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arXiv 2024年

作者： Moghadas, Emin Dräger, Nikolaus Toschi, Alessandro Zang, Jiawei Medvidović, Matija Kiese, Dominik Millis, Andrew J. Sengupta, Anirvan M. Andergassen, Sabine Sante, Domenico Di Institute for Solid State Physics TU Wien Vienna1040 Austria Institute for Solid State Physics Institute of Information Systems Engineering TU Wien Vienna1040 Austria Department of Physics Columbia University 538 W 120th Street New YorkNY10027 United States Center for Computational Quantum Physics Flatiron Institute 162 5th Avenue New YorkNY10010 United States Center for Computational Mathematics Flatiron Institute 162 5th Avenue New YorkNY10010 United States Department of Physics and Astronomy Rutgers University PiscatawayNJ08854 United States Department of Physics and Astronomy University of Bologna Bologna40127 Italy

Precise algorithms capable of providing controlled solutions in the presence of strong interactions are transforming the landscape of quantum many-body physics. Particularly exciting breakthroughs are enabling the computation of non-zero temperature correlation functions. However, computational challenges arise due to constraints in resources and memory limitations, especially in scenarios involving complex Green’s functions and lattice effects. Leveraging the principles of signal processing and data compression, this paper explores the wavelet decomposition as a versatile and efficient method for obtaining compact and resource-efficient representations of the many-body theory of interacting systems. The effectiveness of the wavelet decomposition is illustrated through its application to the representation of generalized susceptibilities and self-energies in a prototypical interacting fermionic system, namely the Hubbard model at half-filling in its atomic limit. These results are the first proof-of-principle application of the wavelet compression within the realm of many-body physics and demonstrate the potential of this wavelet-based compression scheme for understanding the physics of correlated electron systems. © 2024, CC BY.

关键词： Hubbard model

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The Critical Behavior of quantum Stirling Heat Engine

arXiv

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arXiv 2023年

作者： Wang, Yuan-Sheng Yung, Man-Hong Xu, Dazhi Liu, Maoxin Chen, Xiaosong School of Systems Science Beijing Normal University Beijing100875 China Lanzhou Center for Theoretic Physics Lanzhou University Gansu Lanzhou730000 China Department of Physics Southern University of Science and Technology Shenzhen518055 China Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Shenzhen Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Department of Physics Beijing Institute of Technology Beijing100081 China

We investigate the performance of a Stirling cycle with a working substance (WS) modeled as the quantum Rabi model (QRM), exploring the impact of criticality on its efficiency. Our findings indicate that the criticality of the QRM has a positive effect on improving the efficiency of the Stirling cycle. Furthermore, we observe that the Carnot efficiency is asymptotically achievable as the WS parameter approaches the critical point, even when both the temperatures of the cold and hot reservoirs are finite. Additionally, we derive the critical behavior for the efficiency of the Stirling cycle, demonstrating how the efficiency asymptotically approaches the Carnot efficiency as the WS parameter approaches the critical point. Our work deepens the understanding of the impact of criticality on the performance of a Stirling heat engine. Copyright © 2023, The Authors. All rights reserved.

关键词： Stirling cycle

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quantum refrigerator driven by nonclassical light

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Physical Review Research 2022年第4期4卷 043158-043158页

作者： Hui-Jing Cao (曹会静) Fu Li (李福) Sheng-Wen Li (李圣文) Center for Quantum Technology Research and Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements School of Physics Beijing Institute of Technology Beijing 100081 China Department of Electrical and Systems Engineering Washington University St. Louis Missouri 63130 USA

We study a three-level quantum refrigerator which is driven by a generic light state, even a nonclassical one. With the help of P function expansion of the driving light, we obtain the heat current generated by different types of light states. It turns out all different input light states give the same coefficient of performance for this refrigerator, while the cooling power depends not only on the light intensity but also the specific photon statistics of the driving light. Comparing the coherent light with the same intensity, the driving light with super(sub)-Poissonian photon statistics could raise a smaller (stronger) cooling power. We find that this is because the bunching photons would first excite the system but then successively induce the stimulated emission, which draws the refrigerator back to the starting state of the cooling process and thus decreases the cooling current generation. This mechanism provides a more delicate control method via the high order coherence of the input light.

