For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SF...For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SFC)is proposed to realize the state transition the pure state of the target state including eigenstate and superposition state.The proposed switching control consists of a constant control and a control law designed based on the Lyapunov method,in which the Lyapunov function is the state distance of the system.The constant control is used to drive the system state from an initial state to the convergence domain only containing the target state,and a Lyapunov-based control is used to make the state enter the convergence domain and then continue to converge to the target state.At the same time,the continuous weak measurement of quantum system and the quantum state tomography method based on the on-line alternating direction multiplier(QST-OADM)are used to obtain the system information and estimate the quantum state which is used as the input of the quantum system controller.Then,the pure state feedback switching control method based on the on-line estimated state feedback is realized in an n-qubit stochastic open quantum system.The complete derivation process of n-qubit QST-OADM algorithm is given;Through strict theoretical proof and analysis,the convergence conditions to ensure any initial state of the quantum system to converge the target pure state are given.The proposed control method is applied to a 2-qubit stochastic open quantum system for numerical simulation experiments.Four possible different position cases between the initial estimated state and that of the controlled system are studied and discussed,and the performances of the state transition under the corresponding cases are analyzed.展开更多
A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser (DFB QCL) structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupl...A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser (DFB QCL) structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet-Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22% and a low threshold gain of 10 cm-1. Using a π phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.展开更多
By introducing the von Neumann entropy as a measure of the extent of noise, this paper discusses the entropy evolution in a two-level quantum feedback controlled system. The results show that the feedback control can ...By introducing the von Neumann entropy as a measure of the extent of noise, this paper discusses the entropy evolution in a two-level quantum feedback controlled system. The results show that the feedback control can induce the reduction of the degree of noise, and different control schemes exhibit different noise controlling ability, the extent of the reduction also related with the position of the target state on the Bloch sphere. It is shown that the evolution of entropy can provide a real time noise observation and a systematic guideline to make reasonable choice of control strategy.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
Based on three-level exciton model,the enhanced photonic microwave signal generation by using a sole excited-state(ES)emitting quantum dot(QD)laser under both optical injection and optical feedback is numerically stud...Based on three-level exciton model,the enhanced photonic microwave signal generation by using a sole excited-state(ES)emitting quantum dot(QD)laser under both optical injection and optical feedback is numerically studied.Within the range of period-one(P1)dynamics caused by the optical injection,the variations of microwave frequency and microwave intensity with the parameters of frequency detuning and injection strength are demonstrated.It is found that the microwave frequency can be continuously tuned by adjusting the injection parameters,and the microwave intensity can be enhanced by changing the injection strength.Moreover,considering that the generated microwave has a wide linewidth,an optical feedback loop is further employed to compress the linewidth,and the effect of feedback parameters on the linewidth is investigated.It is found that with the increase of feedback strength or delay time,the linewidth is evidently decreased due to the locking effect.However,for the relatively large feedback strength or delay time,the linewidth compression effect becomes worse due to the gradually destroyed P1 dynamics.Besides,through optimizing the feedback parameters,the linewidth can be reduced by up to more than one order of magnitude for different microwave frequencies.展开更多
For an open quantum system containing two qubits under homodyne-based feedback control, we investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty.Moreover, we analyze the influence of feed...For an open quantum system containing two qubits under homodyne-based feedback control, we investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty.Moreover, we analyze the influence of feedback modes and coefficients on the entropic uncertainty.Numerical investigations show that the memory qubit should be placed in a non-dissipative channel if the single dissipative channel condition can be chosen, which helps reduce the entropic uncertainty of the system.For the homodyne feedback control F =λσx(or F =λσy), due to different roles of the entangled qubits A and B, when they are subject to feedback control with different feedback coefficients λ, the exchange of feedback coefficients will cause variations of the entropic uncertainty.When the feedback coefficient corresponding to the memory qubit B is larger(λB >λA), the steady value of the entropic uncertainty will be small, which is conducive to enhancing the robustness of the system.However, for the feedback control F =λσz, the difference between the feedback coefficients has no effect on the steady values of the entropic uncertainty.展开更多
