We investigate the quantum speed limit time （QSLT） of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes h...We investigate the quantum speed limit time （QSLT） of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes have different influences on the evolutionary speed. By adjusting the feedback parameters, the quantum-jump-based feedback control can induce speedup of the atomic evolution from an excited state, but the homodyne-based feedback control cannot change the evolutionary speed. Additionally, the QSLT for the whole dynamical process is explored. Under the quantum-jump-based feedback control, the QSLT displays oscillatory behaviors, which implies multiple speed-up and speed-down processes during the evolution. While, the homodyne-based feedback control can accelerate the speed-up process and improve the uniform speed in the uniform evolution process.展开更多
We consider the system consisting of two qubits collectively damped, with the output being unit-efficiency measured and subsequently fed back to control the system state. Our primary goal in this paper is （i） to sol...We consider the system consisting of two qubits collectively damped, with the output being unit-efficiency measured and subsequently fed back to control the system state. Our primary goal in this paper is （i） to solve the feedback-modified master equation, （ii） to demonstrate the ability of feedback control based on the solutions, and （iii） to pick out different steady states by choosing different driving strengths and feedback strengths to counteract the effects of both damping and the measurement back-action on the system. We further investigate some properties of the equilibrium steady state, its distribution probability and entanglement vs. the driving and feedback amplitudes. We find that in our feedback model feedback plays a negative role in producing entanglement.展开更多
We consider an open quantum system subjected to a noise channel under measurement-based feedback control and two prototypical classes of decoherence channels are considered： phase damping and generalized amplitude da...We consider an open quantum system subjected to a noise channel under measurement-based feedback control and two prototypical classes of decoherence channels are considered： phase damping and generalized amplitude damping. Based on quantum trajectory theory, we obtain an extended master equation for the dynamics of the reduced system in the presence of feedback control. For a qubit system we analytically solve this master equation and obtain the solution of the state vector dynamics. Then we propose an effective feedback control scheme for preparing an arbitrary quantum pure state. We also study how to protect two nonorthogonai states effectively, and find that projective measurement with unbiazed basis is not optimal for this task, while weak measurement with biased basis could realize the best protection of two nonorthogonal states. Furthermore, the inefficiencies in the feedback process are also discussed展开更多
For an N-dimensional quantum system under the influence of continuous measurement, this paper presents a switching control scheme where the control law is of bang-bang type and achieves asymptotic preparation of an ar...For an N-dimensional quantum system under the influence of continuous measurement, this paper presents a switching control scheme where the control law is of bang-bang type and achieves asymptotic preparation of an arbitrarily given eigenstate of a non-degenerate and degenerate measurement operator, respectively. In the switching control strategy, we divide the state space into two parts： a set containing a target state, and its complementary set. By analyzing the stability of the stochastic system model under consideration, we design a constant control law and give some conditions that the control Hamiltonian satisfies so that the system trajectories in the complementary set converge to the set which contains the target state. Further, for the case of a non-degenerate measurement operator, we show that the system trajectories in the set containing the target state will automatically converge to the target state via quantum continuous measurement theory; while for the case of a degenerate measurement operator, the corresponding system trajectories will also converge to the target state via the construction of the control Hamiltonians. The convergence of the whole closed-loop systems under the cases of a non-degenerate and a degenerate measurement operator is strictly proved. The effectiveness of the proposed switching control scheme is verified by the simulation experiments on a finite-dimensional angular momentum system and a two-qubit system.展开更多
Based on Bures distance, a Lyapunov function that represents the distance between a desired state and the actual state of a quantum system is selected. Considering the cases that an initial state is and is not orthogo...Based on Bures distance, a Lyapunov function that represents the distance between a desired state and the actual state of a quantum system is selected. Considering the cases that an initial state is and is not orthogonal to the desired state respectively, we propose a class of control strategies with state feedback that ensures the stability of the closed-loop control system. Especially, the asymptotic stability of the control system is analyzed, deduced and proved in detail. Finally, a simulation experiment on a spin-1/2 particle system is done and the relation between the system state evolution time and control value is analyzed with diffierent parameters . Research results have general theoretical meaning for control of quantum systems.展开更多
