here are applied to a transmon-based computer, many of them are portable to other architectures.
- [14] arXiv:2411.13060 [pdf, html, other]
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Title: Entanglement teleportation along a regenerating hamster-wheel graph stateComments: 6 pages, 3 figuresSubjects: Quantum Physics (quant-ph)
We scheme an efficient and reusable approach to quantum teleportation that allows cyclic teleportation of a two-qubit graph state around a quantum hamster wheel -- a ring of qubits entangled as a one-dimensional line prepared on the 20-qubit Quantinuum H1-1 ion-trap quantum processor. The qubits on the ring are periodically measured and reused to achieve a teleportation depth that exceeds the total number of available qubits in the quantum processor. Using the outcomes measured during teleportation, we calculate and apply byproduct operators through dynamic circuits to correct local transformations induced on the teleported state. We evaluate the quality of teleportation by tracing the preserved entanglement and fidelity of the teleported two-qubit graph state from its density matrix. In the real-machine experiments, we demonstrate that 58% of the entanglement of the teleported state is sustained with a measured two-qubit negativity of $0.291\pm0.018$ after three complete revolutions around the hamster wheel, or equivalently, after hopping across 56 qubits. By performing teleportation along a regenerating graph state, our work is a step forward in demonstrating the feasibility of measurement-based quantum computation.
- [15] arXiv:2411.13106 [pdf, html, other]
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Title: Quantum uncertainty of optical coherenceSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
Light is known to exhibit quantum uncertainty in terms of its amplitude, phase, and polarization. However, quantum uncertainty related to coherence, which is also a fundamental physical property of light, has not been considered to date. Here, we formulate and explore the concept of quantum optical coherence uncertainty. We focus on the first-order coherence of the simplest possible light field, a purely monochromatic plane wave, which is classically completely stable. Starting from a scalar treatment, we show that the field displays zero coherence uncertainty only for a number state. We then proceed to the vectorial regime and establish that any state leads to coherence fluctuations, governed by a set of uncertainty relations depending on the polarization state and space-time points. Our work thus provides fundamental insights into the quantum character of optical coherence, with potential benefits in applications using highly sensitive interferometric and polarimetric techniques.
- [16] arXiv:2411.13113 [pdf, other]
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Title: Some mathematical issues regarding a new approach towards quantum foundationComments: 12 pagesSubjects: Quantum Physics (quant-ph)
In this article the weakest possible theorem giving a foundation behind the Hilbert space formalism of quantum theory is stated. The necessary postulates are formulated, and the mathematics is spelled out in details. It is argued that, from this approach, a general epistemic interpretation of quantum mechanics is natural. Some applications to the Bell experiment and to decision theory are briefly discussed. The article represents the conclusion of a series of articles and books on quantum foundation.
- [17] arXiv:2411.13114 [pdf, html, other]
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Title: Quantum versatility in PageRankComments: 12pagesJournal-ref: Phys. Rev. Research 6, 043163 (2024)Subjects: Quantum Physics (quant-ph); Physics and Society (physics.soc-ph)
Quantum mechanics empowers the emergence of quantum advantages in various fields, including quantum algorithms. Quantum PageRank is a promising tool for a future quantum internet. Recently, arbitrary phase rotations (APR) have been introduced in the underlying Szegedy's quantum walk of quantum PageRank algorithm. In this work, we thoroughly study the role APR plays in quantum PageRank. We discover the versatility resulting from quantumness. Specifically, we discover the emergence of a cluster phenomenon in rankings considering the rotation phases, i.e. the existence of similar clusters in the distribution of the rankings and their fidelity with the corresponding classical PageRanks, the ranking distribution variance, the coherence and entanglement of PageRank states, and the power law parameter in the ranking distributions on a scale-free network concerning the two rotation phases. Furthermore, we propose an alternate quantum PageRank with APR which provides an extra tunnel for the analysis of PageRank. We also study the PageRank on the trackback graph of a scale-free graph for the investigation of network information traffic tracking. We demonstrate the rich cluster diversity formed in our alternate quantum PageRank, which offers a novel perspective on the quantum versatility of PageRank. Our results present the quantum-enabled perspective for PageRanking and shed light on the design and application of practical quantum PageRank algorithms.
- [18] arXiv:2411.13142 [pdf, html, other]
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Title: Measurement-free code-switching for low overhead quantum computation using permutation invariant codesComments: 11 pages, two sidesSubjects: Quantum Physics (quant-ph)
Transversal gates on quantum error correction codes have been a promising approach for fault-tolerant quantum computing, but are limited by the Eastin-Knill no-go theorem. Existing solutions like gate teleportation and magic state distillation are resource-intensive. We present a measurement-free code-switching protocol for universal quantum computation, switching between a stabiliser code for transversal Cliffords and a permutation-invariant code for transversal non-Cliffords that are logical $Z$ rotations for any rational multiple of $\pi$. The novel non-Clifford gates enabled by this code-switching protocol enable implementation of a universal gate set more efficient than the Clifford$+T$ gate set. To achieve this, we present a protocol for performing controlled-NOTs between the codes using near-term quantum control operations that employ a catalytic bosonic mode.
- [19] arXiv:2411.13155 [pdf, html, other]
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Title: On algebraic analysis of Baker-Campbell-Hausdorff formula for Quantum Control and Quantum Speed LimitComments: 27 pages, 2 figures. In order to make the paper as accessible as possible, we have added a bit lengthy appendicesSubjects: Quantum Physics (quant-ph)
The necessary time required to control a many-body quantum system is a critically important issue for the future development of quantum technologies. However, it is generally quite difficult to analyze directly, since the time evolution operator acting on a quantum system is in the form of time-ordered exponential. In this work, we examine the Baker-Campbell-Hausdorff (BCH) formula in detail and show that a distance between unitaries can be introduced, allowing us to obtain a lower bound on the control time. We find that, as far as we can compare, this lower bound on control time is tighter (better) than the standard quantum speed limits. This is because this distance takes into account the algebraic structure induced by Hamiltonians through the BCH formula, reflecting the curved nature of operator space. Consequently, we can avoid estimates based on shortcuts through algebraically impossible paths, in contrast to geometric methods that estimate the control time solely by looking at the target state or unitary operator.
- [20] arXiv:2411.13158 [pdf, html, other]
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Title: Cooperative quantum interface for noise mitigation in quantum networksYan-Lei Zhang, Ming Li, Xin-Biao Xu, Chun-Hua Dong, Guang-Can Guo, Ze-Liang Xiang, Chang-Ling Zou, and Xu-Bo ZouComments: 7 pages, 3 figuresSubjects: Quantum Physics (quant-ph)
Quantum frequency converters that enable the interface between the itinerant photons and qubits are indispensable for realizing long-distance quantum network. However, the cascaded connection between converters and qubits usually brings additional insertion loss and intermediate noises. Here, we propose a cooperative quantum interface (CQI) that integrates the converter and qubit coupling into a single device for efficient long-distance entanglement generation. Compared to traditional cascaded systems, our scheme offers several advantages, including compactness, reduced insertion loss, and suppression of noise from intermediate modes. We prove the excellent performance over the separated devices by about two orders of magnitude for the entangled infidelity of two remote nodes. Moreover, we discuss an extended scheme for multiple remote nodes, revealing an exponential advantage in performance as the number of nodes increases. The cooperative effect is universal that can be further applied to multifunctional integrated quantum devices. This work opens up novel prospects for quantum networks, distributed quantum computing, and sensing.
- [21] arXiv:2411.13160 [pdf, html, other]
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Title: Fundamental limits of free-space microwave-to-optical frequency conversion efficiency using Rydberg atomsComments: 6 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
Efficient microwave-to-optical frequency conversion (MOC) is crucial for applications such as radiometry, electrometry, quantum microwave illumination and quantum networks. Rydberg atoms provide a unique platform for realizing free-space MOC, promising wide-bandwidth, scalable, and flexible quantum interfaces. Here, we develop a theoretical framework to evaluate the system conversion efficiency, accounting for the mismatch between microwave and optical wavelengths comparing with the atomic ensemble size. Our analysis reveals that the conversion efficiency is fundamentally limited by the focusing of the free-space microwave field, with an upper bound of about 3/16 for diffraction-limited focusing. We propose using a microwave near-field antenna to overcome this limit. Our work provides a foundation for assessing and optimizing free-space MOC, paving the way for a variety of applications based on free-space MOC.
- [22] arXiv:2411.13161 [pdf, html, other]
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Title: A universal framework for the quantum simulation of Yang-Mills theoryComments: 42 pages, 6 figures, 1 tableSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Lattice (hep-lat)
We provide a universal framework for the quantum simulation of SU(N) Yang-Mills theories on fault-tolerant digital quantum computers adopting the orbifold lattice formulation. As warm-up examples, we also consider simple models, including scalar field theory and the Yang-Mills matrix model, to illustrate the universality of our formulation, which shows up in the fact that the truncated Hamiltonian can be expressed in the same simple form for any N, any dimension, and any lattice size, in stark contrast to the popular approach based on the Kogut-Susskind formulation. In all these cases, the truncated Hamiltonian can be programmed on a quantum computer using only standard tools well-established in the field of quantum computation. As a concrete application of this universal framework, we consider Hamiltonian time evolution by Suzuki-Trotter decomposition. This turns out to be a straightforward task due to the simplicity of the truncated Hamiltonian. We also provide a simple circuit structure that contains only CNOT and one-qubit gates, independent of the details of the theory investigated.
- [23] arXiv:2411.13166 [pdf, html, other]
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Title: Making Quantum Collision Models ExactComments: 17 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
Quantum collision describe open quantum systems through repeated interactions with a coarse-grained environment. However, a complete certification of these models is lacking, as no complete error bounds on the simulation of system observables have been established. Here, we show that Markovian and non-Markovian collision models can be recovered analytically from chain mapping techniques starting from a general microscopic Hamiltonian. This derivation reveals a previously unidentified source of error -- induced by an unfaithful sampling of the environment -- in dynamics obtained with collision models that can become dominant for small but finite time-steps. With the complete characterization of this error, all collision models errors are now identified and quantified, which enables the promotion of collision models to the class of numerically exact methods. To confirm the predictions of our equivalence results, we implemented a non-Markovian collision model of the Spin Boson Model, and identified, as predicted, a regime in which the collision model is fundamentally inaccurate.
- [24] arXiv:2411.13190 [pdf, html, other]
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Title: Ab-initio approach to Many-Body Quantum Spin DynamicsComments: 12 pages, 9 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
A fundamental longstanding problem in studying spin models is the efficient and accurate numerical simulation of the long-time behavior of larger systems. The exponential growth of the Hilbert space and the entanglement accumulation at long times pose major challenges for current methods. To address these issues, we employ the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) framework to simulate the many-body spin dynamics of the Heisenberg model in various settings, including the Ising and XYZ limits with different interaction ranges and random couplings. Benchmarks with analytical and exact numerical approaches show that ML-MCTDH accurately captures the time evolution of one- and two-body observables in both one- and two-dimensional lattices. A comparison of ML-MCTDH with the discrete truncated Wigner approximation (DTWA) demonstrates that our approach excels in handling anisotropic models and consistently provides better results for two-point observables in all simulation instances. Our results indicate that the multilayer structure of ML-MCTDH is a promising numerical framework for handling the dynamics of generic many-body spin systems.