This paper studies quantum discord of two qutrits coupled to their own environments independently and coupled to the same environment simultaneously under quantum-jump-based feedback control. Our results show that spo...This paper studies quantum discord of two qutrits coupled to their own environments independently and coupled to the same environment simultaneously under quantum-jump-based feedback control. Our results show that spontaneous emission, quantum feedback parameters, classical driving, initial state, and detection efficiency all affect the evolution of quantum discord in a two-qutrit system. We find that under the condition of designing proper quantum-jump-based feedback parameters, quantum discord can be protected and prepared. In the case where two qutrits are independently coupled to their own environments, classical driving, spontaneous emission, and low detection efficiency have negative effect on the protection of quantum discord. For different initial states, it is found that the evolution of quantum discord under the control of appropriate parameters is similar. In the case where two qutrits are simultaneously coupled to the same environment,the classical driving plays a positive role in the generation of quantum discord, but spontaneous emission and low detection efficiency have negative impact on the generation of quantum discord. Most importantly, we find that the steady discord depends on feedback parameters, classical driving, and detection efficiency, but not on the initial state.展开更多
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
Quantum sensing has been receiving researcher's attention these years due to its ultrahigh sensitivity and precision. However, the bandwidth of the sensors may be low, thus limiting the scope of their practical ap...Quantum sensing has been receiving researcher's attention these years due to its ultrahigh sensitivity and precision. However, the bandwidth of the sensors may be low, thus limiting the scope of their practical applications. The low-bandwidth problem is conquered by feedback control methods, which are widely utilized in classic control fields. Based on a quantum harmonic oscillator model operating near the resonant point, the bandwidth and sensitivity of the quantum sensor are analyzed. The results give two important conclusions: (a) the bandwidth and sensitivity are two incompatible performance parameters of the sensor, so there must be a trade-off between bandwidth and sensitivity in practical applications;(b) the quantum white noise affects the signal to be detected in a non-white form due to the feedback control.展开更多
Quantum metrology provides a fundamental limit on the precision of multi-parameter estimation,called the Heisenberg limit,which has been achieved in noiseless quantum systems.However,for systems subject to noises,it i...Quantum metrology provides a fundamental limit on the precision of multi-parameter estimation,called the Heisenberg limit,which has been achieved in noiseless quantum systems.However,for systems subject to noises,it is hard to achieve this limit since noises are inclined to destroy quantum coherence and entanglement.In this paper,a combined control scheme with feedback and quantum error correction(QEC)is proposed to achieve the Heisenberg limit in the presence of spontaneous emission,where the feedback control is used to protect a stabilizer code space containing an optimal probe state and an additional control is applied to eliminate the measurement incompatibility among three parameters.Although an ancilla system is necessary for the preparation of the optimal probe state,our scheme does not require the ancilla system to be noiseless.In addition,the control scheme in this paper has a low-dimensional code space.For the three components of a magnetic field,it can achieve the highest estimation precision with only a 2-dimensional code space,while at least a4-dimensional code space is required in the common optimal error correction protocols.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
The optical feedback modulations of a passively mode-locked semiconductor laser with quantum dot structure were investigated in this study. The delay-induced dynamics of QD MLL under the condition of optical feedback ...The optical feedback modulations of a passively mode-locked semiconductor laser with quantum dot structure were investigated in this study. The delay-induced dynamics of QD MLL under the condition of optical feedback have been studied by exploiting a time domain traveling wave(TDTW) model. The conventional TDTW model was improved to make it suitable for studying optical feedback system, especially the system with long external cavity structure. Combing the TDTW model with optical feedback and carrier rate equations, the pulse variation of a single section QD MLL was studied. This new model shows good agreement with the published experimental data. The roundtrip time and local light intensity modulation to the pulse evolution of QD MLL were studied. The results show that when the time for a light to go to and return from external cavity is equal to the integral times of the period of laser pulse without external feedback, resonance will be formed, and the period of pulse sequence is the shortest. The results also show that the stronger the local light intensity modulation is, the shorter the pulse period is.展开更多