A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on...A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.展开更多
Reservoir engineering is the term used in quantum control and information technologies to describe manipulating the environment within which an open quantum system operates. Reservoir engineering is essential in appli...Reservoir engineering is the term used in quantum control and information technologies to describe manipulating the environment within which an open quantum system operates. Reservoir engineering is essential in applications where storing quantum information is required. From the control theory perspective, a quantum system is capable of storing quantum information if it possesses a so-called decoherence free subsystem （DFS）. This paper explores pole placement techniques to facilitate synthesis of decoherence free subsystems via coherent quantum feedback control. We discuss limitations of the conventional ＇open loop＇ approach and propose a constructive feedback design methodology for decoherence free subsystem engineering. It captures a quite general dynamic coherent feedback structure which allows systems with decoherence free modes to be synthesized from components which do not have such modes.展开更多
研究了n比特随机量子系统实时状态估计及其反馈控制的问题.对于连续弱测量(Continuous weak measurement, CWM)过程存在高斯噪声的情况,基于在线交替方向乘子法(Online alternating direction multiplier method,OADM)推导出一种适用于...研究了n比特随机量子系统实时状态估计及其反馈控制的问题.对于连续弱测量(Continuous weak measurement, CWM)过程存在高斯噪声的情况,基于在线交替方向乘子法(Online alternating direction multiplier method,OADM)推导出一种适用于n比特随机量子系统的实时量子状态估计算法,即QSE-OADM (Quantum state estimation based on OADM).运用李雅普诺夫方法设计控制律,实现基于实时量子状态估计的反馈控制,并证明所提控制律的收敛性.以2比特随机量子系统为例进行数值仿真实验,通过与基于QST-OADM (Quantum state tomography based on OADM)算法和OPG-ADMM (Online proximal gradient-based alternating direction method of multipliers)算法的量子反馈控制方案的性能对比,验证了所提控制方案的优越性.展开更多
This paper studies the real-time optimal state estimation-based feedback control for twolevel stochastic quantum systems in the non-Markovian case.The system model is established by combining the time-convolutionless ...This paper studies the real-time optimal state estimation-based feedback control for twolevel stochastic quantum systems in the non-Markovian case.The system model is established by combining the time-convolutionless non-Markovian master equation and the stochastic master equation.A nonlinear filter based on the state-dependent Riccati equation is designed in order to achieve the realtime optimal estimation of quantum states.A quadratic function multiplied with an exponential term is selected as the Lyapunov function,and a continuous-time control law is deduced via the stochastic Lyapunov stability theorem to realize eigenstate feedback control based on real-time optimal state estimation.Numerical simulation results illustrate that the proposed control scheme is capable of steering the two-level quantum system from an arbitrary initial state to the desired eigenstate with a fidelity higher than 99%within a time of 3 a.u.展开更多
The purpose of this paper is to provide a brief review of some recent developments in quantum feedback networks and control.A quantum feedback network (QFN) is an interconnected system consisting of open quantum syste...The purpose of this paper is to provide a brief review of some recent developments in quantum feedback networks and control.A quantum feedback network (QFN) is an interconnected system consisting of open quantum systems linked by free fields and/or direct physical couplings.Basic network constructs,including series connections as well as feedback loops,are discussed.The quantum feedback network theory provides a natural framework for analysis and design.Basic properties such as dissipation,stability,passivity and gain of open quantum systems are discussed.Control system design is also discussed,primarily in the context of open linear quantum stochastic systems.The issue of physical realizability is discussed,and explicit criteria for stability,positive real lemma,and bounded real lemma are presented.Finally for linear quantum systems,coherent H∞ and LQG control are described.展开更多
Bosonic modes have wide applications in various quantum technologies,such as optical photons for quantum communication,magnons in spin ensembles for quantum information storage and mechanical modes for reversible micr...Bosonic modes have wide applications in various quantum technologies,such as optical photons for quantum communication,magnons in spin ensembles for quantum information storage and mechanical modes for reversible microwave-to-optical quantum transduction.There is emerging interest in utilizing bosonic modes for quantum information processing,with circuit quantum electrodynamics(circuit QED)as one of the leading architectures.Quantum information can be encoded into subspaces of a bosonic superconducting cavity mode with long coherence time.However,standard Gaussian operations(e.g.,beam splitting and two-mode squeezing)are insufficient for universal quantum computing.The major challenge is to introduce additional nonlinear control beyond Gaussian operations without adding significant bosonic loss or decoherence.Here we review recent advances in universal control of a single bosonic code with superconducting circuits,including unitary control,quantum feedback control,drivendissipative control and holonomic dissipative control.Various approaches to entangling different bosonic modes are also discussed.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11374096)Hunan Provincial Innovation Foundation for Postgraduate,China(Grant No.CX2017B177)the Scientific Research Project of Hunan Provincial Education Department,China(Grant No.16C0949)