- [25] arXiv:2411.13225 [pdf, html, other]
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Title: Quantum Kernel-Based Long Short-term MemorySubjects: Quantum Physics (quant-ph); Artificial Intelligence (cs.AI)
The integration of quantum computing into classical machine learning architectures has emerged as a promising approach to enhance model efficiency and computational capacity. In this work, we introduce the Quantum Kernel-Based Long Short-Term Memory (QK-LSTM) network, which utilizes quantum kernel functions within the classical LSTM framework to capture complex, non-linear patterns in sequential data. By embedding input data into a high-dimensional quantum feature space, the QK-LSTM model reduces the reliance on large parameter sets, achieving effective compression while maintaining accuracy in sequence modeling tasks. This quantum-enhanced architecture demonstrates efficient convergence, robust loss minimization, and model compactness, making it suitable for deployment in edge computing environments and resource-limited quantum devices (especially in the NISQ era). Benchmark comparisons reveal that QK-LSTM achieves performance on par with classical LSTM models, yet with fewer parameters, underscoring its potential to advance quantum machine learning applications in natural language processing and other domains requiring efficient temporal data processing.
- [26] arXiv:2411.13274 [pdf, html, other]
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Title: Optimization of two-photon absorption for three-level atomComments: 16 pages, 14 figuresSubjects: Quantum Physics (quant-ph)
This work discusses the problem of optimal excitation of a three-level atom of ladder-configuration by light in the two-photon state and coherent light carrying an average of two photons. The applied atom-light interaction model is based on the Wigner-Weisskopf approximation. We characterize the properties of the optimal two-photon state that excites an atom perfectly, i.e. with probability equal to one: We find that the spectro-temporal shape of the optimal state of light is determined by the lifetimes of the atomic states, with the degree of photonic entanglement in the optimal state depends on the lifetime ratio. In consequence, two distinct interaction regimes can be identified in which the entanglement of the input state of light has qualitatively different impact.
As the optimal states may be challenging to prepare in general, we compare the results with those obtained for photon pairs of selected experimentally-relevant pulse shapes. As these shapes are optimized for maximal atomic excitation probability, the results can be interpreted in terms of the overlap between the optimal and investigated pulse shapes. - [27] arXiv:2411.13313 [pdf, html, other]
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Title: Anomalous dependence of sensitivity on observation time induced by time crystal orderSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
In this letter, we consider a composite atom-cavity system interacting with a ring resonator. In such a system, time crystal regime can be observed. We show that this regime can lead to a quadratic observation time dependence of the system's sensitivity to perturbations due to ability to retain the memory of the atom's initial state. Outside the time crystal regime, the system is not able to retain the memory of the atom's initial state and the sensitivity scales linearly on the observation time. Our results open up a new way for implementation of discrete time crystals in sensing and metrology.
- [28] arXiv:2411.13349 [pdf, html, other]
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Title: Multicomponent cat states with sub-Planck structures and their optomechanical analoguesComments: 13 pages, 12 figuresSubjects: Quantum Physics (quant-ph)
We investigate the superposition of coherent states, emphasizing quantum states with distinct Wigner phase-space features relevant to quantum information applications. In this study, we introduce generalized versions of the compass state, which display enhanced phase-space characteristics compared to the conventional compass state, typically a superposition of four coherent states. Our findings reveal that, unlike sub-Planck structures and phase-space sensitivity of the compass state, these generalized states produce isotropic sub-Planck structures and sensitivity to phase-space displacements. We demonstrate that these desirable phase-space characteristics are maintained in superpositions comprising at least six distinct coherent states. Furthermore, we show that increasing the number of coherent states in the superposition preserves these characteristics, provided the number remains even. Finally, we examine an optomechanical system capable of generating the proposed quantum states, resulting in optomechanical counterparts with nearly identical phase-space structures, thereby suggesting the feasibility of physically realizing these generalized compass states.
- [29] arXiv:2411.13401 [pdf, html, other]
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Title: Quantum reservoir computing in atomic latticesSubjects: Quantum Physics (quant-ph)
Quantum reservoir computing (QRC) exploits the dynamical properties of quantum systems to perform machine learning tasks. We demonstrate that optimal performance in QRC can be achieved without relying on disordered systems. Systems with all-to-all topologies and random couplings are generally considered to minimize redundancies and enhance performance. In contrast, our work investigates the one-dimensional Bose-Hubbard model with homogeneous couplings, where a chaotic phase arises from the interplay between coupling and interaction terms. Interestingly, we find that performance in different tasks can be enhanced either in the chaotic regime or in the weak interaction limit. Our findings challenge conventional design principles and indicate the potential for simpler and more efficient QRC implementations tailored to specific tasks in Bose-Hubbard lattices.
- [30] arXiv:2411.13421 [pdf, html, other]
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Title: Theory-independent monitoring of the decoherence of a superconducting qubit with generalized contextualityComments: 15 pages, 9 figuresSubjects: Quantum Physics (quant-ph)
Characterizing the nonclassicality of quantum systems under minimal assumptions is an important challenge for quantum foundations and technology. Here we introduce a theory-independent method of process tomography and perform it on a superconducting qubit. We demonstrate its decoherence without assuming quantum theory or trusting the devices by modelling the system as a general probabilistic theory. We show that the superconducting system is initially well-described as a quantum bit, but that its realized state space contracts over time, which in quantum terminology indicates its loss of coherence. The system is initially nonclassical in the sense of generalized contextuality: it does not admit of a hidden-variable model where statistically indistinguishable preparations are represented by identical hidden-variable distributions. In finite time, the system becomes noncontextual and hence loses its nonclassicality. Moreover, we demonstrate in a theory-independent way that the system undergoes non-Markovian evolution at late times. Our results extend theory-independent tomography to time-evolving systems, and show how important dynamical physical phenomena can be experimentally monitored without assuming quantum theory.
- [31] arXiv:2411.13437 [pdf, html, other]
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Title: Improved fluxonium readout through dynamic flux pulsingTaryn V. Stefanski, Figen Yilmaz, Eugene Y. Huang, Martijn F.S. Zwanenburg, Siddharth Singh, Siyu Wang, Lukas J. Splitthoff, Christian Kraglund AndersenComments: 9 pages, 6 figures, 1 tableSubjects: Quantum Physics (quant-ph)
The ability to perform rapid, high fidelity readout of a qubit state is an important requirement for quantum algorithms and, in particular, for enabling operations such as mid-circuit measurements and measurement-based feedback for error correction schemes on large quantum processors. The growing interest in fluxonium qubits, due to their long coherence times and high anharmonicity, merits further attention to reducing the readout duration and measurement errors. We find that this can be accomplished by exploiting the flux tunability of fluxonium qubits. In this work, we experimentally demonstrate flux-pulse-assisted readout, as proposed in Phys. Rev. Applied 22, 014079 (this https URL), in a setup without a quantum-limited parametric amplifier. Increasing the dispersive shift magnitude by almost 20% through flux pulsing, we achieve an assignment fidelity of 94.3% with an integration time of 280 ns. The readout performance is limited by state initialization, but we find that the limit imposed only by the signal-to-noise ratio corresponds to an assignment fidelity of 99.9% with a 360 ns integration time. We also verify these results through simple semi-classical simulations. These results constitute the fastest reported readout of a fluxonium qubit, with the prospect of further improvement by incorporation of a parametric amplifier in the readout chain to enhance measurement efficiency.
- [32] arXiv:2411.13468 [pdf, other]
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Title: Benchmarking Quantum Convolutional Neural Networks for Classification and Data Compression TasksComments: 3 pages, 2 figuresSubjects: Quantum Physics (quant-ph)
Quantum Convolutional Neural Networks (QCNNs) have emerged as promising models for quantum machine learning tasks, including classification and data compression. This paper investigates the performance of QCNNs in comparison to the hardware-efficient ansatz (HEA) for classifying the phases of quantum ground states of the transverse field Ising model and the XXZ model. Various system sizes, including 4, 8, and 16 qubits, through simulation were examined. Additionally, QCNN and HEA-based autoencoders were implemented to assess their capabilities in compressing quantum states. The results show that QCNN with RY gates can be trained faster due to fewer trainable parameters while matching the performance of HEAs.
- [33] arXiv:2411.13469 [pdf, html, other]
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Title: Information scrambling and entanglement dynamics in Floquet Time CrystalsComments: 9 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
We study the dynamics of out-of-time-ordered correlators (OTOCs) and entanglement of entropy as quantitative measures of information propagation in disordered many-body systems exhibiting Floquet time-crystal (FTC) phases. We find that OTOC spreads in the FTC with different characteristic timescales due to the existence of a preferred ``quasi-protected'' direction - denoted as $\ell$-bit direction - along which the spins stabilize their period-doubling magnetization for exponentially long times. While orthogonal to this direction the OTOC thermalizes as an usual MBL time-independent system (at stroboscopic times), along the $\ell$-bit direction the system features a more complex structure. The scrambling appears as a combination of an initially frozen dynamics (while in the stable period doubling magnetization time window) and a later logarithmic slow growth (over its decoherence regime) till full thermalization. Interestingly, in the late time regime, since the wavefront propagation of correlations has already settled through the whole chain, scrambling occurs at the same rate regardless of the distance between the spins, thus resulting in an overall envelope-like structure of all OTOCs, independent of their distance, merging into a single growth. Alongside, the entanglement entropy shows a logarithmic growth over all time, reflecting the slow dynamics up to a thermal volume-law saturation.
- [34] arXiv:2411.13471 [pdf, html, other]
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Title: Superclassical non-Markovian open quantum dynamicsComments: 11 pagesSubjects: Quantum Physics (quant-ph)
We characterize a class of superclassical non-Markovian open quantum system dynamics that are defined by their lack of measurement invasiveness when the corresponding observable commutates with the pre-measurement state. This diagonal non-invasiveness guarantees that joint probabilities for measurement outcomes fulfill classical Kolmogorov consistency conditions. These features are fulfilled regardless of the previous (measurement) system history and are valid at arbitrary later times after an arbitrary system initialization. It is shown that a subclass of depolarizing dynamics, which are based on a (time-irreversible) non-unitary system-environment coupling, satisfy the required properties. The relationship with other operational [Milz et al., Phys. Rev. X 10, 041049 (2020)] and non-operational [Banacki et al., Phys. Rev. A 107, 032202 (2023)] notions of classicality in non-Markovian open quantum systems is studied in detail and exemplified through different examples.
- [35] arXiv:2411.13509 [pdf, html, other]
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Title: Degenerate quantum erasure decodingComments: 21 pages, 20 figures, 4 tablesSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT)
Erasures are the primary type of errors in physical systems dominated by leakage errors. While quantum error correction (QEC) using stabilizer codes can combat these error, the question of achieving near-capacity performance with explicit codes and efficient decoders remains a challenge. Quantum decoding is a classical computational problem that decides what the recovery operation should be based on the measured syndromes. For QEC, using an accurate decoder with the shortest possible runtime will minimize the degradation of quantum information while awaiting the decoder's decision. We examine the quantum erasure decoding problem for general stabilizer codes and present decoders that not only run in linear-time but are also accurate. We achieve this by exploiting the symmetry of degenerate errors. Numerical evaluations show near maximum-likelihood decoding for various codes, achieving capacity performance with topological codes and near-capacity performance with non-topological codes. We furthermore explore the potential of our decoders to handle other error models, such as mixed erasure and depolarizing errors, and also local deletion errors via concatenation with permutation invariant codes.
- [36] arXiv:2411.13520 [pdf, html, other]
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Title: Quantum Attention for Vision Transformers in High Energy PhysicsAlessandro Tesi, Gopal Ramesh Dahale, Sergei Gleyzer, Kyoungchul Kong, Tom Magorsch, Konstantin T. Matchev, Katia MatchevaComments: 9 pages, 7 figuresSubjects: Quantum Physics (quant-ph); Machine Learning (cs.LG); High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph)
We present a novel hybrid quantum-classical vision transformer architecture incorporating quantum orthogonal neural networks (QONNs) to enhance performance and computational efficiency in high-energy physics applications. Building on advancements in quantum vision transformers, our approach addresses limitations of prior models by leveraging the inherent advantages of QONNs, including stability and efficient parameterization in high-dimensional spaces. We evaluate the proposed architecture using multi-detector jet images from CMS Open Data, focusing on the task of distinguishing quark-initiated from gluon-initiated jets. The results indicate that embedding quantum orthogonal transformations within the attention mechanism can provide robust performance while offering promising scalability for machine learning challenges associated with the upcoming High Luminosity Large Hadron Collider. This work highlights the potential of quantum-enhanced models to address the computational demands of next-generation particle physics experiments.
