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Quantum thermalization and thermal entanglement in the open quantum Rabi model

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arXiv 2022年

作者： Liu, Wang-Yan Fan, Li-Bao Zeng, Ye-Xiong Huang, Jin-Feng Liao, Jie-Qiao Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha410083 China Theoretical Quantum Physics Laboratory RIKEN Cluster for Pioneering Research Saitama Wako-shi351-0198 Japan

We study quantum thermalization and thermal entanglement in the open quantum Rabi model (QRM), in which a two-level system and a single-mode bosonic field are coupled to either two individual heat baths or a common heat bath. By treating the QRM as an effective multilevel system and deriving global quantum master equations in the eigenstate representation of the QRM, we study the physical conditions for quantum thermalization of the QRM. It is found that, in the individual heat-bath case, the QRM can only be thermalized when either the two heat baths have the same temperature or the QRM is only coupled to one of the two baths. In the common heat-bath case, differently, the QRM can always be thermalized. We also study thermal entanglement of the QRM in both the resonant- and non-resonant coupling cases. The logarithmic negativity for the thermal state of the QRM is obtained in a wide parameter space, ranging from the low- to high-temperature limits, and from the weak- to deep-strong-coupling regimes. This work paves the way towards the study of quantum effects in nonequilibrium ultrastrongly-coupled light-matter systems. Copyright © 2022, The Authors. All rights reserved.

关键词： Quantum entanglement

Nonequilibrium thermal transport and photon squeezing in a quadratic qubit-resonator system

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arXiv 2021年

作者： Wang, Chen Chen, Hua Liao, Jie-Qiao Department of Physics Zhejiang Normal University Zhejiang Jinhua321004 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China

We investigate steady-state thermal transport and photon statistics in a nonequilibrium hybrid quantum system, in which a qubit is longitudinally and quadratically coupled to an optical resonator. Our calculations are conducted with the method of the quantum dressed master equation combined with full counting statistics. The effect of negative differential thermal conductance is unravelled at finite temperature bias, which stems from the suppression of cyclic heat transitions and large mismatch of two squeezed photon modes at weak and strong qubit-resonator hybridizations, respectively. The giant thermal rectification is also exhibited at large temperature bias. It is found that the intrinsically asymmetric structure of the hybrid system and negative differential thermal conductance show the cooperative contribution. Noise power and skewness, as typical current fluctuations, exhibit global maximum with strong hybridization at small and large temperature bias limits, respectively. Moreover, the effect of photon quadrature squeezing is discovered in the strong hybridization and low-temperature regime, which shows asymmetric response to two bath temperatures. These results would provide some insight to thermal functional design and photon manipulation in qubit-resonator hybrid quantum systems. © 2021, CC BY.

关键词： Resonators

Tunable Chiral Bound States in a Dimer Chain of Coupled Resonators

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arXiv 2022年

作者： Li, Jing Lu, Jing Gong, Z.R. Zhou, Lan Synergetic Innovation Center for Quantum Effects and Applications Key Laboratory for Matter Microstructure and Function of Hunan Province Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education School of Physics and Electronics Hunan Normal University Changsha410081 China College of Physics and Optoelectronic Engineering Shenzhen University Shenzhen518060 China

We study an excitation hopping on a one-dimensional (1D) dimer chain of coupled resonators with the alternate on-site photon energies, which interacts with a two-level emitter (TLE) by a coupling point or two adjacent coupling points. In the single-excitation subspace, this system not only possesses two energy bands with propagating states, but also possesses photonic bound states. The number of bound states depends on the coupling forms between the TLE and the dimer chain. It is found that when the TLE is locally coupled to one resonator of the dimer chain, the bound-state has mirror reflection symmetry. When the TLE is nonlocally coupled to two adjacent resonators, three bound states with preferred direction arise due to the mirror symmetry breaking. By using chirality to measure the asymmetry, it is found that the chirality of these bound states can be tuned by changing the energy differences of single photon in the adjacent resonators, the coupling strengths and the transition energy of the TLE. © 2022, CC BY.

关键词： Mirrors

Non-locality sharing for a three-qubit system via multilateral sequential measurements

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arXiv 2021年

作者： Ren, Changliang Liu, Xiaowei Hou, Wenlin Feng, Tianfeng Zhou, Xiaoqi Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China State Key Laboratory of Optoelectronic Materials and Technologies School of Physics Sun Yat-sen University Guangzhou China

Non-locality sharing for a three-qubit system via multilateral sequential measurements was deeply discussed. Different from 2-qubit cases, it is shown that non-locality sharing between Alice1 − Bob1 − Charlie1 and Alice2 − Bob2 − Charlie2 in a 3-qubit system can be observed, where two Mermin-Ardehali-Belinskii-Klyshko (MABK) inequalities can be violated simultaneously. Whats more, a complete non-locality sharing with all of 8 MABK inequalities simultaneous violations can be also observed. Compared with 2-qubit cases, the nonlocal sharing in a 3-qubit system shows more novel characteristics. Finally a general interpretation of nonlocal sharing according to joint conditional probability was discussed. Copyright © 2021, The Authors. All rights reserved.

关键词： Qubits

Superradiant Phase Transition in the Strong Coupling Regime

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arXiv 2022年

作者： Huang, Jin-Feng Tian, Lin Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China School of Natural Sciences University of California MercedCA95343 United States

The Dicke model can exhibit quantum phase transition between the normal and the superradiant phases when the strength of the light-matter coupling exceeds the ultrastrong coupling regime. However, it is challenging to observe this phase transition in practical systems due to limited coupling strength or finite two-photon A2 terms. Here we show that by applying a periodic modulation to the frequency of the two-level systems in a standard Dicke model in the strong coupling regime, an anisotropic Dicke model with tunable rotating and counter-rotating terms in the ultrastrong coupling regime can be achieved. We calculate the ground state and the excitation spectrum of this model in terms of the modulation parameters. Our result shows that the superradiant phases can be observed in cavity- or circuit-quantum electrodynamics systems with strong coupling. © 2022, CC BY.

