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Entanglement-enhanced quantum strategies for accurate estimation of multibody-group motion and moving-object characteristics

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Physical Review A 2023年第6期108卷 062605-062605页

作者： Yongqiang Li Changliang Ren 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 and Institute of Interdisciplinary Studies Hunan Normal University Changsha 410081 China

This study presents a quantum strategy for simultaneous estimation of two physical quantities using different entanglement resources. We explore the utilization of positively or negatively time-correlated photons. The proposed method enables the detection of the central position and relative velocity of multibody systems, as well as precise measurement of the size and velocity of moving objects. Comparative analysis with other strategies reveals the superior quantum advantage of our approach, particularly when appropriate entanglement sources with a high degree of entanglement are employed. These findings contribute to advancing our understanding of quantum strategies for accurate measurements.

关键词： Quantum correlations in quantum information Quantum metrology Quantum parameter estimation Quantum protocols

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Scaling enhancement of photon blockade in output fields

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Physical Review A 2024年第6期110卷 063705-063705页

作者： Zhi-Hao Liu Xun-Wei Xu 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 Institute of Interdisciplinary Studies Hunan Normal University Changsha 410081 China

Photon blockade enhancement is an exciting and promising subject that has been well studied for photons in cavities. However, whether photon blockade can be enhanced in the output fields remains largely unexplored. We show that photon blockade can be greatly enhanced in the mixing output field of a nonlinear cavity and an auxiliary (linear) cavity, where no direct coupling between the nonlinear and auxiliary cavities is needed. We uncover a biquadratic scaling relation between the second-order correlation of the photons in the output field and intracavity nonlinear interaction strength, in contrast to a quadratic scaling relation for the photons in a nonlinear cavity. We identify that this scaling enhancement of photon blockade in the output field is induced by the destructive interference between two of the paths for two photons passing through the two cavities. We then extend the theory to the experimentally feasible Jaynes-Cummings model consisting of a two-level system strongly coupled to one of the two uncoupled cavities, and also predict a biquadratic scaling law in the mixing output field. Our proposed scheme is general and can be extended to enhance blockade in other bosonic systems.

关键词： Jaynes-Cummings model

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Broadband optical nonreciprocity via nonreciprocal band structure

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Physical Review A 2023年第6期108卷 063516-063516页

作者： Ning Hu Zhi-Xiang Tang Xun-Wei Xu Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Key Laboratory for Matter Microstructure and Function of Hunan Province Hunan Normal University Changsha 410081 China Institute of Interdisciplinary Studies Hunan Normal University Changsha 410081 China

As a promising approach for optical nonreciprocity without magnetic materials, optomechanically induced nonreciprocity has great potential for all-optical controllable isolators and circulators on integrated photonic chips. However, as a very important issue in practical applications, the bandwidth for nonreciprocal transmission with high isolation has not been fully investigated yet. In this study we first review the nonreciprocity in a Brillouin optomechanical system with single cavity mode and point out the challenge in achieving broad bandwidth with high isolation. To overcome this challenge, we propose a one-dimensional optomechanical array to realize broadband optical nonreciprocity via nonreciprocal band structure. We exploit nonreciprocal band structure induced by the stimulated Brillouin scattering with directional optical pumping and show that it is possible to demonstrate optical nonreciprocity with both broad bandwidth and high isolation. Such optomechanical lattices with nonreciprocal band structure, offer an avenue to explore nonreciprocal collective effects of both photons and phonons in different frequency regimes.

关键词： Non-reciprocal transmission Optomechanics

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Nonreciprocal ground-state cooling of multiple mechanical resonators

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Physical Review A 2020年第1期102卷 011502(R)-011502(R)页

作者： Deng-Gao Lai Jin-Feng Huang Xian-Li Yin Bang-Pin Hou Wenlin Li David Vitali Franco Nori Jie-Qiao Liao 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 Theoretical Quantum Physics Laboratory RIKEN Saitama 351-0198 Japan College of Physics and Electronic Engineering Institute of Solid State Physics Sichuan Normal University Chengdu 610068 China School of Science and Technology Physics Division University of Camerino I-62032 Camerino (MC) Italy INFN Sezione di Perugia I-06123 Perugia Italy CNR-INO Largo Enrico Fermi 6 I-50125 Firenze Italy Physics Department The University of Michigan Ann Arbor Michigan 48109-1040 USA