- [37] arXiv:2411.13523 [pdf, html, other]
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Title: Quantum gravitational decoherence of a mechanical oscillator from spacetime fluctuationsComments: Comments are welcomeSubjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
We consider the scenario of a fluctuating spacetime due to a deformed commutation relation with a fluctuating deformation parameter, or to a fluctuating metric tensor. By computing the resulting dynamics and averaging over these fluctuations, we find that a system experiences a decoherence in the momentum basis. We studied the predictions of the model for a free particle and an harmonic oscillator. Using experimental data taken from a mechanical oscillator prepared in quantum states of motion, we put a bound on the free parameters of the considered model. In addition, we comment on how these measurements can also provide bounds to other phenomenological quantum gravity models, such as the length scale for nonlocal dynamics.
New submissions (showing 37 of 37 entries)
- [38] arXiv:2411.12806 (cross-list from hep-th) [pdf, html, other]
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Title: D-commuting SYK model: building quantum chaos from integrable blocksComments: 26 pages plus appendix, 16 figures, 2 tablesSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We construct a new family of quantum chaotic models by combining multiple copies of integrable commuting SYK models. As each copy of the commuting SYK model does not commute with others, this construction breaks the integrability of each commuting SYK and the family of models demonstrates the emergence of quantum chaos. We study the spectrum of this model analytically in the double-scaled limit. As the number of copies tends to infinity, the spectrum becomes compact and equivalent to the regular SYK model. For finite $d$ copies, the spectrum is close to the regular SYK model in UV but has an exponential tail $e^{E/T_c}$ in the IR. We identify the reciprocal of the exponent in the tail as a critical temperature $T_c$, above which the model should be quantum chaotic. $T_c$ monotonically decreases as $d$ increases, which expands the chaotic regime over the non-chaotic regime. We propose the existence of a new phase around $T_c$, and the dynamics should be very different in two phases. We further carry out numeric analysis at finite $d$, which supports our proposal.
Given any finite dimensional local Hamiltonian, by decomposing it into $d$ groups, in which all terms in one group commute with each other but terms from different groups may not, our analysis can give an estimate of the critical temperature for quantum chaos based on the decomposition. We also comment on the implication of the critical temperature to future quantum simulations of quantum chaos and quantum gravity. - [39] arXiv:2411.12816 (cross-list from nucl-th) [pdf, html, other]
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Title: Intertwined Quantum Phase Transitions in Bose and Bose-Fermi SystemsComments: 18 pages, 13 figures, talk at Symposium "Symmetries in Science XIX", July 30 - August 4, 2023, Bregenz, AustriaSubjects: Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Pronounced structural changes within individual configurations (Type I QPT), superimposed on an abrupt crossing of these configurations (Type II QPT), define the notion of intertwined quantum phase transitions (QPTs). We discuss and present evidence for such a scenario in finite Bose and Bose-Fermi systems. The analysis is based on algebraic models with explicit configuration mixing, where the two types of QPTs describe shape-phase transitions in-between different dynamical symmetries and shape-coexistence with crossing.
- [40] arXiv:2411.12997 (cross-list from gr-qc) [pdf, html, other]
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Title: Gravitational entanglement witness through Einstein ring imageComments: 46 pages, 16 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
We investigate the interplay between quantum theory and gravity by exploring gravitational lensing and Einstein ring images in a weak gravitational field induced by a mass source in spatial quantum superposition. We analyze a quantum massless scalar field propagating in two distinct models of gravity: the first quantized Newtonian gravity (QG) model, which generates quantum entanglement between the mass source and other systems, and the Schrödinger-Newton (SN) gravity model, which does not produce entanglement. Visualizing the two-point correlation function of the scalar field, we find that the QG model produces a composition of multiple Einstein rings, reflecting the spatial superposition of the mass source. By contrast, the SN model yields a single deformed ring image, representing a classical spacetime configuration. Furthermore, we introduce a specific quantity named the which-path information indicator and visualize its image. The QG model again reveals multiple Einstein rings, while the image intensity in the SN model notably vanishes. Our findings provide a visual approach to witness gravity-induced entanglement through distinct features in Einstein ring images. This study advances our understanding of quantum effects in general relativistic contexts and establishes a foundation for future studies of other relativistic phenomena.
- [41] arXiv:2411.13031 (cross-list from cond-mat.mes-hall) [pdf, html, other]
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Title: Two-terminal transport in biased lattices: transition from ballistic to diffusive currentComments: 5 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We analyze quantum transport of charged fermionic particles in the tight-binding lattice connecting two particle reservoirs (the leads). If the lead chemical potentials are different they create an electric field which tilts the lattice. We study the effect of this tilt on quantum transport in the presence of weak relaxation/decoherence processes in the lattice. It is shown that the Landauer ballistic transport regime for a weak tilt (small chemical potential difference) changes to the diffusive Esaki-Tsu transport regime for a strong tilt (large chemical potential difference), where the critical tilt for this crossover is determined by the condition that the Wannier-Stark localization length coincides with the lattice length.
- [42] arXiv:2411.13046 (cross-list from physics.optics) [pdf, html, other]
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Title: Active Stabilization of Laser Diode Injection Using a Polarization-Spectroscopy TechniqueSubjects: Optics (physics.optics); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
Laser diode injection-locking is a commonly used method to amplify laser light, while preserving its spectral properties. Fluctuations in the environmental conditions can cause injection-locking to fail, especially when operating with low seed powers or with a swept seed frequency. We present a method inspired by the Hänsch-Couillaud scheme to monitor and actively stabilize the conditions required for injection-locking a laser diode. Using only a few optical components, our scheme can run continuously in the background and is modulation-free. We demonstrate its efficacy by showing its robustness to large fluctuations in diode temperature, seed frequency and power, effectively extending the reliable operating range and stability over time.
- [43] arXiv:2411.13087 (cross-list from cond-mat.mes-hall) [pdf, html, other]
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Title: Time-resolved diamond magnetic microscopy of superparamagnetic iron-oxide nanoparticlesB. A. Richards, N. Ristoff, J. Smits, A. Jeronimo Perez, I. Fescenko, M. D. Aiello, F. Hubert, Y. Silani, N. Mosavian, M. Saleh Ziabari, A. Berzins, J. T. Damron, P. Kehayias, D. L. Huber, A. M. Mounce, M. P. Lilly, T. Karaulanov, A. Jarmola, A. Laraoui, V. M. AcostaComments: Main text: 8 pages, 5 figures. Entire manuscript including Appendices: 28 pages, 22 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Instrumentation and Detectors (physics.ins-det); Medical Physics (physics.med-ph); Quantum Physics (quant-ph)
Superparamagnetic iron-oxide nanoparticles (SPIONs) are promising probes for biomedical imaging, but the heterogeneity of their magnetic properties is difficult to characterize with existing methods. Here, we perform widefield imaging of the stray magnetic fields produced by hundreds of isolated ~30-nm SPIONs using a magnetic microscope based on nitrogen-vacancy centers in diamond. By analyzing the SPION magnetic field patterns as a function of applied magnetic field, we observe substantial field-dependent transverse magnetization components that are typically obscured with ensemble characterization methods. We find negligible hysteresis in each of the three magnetization components for nearly all SPIONs in our sample. Most SPIONs exhibit a sharp Langevin saturation curve, enumerated by a characteristic polarizing applied field, B_c. The B_c distribution is highly asymmetric, with a standard deviation (1.4 mT) that is larger than the median (0.6 mT). Using time-resolved magnetic microscopy, we directly record SPION Néel relaxation, after switching off a 31 mT applied field, with a temporal resolution of ~60 ms that is limited by the ring-down time of the electromagnet coils. For small bias fields B_{hold}=1.5-3.5 mT, we observe a broad range of SPION Néel relaxation times--from milliseconds to seconds--that are consistent with an exponential dependence on B_{hold}. Our time-resolved diamond magnetic microscopy study reveals rich SPION sample heterogeneity and may be extended to other fundamental studies of nanomagnetism.
- [44] arXiv:2411.13232 (cross-list from cond-mat.mes-hall) [pdf, other]
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Title: Dissipation in quantum tunnel junctionsComments: 10 pages, 9 figuresJournal-ref: J. Appl. Phys. 136, 184401 (2024)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
Based on experimental data, we propose a model to evaluate the energy dissipated during quantum tunneling processes in solid-state junctions. This model incorporates a nonlinear friction force expressed in the general form f(x)={\gamma} v(x)^{\alpha}, where {\gamma} is the frictional coefficient, which is fitted to data. We study this by applying voltages just below the barrier height up to near break down voltages. Furthermore, by lowering the temperature and adjusting the applied voltage to the junction, the effect on dissipation caused by the variation in barrier height is examined. We underline that the crucial dependency of dissipation on the fraction of particle energy lost is modulated by two primary mechanisms: the application of voltage and the variation of temperature. The fraction of energy dissipated decreases in general for increasing energies of the tunneling particles at a given temperature. However, for a given energy of the tunneling particle, the present work demonstrates a turning point at a temperature of 137 K, after which the dissipated energy starts increasing for higher temperatures. The latter can possibly be due to the increase of electron-phonon interactions which become predominant over barrier height reduction at higher temperatures and hence we identify T = 137 K as a critical temperature for change in dissipative characteristics of the solid-state junction under consideration. Notably, also the study identifies significant changes in dissipation parameters, {\gamma} and {\alpha}, above 137 K, exhibiting a linear decline and underscoring the importance of further research at higher temperatures.
- [45] arXiv:2411.13331 (cross-list from physics.optics) [pdf, html, other]
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Title: Versatile photonic frequency synthetic dimensions using a single Mach-Zehnder-interferometer-assisted device on thin-film lithium niobateZhao-An Wang, Xiao-Dong Zeng, Yi-Tao Wang, Jia-Ming Ren, Chun Ao, Zhi-Peng Li, Wei Liu, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Shuang Wang, Jian-Shun Tang, Chuan-Feng Li, Guang-Can GuoSubjects: Optics (physics.optics); Quantum Physics (quant-ph)
Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupling resonators with fixed beam splitters is a common experimental approach, it often lacks tunability and limits coupling between adjacent lattices to sites occupying the same frequency domain positions. Here, on the contrary, we conceive the resonator arrays connected by electro-optic tunable Mach-Zehnder interferometers in our configuration instead of fixed beam splitters. By applying bias voltage and RF modulation on the interferometers, our design extends such coupling to long-range scenario and allows for continuous tuning on each coupling strength and synthetic effective magnetic flux. Therefore, our design enriches controllable coupling types that are essential for building programmable lattice networks and significantly increases versatility. As the example, we experimentally fabricate a two-resonator prototype on the TFLN platform, and on this single chip we realize well-known models including tight-binding lattices, topological Hall ladder and Creutz ladder. We directly observe the band structures in the quasi-momentum space and important phenomena such as spin-momentum locking and the Aharonov-Bohm cage effect. These results demonstrate the potential for convenient simulations of more complex models in our configuration.