关键词： quantum description of light-matter interaction quantum states of light quantum thermodynamics quantum heat engines & refrigerators Master equation

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First Passage Times for Continuous quantum Measurement Currents

arXiv

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arXiv 2023年

作者： Kewming, Michael J. Kiely, Anthony Campbell, Steve Landi, Gabriel T. School of Physics Trinity College Dublin College Green Dublin 2 Ireland School of Physics University College Dublin Belfield Dublin 4 Ireland Centre for Quantum Engineering Science and Technology University College Dublin Belfield Dublin 4 Ireland Dahlem Center for Complex Quantum Systems Freie Universität Berlin Arnimallee 14 Berlin14195 Germany Department of Physics and Astronomy University of Rochester RochesterNY14627 United States

The First Passage Time (FPT) is the time taken for a stochastic process to reach a desired threshold. In this letter we address the FPT of the stochastic measurement current in the case of continuously measured quantum systems. We find that our approach, based on a charge-resolved master equation related to Full-Counting statistics of charge detection, enables efficient and analytical computation of the FPT. We develop a versatile framework applicable to quantum jump unravelling and quantum diffusion scenarios, demonstrating that the FPT can be obtained by introducing absorbing boundary conditions. Our framework is demonstrated with two relevant examples: First, we examine the tightness of recently proposed kinetic uncertainty relations (KURs) for quantum jumps, which place bounds on the signal-to-noise ratio of the FPT. Second, we investigate the usage of qubits as threshold detectors for Rabi pulses, showing how our method can optimize detection probability while minimizing false positives. This work offers insights into the applications of the FPT for continuous measurements including the signal-to-noise ratio bounds and false positive minimization strategies, advancing quantum information processing applications. Copyright © 2023, The Authors. All rights reserved.

关键词： Signal to noise ratio

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Universally Robust quantum Control

arXiv

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arXiv 2023年

作者： Poggi, Pablo M. De Chiara, Gabriele Campbell, Steve Kiely, Anthony Department of Physics SUPA University of Strathclyde GlasgowG4 0NG United Kingdom Center for Quantum Information and Control Department of Physics and Astronomy University of New Mexico AlbuquerqueNM87131 United States Centre for Quantum Materials and Technology School of Mathematics and Physics Queen's University Belfast BelfastBT7 1NN United Kingdom School of Physics University College Dublin Dublin 4 Belfield Ireland Centre for Quantum Engineering Science and Technology University College Dublin Dublin 4 Belfield Ireland Dahlem Center for Complex Quantum Systems Freie Universität Berlin Arnimallee 14 Berlin14195 Germany

We study the robustness of the evolution of a quantum system against small uncontrolled variations in parameters in the Hamiltonian. We show that the fidelity susceptibility, which quantifies the perturbative error to leading order, can be expressed in superoperator form and use this to derive control pulses which are robust to any class of systematic unknown errors. The proposed optimal control protocol is equivalent to searching for a sequence of unitaries that mimics the first-order moments of the Haar distribution, i.e. it constitutes a 1-design. We highlight the power of our results for error-resistant single- and two-qubit gates. Copyright © 2023, The Authors. All rights reserved.