The simultaneous ground-state cooling of multiple degenerate or near-degenerate mechanical modes coupled to a common cavity-field mode has become an outstanding challenge in cavity optomechanics. This is because the dark modes formed by these mechanical modes decouple from the cavity mode and prevent extracting energy from the dark modes through the cooling channel of the cavity mode. Here we propose a universal and reliable dark-mode-breaking method to realize the simultaneous ground-state cooling of two degenerate or nondegenerate mechanical modes by introducing a phase-dependent phonon-exchange interaction, which is used to form a loop-coupled configuration. We find an asymmetrical cooling performance for the two mechanical modes and expound this phenomenon based on the nonreciprocal energy transfer mechanism, which leads to the directional flow of phonons between the two mechanical modes. We also generalize this method to cool multiple mechanical modes. The physical mechanism in this cooling scheme has general validity and this method can be extended to break other dark-mode and dark-state effects in physics.

关键词： Optomechanics

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Nonreciprocal photon blockade and directional amplification in a spinning resonator coupled to a two-level atom

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Physical Review A 2021年第3期104卷 033707-033707页

作者： Yu-Wei Jing Hai-Quan Shi Xun-Wei Xu 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 Department of Applied Physics East China Jiaotong University Nanchang 330013 China

We propose a scheme to realize nonreciprocal photon blockade and directional amplification in a spinning resonator with clockwise and counterclockwise traveling modes coupled to a stationary two-level atom. By manipulating the rotational frequency of the resonator, the two-level atom can be resonant with one of the traveling modes and largely detuned from the other one. Nonreciprocal conventional photon blockade is induced by the difference of the detunings between the two-level atom and the optical modes traveling in different directions. Besides that, nonreciprocal unconventional photon blockade (UPB) based on the quantum interference can also be observed in the system. Based on the mechanism for nonreciprocal UPB, directional amplification of the blockaded photons is predicted by driving the spinning resonator and stationary two-level atom simultaneously. Our proposal will be applicable to achieve highly efficient nonreciprocal single-photon devices for applications in chiral quantum information processing.

关键词： Cavity quantum electrodynamics Coherent control Optomechanics Photon statistics Quantum optics Optical microcavities Jaynes-Cummings model

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Multiphoton blockade in the two-photon Jaynes-Cummings model

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Physical Review A 2020年第5期102卷 053710-053710页

作者： Fen Zou Xiao-Ya Zhang Xun-Wei Xu Jin-Feng Huang Jie-Qiao Liao 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 Department of Applied Physics East China Jiaotong University Nanchang 330013 China

We study multiphoton blockade and photon-induced tunneling effects in the two-photon Jaynes-Cummings model, where a single-mode cavity field and a two-level atom are coupled via a two-photon interaction. We consider both the cavity-field-driving and the atom-driving cases and find that single-photon blockade and photon-induced tunneling effects can be observed when the cavity mode is driven, while the two-photon blockade effect appears when the atom is driven. For the atom-driving case (the two-photon transition process), we present a criterion of the correlation functions for the multiphoton blockade effect. Specifically, we show that quantum interference can enhance the photon blockade effect in the single-photon cavity-field-driving case. Our results are confirmed by analytically and numerically calculating the correlation function of the cavity-field mode. Our work has potential applications in quantum information processing and paves the way for the study of multiphoton quantum coherent devices.