We report on the room-temperature cascade laser (QCL) at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback (DFB) quantum optimization are used to decrease the thre...We report on the room-temperature cascade laser (QCL) at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback (DFB) quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.展开更多
A quantum teleportation network involving multiple users is essential for future quantum internet.So far,controlled quantum teleportation has been demonstrated in a three-user network.However,versatile and controlled ...A quantum teleportation network involving multiple users is essential for future quantum internet.So far,controlled quantum teleportation has been demonstrated in a three-user network.However,versatile and controlled quantum teleportation network involving more users is in demand,which satisfies different combinations of users for practical requirements.Here we propose a highly versatile and controlled teleportation network that can switch among various combinations of different users.We use a single continuous-variable six-partite Greenberger-Horne-Zeilinger(GHZ)state to realize such a task by choosing the different measurement and feedback operations.The controlled teleportation network,which includes one sub-network,two sub-networks and three sub-networks,can be realized for different application of user combinations.Furthermore,the coherent feedback control(CFC)can manipulate and improve the teleportation performance.Our approach is flexible and scalable,and would provide a versatile platform for demonstrations of complex quantum communication and quantum computing protocols.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
This work conducts robust H^(∞)analysis for a class of quantum systems subject to perturbations in the interaction Hamiltonian.A necessary and sufficient condition for the robustly strict bounded real property of thi...This work conducts robust H^(∞)analysis for a class of quantum systems subject to perturbations in the interaction Hamiltonian.A necessary and sufficient condition for the robustly strict bounded real property of this type of uncertain quantum system is proposed.This paper focuses on the study of coherent robust H^(∞)controller design for quantum systems with uncertainties in the interaction Hamiltonian.The desired controller is connected with the uncertain quantum system through direct and indirect couplings.A necessary and sufficient condition is provided to build a connection between the robust H^(∞)control problem and the scaled H^(∞)control problem.A numerical procedure is provided to obtain coefficients of a coherent controller.An example is presented to illustrate the controller design method.展开更多
In quantum information technologies,quantum weak measurement is beneficial for protecting coherence of systems.In order to further improve the protection effect of quantum weak measurement on coherence,we propose an o...In quantum information technologies,quantum weak measurement is beneficial for protecting coherence of systems.In order to further improve the protection effect of quantum weak measurement on coherence,we propose an optimization scheme of quantum Fisher information(QFI)protection in an open quantum system by combing no-knowledge quantum feedback control with quantum weak measurement.On the basis of solving the dynamic equations of a stochastic two-level quantum system under feedback control,we compare the effects of different feedback Hamiltonians on QFI and find that via no-knowledge quantum feedback,the observation operatorσx(orσx andσz)can protect QFI for a long time.Namely,no-knowledge quantum feedback can improve the estimation precision of feedback coefficient as well as that of detection coefficient.展开更多
Rapid stabilization of general stochastic quantum systems is investigated based on the rapid stability of stochastic differential equations.We introduce a Lyapunov-LaSalle-like theorem for a class of nonlinear stochas...Rapid stabilization of general stochastic quantum systems is investigated based on the rapid stability of stochastic differential equations.We introduce a Lyapunov-LaSalle-like theorem for a class of nonlinear stochastic systems first,based on which a unified framework of rapidly stabilizing stochastic quantum systems is proposed.According to the proposed unified framework,we design the switching state feedback controls to achieve the rapid stabilization of singlequbit systems,two-qubit systems,and N-qubit systems.From the unified framework,the state space is divided into two state subspaces,and the target state is located in one state subspace,while the other system equilibria are located in the other state subspace.Under the designed state feedback controls,the system state can only transit through the boundary between the two state subspaces no more than two times,and the target state is globally asymptotically stable in probability.In particular,the system state can converge exponentially in(all or part of)the state subspace where the target state is located.Moreover,the effectiveness and rapidity of the designed state feedback controls are shown in numerical simulations by stabilizing GHZ states for a three-qubit system.展开更多