关键词： Hamiltonians

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Decoherence-Induced Exceptional Points in a Dissipative Superconducting Qubit

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Physical Review Letters 2022年第11期128卷 110402-110402页

作者： Weijian Chen Maryam Abbasi Byung Ha Serra Erdamar Yogesh N. Joglekar Kater W. Murch Department of Physics Washington University St. Louis Missouri 63130 USA Center for Quantum Sensors Washington University St. Louis Missouri 63130 USA Department of Electrical and Systems Engineering Washington University St. Louis Missouri 63130 USA Department of Physics Indiana University-Purdue University Indianapolis Indianapolis Indiana 46202 USA

Open quantum systems interacting with an environment exhibit dynamics described by the combination of dissipation and coherent Hamiltonian evolution. Taken together, these effects are captured by a Liouvillian superoperator. The degeneracies of the (generically non-Hermitian) Liouvillian are exceptional points, which are associated with critical dynamics as the system approaches steady state. We use a superconducting transmon circuit coupled to an engineered environment to observe two different types of Liouvillian exceptional points that arise either from the interplay of energy loss and decoherence or purely due to decoherence. By dynamically tuning the Liouvillian superoperators in real time we observe a non-Hermiticity-induced chiral state transfer. Our study motivates a new look at open quantum system dynamics from the vantage of Liouvillian exceptional points, enabling applications of non-Hermitian dynamics in the understanding and control of open quantum systems.

关键词： Open quantum systems & decoherence PT-symmetric quantum mechanics Superconducting qubits

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Homodyne measurement with a Schrödinger cat state as a local oscillator

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Physical Review A 2022年第6期106卷 063706-063706页

作者： Joshua Combes Austin P. Lund Department of Electrical Computer and Energy Engineering University of Colorado Boulder Colorado 80309 USA Dahlem Center for Complex Quantum Systems Freie Universität Berlin 14195 Berlin Germany Centre for Quantum Computation and Communications Technology School of Mathematics and Physics The University of Queensland St Lucia QLD Australia

Homodyne measurements are a widely used quantum measurement. Using a coherent state of large amplitude as the local oscillator, it can be shown that the quantum homodyne measurement limits to a field quadrature measurement. In this work, we give an example of a general idea: injecting nonclassical states as a local oscillator can lead to nonclassical measurements. Specifically, we consider injecting a superposition of coherent states, a Schrödinger cat state, as a local oscillator. We derive the Kraus operators and the positive operator-valued measure in this situation.

关键词： Optics & lasers quantum engineering quantum optics quantum sensing

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Holes and magnetic polarons in a triangular lattice antiferromagnet

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Physical Review B 2022年第23期106卷 235143-235143页

作者： Jasper van de Kraats Kristian K. Nielsen Georg M. Bruun Eindhoven University of Technology P. O. Box 513 5600 MB Eindhoven The Netherlands Max-Planck Institute for Quantum Optics Hans-Kopfermann-Str. 1 D-85748 Garching Germany Center for Complex Quantum Systems Department of Physics and Astronomy Aarhus University Ny Munkegade DK-8000 Aarhus C Denmark Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518055 China

The intricate interplay between charge motion and magnetic order in geometrically frustrated lattices is central for the properties of many two-dimensional quantum materials. The triangular lattice antiferromagnet is a canonical example of a frustrated system, and here we analyze the dynamics of a hole in such a lattice focusing on observables that have become accessible in a new generation of experiments. Using the t−J model, we solve the problem exactly within linear spin wave theory in the limit of strong magnetic interactions, showing that the ground state is described by a coherent state of spin waves. The derivation highlights the crucial role played by the interaction between a static hole and the neighboring spins, which originates in the geometric frustration and has often been omitted in earlier works. Furthermore, we show that the nonequilibrium dynamics after a hole has abruptly been inserted at a lattice site is given by a coherent state with time-dependent oscillatory coefficients. Physically, this describes a burst of magnetic frustration propagating through only two-thirds of the lattice sites, since a destructive interference of spin waves leaves spins parallel to that removed by the hole unperturbed. After the wave has propagated through the lattice, the magnetization relaxes to that of the ground state. We then use our analytical solution to benchmark the widely used self-consistent Born approximation (SCBA) in the limit of strong magnetic interactions, showing that it is very accurate also for a triangular lattice. The magnetic polaron spectrum is analyzed for general magnetic interactions using the SCBA, and we compare our results with those for a square lattice.