- [46] arXiv:2411.13337 (cross-list from hep-th) [pdf, html, other]
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Title: Non-Abelian entanglement asymmetry in random statesComments: 28 pages, 6 figuresSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The entanglement asymmetry measures the extent to which a symmetry is broken within a subsystem of an extended quantum system. Here, we analyse this quantity in Haar random states for arbitrary compact, semi-simple Lie groups, building on and generalising recent results obtained for the $U(1)$ symmetric case. We find that, for any symmetry group, the average entanglement asymmetry vanishes in the thermodynamic limit when the subsystem is smaller than its complement. When the subsystem and its complement are of equal size, the entanglement asymmetry jumps to a finite value, indicating a sudden transition of the subsystem from a fully symmetric state to one devoid of any symmetry. For larger subsystem sizes, the entanglement asymmetry displays a logarithmic scaling with a coefficient fixed by the dimension of the group. We also investigate the fluctuations of the entanglement asymmetry, which tend to zero in the thermodynamic limit. We check our findings against exact numerical calculations for the $SU(2)$ and $SU(3)$ groups. We further discuss their implications for the thermalisation of isolated quantum systems and black hole evaporation.
- [47] arXiv:2411.13393 (cross-list from physics.atom-ph) [pdf, html, other]
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Title: Making molecules by mergoassociation: the role of center-of-mass motionSubjects: Atomic Physics (physics.atom-ph); Chemical Physics (physics.chem-ph); Quantum Physics (quant-ph)
In mergoassociation, two atoms in separate optical traps are combined to form a molecule when the traps are merged. Previous theoretical treatments have considered only the relative motion of the atoms, neglecting coupling to the motion of the center of mass. We develop a theoretical method to include the coupling to center-of-mass motion and consider its consequences for experiments for both weak and strong coupling. We consider the example of RbCs and then extend the treatment to other systems where mergoassociation may be effective, namely RbSr, RbYb and CsYb. We consider the role of the coupling when the traps are anisotropic and the potential use of moveable traps to construct quantum logic gates.
- [48] arXiv:2411.13408 (cross-list from cond-mat.mes-hall) [pdf, html, other]
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Title: Current noise in quantum dot thermoelectric enginesComments: 11 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We theoretically investigate a thermoelectric heat engine based on a single-level quantum dot, calculating average quantities such as current, heat current, output power, and efficiency, as well as fluctuations (noise). Our theory is based on a diagrammatic expansion of the memory kernel together with counting statistics, and we investigate the effects of strong interactions and next-to-leading order tunneling. Accounting for next-to-leading order tunneling is crucial for a correct description when operating at high power and high efficiency, and in particular affect the qualitative behavior of the Fano factor and efficiency. We compare our results with the so-called thermodynamic uncertainty relations, which provide a lower bound on the fluctuations for a given efficiency. In principle, the conventional thermodynamic uncertainty relations can be violated by the non-Markovian quantum effects originating from next-to-leading order tunneling, providing a type of quantum advantage. However, for the specific heat engine realization we consider here, we find that next-to-leading order tunneling does not lead to such violations, but in fact always pushes the results further away from the bound set by the thermodynamic uncertainty relations.
- [49] arXiv:2411.13429 (cross-list from cond-mat.mes-hall) [pdf, html, other]
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Title: Coulomb impurities in graphene driven by fast ionsSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
We provide a theoretical model for electronic transitions in a two-dimensional (2D) artificial atom in a graphene monolayer. The artificial atom is due to the presence of a charged adatom (Coulomb impurity) in the layer and interacts with a fast ultrarelativistic ion moving parallel to the layer. We compute the probability and cross sections for the corresponding electronic transitions by means of an exact solution of the time-dependent 2D Dirac equation describing the interaction of the planar atom with the electromagnetic field of the ultrarelativistic projectile.
- [50] arXiv:2411.13464 (cross-list from hep-ph) [pdf, html, other]
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Title: $H \to ZZ$ as a double-slit experimentComments: LaTeX 6 pagesSubjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex); Quantum Physics (quant-ph)
The decay $H \to ZZ \to 4\ell$, with $\ell = e,\mu$, can be used to test quantum interference in analogy to the famous double-slit experiment. The observations corresponding to `covering a slit' can be extracted from data in the $ee\mu\mu$ channel, while the observations when both `slits' are open, which include the interference, are measured in the $4e/4\mu$ channels. Furthermore, this process offers a unique opportunity to investigate identical-particle effects at high energies, and provide the first evidence of identical-particle behaviour for muons. Sensitivity at the $4\sigma$ level could be achieved at the high-luminosity upgrade of the Large Hadron Collider.
Cross submissions (showing 13 of 13 entries)
- [51] arXiv:2008.10100 (replaced) [pdf, html, other]
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Title: Qualitative equivalence between incompatibility and Bell nonlocalityComments: 13 pages, 4 figures. Accepted in PRA LettersSubjects: Quantum Physics (quant-ph)
Measurements in quantum theory can fail to be jointly measurable. Like entanglement, this incompatibility of measurements is necessary but not sufficient for violating Bell inequalities. The (in)compatibility relations among a set of measurements can be represented by a joint measurability structure, i.e., a hypergraph whose vertices denote measurements and hyperedges denote all and only compatible sets of measurements. Since incompatibility is necessary for a Bell violation, the joint measurability structure on each wing of a Bell experiment must necessarily be non-trivial, i.e., it must admit a subset of incompatible vertices. Here we show that for any non-trivial joint measurability structure with a finite set of vertices, there exists a quantum realization with a set of measurements that enables a Bell violation, i.e., given that Alice has access to this incompatible set of measurements, there exists a set of measurements for Bob and an entangled state shared between them such that they can jointly violate a Bell inequality. Hence, a non-trivial joint measurability structure is not only necessary for a Bell violation, but also sufficient.
- [52] arXiv:2207.05942 (replaced) [pdf, other]
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Title: Syndrome decoding by quantum approximate optimizationComments: with appendix, totally 16 figuresJournal-ref: Quantum Inf Process 23, 368 (2024)Subjects: Quantum Physics (quant-ph); Optimization and Control (math.OC)
The syndrome decoding problem is known to be NP-complete. The goal of the decoder is to find an error of low weight that corresponds to a given syndrome obtained from a parity-check matrix. We use the quantum approximate optimization algorithm (QAOA) to address the syndrome decoding problem with elegantly-designed reward Hamiltonians based on both generator and check matrices for classical and quantum codes. We evaluate the level-4 check-based QAOA decoding of the [7,4,3] Hamming code, as well as the level-4 generator-based QAOA decoding of the [[5,1,3]] quantum code. Remarkably, the simulation results demonstrate that the decoding performances match those of the maximum likelihood decoding. Moreover, we explore the possibility of enhancing QAOA by introducing additional redundant clauses to a combinatorial optimization problem while keeping the number of qubits unchanged. Finally, we study QAOA decoding of degenerate quantum codes. Typically, conventional decoders aim to find a unique error of minimum weight that matches a given syndrome. However, our observations reveal that QAOA has the intriguing ability to identify degenerate errors of comparable weight, providing multiple potential solutions that match the given syndrome with comparable probabilities. This is illustrated through simulations of the generator-based QAOA decoding of the [[9,1,3]] Shor code on specific error syndromes.
- [53] arXiv:2211.13362 (replaced) [pdf, html, other]
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Title: Double-slit experiment revisitedComments: 15 pages Latex, 6 figures; v2 substantial extension and revision, extra co-authorSubjects: Quantum Physics (quant-ph); Computational Physics (physics.comp-ph); Popular Physics (physics.pop-ph)
The double-slit experiment is one of the quintessential quantum experiments. However, it tends to be overlooked that a theoretical account of this experiment requires the specification of the joint position and time distribution of detection at the screen, whose position marginal yields the famous interference pattern. The difficulty then arises what this distribution should be. While there exists a variety of proposals for a quantum mechanical time observable, there is no consensus about the right choice. Here, we consider Bohmian mechanics, which allows for a natural and practical approach to this problem. We simulate this distribution in the case of an initial Gaussian wave packet passing through a double-slit potential. We also consider a more challenging setup in which one of the slits is shut during flight. To experimentally probe the quantum nature of the time distribution, a sufficient longitudinal spread of the initial wave packet is required, which has not been achieved so far. Without sufficient spread, the temporal aspect of the distribution can be treated classically. We illustrate this for the case of the double-slit experiment with helium atoms by Kurtsiefer et al. [Nature 386, 150 (1997)], which reports the joint position and time distribution.
- [54] arXiv:2305.09957 (replaced) [pdf, html, other]
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Title: Quantum neural networks form Gaussian processesComments: 14+37 pages, 4+6 figuresSubjects: Quantum Physics (quant-ph); Machine Learning (cs.LG); Machine Learning (stat.ML)
It is well known that artificial neural networks initialized from independent and identically distributed priors converge to Gaussian processes in the limit of a large number of neurons per hidden layer. In this work we prove an analogous result for Quantum Neural Networks (QNNs). Namely, we show that the outputs of certain models based on Haar random unitary or orthogonal deep QNNs converge to Gaussian processes in the limit of large Hilbert space dimension $d$. The derivation of this result is more nuanced than in the classical case due to the role played by the input states, the measurement observable, and the fact that the entries of unitary matrices are not independent. Then, we show that the efficiency of predicting measurements at the output of a QNN using Gaussian process regression depends on the observable's bodyness. Furthermore, our theorems imply that the concentration of measure phenomenon in Haar random QNNs is worse than previously thought, as we prove that expectation values and gradients concentrate as $\mathcal{O}\left(\frac{1}{e^d \sqrt{d}}\right)$. Finally, we discuss how our results improve our understanding of concentration in $t$-designs.
- [55] arXiv:2310.17819 (replaced) [pdf, html, other]
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Title: Multiplexed Processing of Quantum Information Across an Ultra-wide Optical BandwidthSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
Protocols for processing of quantum information are the foundation of quantum technology, enabling to share secrets at a distance, teleport quantum states, and to implement quantum computation. While many protocols were realized, and even commercialized, the throughput and processing speed of current protocols is limited by the narrow electronic bandwidth of standard measurement devices (typically in the MHz-to-GHz range), which is orders-of-magnitude lower than the optical bandwidth of available quantum optical sources (10-100 THz), indicating that the bandwidth resource is dramatically underutilized in current quantum optical technology. We present a general concept of frequency multiplexed quantum channels and a set of methods to process quantum information efficiently across the available optical bandwidth. Using a broadband source of squeezed light, spectral manipulation methods and parametric homodyne detection, we are able to generate, process and measure all the channels in parallel, thereby harnessing the optical bandwidth for quantum information in an efficient manner. We exemplify the concept through two basic protocols: Multiplexed Continuous-Variable Quantum Key Distribution (CV-QKD) and multiplexed continuous-variable quantum teleportation. The multiplexed QKD protocol is demonstrated in a proof-of-principle experiment, where we successfully carry out QKD over 23 uncorrelated spectral channels, with capability to detect eavesdropping in any channel. These multiplexed methods (and similar) will enable to carry out quantum processing in parallel over hundreds of channels, potentially increasing the throughput of quantum protocols by orders of magnitude.
- [56] arXiv:2312.13877 (replaced) [pdf, html, other]
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Title: A complete continuous-variable quantum computation architecture based on the 2D spatiotemporal cluster stateComments: 15 pages,7 figuresSubjects: Quantum Physics (quant-ph)
Continuous-variable measurement-based quantum computation, which requires deterministically generated large-scale cluster state, is a promising candidate for practical, scalable, universal, and fault-tolerant quantum computation. In this work, based on our compact and scalable scheme of generating a two-dimensional spatiotemporal cluster state, a complete architecture including cluster state preparation, gate implementations, and error correction, is demonstrated. First, a scheme for generating two-dimensional large-scale continuous-variable cluster state by multiplexing both the temporal and spatial domains is proposed. Then, the corresponding gate implementations by gate teleportation are discussed and the actual gate noise from the generated cluster state is considered. After that, the quantum error correction can be further achieved by utilizing the square-lattice Gottesman-Kitaev-Preskill (GKP) code. Finally, a fault-tolerant quantum computation can be realized by introducing bias into the square-lattice GKP code (to protect against phase-flip errors) and concatenating a repetition code (to handle the residual bit-flip errors), with a squeezing threshold of 12.3 dB. Our work provides a possible option for a complete fault-tolerant quantum computation architecture in the future.