关键词： Ground state

Dynamic sensitivity of quantum Rabi model with quantum criticality

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arXiv 2021年

作者： Hu, Ying Huang, Jian Huang, Jin-Feng Xie, Qiong-Tao Liao, Jie-Qiao Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China College of Physics and Electronic Engineering Hainan Normal University Haikou571158 China

We study the dynamic sensitivity of the quantum Rabi model, which exhibits quantum criticality in the finite-component-system case. This dynamic sensitivity can be detected by introducing an auxiliary two-level atom far-off-resonantly coupled to the cavity field of the quantum Rabi model. We find that when the quantum Rabi model goes through the critical point, the auxiliary atom experiences a sudden decoherence, which can be characterised by a sharp decay of the Loschmidt echo. Our scheme will provide a reliable way to observe quantum phase transition in ultrastrongly coupled quantum systems. Copyright © 2021, The Authors. All rights reserved.

关键词： Quantum optics

Direct measurement of density matrix elements using phase-shifting technique

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arXiv 2021年

作者： Feng, Tianfeng Ren, Changliang Zhou, Xiaoqi State Key Laboratory of Optoelectronic Materials and Technologies School of Physics Sun Yat-sen University Guangzhou China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha410081 China

Direct measurement protocol allows reconstructing specific elements of the density matrix of a quantum state without using quantum state tomography. However, the direct measurement protocols to date are primarily based on weak or strong measurements with ancillary pointer, which interacts with the investigated system to extract information about the specified elements. Here we present a new direct measurement scheme based on phase-shifting operations which do not need ancillary pointers. In this method, estimates of at most 6 expectation values of projective observables suffice to determine any specific element of an unknown quantum density matrix. A concrete quantum circuit to implement this direct measurement protocol for multi-qubit states is provided, which is composed of just single-qubit gates and two multi-qubit controlled-phase gates. This scheme is also extended for direct measurement of the density matrix of continuous-variable quantum states. Our method can be used in quantum information applications where only partial information about the quantum state needs to be extracted, for example, problems such as entanglement witnessing, fidelity estimation of quantum systems, and quantum coherence estimation. Copyright © 2021, The Authors. All rights reserved.

关键词： Quantum optics

Outstanding long-cycling lithium−sulfur batteries by core-shell structure of S@Pt composite with ultrahigh sulfur content

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Advanced Powder Materials

Advanced Powder Materials 2022年第1期1卷 88-96页

作者： Mengqin Gao Wan-Ying Zhou Yu-Xue Mo Tian Sheng Yanhong Deng Liezun Chen Kai Wang Yanliang Tan Haiqing Zhou College of Physics and Electronic Engineering Hengyang Normal UniversityHenghua Road No.16Hengyang City421002Hunan ProvinceChina College of Chemistry and Materials Science Anhui Normal UniversityWuhu241000China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan ProvinceHunan Normal UniversityChangsha410081China Institute of Nanotechnology Karlsruhe Institute of TechnologyEggenstein-Leopoldshafen76344Germany

Here we proposed a novel approach to greatly enhance the electrochemical performance of Li-S batteries by designing a composite electrode material composed of a core-shell structure of S@Pt composite(sulfur content,85%)grown on the S *** platinum(Pt)nanosheets provide physical barrier and strong chemical binding to anchor LiPSs and improve the electronic conductivity of ***,by introducing carbon nanofibers(CNFs)as the interlayer,we achieved outstanding Li-S battery with a high initial discharge capacity of 1040 mAh g^(-1)at 1.0C and a reversible capacity of 742 mAh g^(-1)after 350 cycles,demonstrating its excellent long-term cycling stability with a low capacity decay rate of 0.08%per *** to the density functional theory(DFT)calculations,we proposed that the superior performance is attributed to the cooperative effects of the strong interfacial interaction between Pt(111)surface and the S8 molecule,and very low reaction energy of decomposition,−6.4eV.

关键词： Lithium-sulfur batteries Wet chemistry High sulfur content Pt nanoshell Carbon fibers layer

Spin Quantum Heat Engine Quantified by Quantum Steering

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Physical Review Letters 2022年第9期128卷 090602-090602页

作者： Wentao Ji Zihua Chai Mengqi Wang Yuhang Guo Xing Rong Fazhan Shi Changliang Ren Ya Wang Jiangfeng Du CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences University of Science and Technology of China Hefei 230026 China CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Hefei 230026 China Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China

Following the rising interest in quantum information science, the extension of a heat engine to the quantum regime by exploring microscopic quantum systems has seen a boon of interest in the last decade. Although quantum coherence in the quantum system of the working medium has been investigated to play a nontrivial role, a complete understanding of the intrinsic quantum advantage of quantum heat engines remains elusive. We experimentally demonstrate that the quantum correlation between the working medium and the thermal bath is critical for the quantum advantage of a quantum Szilárd engine, where quantum coherence in the working medium is naturally excluded. By quantifying the nonclassical correlation through quantum steering, we reveal that the heat engine is quantum when the demon can truly steer the working medium. The average work obtained by taking different ways of work extraction on the working medium can be used to verify the real quantum Szilárd engine.

关键词： Quantum correlations in quantum information Quantum heat engines & refrigerators