A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The phys...A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The physical package realizes the microwave interrogation of a rubidium-atomic beam. The optical systems, equipped with two 780-nm distributed feedback laser diodes, yield light for pumping and detecting. The servo loops control the frequency of a local oscillator with respect to the microwave spectrum. With the experimental systems, the microwave spectrum, which has an amplitude of 4 n A and a line width of 700 Hz, is obtained. Preliminary tests show that the clock short-term frequency stability is 7 × 10^-11 at 1 s, and 3 × 10^-12 at 1000 s. These experimental results demonstrate the feasibility of the scheme for a manufactured clock.展开更多
This paper outlines our studies of bifurcation, quasi-periodic road to chaos and other dynamic characteristics in an external-cavity multi-quantum-well laser with delay optical feedback. The bistable state of the lase...This paper outlines our studies of bifurcation, quasi-periodic road to chaos and other dynamic characteristics in an external-cavity multi-quantum-well laser with delay optical feedback. The bistable state of the laser is predicted by finding theoretically that the gain shifts abruptly between two values due to the feedback. We make a linear stability analysis of the dynamic behavior of the laser. We predict the stability scenario by using the characteristic equation while we make an approximate analysis of the stability of the equilibrium point and discuss the quantitative criteria of bifurcation. We deduce a formula for the relaxation oscillation frequency and prove theoretically that this formula function relates to the loss of carriers transferring between well regime and barrier regime, the feedback level, the delayed time and the other intrinsic parameters. We demonstrate the dynamic distribution and double relaxation oscillation frequency abruptly changing in periodic states and find the multi-frequency characteristic in a chaotic state. We illustrate a road to chaos from a stable state to quasi-periodic states by increasing the feedback level. The effects of the transfers of carriers and the escaping of carriers on dynamic behavior are analyzed, showing that they are contrary to each other via the bifurcation diagram. Also,we show another road to chaos after bifurcation through changing the linewidth enhancement factor, the photon loss rate and the transfer rate of carriers.展开更多
基金supported by the National Natural Science Foundation of China(62473354).
文摘For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SFC)is proposed to realize the state transition the pure state of the target state including eigenstate and superposition state.The proposed switching control consists of a constant control and a control law designed based on the Lyapunov method,in which the Lyapunov function is the state distance of the system.The constant control is used to drive the system state from an initial state to the convergence domain only containing the target state,and a Lyapunov-based control is used to make the state enter the convergence domain and then continue to converge to the target state.At the same time,the continuous weak measurement of quantum system and the quantum state tomography method based on the on-line alternating direction multiplier(QST-OADM)are used to obtain the system information and estimate the quantum state which is used as the input of the quantum system controller.Then,the pure state feedback switching control method based on the on-line estimated state feedback is realized in an n-qubit stochastic open quantum system.The complete derivation process of n-qubit QST-OADM algorithm is given;Through strict theoretical proof and analysis,the convergence conditions to ensure any initial state of the quantum system to converge the target pure state are given.The proposed control method is applied to a 2-qubit stochastic open quantum system for numerical simulation experiments.Four possible different position cases between the initial estimated state and that of the controlled system are studied and discussed,and the performances of the state transition under the corresponding cases are analyzed.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 60525406)the National Natural Science Foundation of China (Grant Nos. 60736031,60806018,and 60906026)+1 种基金the National Basic Research Program of China (Grant No. 2006CB604903)the National High Technology Research and Development Program of China (Grant Nos. 2007AA03Z446 and 2009AA03Z403)
文摘A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser (DFB QCL) structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet-Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22% and a low threshold gain of 10 cm-1. Using a π phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.
基金Project supported by the National Natural Science Foundation of China (Grant No 10374025).
文摘By introducing the von Neumann entropy as a measure of the extent of noise, this paper discusses the entropy evolution in a two-level quantum feedback controlled system. The results show that the feedback control can induce the reduction of the degree of noise, and different control schemes exhibit different noise controlling ability, the extent of the reduction also related with the position of the target state on the Bloch sphere. It is shown that the evolution of entropy can provide a real time noise observation and a systematic guideline to make reasonable choice of control strategy.