- [57] arXiv:2401.10408 (replaced) [pdf, html, other]
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Title: Separating a particle's mass from its momentumComments: 13 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
The Quantum Cheshire Cat experiment showed that when weak measurements are performed on pre- and post-selected system, the counterintuitive result has been obtained that a neutron is measured to be in one place without its spin, and its spin is measured to be in another place without the neutron. A generalization of this effect is presented with a massive particle whose mass is measured to be in one place with no momentum, while the momentum is measured to be in another place without the mass. The new result applies to any massive particle, independent of its spin or charge. A gedanken experiment which illustrates this effect is presented using a nested pair of Mach-Zehnder interferometers, but with some of the mirrors and beam splitters moving relative to the laboratory frame. The titular interpretation of this experiment is extremely controversial, and rests on several assumptions, which are discussed in detail. An alternative interpretation using the counterparticle model of Aharonov et al. is also discussed.
- [58] arXiv:2401.16666 (replaced) [pdf, html, other]
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Title: Labeling eigenstates of qubit-cavity systems based on the continuity of qubit occupancy: Detecting resonances to higher excited qubit statesComments: 8 pages, 5 figures, accepted versionSubjects: Quantum Physics (quant-ph)
We propose a new method for labeling the eigenstates of qubit-cavity systems based on the continuity of the qubit occupancy. The labeled eigenstates give a rough estimate of the evolution of a quantum state under cavity driving. The photon-number dependence of the resonant cavity frequency can be estimated from the labeled eigenenergies, and resonances to higher excited qubit states are visible in the dependence. Our proposed method can be applied to a broader parameter region compared to an existing method. With the proposed method, we investigate the offset-charge dependence of the resonances to higher excited states that can induce leakage effects from the computational basis. The results imply that the leakage can occur with only around ten photons.
- [59] arXiv:2401.17372 (replaced) [pdf, html, other]
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Title: Optically-Trapped Nanodiamond-Relaxometry Detection of Nanomolar Paramagnetic Spins in Aqueous EnvironmentsShiva Iyer, Changyu Yao, Olivia Lazorik, Md Shakil Bin Kashem, Pengyun Wang, Gianna Glenn, Michael Mohs, Yinyao Shi, Michael Mansour, Erik Henriksen, Kater Murch, Shankar Mukherji, Chong ZuComments: 7 pages, 3 figuresSubjects: Quantum Physics (quant-ph); Biological Physics (physics.bio-ph)
Probing electrical and magnetic properties in aqueous environments remains a frontier challenge in nanoscale sensing. Our inability to do so with quantitative accuracy imposes severe limitations, for example, on our understanding of the ionic environments in a diverse array of systems, ranging from novel materials to the living cell. The Nitrogen-Vacancy (NV) center in fluorescent nanodiamonds (FNDs) has emerged as a good candidate to sense temperature, pH, and the concentration of paramagnetic species at the nanoscale, but comes with several hurdles such as particle-to-particle variation which render calibrated measurements difficult, and the challenge to tightly confine and precisely position sensors in aqueous environment. To address this, we demonstrate relaxometry with NV centers within optically-trapped FNDs. In a proof of principle experiment, we show that optically-trapped FNDs enable highly reproducible nanomolar sensitivity to the paramagnetic ion, (\mathrm{Gd}^{3+}). We capture the three distinct phases of our experimental data by devising a model analogous to nanoscale Langmuir adsorption combined with spin coherence dynamics. Our work provides a basis for routes to sense free paramagnetic ions and molecules in biologically relevant conditions.
- [60] arXiv:2402.04339 (replaced) [pdf, html, other]
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Title: Bilateral photon emission from a vibrating mirror and multiphoton entanglement generationAlberto Mercurio, Enrico Russo, Fabio Mauceri, Salvatore Savasta, Franco Nori, Vincenzo Macrì, Rosario Lo FrancoSubjects: Quantum Physics (quant-ph)
Entanglement plays a crucial role in the development of quantum-enabled devices. One significant objective is the deterministic creation and distribution of entangled states, achieved, for example, through a mechanical oscillator interacting with confined electromagnetic fields. In this study, we explore a cavity resonator containing a two-sided perfect mirror. Although the mirror separates the cavity modes into two independent confined electromagnetic fields, the radiation pressure interaction gives rise to high-order effective interactions across all subsystems. Depending on the chosen resonant conditions, which are also related to the position of the mirror, we study $2n$-photon entanglement generation and bilateral photon pair emission. Demonstrating the non-classical nature of the mechanical oscillator, we provide a pathway to control these phenomena, opening potential applications in quantum technologies. Looking ahead, similar integrated devices could be used to entangle subsystems across vastly different energy scales, such as microwave and optical photons.
- [61] arXiv:2402.09333 (replaced) [pdf, html, other]
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Title: Bosonic Pauli+: Efficient Simulation of Concatenated Gottesman-Kitaev-Preskill CodesComments: v3: addressed reviewer comments. 22 pages + references + appendices, 12 figuresSubjects: Quantum Physics (quant-ph)
A promising route towards fault-tolerant quantum error correction is the concatenation of a Gottesman-Kitaev-Preskill (GKP) code with a qubit code. Development of such concatenated codes requires simulation tools which realistically model noise, while being able to simulate the dynamics of many modes. However, so far, large-scale simulation tools for concatenated GKP codes have been limited to idealized noise models and GKP code implementations. Here, we introduce the Bosonic Pauli+ model (BP+), which can be simulated efficiently for a large number of modes, while capturing the rich dynamics in the bosonic multi-mode Hilbert space. We demonstrate the method by simulating a hybrid surface code, where the data qubits are finite-energy GKP qubits stabilized using the small-Big-small (sBs) protocol, and the syndrome qubits are standard two-level systems. Using BP+, we present logical error rates of such an implementation. Confidence in the accuracy of the method is gained by comparing its predictions with full time evolution simulations for several relevant quantum circuits. While developed specifically for GKP qubits stabilized using the sBs protocol, the mathematical structure of BP+ is generic and may be applicable also to the simulation of concatenations using other bosonic codes.
- [62] arXiv:2402.15878 (replaced) [pdf, html, other]
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Title: One-dimensional Continuous-Time Quantum Markov Chains: qubit probabilities and measuresComments: 21 pages, 3 figuresJournal-ref: J. Phys. A: Math. Theor. 57 (2024) 295301 (33pp)Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Classical Analysis and ODEs (math.CA)
Quantum Markov chains (QMCs) are positive maps on a trace-class space describing open quantum dynamics on graphs. Such objects have a statistical resemblance with classical random walks, while at the same time it allows for internal (quantum) degrees of freedom. In this work we study continuous-time QMCs on the integer line, half-line and finite segments, so that we are able to obtain exact probability calculations in terms of the associated matrix-valued orthogonal polynomials and measures. The methods employed here are applicable to a wide range of settings, but we will restrict to classes of examples for which the Lindblad generators are induced by a single positive map, and such that the Stieltjes transforms of the measures and their inverses can be calculated explicitly.
- [63] arXiv:2402.19123 (replaced) [pdf, html, other]
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Title: Sensing atomic superfluid rotation beyond the standard quantum limitComments: 16 pages, 13 figuresJournal-ref: Phys. Rev. A 110, 053514 (2024)Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Optics (physics.optics)
Atomic superfluids formed using Bose-Einstein condensates (BECs) in a ring trap are currently being investigated in the context of superfluid hydrodynamics, quantum sensing and matter-wave interferometry. The characterization of the rotational properties of such superfluids is important, but can presently only be performed by using optical absorption imaging, which completely destroys the condensate. Recent studies have proposed coupling the ring BEC to optical cavity modes carrying orbital angular momentum to make minimally destructive measurements of the condensate rotation. The sensitivity of these proposals, however, is bounded below by the standard quantum limit set by the combination of laser shot noise and radiation pressure noise. In this work, we provide a theoretical framework that exploits the fact that the interaction between the scattered modes of the condensate and the light reduces to effective optomechanical equations of motion. We present a detailed theoretical analysis to demonstrate that the use of squeezed light and backaction evasion techniques allows the angular momentum of the condensate to be sensed with noise well below the standard quantum limit. Our proposal is relevant to atomtronics, quantum sensing and quantum information.
- [64] arXiv:2402.19247 (replaced) [pdf, html, other]
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Title: Noisy intermediate-scale quantum simulation of the one-dimensional wave equationLewis Wright, Conor Mc Keever, Jeremy T. First, Rory Johnston, Jeremy Tillay, Skylar Chaney, Matthias Rosenkranz, Michael LubaschComments: 11 pages, 8 figures, 1 tableJournal-ref: Phys. Rev. Research 6, 043169 (2024)Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Applied Physics (physics.app-ph); Classical Physics (physics.class-ph); Computational Physics (physics.comp-ph)
We design and implement quantum circuits for the simulation of the one-dimensional wave equation on the Quantinuum H1-1 quantum computer. The circuit depth of our approach scales as $O(n^{2})$ for $n$ qubits representing the solution on $2^{n}$ grid points, and leads to infidelities of $O(2^{-4n} t^{2})$ for simulation time $t$ assuming smooth initial conditions. By varying the qubit count we study the interplay between the algorithmic and physical gate errors to identify the optimal working point of minimum total error. Our approach to simulating the wave equation can be used with appropriate state preparation algorithms across different quantum processors and serve as an application-oriented benchmark.
- [65] arXiv:2403.01762 (replaced) [pdf, html, other]
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Title: Contextuality, superlocality and nonclassicality of supernoncontextualityComments: v2 (submitted to another journal): error in "which range noisy Peres box contextual" corrected- nonclassicality based on supernoncontextuality termed as "semi-device-independent contextuality"- a criterion and quantification of semi-device-independent contextuality studied - removed contents related to information-theoretic measures of simultaneous correlations in MUBs. 16 pagesSubjects: Quantum Physics (quant-ph)
Contextuality is a fundamental manifestation of nonclassicality, indicating that for certain quantum correlations, sets of jointly measurable variables cannot be pre-assigned values independently of the measurement context. In this work, we characterize nonclassical quantum correlation beyond contextuality, in terms of supernoncontextuality, namely the higher-than-quantum hidden-variable(HV) dimensionality required to reproduce the given noncontextual quantum correlations. Thus supernoncontextuality is the contextuality analogue of superlocality. Specifically, we study the quantum system of two-qubit states in a scenario composed of five contexts that demonstrate contextuality in a state-dependent fashion. For this purpose, we use the framework of boxes, whose behavior is described by a set of probabilities satisfying the no-disturbance conditions. We first demonstrate that while superlocality is necessary to observe a contextual box, superlocality is not sufficient for contextuality. On the other hand, a noncontextual superlocal box can be supernoncontextual, but superlocality is not a necessary condition. We then introduce a notion of nonclassicality beyond the standard contextuality, called semi-device-independent contextuality. We study semi-device-independent contextuality of two-qubit states in the above mentioned scenario and demonstrate how supernoncontextuality implies this nonclassicality. To this end, we propose a criterion and a measure of semi-device-independent contextuality.
