The fractional shortcut to adiabaticity(f-STA)for the production of quantum superposition states is proposed firstly via a three-level system with aΛ-type linkage pattern and a four-level system with a tripod structu...The fractional shortcut to adiabaticity(f-STA)for the production of quantum superposition states is proposed firstly via a three-level system with aΛ-type linkage pattern and a four-level system with a tripod structure.The fast and robust production of the coherent superposition states is studied by comparing the populations for the f-STA and the fractional stimulated Raman adiabatic passage(f-STIRAP).The states with equal proportions can be produced by fixing the controllable parameters of the driving pulses at the final moment of the whole process.The effects of the pulse intensity and the time delay of the pulses on the production process are discussed by monitoring the populations on all of the quantum states.In particular,the spontaneous emission arising from the intermediate state is investigated by the quantum master equation.The result reveals that the f-STA exhibits superior advantages over the f-STIRAP in producing the superposition states.展开更多
Preparing quantum superposition states is a crucial step in realizing quantum algorithms,which demands substantial resources.In this paper,we propose a new method for preparing quantum uniform superposition states via...Preparing quantum superposition states is a crucial step in realizing quantum algorithms,which demands substantial resources.In this paper,we propose a new method for preparing quantum uniform superposition states via quantum measurement,and design the bitwise implementation circuit,which only contains Hadamard,CNOT,and π/8 phase gates.Compared to the Shukla–Vedula method,the number of quantum gates required by both methods scales the same,while,the new method offers stronger fault tolerance,and the ancillary qubits employed during the implementation process can be reused,making it more suitable for implementation on real quantum computers.As an application,we provide the circuit for Shor's discrete logarithm quantum algorithm,based on the new method,demonstrating its technical advantage for implementation of quantum algorithms.展开更多
We present a simple method on the generation of any bi-photon superposition state using only linear optics.In this scheme, the input states, a two-mode squeezed state and a bi-photon state, meet on a beam-splitter and...We present a simple method on the generation of any bi-photon superposition state using only linear optics.In this scheme, the input states, a two-mode squeezed state and a bi-photon state, meet on a beam-splitter and the output states are post-selected with two threshold single-photon detectors. We carry out corresponding numerical simulations by accounting for practical experimental conditions, calculating both the Wigner function and the state fidelity of those generated bi-photon superposition states. Our simulation results demonstrate that not only distinct nonclassical characteristics but also very high state fidelities can be achieved even under imperfect experimental conditions.展开更多
We find tight upper bound on the coherence of a superposition of two states in terms of the coherence of the two states constituting the superposition with l1-norm of coherence.Our upper bound is tighter than the one ...We find tight upper bound on the coherence of a superposition of two states in terms of the coherence of the two states constituting the superposition with l1-norm of coherence.Our upper bound is tighter than the one presented by Liu,et al.[Quantum Inf.Process.15(2016)4209.]We also generalize the results to the case that the superposition is constituted with more than two states in high dimension,and we give the corresponding upper bounds.展开更多
A powerful approach to generate multilevel superposition state in A-type manifold of levels is proposed. In the analysis, we introduce a group of rotations to transform the coupled system to a simpler form, which invo...A powerful approach to generate multilevel superposition state in A-type manifold of levels is proposed. In the analysis, we introduce a group of rotations to transform the coupled system to a simpler form, which involves one coupled and several decoupled, dark states in the ground state manifold. Then an arbitrary superposition state of initial and final states can be created. In particular, when the Rabi frequencies of the Stokes pulses have equal magnitudes, a superposition state （equal population of the （n - 2） superposition states） will be generated. A numerical simulation of coherence generation is given. It is shown that a small transient population in metastable state decreases as the intensity of Stokes pulses increases. Experimental implementation in Neon atom is given.展开更多
In this paper the superpositions of two arbitrary coherent states ｜ψ〉 = α ｜β｜ ＋ be^iψ ｜mβe^iδ〉 are constructed by using the superposition principle of quantum mechanics. The entropic squeezing effects of ...In this paper the superpositions of two arbitrary coherent states ｜ψ〉 = α ｜β｜ ＋ be^iψ ｜mβe^iδ〉 are constructed by using the superposition principle of quantum mechanics. The entropic squeezing effects of the quantum states are studied. The numerical results indicate that the amplitudes, the ratio between the amplitudes of two coherent states, the phase difference between the two components and the relative phase of the two coefficients play important roles in the squeezing effects of the position entropy and momentum entropy.展开更多
A scheme for creating an arbitrary coherent superposition of two atomic states in serial multi-A-type system is proposed. This technique with the application of a control field is based on the existence of two degener...A scheme for creating an arbitrary coherent superposition of two atomic states in serial multi-A-type system is proposed. This technique with the application of a control field is based on the existence of two degenerate dark states and their interaction. The mixing of the dark states can be controlled by changing the relative delay time of the control pulse. One can get any desired superposition by changing the delay time of the control pulse.展开更多
Quantum superposition is a fundamental principle of quantum mechanics, so it is not surprising that equal superposition states(ESS) serve as powerful resources for quantum information processing. In this work, we prop...Quantum superposition is a fundamental principle of quantum mechanics, so it is not surprising that equal superposition states(ESS) serve as powerful resources for quantum information processing. In this work, we propose a quantum circuit that creates an arbitrary dimensional ESS. The circuit construction is efficient as the number of required elementary gates scales polynomially with the number of required qubits. For experimental realization of the method, we use techniques of nuclear magnetic resonance(NMR). We have succeeded in preparing a 9-dimensional ESS on a 4-qubit NMR quantum register. The full tomography indicates that the fidelity of our prepared state with respect to the ideal 9-dimensional ESS is over 96%. We also prove the prepared state is pseudo-entangled by directly measuring an entanglement witness operator. Our result can be useful for the implementation of those quantum algorithms that require an ESS as an input state.展开更多