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.
基金the National Natural Science Foundation of China(Grant Nos.61775184 and 61875167).
文摘Based on three-level exciton model,the enhanced photonic microwave signal generation by using a sole excited-state(ES)emitting quantum dot(QD)laser under both optical injection and optical feedback is numerically studied.Within the range of period-one(P1)dynamics caused by the optical injection,the variations of microwave frequency and microwave intensity with the parameters of frequency detuning and injection strength are demonstrated.It is found that the microwave frequency can be continuously tuned by adjusting the injection parameters,and the microwave intensity can be enhanced by changing the injection strength.Moreover,considering that the generated microwave has a wide linewidth,an optical feedback loop is further employed to compress the linewidth,and the effect of feedback parameters on the linewidth is investigated.It is found that with the increase of feedback strength or delay time,the linewidth is evidently decreased due to the locking effect.However,for the relatively large feedback strength or delay time,the linewidth compression effect becomes worse due to the gradually destroyed P1 dynamics.Besides,through optimizing the feedback parameters,the linewidth can be reduced by up to more than one order of magnitude for different microwave frequencies.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61663016 and 11404150)
文摘For an open quantum system containing two qubits under homodyne-based feedback control, we investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty.Moreover, we analyze the influence of feedback modes and coefficients on the entropic uncertainty.Numerical investigations show that the memory qubit should be placed in a non-dissipative channel if the single dissipative channel condition can be chosen, which helps reduce the entropic uncertainty of the system.For the homodyne feedback control F =λσx(or F =λσy), due to different roles of the entangled qubits A and B, when they are subject to feedback control with different feedback coefficients λ, the exchange of feedback coefficients will cause variations of the entropic uncertainty.When the feedback coefficient corresponding to the memory qubit B is larger(λB >λA), the steady value of the entropic uncertainty will be small, which is conducive to enhancing the robustness of the system.However, for the feedback control F =λσz, the difference between the feedback coefficients has no effect on the steady values of the entropic uncertainty.
基金Project supported by the National Natural Science Foundation of China(Grant No.11374096)
文摘This paper studies quantum discord of two qutrits coupled to their own environments independently and coupled to the same environment simultaneously under quantum-jump-based feedback control. Our results show that spontaneous emission, quantum feedback parameters, classical driving, initial state, and detection efficiency all affect the evolution of quantum discord in a two-qutrit system. We find that under the condition of designing proper quantum-jump-based feedback parameters, quantum discord can be protected and prepared. In the case where two qutrits are independently coupled to their own environments, classical driving, spontaneous emission, and low detection efficiency have negative effect on the protection of quantum discord. For different initial states, it is found that the evolution of quantum discord under the control of appropriate parameters is similar. In the case where two qutrits are simultaneously coupled to the same environment,the classical driving plays a positive role in the generation of quantum discord, but spontaneous emission and low detection efficiency have negative impact on the generation of quantum discord. Most importantly, we find that the steady discord depends on feedback parameters, classical driving, and detection efficiency, but not on the initial state.
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Project supported by the National Natural Science Foundation of China (Grant Nos. 11534002, U1930402, and U1930403).
文摘Quantum sensing has been receiving researcher's attention these years due to its ultrahigh sensitivity and precision. However, the bandwidth of the sensors may be low, thus limiting the scope of their practical applications. The low-bandwidth problem is conquered by feedback control methods, which are widely utilized in classic control fields. Based on a quantum harmonic oscillator model operating near the resonant point, the bandwidth and sensitivity of the quantum sensor are analyzed. The results give two important conclusions: (a) the bandwidth and sensitivity are two incompatible performance parameters of the sensor, so there must be a trade-off between bandwidth and sensitivity in practical applications;(b) the quantum white noise affects the signal to be detected in a non-white form due to the feedback control.