- [66] arXiv:2404.11306 (replaced) [pdf, other]
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Title: Existential Unforgeability in Quantum Authentication From Quantum Physical Unclonable Functions Based on Random von Neumann MeasurementComments: 20 pages, 6 figuresJournal-ref: 2024 IEEE International Symposium on Information Theory (ISIT), Athens, Greece, 2024, pp. 3112-3117Subjects: Quantum Physics (quant-ph)
Physical Unclonable Functions (PUFs) leverage inherent, non-clonable physical randomness to generate unique input-output pairs, serving as secure fingerprints for cryptographic protocols like authentication. Quantum PUFs (QPUFs) extend this concept by using quantum states as input-output pairs, offering advantages over classical PUFs, such as challenge reusability via public channels and eliminating the need for trusted parties due to the no-cloning theorem. Recent work introduced a generalized mathematical framework for QPUFs. It was shown that random unitary QPUFs cannot achieve existential unforgeability against Quantum Polynomial Time (QPT) adversaries. Security was possible only with additional uniform randomness. To avoid the cost of external randomness, we propose a novel measurement-based scheme. Here, the randomness naturally arises from quantum measurements. Additionally, we introduce a second model where the QPUF functions as a nonunitary quantum channel, which guarantees existential unforgeability. These are the first models in the literature to demonstrate a high level of provable security. Finally, we show that the Quantum Phase Estimation (QPE) protocol, applied to a Haar random unitary, serves as an approximate implementation of the second type of QPUF by approximating a von Neumann measurement on the unitary's eigenbasis.
- [67] arXiv:2404.11360 (replaced) [pdf, html, other]
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Title: Open-system eigenstate thermalization in a noninteracting integrable modelComments: 17 pages, 13 figuresSubjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
Significant attention has been devoted to the problem of thermalization of observables in isolated quantum setups by individual eigenstates. Here, we address this issue from an open quantum system perspective, examining an isolated setup where a small system (specifically, a single fermionic level) is coupled to a macroscopic fermionic bath. We argue that in such a model, despite its full integrability, the system observables exhibit thermalization when the system-bath setup resides in a typical eigenstate of its Hamiltonian, a phenomenon known as weak eigenstate thermalization. This thermalization occurs unless it is suppressed by localization due to strong coupling. We further show that following the quench of the system Hamiltonian, the system occupancy typically relaxes to the thermal value corresponding to the new Hamiltonian. Finally, we demonstrate that system thermalization also arises when the system is coupled to a bath that has been initialized in a typical eigenstate of its Hamiltonian. Our findings suggest that nonintegrability is not the sole driver of thermalization, highlighting the need for complementary approaches to fully understand the emergence of statistical mechanics.
- [68] arXiv:2405.01518 (replaced) [pdf, html, other]
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Title: Driven Multiphoton Qubit-Resonator InteractionsComments: Updated to match published versionJournal-ref: Phys. Rev. A 110, 053711 (2024)Subjects: Quantum Physics (quant-ph)
We develop a general theory for multiphoton qubit-resonator interactions enhanced by a qubit drive. The interactions generate qubit-conditional operations in the resonator when the driving is near $n$-photon cross-resonance, namely, the qubit drive is $n$-times the resonator frequency. We pay special attention to the strong driving regime, where the interactions are conditioned on the qubit dressed states. We consider the specific case where $n=2$, which results in qubit-conditional squeezing (QCS). We show that the QCS protocol can be used to generate a superposition of orthogonally squeezed states following a properly chosen qubit measurement. We outline quantum information processing applications for these states, including encoding a qubit in a resonator via the superposition of orthogonally squeezed states. We show how the QCS operation can be used to realize a controlled-squeeze gate and its use in bosonic phase estimation. The QCS protocol can also be utilized to achieve faster unitary operator synthesis on the joint qubit-resonator Hilbert space. Next, we investigate the use of a two-tone drive to engineer an effective $n$-photon Rabi Hamiltonian with widely tunable effective system parameters, which could enable the realization of new regimes that have so far been inaccessible. Finally, we propose a multiphoton circuit QED implementation based on a transmon qubit coupled to a resonator via an asymmetric SQUID. We provide realistic parameter estimates for the two-photon operation regime that can host the aforementioned two-photon protocols. We use numerical simulations to show that even in the presence of spurious terms and decoherence, our analytical predictions are robust.
- [69] arXiv:2405.06752 (replaced) [pdf, html, other]
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Title: Polarization Entanglement with highly non-degenerate photon pairs enhanced by effective walk-off compensation methodSubjects: Quantum Physics (quant-ph)
We demonstrate polarization entanglement in highly non-degenerate photon pairs, generated through Type-0 spontaneous parametric down conversion (SPDC) using bulk periodically poled Lithium Niobate (PPLN) crystals. Through the utilization of both a beam displacer interferometer scheme and a Sagnac interferometer, we ensure high polarisation contrast and stable interference of the highly non-degenerate photon pairs, which however causes substantial spatial and temporal walk-offs of the photon paths which poses a formidable challenge. We introduce an effective compensation method using birefringent crystal wedges to eliminate spatial and temporal walkoffs simultaneously. This method is implemented in our entangled photon source (EPS) designed specifically for testing entanglement-based quantum key distribution (EBQKD) between ground and satellite, as part of the Quantum Encryption and Science Satellite (QEYSSat) mission funded by the Canadian Space Agency (CSA). We observed a coincidence rate of N = (33.33+-0.05)kHz, a significant improvement compared to the absence of the spatial compensation. We also observed an estimated pair generation rate of (2.92+-0.12)MHz and an entanglement visibility of (96.6+-0.3)% from only 1.0mW of pump power, making it a promising source for long-distance quantum communication for ground-to-satellite and fiber optic links.
- [70] arXiv:2405.17388 (replaced) [pdf, html, other]
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Title: Non-Unitary Quantum Machine LearningComments: 43 pages, 23 figuresSubjects: Quantum Physics (quant-ph)
We introduce several probabilistic quantum algorithms that overcome the normal unitary restrictions in quantum machine learning by leveraging the Linear Combination of Unitaries (LCU) method. Among our investigations are quantum native implementations of Residual Networks (ResNet), where we show that residual connections between layers of a variational ansatz can prevent barren plateaus in models which would otherwise contain them. Secondly, we implement a quantum analogue of average pooling layers from convolutional networks using single qubit controlled basic arithmetic operators and show that the LCU success probability remains stable for the MNIST database. This method can be further generalised to convolutional filters, while using exponentially fewer controlled unitaries than previous approaches. Finally, we propose a general framework for applying a linear combination of irreducible subspace projections on quantum encoded data. This enables a quantum state to remain within an exponentially large space, while selectively amplifying specific subspaces relative to others, alleviating simulability concerns that arise when fully projecting to a polynomially sized subspace. We demonstrate improved classification performance for partially amplified permutation invariant encoded point cloud data when compared to non-invariant or fully permutation invariant encodings. We also demonstrate a novel rotationally invariant encoding for point cloud data via Schur-Weyl duality. These quantum computing frameworks are all constructed using the LCU method, suggesting that further novel quantum machine learning algorithms could be created by utilising the LCU technique.
- [71] arXiv:2406.16622 (replaced) [pdf, html, other]
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Title: Simultaneous Generation of Quantum Frequency Combs across Distinct Modal Families in a Single $Si_3 N_4$ Whispering Gallery Mode ResonatorComments: 20 pages, 9 figuresSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal families. It presents a micro-ring resonator with a radius of 240 $\mathrm{\mu m}$, capable of supporting four modal families within the 130 to 260 $\mathrm{THz}$ frequency range for consistency regulation. The results indicate that, by carefully designing the structure of silicon nitride WGMRs, it is possible to generate quantum entangled frequency combs across distinct modal families simultaneously using monochromatic pump light. It is achieved by modulating the pump mode profiles with a spatial light modulator (SLM) or an on-chip inverse-designed mode converter. This approach offers a simple and low-cost method to achieve higher-density entanglement integration on-chip.
- [72] arXiv:2407.09411 (replaced) [pdf, html, other]
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Title: Ambiguous Resonances in Multipulse Quantum Sensing with Nitrogen Vacancy CentersLucas Tsunaki, Anmol Singh, Kseniia Volkova, Sergei Trofimov, Tommaso Pregnolato, Tim Schröder, Boris NaydenovComments: 14 pages, 8 figures, for associated dataset, see this https URLSubjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other)
Dynamical decoupling multipulse sequences can be applied to solid state spins for sensing weak oscillating fields from nearby single nuclear spins. By periodically reversing the probing system's evolution, other noises are counteracted and filtered out over the total evolution. However, the technique is subject to intricate interactions resulting in additional resonant responses, which can be misinterpreted with the actual signal intended to be measured. We experimentally characterized three of these effects present in single nitrogen vacancy centers in diamond, where we also developed a numerical simulations model without rotating wave approximation, showing robust correlation to the experimental data. Regarding centers with the $^{15}$N nitrogen isotope, we observed that a small misalignment in the bias magnetic field causes the precession of the nitrogen nuclear spin to be sensed by the electronic spin of the center. Another studied case of ambiguous resonances comes from the coupling with lattice $^{13}$C nuclei, where we used the echo modulation frequencies to obtain the interaction Hamiltonian and then utilized the latter to simulate multipulse sequences. Finally, we also measured and simulated the effects from the free evolution of the quantum system during finite pulse durations. Due to the large data volume and the strong dependency of these ambiguous resonances with specific experimental parameters, we provide a simulations dataset with a user-friendly graphical interface, where users can compare simulations with their own experimental data for spectral disambiguation. Although focused with nitrogen vacancy centers and dynamical decoupling sequences, these results and the developed model can potentially be applied to other solid state spins and quantum sensing techniques.
- [73] arXiv:2408.08265 (replaced) [pdf, html, other]
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Title: On the Constant Depth Implementation of Pauli ExponentialsComments: expanded on applications and discussed nearest-neighbour constructionsSubjects: Quantum Physics (quant-ph)
We decompose for the first time, under the very restrictive linear nearest-neighbour connectivity, $Z\otimes Z \ldots \otimes Z$ exponentials of arbitrary length into circuits of constant depth using $\mathcal{O}(n)$ ancillae and two-body XX and ZZ interactions. Consequently, a similar method works for arbitrary Pauli exponentials. We prove the correctness of our approach, after introducing novel rewrite rules for circuits which benefit from qubit recycling. The decomposition has a wide variety of applications ranging from the efficient implementation of fault-tolerant lattice surgery computations, to expressing arbitrary stabilizer circuits via two-body interactions only, parallel decoding of quantum error-correcting computations and to reducing the depth of NISQ computations, such as VQE.
- [74] arXiv:2409.14386 (replaced) [pdf, html, other]
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Title: Scattering of TE and TM waves and quantum dynamics generated by non-Hermitian HamiltoniansComments: Expanded version, 22 pages, 6 figures; accepted for publication in in Prog. Theor. Exp. PhysSubjects: Quantum Physics (quant-ph); Optics (physics.optics)
The study of the scattering of electromagnetic waves by a linear isotropic medium with planar symmetry can be reduced to that of their TE and TM modes. For situations where the medium consists of parallel homogeneous slabs, one may use the standard transfer matrix technique to address the scattering problem for these modes. We extend the utility of this technique to inhomogeneous permittivity and permeability profiles by proposing a dynamical formulation of the scattering of TE and TM waves in which the transfer matrix for the medium is given in terms of the evolution operator for an effective non-unitary quantum system. This leads to a system of dynamical equations for the reflection and transmission amplitudes. Decoupling these equations we reduce the solution of the scattering problem for TE and TM modes to that of an initial-value problem for a Riccati equation. We discuss the application of this observation in identifying media that do not reflect TE or TM waves with given wavenumber and incidence angle.