文摘We investigate the quantum speed limit time （QSLT） of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes have different influences on the evolutionary speed. By adjusting the feedback parameters, the quantum-jump-based feedback control can induce speedup of the atomic evolution from an excited state, but the homodyne-based feedback control cannot change the evolutionary speed. Additionally, the QSLT for the whole dynamical process is explored. Under the quantum-jump-based feedback control, the QSLT displays oscillatory behaviors, which implies multiple speed-up and speed-down processes during the evolution. While, the homodyne-based feedback control can accelerate the speed-up process and improve the uniform speed in the uniform evolution process.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10775100,10974137 and 10805034the Fund of Theoretical Nuclear Center of HIRFL of Chinathe Scientific Research Foundation of CUIT under Grant No.KYTZ201024
文摘We consider the system consisting of two qubits collectively damped, with the output being unit-efficiency measured and subsequently fed back to control the system state. Our primary goal in this paper is （i） to solve the feedback-modified master equation, （ii） to demonstrate the ability of feedback control based on the solutions, and （iii） to pick out different steady states by choosing different driving strengths and feedback strengths to counteract the effects of both damping and the measurement back-action on the system. We further investigate some properties of the equilibrium steady state, its distribution probability and entanglement vs. the driving and feedback amplitudes. We find that in our feedback model feedback plays a negative role in producing entanglement.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11274043 and 11375025
文摘We consider an open quantum system subjected to a noise channel under measurement-based feedback control and two prototypical classes of decoherence channels are considered： phase damping and generalized amplitude damping. Based on quantum trajectory theory, we obtain an extended master equation for the dynamics of the reduced system in the presence of feedback control. For a qubit system we analytically solve this master equation and obtain the solution of the state vector dynamics. Then we propose an effective feedback control scheme for preparing an arbitrary quantum pure state. We also study how to protect two nonorthogonai states effectively, and find that projective measurement with unbiazed basis is not optimal for this task, while weak measurement with biased basis could realize the best protection of two nonorthogonal states. Furthermore, the inefficiencies in the feedback process are also discussed
基金This paper is dedicated to Professor lan R. Petersen on the occasion of his 60th birthday. This work was supported by the Anhui Provincial Natural Science Foundation （No. 1708085MF144） and the National Natural Science Foundation of China （No. 61573330）.Acknowledgements We thank Dr. Daoyi Dong for helpful discussion.
文摘For an N-dimensional quantum system under the influence of continuous measurement, this paper presents a switching control scheme where the control law is of bang-bang type and achieves asymptotic preparation of an arbitrarily given eigenstate of a non-degenerate and degenerate measurement operator, respectively. In the switching control strategy, we divide the state space into two parts： a set containing a target state, and its complementary set. By analyzing the stability of the stochastic system model under consideration, we design a constant control law and give some conditions that the control Hamiltonian satisfies so that the system trajectories in the complementary set converge to the set which contains the target state. Further, for the case of a non-degenerate measurement operator, we show that the system trajectories in the set containing the target state will automatically converge to the target state via quantum continuous measurement theory; while for the case of a degenerate measurement operator, the corresponding system trajectories will also converge to the target state via the construction of the control Hamiltonians. The convergence of the whole closed-loop systems under the cases of a non-degenerate and a degenerate measurement operator is strictly proved. The effectiveness of the proposed switching control scheme is verified by the simulation experiments on a finite-dimensional angular momentum system and a two-qubit system.
基金Supported by National Natural Science Foundation of P.R.China(No. 50375148)
文摘Based on Bures distance, a Lyapunov function that represents the distance between a desired state and the actual state of a quantum system is selected. Considering the cases that an initial state is and is not orthogonal to the desired state respectively, we propose a class of control strategies with state feedback that ensures the stability of the closed-loop control system. Especially, the asymptotic stability of the control system is analyzed, deduced and proved in detail. Finally, a simulation experiment on a spin-1/2 particle system is done and the relation between the system state evolution time and control value is analyzed with diffierent parameters . Research results have general theoretical meaning for control of quantum systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61068001 and 11264042)the Postdoctoral Science Foundation of China(Grant No.2012M520612)the Talent Program of Yanbian University of China(Grant No.950010001)
文摘A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.