关键词： Cavity quantum electrodynamics Photon statistics

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Structural and functional analysis of a potent human neutralizing antibody against enterovirus A71

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Science China(Life Sciences) 2022年第12期65卷 2517-2526页

作者： Zhe Chen Linlin Bao Bin Zhu Hua Fu Shuangli Zhu Tianjiao Ji Ying Xue Chuan Liu Xurong Wang Fengdi Li Qi Lv Feifei Qi Pin Yu Wei Deng Wenbo Xu Chuan Qin Hongrong Liu Qi Jin MOH Key Laboratory of Systems Biology of Pathogens Institute of Pathogen BiologyChinese Academy of Medical Sciences&Peking Union Medical CollegeBeijing 100730China Beijing Key Laboratory for Animal Models of Emerging and Remerging Infectious Diseases NHC Key Laboratory of Human Disease Comparative MedicineInstitute of Laboratory Animal ScienceChinese Academy of Medical Sciences and Comparative Medicine CenterPeking Union Medical CollegeBeijing 100021China School of Computer Science and Engineering Hunan University of Science and TechnologyXiangtan 411201China National Institute for Viral Disease Control and Prevention China CDCBeijing 102206China Ministry of Education Key Laboratory of Protein Sciences Beijing Advanced Innovation Center for Structural BiologyTsinghua UniversityBeijing 100084China Key Laboratory for Matter Microstructure and Function of Hunan Province Key Laboratory of Low-dimensional Quantum Structures and Quantum ControlSchool of Physics and ElectronicsHunan Normal UniversityChangsha 410081China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases Hangzhou 310058China

Enterovirus A71(EV-A71) causes major outbreaks of hand,foot,and mouth disease(HFMD) in many countries,most frequently affecting children,and a small proportion of cases may lead to ***,no vaccine is available in most endemic regions,and no licenced treatments for EV-A71 infection are ***,we characterize a human monoclonal antibody(Hu MAb),E1,by screening a Fab antibody phage library derived from patients who recovered from EV-A71 infection.E1 exhibits strong neutralizing activity against EV-A71 virus in *** cryo-electron microscopy(cryo-EM) structures of the EV-A71 virion in complex with E1 Fab fragments demonstrated that E1 recognized an epitope formed by residues in the BC and HI loops of *** a mouse model,E1 effectively protected against lethal EV-A71 challenge in both prophylactic and therapeutic *** particular,E1 significantly reduces virus titers and muscle damage.E1 might represent a potential adjunct to EV-A71 treatment.

关键词： enterovirus A71 antibody mouse models cryo-electron microscopy

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Direct measurement of density-matrix elements using a phase-shifting technique

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Physical Review A 2021年第4期104卷 042403-042403页

作者： Tianfeng Feng Changliang Ren Xiaoqi Zhou State Key Laboratory of Optoelectronic Materials and Technologies and 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 and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China

A 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 an ancillary pointer, which interacts with the investigated system to extract information about the specified elements. Here, we present a direct measurement scheme based on phase-shifting operations which do not need ancillary pointers. In this method, estimates of at most six 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 multiqubit states is provided, which is composed of just single-qubit gates and two multiqubit controlled-phase gates. This scheme is also extended for the 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.

关键词： Quantum algorithms Quantum information processing Quantum measurements Quantum protocols Quantum tomography

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Multinode State Transfer and Nonlocal State Preparation via a Unidirectional Quantum Network

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Physical Review Applied 2022年第5期17卷 054021-054021页

作者： Hao Ai Ying-Yü Fang Cheng-Rui Feng Zhihui Peng Ze-Liang Xiang School of Physics Sun Yat-sen University Guangzhou 510275 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

Quantum networks with the ability to coherently transfer quantum states between different nodes open up possibilities for upscaling quantum technologies. In this work, we propose a theoretical protocol to implement the multinode state transfer and nonlocal state preparation in a one-dimensional network consisting of many quantum nodes coupled to a common unidirectional channel. By time-dependently modulating the coupling strength between the nodes and the channel, a quantum state stored in one node can be distributed to the other nodes through the channel, while a series of dark-state conditions ensure a desired final state. This protocol can also be used to prepare nonlocal entanglement states of these nodes, such as the W -type state. Importantly, it can be realized in various quantum platforms with currently available technologies.

关键词： Quantum control Quantum networks

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Modulation-based superradiant phase transition in the strong-coupling regime

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Physical Review A 2023年第6期107卷 063713-063713页

作者： Jin-Feng Huang Lin Tian 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 School of Natural Sciences University of California Merced California 95343 USA

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.

关键词： Coherent control Quantum communication Quantum computation Quantum information processing Superradiance & subradiance

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