- [75] arXiv:2409.14622 (replaced) [pdf, html, other]
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Title: LatentQGAN: A Hybrid QGAN with Classical Convolutional AutoencoderAlexis Vieloszynski, Soumaya Cherkaoui, Ola Ahmad, Jean-Frédéric Laprade, Oliver Nahman-Lévesque, Abdallah Aaraba, Shengrui WangComments: This paper was accepted for publication on the 10th IEEE World Forum on Internet of Things (IEEE WFIoT2024), in the session SS - QIoT-1: Special Session - Quantum Internet of Things (QIoT)-1, November 10th, from 14:00 to 15:30 ESTSubjects: Quantum Physics (quant-ph); Artificial Intelligence (cs.AI); Machine Learning (cs.LG)
Quantum machine learning consists in taking advantage of quantum computations to generate classical data. A potential application of quantum machine learning is to harness the power of quantum computers for generating classical data, a process essential to a multitude of applications such as enriching training datasets, anomaly detection, and risk management in finance. Given the success of Generative Adversarial Networks in classical image generation, the development of its quantum versions has been actively conducted. However, existing implementations on quantum computers often face significant challenges, such as scalability and training convergence issues. To address these issues, we propose LatentQGAN, a novel quantum model that uses a hybrid quantum-classical GAN coupled with an autoencoder. Although it was initially designed for image generation, the LatentQGAN approach holds potential for broader application across various practical data generation tasks. Experimental outcomes on both classical simulators and noisy intermediate scale quantum computers have demonstrated significant performance enhancements over existing quantum methods, alongside a significant reduction in quantum resources overhead.
- [76] arXiv:2410.00353 (replaced) [pdf, html, other]
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Title: Bringing multilevel quantum master equations into Lindblad form for complete positivity tests: Two approachesSubjects: Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph); Chemical Physics (physics.chem-ph)
While quantum master equations (QMEs) are the primary workhorse in quantum information science, quantum optics, spectroscopy, and quantum thermodynamics, bringing an arbitrary $N$-level QME into Lindbladian form and verifying complete positivity of the associated quantum dynamical map remain open challenges for $N\ge 3$. We explore and implement two independent methods to accomplish these tasks, which enable one to directly compute the Kossakowski matrix of an arbitrary Markovian QME from its Liouvillian. In the first method, due to Hall, Cresser, Li, and Andersson, the Kossakowski matrix elements are obtained by evaluating the action of the Liouvillian on the orthonormal SU($N$) basis matrices and then computing a sum of matrix-product traces. The second method, developed in this work, is based on the real $N$-level coherence vector and relies on the Moore-Penrose pseudo-inverse of a rectangular matrix composed of the structure constants of SU$(N)$. We show that both methods give identical results, and apply them to establish the complete positivity of the partial secular Bloch-Redfield QME for the $\Lambda$ and V-systems driven by incoherent light. We find that the eigenvalues of the Kossakowski matrix of these seemingly different three-level systems are identical, implying close similarities of their dissipative dynamics. By facilitating the expression of multilevel Markovian QMEs in Lindblad form, our results enable testing the QMEs for complete positivity without solving them, as well as restoring complete positivity by keeping only non-negative eigenvalues of the Kossakowski matrix.
- [77] arXiv:2410.13048 (replaced) [pdf, html, other]
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Title: p-Adic quantum mechanics, infinite potential wells, and continuous-time quantum walksComments: The main theorems were strengthened. A new section, Discussion, was added at the end of the paper. Several typos were corrected. arXiv admin note: text overlap with arXiv:2308.01283Subjects: Quantum Physics (quant-ph)
This article discusses a p-adic version of the infinite potential well in quantum mechanics (QM). This model describes the confinement of a particle in a p-adic ball. We rigorously solve the Cauchy problem for the Schrödinger equation and determine the stationary solutions. The p-adic balls are fractal objects. By dividing a p-adic ball into a finite number of sub-balls and using the wavefunctions of the infinite potential well, we construct a continuous-time quantum walk (CTQW) on a fully connected graph, where each vertex corresponds to a sub-ball in the partition of the original ball. In this way, we establish a connection between p-adic QM and quantum computing.
- [78] arXiv:2410.23018 (replaced) [pdf, html, other]
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Title: Optimizing Temperature Distributions for Training Neural Quantum States using Parallel TemperingSubjects: Quantum Physics (quant-ph)
Parameterized artificial neural networks (ANNs) can be very expressive ansatzes for variational algorithms, reaching state-of-the-art energies on many quantum many-body Hamiltonians. Nevertheless, the training of the ANN can be slow and stymied by the presence of local minima in the parameter landscape. One approach to mitigate this issue is to use parallel tempering methods, and in this work we focus on the role played by the temperature distribution of the parallel tempering replicas. Using an adaptive method that adjusts the temperatures in order to equate the exchange probability between neighboring replicas, we show that this temperature optimization can significantly increase the success rate of the variational algorithm with negligible computational cost by eliminating bottlenecks in the replicas' random walk. We demonstrate this using two different neural networks, a restricted Boltzmann machine and a feedforward network, which we use to study a toy problem based on a permutation invariant Hamiltonian with a pernicious local minimum and the J1-J2 model on a rectangular lattice.
- [79] arXiv:2411.07603 (replaced) [pdf, html, other]
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Title: $\mathscr{H}_2$ Model Reduction for Linear Quantum SystemsComments: 13 pages,3 figuresSubjects: Quantum Physics (quant-ph); Systems and Control (eess.SY)
In this paper, an $\mathscr{H}_2$ norm-based model reduction method for linear quantum systems is presented, which can obtain a physically realizable model with a reduced order for closely approximating the original system. The model reduction problem is described as an optimization problem, whose objective is taken as an $\mathscr{H}_2$ norm of the difference between the transfer function of the original system and that of the reduced one. Different from classical model reduction problems, physical realizability conditions for guaranteeing that the reduced-order system is also a quantum system should be taken as nonlinear constraints in the optimization. To solve the optimization problem with such nonlinear constraints, we employ a matrix inequality approach to transform nonlinear inequality constraints into readily solvable linear matrix inequalities (LMIs) and nonlinear equality constraints, so that the optimization problem can be solved by a lifting variables approach. We emphasize that different from existing work, which only introduces a criterion to evaluate the performance after model reduction, we guide our method to obtain an optimal reduced model with respect to the $\mathscr{H}_2$ norm. In addition, the above approach for model reduction is extended to passive linear quantum systems. Finally, examples of active and passive linear quantum systems validate the efficacy of the proposed method.
- [80] arXiv:2411.08543 (replaced) [pdf, html, other]
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Title: Quantum Time Travel Revisited: Noncommutative M\"{o}bius Transformations and Time LoopsComments: 18 pages, 11 FiguresSubjects: Quantum Physics (quant-ph)
We extend the theory of quantum time loops introduced by Greenberger and Szovil [1] from the scalar situation (where paths have just an associated complex amplitude) to the general situation where the time traveling system has multi-dimensional underlying Hilbert space. The main mathematical tool which emerges is the noncommutative M\{o}bius Transformation and this affords a formalism similar to the modular structure well known to feedback control problems. We argue that a sum-over-all-paths approach may be carried out in the scalar case, but quickly becomes unwieldy in the general case. It is natural to replace the beamsplitters of [1] with more general components having their own quantum structure, in which case the theory starts to resemble the quantum feedback networks theory for open quantum optical models and indeed we exploit this to look at more realistic physical models of time loops. We analyze some Grandfather paradoxes in the new setting
- [81] arXiv:2411.08594 (replaced) [pdf, other]
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Title: Encodings of the weighted MAX k-CUT on qubit systemsSubjects: Quantum Physics (quant-ph)
The weighted MAX k-CUT problem involves partitioning a weighted undirected graph into k subsets to maximize the sum of the weights of edges between vertices in different subsets. This problem has significant applications across multiple domains. This paper explores encoding methods for MAX k-CUT on qubit systems, utilizing quantum approximate optimization algorithms (QAOA) and addressing the challenge of encoding integer values on quantum devices with binary variables. We examine various encoding schemes and evaluate the efficiency of these approaches. The paper presents a systematic and resource efficient method to implement phase separation for diagonal square binary matrices. When encoding the problem into the full Hilbert space, we show the importance of balancing the "bin sizes". We also explore the option to encode the problem into a suitable subspace, by designing suitable state preparations and constrained mixers (LX- and Grover-mixer). Numerical simulations on weighted and unweighted graph instances demonstrate the effectiveness of these encoding schemes, particularly in optimizing circuit depth, approximation ratios, and computational efficiency.
- [82] arXiv:2411.10126 (replaced) [pdf, html, other]
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Title: Infinite series involving special functions obtained using simple one-dimensional quantum mechanical problemsSonja Gombar, Milica Rutonjski, Petar Mali, Slobodan Radošević, Milan Pantić, Milica Pavkov-HrvojevićComments: 9 pages, 1 figure, 4 tablesSubjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph)
In this paper we analytically evaluate certain classes of infinite sums involving special functions such as generalized hypergeometric functions, associated Laguerre polynomials, Bessel and Struve functions. The calculations are founded on the basic quantum mechanical principles applied to simple quantum mechanical models, namely half harmonic oscillator and model of a particle trapped inside an infinite potential well. We also show that some classes of functions which are not regular wave functions allow evaluation of additional infinite sums.
- [83] arXiv:2411.12550 (replaced) [pdf, html, other]
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Title: Sequential Quantum Maximum Confidence DiscriminationComments: 7 pages, 1 figureSubjects: Quantum Physics (quant-ph)
Sequential quantum information processing may lie in the peaceful coexistence of no-go theorems on quantum operations, such as the no-cloning theorem, the monogamy of correlations, and the no-signalling principle. In this work, we investigate a sequential scenario of quantum state discrimination with maximum confidence, called maximum-confidence discrimination, which generalizes other strategies including minimum-error and unambiguous state discrimination. We show that sequential state discrimination with equally high confidence can be realized only when positive-operator-valued measure elements for a maximum-confidence measurement are linearly independent; otherwise, a party will have strictly less confidence in measurement outcomes than the previous one. We establish a tradeoff between the disturbance of states and information gain in sequential state discrimination, namely, that the less a party learn in state discrimination in terms of a guessing probability, the more parties can participate in the sequential scenario.
- [84] arXiv:2307.05681 (replaced) [pdf, html, other]
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Title: Timescales of quantum and classical chaotic spin models evolving toward equilibriumComments: 13 pages, 10 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We investigate quench dynamics in a one-dimensional spin model, comparing both quantum and classical descriptions. Our primary focus is on the different timescales involved in the evolution of the observables as they approach statistical relaxation. Numerical simulations, supported by semi-analytical analysis, reveal that the relaxation of single-particle energies (global quantity) and on-site magnetization (local observable) occurs on a timescale independent of the system size $L$. This relaxation process is equally well-described by classical equations of motion and quantum solutions, demonstrating excellent quantum-classical correspondence, provided the system be strongly chaotic. The correspondence persists even for small quantum spin values ($S=1$), where a semi-classical approximation is not applicable. Conversely, for the participation ratio, which characterizes the initial state spread in the many-body Hilbert space and which lacks a classical analogue, the relaxation timescale is system-size dependent.