基金Project supported by the National Natural Science Foundation of China(Grant No.61873251)。
文摘Quantum metrology provides a fundamental limit on the precision of multi-parameter estimation,called the Heisenberg limit,which has been achieved in noiseless quantum systems.However,for systems subject to noises,it is hard to achieve this limit since noises are inclined to destroy quantum coherence and entanglement.In this paper,a combined control scheme with feedback and quantum error correction(QEC)is proposed to achieve the Heisenberg limit in the presence of spontaneous emission,where the feedback control is used to protect a stabilizer code space containing an optimal probe state and an additional control is applied to eliminate the measurement incompatibility among three parameters.Although an ancilla system is necessary for the preparation of the optimal probe state,our scheme does not require the ancilla system to be noiseless.In addition,the control scheme in this paper has a low-dimensional code space.For the three components of a magnetic field,it can achieve the highest estimation precision with only a 2-dimensional code space,while at least a4-dimensional code space is required in the common optimal error correction protocols.
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Sponsored by the Research Project of Xiamen University of Technology(Grant No.KCZX2019148)the Research Project of Xiamen Municipal Bureau of Science and Technology(Grant No.3502Z20193055)。
文摘The optical feedback modulations of a passively mode-locked semiconductor laser with quantum dot structure were investigated in this study. The delay-induced dynamics of QD MLL under the condition of optical feedback have been studied by exploiting a time domain traveling wave(TDTW) model. The conventional TDTW model was improved to make it suitable for studying optical feedback system, especially the system with long external cavity structure. Combing the TDTW model with optical feedback and carrier rate equations, the pulse variation of a single section QD MLL was studied. This new model shows good agreement with the published experimental data. The roundtrip time and local light intensity modulation to the pulse evolution of QD MLL were studied. The results show that when the time for a light to go to and return from external cavity is equal to the integral times of the period of laser pulse without external feedback, resonance will be formed, and the period of pulse sequence is the shortest. The results also show that the stronger the local light intensity modulation is, the shorter the pulse period is.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB632801 and 2013CB632803the National Natural Science Foundation of China under Grant Nos 61435014,61306058 and 61274094the Beijing Natural Science Foundation under Grant No 4144086
文摘We report on the room-temperature cascade laser (QCL) at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback (DFB) quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.
基金Project supported by the Natural Science Foundation of Shanxi Province of China (Grant No. 202203021221214)the National Natural Science Foundation of China (Grant Nos. 62122044, 62135008, 61925503, 11904218, 12004276, 12147215, and 11834010)+4 种基金the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province of China (Grant Nos. 2019L0092 and 2020L0029)the Key Project of the National Key Research and Development Program of China (Grant No. 2022YFA1404500)the Program for the Innovative Talents of Higher Education Institutions of Shanxi Province of Chinathe Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxithe Fund for Shanxi “1331 Project” Key Subjects Construction
文摘A quantum teleportation network involving multiple users is essential for future quantum internet.So far,controlled quantum teleportation has been demonstrated in a three-user network.However,versatile and controlled quantum teleportation network involving more users is in demand,which satisfies different combinations of users for practical requirements.Here we propose a highly versatile and controlled teleportation network that can switch among various combinations of different users.We use a single continuous-variable six-partite Greenberger-Horne-Zeilinger(GHZ)state to realize such a task by choosing the different measurement and feedback operations.The controlled teleportation network,which includes one sub-network,two sub-networks and three sub-networks,can be realized for different application of user combinations.Furthermore,the coherent feedback control(CFC)can manipulate and improve the teleportation performance.Our approach is flexible and scalable,and would provide a versatile platform for demonstrations of complex quantum communication and quantum computing protocols.