文摘Reservoir engineering is the term used in quantum control and information technologies to describe manipulating the environment within which an open quantum system operates. Reservoir engineering is essential in applications where storing quantum information is required. From the control theory perspective, a quantum system is capable of storing quantum information if it possesses a so-called decoherence free subsystem （DFS）. This paper explores pole placement techniques to facilitate synthesis of decoherence free subsystems via coherent quantum feedback control. We discuss limitations of the conventional ＇open loop＇ approach and propose a constructive feedback design methodology for decoherence free subsystem engineering. It captures a quite general dynamic coherent feedback structure which allows systems with decoherence free modes to be synthesized from components which do not have such modes.
文摘研究了n比特随机量子系统实时状态估计及其反馈控制的问题.对于连续弱测量(Continuous weak measurement, CWM)过程存在高斯噪声的情况,基于在线交替方向乘子法(Online alternating direction multiplier method,OADM)推导出一种适用于n比特随机量子系统的实时量子状态估计算法,即QSE-OADM (Quantum state estimation based on OADM).运用李雅普诺夫方法设计控制律,实现基于实时量子状态估计的反馈控制,并证明所提控制律的收敛性.以2比特随机量子系统为例进行数值仿真实验,通过与基于QST-OADM (Quantum state tomography based on OADM)算法和OPG-ADMM (Online proximal gradient-based alternating direction method of multipliers)算法的量子反馈控制方案的性能对比,验证了所提控制方案的优越性.
基金supported by the National Natural Science Foundation of China under Grant No.61973290。
文摘This paper studies the real-time optimal state estimation-based feedback control for twolevel stochastic quantum systems in the non-Markovian case.The system model is established by combining the time-convolutionless non-Markovian master equation and the stochastic master equation.A nonlinear filter based on the state-dependent Riccati equation is designed in order to achieve the realtime optimal estimation of quantum states.A quadratic function multiplied with an exponential term is selected as the Lyapunov function,and a continuous-time control law is deduced via the stochastic Lyapunov stability theorem to realize eigenstate feedback control based on real-time optimal state estimation.Numerical simulation results illustrate that the proposed control scheme is capable of steering the two-level quantum system from an arbitrary initial state to the desired eigenstate with a fidelity higher than 99%within a time of 3 a.u.
基金supported by the National Natural Science Foundation of China(60804015)RGC Poly U5203/10EAFOSR Grant FA2386-09-1-4089AOARD094089
文摘The purpose of this paper is to provide a brief review of some recent developments in quantum feedback networks and control.A quantum feedback network (QFN) is an interconnected system consisting of open quantum systems linked by free fields and/or direct physical couplings.Basic network constructs,including series connections as well as feedback loops,are discussed.The quantum feedback network theory provides a natural framework for analysis and design.Basic properties such as dissipation,stability,passivity and gain of open quantum systems are discussed.Control system design is also discussed,primarily in the context of open linear quantum stochastic systems.The issue of physical realizability is discussed,and explicit criteria for stability,positive real lemma,and bounded real lemma are presented.Finally for linear quantum systems,coherent H∞ and LQG control are described.
基金support from the ARO (W911NF-18-1-0020 and W911NF-18-1-0212)ARO MURI (W911NF-16-1-0349)+3 种基金AFOSR MURI (FA9550-19-1-0399)NSF (EFMA-1640959, OMA-1936118, EEC-1941583)NTT Research, the Packard Foundation (201339273)the Startup Foundation of Institute of Semiconductors, Chinese Academy of Sciences (E0SEBB11)。
文摘Bosonic modes have wide applications in various quantum technologies,such as optical photons for quantum communication,magnons in spin ensembles for quantum information storage and mechanical modes for reversible microwave-to-optical quantum transduction.There is emerging interest in utilizing bosonic modes for quantum information processing,with circuit quantum electrodynamics(circuit QED)as one of the leading architectures.Quantum information can be encoded into subspaces of a bosonic superconducting cavity mode with long coherence time.However,standard Gaussian operations(e.g.,beam splitting and two-mode squeezing)are insufficient for universal quantum computing.The major challenge is to introduce additional nonlinear control beyond Gaussian operations without adding significant bosonic loss or decoherence.Here we review recent advances in universal control of a single bosonic code with superconducting circuits,including unitary control,quantum feedback control,drivendissipative control and holonomic dissipative control.Various approaches to entangling different bosonic modes are also discussed.