- [85] arXiv:2309.08032 (replaced) [pdf, html, other]
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Title: A substitutional quantum defect in WS$_2$ discovered by high-throughput computational screening and fabricated by site-selective STM manipulationJohn C. Thomas, Wei Chen, Yihuang Xiong, Bradford A. Barker, Junze Zhou, Weiru Chen, Antonio Rossi, Nolan Kelly, Zhuohang Yu, Da Zhou, Shalini Kumari, Edward S. Barnard, Joshua A. Robinson, Mauricio Terrones, Adam Schwartzberg, D. Frank Ogletree, Eli Rotenberg, Marcus M. Noack, Sinéad Griffin, Archana Raja, David A. Strubbe, Gian-Marco Rignanese, Alexander Weber-Bargioni, Geoffroy HautierJournal-ref: Nature Communications, v. 15, n. 3556, April 2024Subjects: Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
Point defects in two-dimensional materials are of key interest for quantum information science. However, the space of possible defects is immense, making the identification of high-performance quantum defects extremely challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS$_2$, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co$_{\rm S}^{0}$) as very promising and fabricate it with scanning tunneling microscopy (STM). The Co$_{\rm S}^{0}$ electronic structure measured by STM agrees with first principles and showcases an attractive new quantum defect. Our work shows how HT computational screening and novel defect synthesis routes can be combined to design new quantum defects.
- [86] arXiv:2310.05726 (replaced) [pdf, html, other]
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Title: New Partial Trace Inequalities and Distillability of Werner StatesSubjects: Mathematical Physics (math-ph); Quantum Physics (quant-ph)
One of the oldest problems in quantum information theory is to study if there exists a state with negative partial transpose which is undistillable. This problem has been open for almost 30 years, and still no one has been able to give a complete answer to it. This work presents a new strategy to try to solve this problem by translating the distillability condition on the family of Werner states into a problem of partial trace inequalities, this is the aim of our first main result. As a consequence we obtain a new bound for the $2$-distillability of Werner states, which does not depend on the dimension of the system. On the other hand, our second main result provides new partial trace inequalities for bipartite systems, connecting some of them also with the separability of Werner states. Throughout this work we also present numerous partial trace inequalities, which are valid for many families of matrices.
- [87] arXiv:2311.09298 (replaced) [pdf, html, other]
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Title: Scattering phase shifts from a quantum computerComments: 6 pages, 5 figuresJournal-ref: Phys. Rev. C 109, L061001 (2024)Subjects: Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
We calculate two-body scattering phase shifts on a quantum computer using a leading order short-range effective field theory Hamiltonian. The algorithm combines the variational quantum eigensolver and the quantum subspace expansion. As an example, we consider scattering in the deuteron $^3$S$_1$ partial wave. We calculate scattering phase shifts with a quantum simulator and on real hardware. We also study how noise impacts these calculations and discuss noise mitigation required to extend our work to larger quantum processing units. With current hardware, up to five superconducting qubits can produce acceptable results, and larger calculations will require a significant noise reduction.
- [88] arXiv:2312.13420 (replaced) [pdf, html, other]
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Title: Ultraslow Growth of Number Entropy in an l-bit Model of Many-Body LocalizationComments: Main: 7 pages, 2 figures. Supplemental material: 7 pages, 9 figures, 1 table, 1 videoJournal-ref: Phys. Rev. Lett. 133, 126502 (2024)Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We demonstrate that slow growth of the number entropy following a quench from a local product state is consistent with many-body localization. To do this we construct a random circuit l-bit model with exponentially localized l-bits and exponentially decaying interactions between them. We observe an ultraslow growth of the number entropy starting from a Néel state, saturating at a value that grows with system size. This suggests that the observation of such growth in microscopic models is not sufficient to rule out many-body localization.
- [89] arXiv:2405.20943 (replaced) [pdf, html, other]
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Title: Optimizing EPR pulses for broadband excitation and refocusingComments: 12 pages, 8 figuresSubjects: Chemical Physics (physics.chem-ph); Quantum Physics (quant-ph)
In this paper, we numerically optimize broadband pulse shapes that maximize Hahn echo amplitudes. Pulses are parameterized as neural networks (NN), nonlinear amplitude limited Fourier series (FS), and discrete time series (DT). These are compared to an optimized choice of the conventional hyperbolic secant (HS) pulse shape. A power constraint is included, as are realistic shape distortions due to power amplifier nonlinearity and the transfer function of the microwave resonator. We find that the NN, FS, and DT parameterizations perform equivalently, offer improvements over the best HS pulses, and contain a large number of equivalent optimal solutions, implying the flexibility to include further constraints or optimization goals in future designs.
- [90] arXiv:2406.05324 (replaced) [pdf, html, other]
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Title: Bipartite reweight-annealing algorithm to extract large-scale data of entanglement entropy and its derivative in high precisionSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
We propose a quantum Monte Carlo (QMC) scheme able to extract large-scale data of entanglement entropy (EE) and its derivative with high precision and low technical barrier. We avoid directly computing the overlap of two partition functions within different spacetime manifolds and instead obtain them separately via reweight-annealing scheme. The incremental process can be designed along the path of real physical parameters in this frame, and all intermediates are EEs of corresponding parameters, so the algorithm efficiency is improved by more than $10^4$ of times. The calculation of EE becomes much cheaper and simpler. It opens a way to numerically detect the novel phases and phase transitions by scanning EE in a wide parameter-region in two and higher dimensional systems. We then show the feasibility of using EE and its derivative to find phase transition points and to probe novel phases.
- [91] arXiv:2407.21786 (replaced) [pdf, other]
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Title: Non-equilibrium dynamics of charged dual-unitary circuitsComments: 31 pages, 8 figures; v2 improved presentationSubjects: Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
The interplay between symmetries and entanglement in out-of-equilibrium quantum systems is currently at the centre of an intense multidisciplinary research effort. Here we introduce a setting where these questions can be characterised exactly by considering dual-unitary circuits with an arbitrary number of $U(1)$ charges. After providing a complete characterisation of these systems we show that one can introduce a class of solvable states, which extends that of generic dual unitary circuits, for which the non-equilibrium dynamics can be solved exactly. In contrast to the known class of solvable states, which relax to the infinite temperature state, these states relax to a family of non-trivial generalised Gibbs ensembles. The relaxation process of these states can be simply described by a linear growth of the entanglement entropy followed by saturation to a non-maximal value but with maximal entanglement velocity. We then move on to consider the dynamics from non-solvable states, combining exact results with the entanglement membrane picture we argue that the entanglement dynamics from these states is qualitatively different from that of the solvable ones. It shows two different growth regimes characterised by two distinct slopes, both corresponding to sub-maximal entanglement velocities. Moreover, we show that non-solvable initial states can give rise to the quantum Mpemba effect, where less symmetric initial states restore the symmetry faster than more symmetric ones.
- [92] arXiv:2407.21793 (replaced) [pdf, other]
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Title: Non-equilibrium dynamics of symmetry-resolved entanglement and entanglement asymmetry: Exact asymptotics in Rule 54Comments: 21 pages, 2 figures; Submitted to the special issue of Journal of Physics A: Mathematical and Theoretical, "Quantum-Circuit Models for Many-Body Physics Out of Equilibrium"; v2 accepted versionSubjects: Statistical Mechanics (cond-mat.stat-mech); Cellular Automata and Lattice Gases (nlin.CG); Exactly Solvable and Integrable Systems (nlin.SI); Quantum Physics (quant-ph)
Symmetry resolved entanglement and entanglement asymmetry are two measures of quantum correlations sensitive to symmetries of the system. Here we discuss their non-equilibrium dynamics in the Rule 54 cellular automaton, a simple, yet interacting, integrable model. Both quantities can be expressed in terms of the more analytically tractable "charged moments", i.e. traces of powers of a suitably deformed density matrix, via a replica trick. We express them in terms of a tensor network, which we contract in space using a system of local algebraic relations. This gives the asymptotic form for the charged moments, valid in the regime of large but finite time that is shorter than all the relevant subsystem sizes. In this regime the charge moments decay exponentially with the rate given by the leading solution to a cubic equation.
- [93] arXiv:2409.07047 (replaced) [pdf, html, other]
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Title: Population Dynamics of Schr\"odinger CatsSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We demonstrate an exact equivalence between classical population dynamics and Lindbladian evolution admitting a dark state and obeying a set of certain local symmetries. We then introduce {\em quantum population dynamics} as models in which this local symmetry condition is relaxed. This allows for non-classical processes in which animals behave like Schrödinger's cat and enter superpositions of live and dead states, thus resulting in coherent superpositions of different population numbers. We develop a field theory treatment of quantum population models as a synthesis of Keldysh and third quantization techniques and draw comparisons to the stochastic Doi-Peliti field theory description of classical population models. We apply this formalism to study a prototypical ``Schrödigner cat'' population model on a $d$-dimensional lattice, which exhibits a phase transition between a dark extinct phase and an active phase that supports a stable quantum population. Using a perturbative renormalization group approach, we find a critical scaling of the Schrödinger cat population distinct from that observed in both classical population dynamics and usual quantum phase transitions.
- [94] arXiv:2409.10010 (replaced) [pdf, html, other]
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Title: Optical resonators constitute a universal spin simulatorSubjects: Optics (physics.optics); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)
NP-hard computational problems can be efficiently recast as finding the ground state of an effective spin model. However, to date no convenient setup exists that can universally simulate all of them, even for a fixed problem size. Here we present such a setup, using a series of optical (or polaritonic) resonators arranged in a chain using the geometry recently introduced in [Phys. Rev. Applied 21, 024057 (2024)]. We demonstrate by example how the simulator solves Hamiltonian Cycle and traveling salesman problems, and show that it generalises to any NP-hard problem of arbitrary size.
- [95] arXiv:2409.10301 (replaced) [pdf, html, other]
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Title: Decomposition Pipeline for Large-Scale Portfolio Optimization with Applications to Near-Term Quantum ComputingAtithi Acharya, Romina Yalovetzky, Pierre Minssen, Shouvanik Chakrabarti, Ruslan Shaydulin, Rudy Raymond, Yue Sun, Dylan Herman, Ruben S. Andrist, Grant Salton, Martin J. A. Schuetz, Helmut G. Katzgraber, Marco PistoiaSubjects: Optimization and Control (math.OC); Data Analysis, Statistics and Probability (physics.data-an); Portfolio Management (q-fin.PM); Risk Management (q-fin.RM); Quantum Physics (quant-ph)
Industrially relevant constrained optimization problems, such as portfolio optimization and portfolio rebalancing, are often intractable or difficult to solve exactly. In this work, we propose and benchmark a decomposition pipeline targeting portfolio optimization and rebalancing problems with constraints. The pipeline decomposes the optimization problem into constrained subproblems, which are then solved separately and aggregated to give a final result. Our pipeline includes three main components: preprocessing of correlation matrices based on random matrix theory, modified spectral clustering based on Newman's algorithm, and risk rebalancing. Our empirical results show that our pipeline consistently decomposes real-world portfolio optimization problems into subproblems with a size reduction of approximately 80%. Since subproblems are then solved independently, our pipeline drastically reduces the total computation time for state-of-the-art solvers. Moreover, by decomposing large problems into several smaller subproblems, the pipeline enables the use of near-term quantum devices as solvers, providing a path toward practical utility of quantum computers in portfolio optimization.
- [96] arXiv:2410.09177 (replaced) [pdf, html, other]
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Title: From {\tt Ferminet} to PINN. Connections between neural network-based algorithms for high-dimensional Schr\"odinger HamiltonianSubjects: Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
In this note, we establish some connections between standard (data-driven) neural network-based solvers for PDE and eigenvalue problems developed on one side in the applied mathematics and engineering communities (e.g. Deep-Ritz and Physics Informed Neural Networks (PINN)), and on the other side in quantum chemistry (e.g. Variational Monte Carlo algorithms, {\tt Ferminet} or {\tt Paulinet} following the pioneer work of {\it Carleo et. al}. In particular, we re-formulate a PINN algorithm as a {\it fitting} problem with data corresponding to the solution to a standard Diffusion Monte Carlo algorithm initialized thanks to neural network-based Variational Monte Carlo. Connections at the level of the optimization algorithms are also established.