关键词： Antiferromagnetism Cold gases in optical lattices Impurities Polarons Spin waves Antiferromagnets Strongly correlated systems Diagrammatic methods Holstein-Primakoff method t-J model

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High-Purity Generation and Switching of Twisted Single Photons

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Physical Review Letters 2023年第18期131卷 183801-183801页

作者： Haoqi Zhao Yichen Ma Zihe Gao Na Liu Tianwei Wu Shuang Wu Xilin Feng James Hone Stefan Strauf Liang Feng Department of Electrical and Systems Engineering University of Pennsylvania Philadelphia Pennsylvania 19104 USA Department of Materials Science and Engineering University of Pennsylvania Philadelphia Pennsylvania 19104 USA Department of Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA Center for Quantum Science and Engineering Stevens Institute of Technology Hoboken New Jersey 07030 USA Department of Mechanical Engineering Columbia University New York New York 10027 USA

quantum technologies, if scaled into a high-dimensional Hilbert space, can dramatically enhance connection capabilities with supporting higher bit rates and ultrasecure information transfer. Twisted single photons, carrying orbital angular momentum (OAM) as an unbounded dimension, could address the growing demand for high-dimensional quantum information encoding and transmission. By hybrid integration of two-dimensional semiconductor WSe2 with a spin-orbit-coupled microring resonator, we demonstrate an integrated tunable twisted single photon source with the ability to precisely define and switch between highly pure spin-OAM states. Our results feature a single photon purity of g(2)(0)∼0.13 with a cavity-enhanced quantum yield of 76% and a high OAM mode purity up to 96.9%. Moreover, the demonstrated quantum-chiral control can also enable new quantum functionality such as single photon routing for efficient quantum information processing on chip.

关键词： Angular momentum of light Integrated optics Single photon sources Structured light

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Single-gate tracking behavior in flat-band multilayer graphene devices

arXiv

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arXiv 2025年

作者： Kolář, Kryštof Waters, Dacen Folk, Joshua Yankowitz, Matthew Lewandowski, Cyprian Dahlem Center for Complex Quantum Systems and Fachbereich Physik Freie Universität Berlin Berlin14195 Germany Department of Applied Physics Aalto University School of Science AaltoFI-00076 Finland Department of Physics University of Washington SeattleWA98195 United States Department of Physics and Astronomy University of Denver DenverCO80210 United States Quantum Matter Institute University of British Columbia VancouverBCV6T 1Z4 Canada Department of Physics and Astronomy University of British Columbia VancouverBCV6T 1Z1 Canada Department of Materials Science and Engineering University of Washington SeattleWA98195 United States National High Magnetic Field Laboratory TallahasseeFL32310 United States Department of Physics Florida State University TallahasseeFL32306 United States

A central feature of many van der Waals (vdW) materials is the ability to precisely control their charge doping, n, and electric displacement field, D, using top and bottom gates. For devices composed of only a few layers, it is commonly assumed that D causes the layer-by-layer potential to drop linearly across the structure. Here, we show that this assumption fails for a broad class of crystalline and moiré vdW structures based on Bernal- or rhombohedral-stacked multilayer graphene. We find that the electronic properties at the Fermi level are largely dictated by special layer–polarized states arising at Bernal-stacked crystal faces, which typically coexist in the same band with layer-delocalized states. We uncover a novel mechanism by which the layer-delocalized states completely screen the layer–polarized states from the bias applied to the remote gate. This screening mechanism leads to an unusual scenario where voltages on either gate dope the band as expected, yet the band dispersion and associated electronic properties remain primarily (and sometimes exclusively) governed by the gate closer to the layer–polarized states. Our results reveal a novel electronic mechanism underlying the atypical single-gate-controlled transport characteristics observed across many flat-band graphitic structures, and provide key theoretical insights essential for accurately modeling these systems. Copyright © 2025, The Authors. All rights reserved.

关键词： Van der Waals forces

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