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supported by the National Natural Science Foundation of China(61803132,61828303,61803389)the U.S.Office of Naval Research Global(N62909-19-1-2129)the Australian Research’s Discovery Projects Funding Scheme under Project DP190101566。
文摘This work conducts robust H^(∞)analysis for a class of quantum systems subject to perturbations in the interaction Hamiltonian.A necessary and sufficient condition for the robustly strict bounded real property of this type of uncertain quantum system is proposed.This paper focuses on the study of coherent robust H^(∞)controller design for quantum systems with uncertainties in the interaction Hamiltonian.The desired controller is connected with the uncertain quantum system through direct and indirect couplings.A necessary and sufficient condition is provided to build a connection between the robust H^(∞)control problem and the scaled H^(∞)control problem.A numerical procedure is provided to obtain coefficients of a coherent controller.An example is presented to illustrate the controller design method.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61663016 and 11264015)。
文摘In quantum information technologies,quantum weak measurement is beneficial for protecting coherence of systems.In order to further improve the protection effect of quantum weak measurement on coherence,we propose an optimization scheme of quantum Fisher information(QFI)protection in an open quantum system by combing no-knowledge quantum feedback control with quantum weak measurement.On the basis of solving the dynamic equations of a stochastic two-level quantum system under feedback control,we compare the effects of different feedback Hamiltonians on QFI and find that via no-knowledge quantum feedback,the observation operatorσx(orσx andσz)can protect QFI for a long time.Namely,no-knowledge quantum feedback can improve the estimation precision of feedback coefficient as well as that of detection coefficient.
基金Project supported in part by the National Natural Science Foundation of China(Grant No.72071183)Research Project Supported by Shanxi Scholarship Council of China(Grant No.2020-114).
文摘Rapid stabilization of general stochastic quantum systems is investigated based on the rapid stability of stochastic differential equations.We introduce a Lyapunov-LaSalle-like theorem for a class of nonlinear stochastic systems first,based on which a unified framework of rapidly stabilizing stochastic quantum systems is proposed.According to the proposed unified framework,we design the switching state feedback controls to achieve the rapid stabilization of singlequbit systems,two-qubit systems,and N-qubit systems.From the unified framework,the state space is divided into two state subspaces,and the target state is located in one state subspace,while the other system equilibria are located in the other state subspace.Under the designed state feedback controls,the system state can only transit through the boundary between the two state subspaces no more than two times,and the target state is globally asymptotically stable in probability.In particular,the system state can converge exponentially in(all or part of)the state subspace where the target state is located.Moreover,the effectiveness and rapidity of the designed state feedback controls are shown in numerical simulations by stabilizing GHZ states for a three-qubit system.
基金Project supported by the National Natural Science Foundation of China(Grant No.11174015)
文摘A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The physical package realizes the microwave interrogation of a rubidium-atomic beam. The optical systems, equipped with two 780-nm distributed feedback laser diodes, yield light for pumping and detecting. The servo loops control the frequency of a local oscillator with respect to the microwave spectrum. With the experimental systems, the microwave spectrum, which has an amplitude of 4 n A and a line width of 700 Hz, is obtained. Preliminary tests show that the clock short-term frequency stability is 7 × 10^-11 at 1 s, and 3 × 10^-12 at 1000 s. These experimental results demonstrate the feasibility of the scheme for a manufactured clock.
文摘This paper outlines our studies of bifurcation, quasi-periodic road to chaos and other dynamic characteristics in an external-cavity multi-quantum-well laser with delay optical feedback. The bistable state of the laser is predicted by finding theoretically that the gain shifts abruptly between two values due to the feedback. We make a linear stability analysis of the dynamic behavior of the laser. We predict the stability scenario by using the characteristic equation while we make an approximate analysis of the stability of the equilibrium point and discuss the quantitative criteria of bifurcation. We deduce a formula for the relaxation oscillation frequency and prove theoretically that this formula function relates to the loss of carriers transferring between well regime and barrier regime, the feedback level, the delayed time and the other intrinsic parameters. We demonstrate the dynamic distribution and double relaxation oscillation frequency abruptly changing in periodic states and find the multi-frequency characteristic in a chaotic state. We illustrate a road to chaos from a stable state to quasi-periodic states by increasing the feedback level. The effects of the transfers of carriers and the escaping of carriers on dynamic behavior are analyzed, showing that they are contrary to each other via the bifurcation diagram. Also,we show another road to chaos after bifurcation through changing the linewidth enhancement factor, the photon loss rate and the transfer rate of carriers.