Special kinds of generalized superposition states, superposition coherent states, are studied in this paper. These states can be produced by superposing a pair of coherent states ｜ α 〉 and ｜- α 〉. Their quan...Special kinds of generalized superposition states, superposition coherent states, are studied in this paper. These states can be produced by superposing a pair of coherent states ｜ α 〉 and ｜- α 〉. Their quantum statistical properties, the fluctuations of field and squeezing have been discussed in detail. These properties are dependent on superposition phase. We also describe the squeezing regions in phase space for these states.展开更多
This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately π/2, 3π/2, and π1, as well as for the superposition state of two pseud...This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately π/2, 3π/2, and π1, as well as for the superposition state of two pseudoclassical states. According to the analysis, it is found that the superposition state of two coherent states with their phase differences π/2 and 3π/2, and the superposition state of two pseudoclassical states both do exhibit the amplitude-squared squeezing. Also, some specific states are found to exhibit even stronger squeezing effects when relative phase of the superposition is equal to the average photon number. Amplitude-squared squeezing is dependent on the difference in phase between two coherent states.展开更多
This paper proposes a scheme for generation of superpositions of coherent states of the effective bosonic mode in a collection of atoms. In the scheme an atomic sample interacts with a slightly detuned cavity mode and...This paper proposes a scheme for generation of superpositions of coherent states of the effective bosonic mode in a collection of atoms. In the scheme an atomic sample interacts with a slightly detuned cavity mode and a resonant strong classical field. Under ceitain conditions the atomic system evolves from a coherent state to a superposition of coherent states.展开更多
This paper proposes a scheme for generating arbitrary superpositions of several coherent states along a straight line for a cavity mode. In the scheme, several atoms are sent through a cavity initially in a strong coh...This paper proposes a scheme for generating arbitrary superpositions of several coherent states along a straight line for a cavity mode. In the scheme, several atoms are sent through a cavity initially in a strong coherent state. The superposition of several coherent states with desired coefficients may be generated if each atom is detected in the excited state after it exits the cavity. The scheme is based on resonant atom-cavity interaction and no classical field is required during and after the atom cavity interaction. Thus, the scheme is very simple and the interaction time is very short, which is important in view of decoherence.展开更多
We propose a method for the generation of superpositions of two-mode coherent states for the center-of-mass and relative vibrational modes of two trapped ions. In the scheme the ions are driven by a single travelling-...We propose a method for the generation of superpositions of two-mode coherent states for the center-of-mass and relative vibrational modes of two trapped ions. In the scheme the ions are driven by a single travelling-wave laser field tuned to the carrier. Then a measurement of the internal states collapses the vibrational modes to the entangled coherent state.展开更多
The present study delves into the application of investigating quantum state behaviour,particularly focusing on coherent and superposition states.These states,characterized by their remarkable stability and precision,...The present study delves into the application of investigating quantum state behaviour,particularly focusing on coherent and superposition states.These states,characterized by their remarkable stability and precision,have found extensive utility in various domains of quantum mechanics and quantum information processing.Coherent states are valuable for manipulating quantum systems with accuracy.Superposition states allow quantum systems to exist in numerous configurations at the same time,which paves the way for quantum computing’s capacity for parallel processing.The research accentuates the crucial role of quantum error correction(QEC)in ensuring the stability and reliability of quantum information processing systems.Quantum systems are prone to errors from decoherence and environmental noise,making QEC essential for ensuring accurate results by employing the Shor code,an error-correcting code devised by Peter Shor,it becomes feasible to detect and rectify errors that may arise during quantum computations.The Shor code detects and corrects both bit-flip and phase-flip errors,greatly enhancing the robustness of quantum information systems.This research offers insights into the multifaceted utility of MZI(Mach-Zehnder interferometer)and its relevance in the advancement of quantum technology.By integrating QEC with the capabilities of MZI,this study offers a holistic approach to advancing the precision and reliability of quantum technologies.展开更多
In this paper, we analytically solve the master equation for Jaynes-Cummings model in the dispersive regime including phase damping and the field is assumed to be initially in a superposition of coherent states. Using...In this paper, we analytically solve the master equation for Jaynes-Cummings model in the dispersive regime including phase damping and the field is assumed to be initially in a superposition of coherent states. Using an established entanglement measure based on the negativity of the eigenvalues of the partially transposed density matrix we find a very strong sensitivity of the maximally generated entanglement to the amount of phase damping. Qualitatively this behavior is also reflected in alternative entanglement measures, but the quantitative agreement between different measures depends on the chosen noise model The phase decoherence for this model results in monotonic increase in the total entropy while the atomic sub-entropy keeps its periodic behaviour without any effect.展开更多
We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on ...We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on impurity atoms. It is found that the nonclassicality of MQSSs can be manipulated by changing the number of the impurities and their interaction with the BEC. It is shown that the BEC matter-wave field exhibits a collapse and revival phenomenon which reveals the quantum nature of the BEC matter-wave field. We investigate the micro-macro entanglement between the impurities and the BEC, and find enhancement of the micro-macro entanglement induced by the initial quantum coherence of the impurity atoms.展开更多
Reinforcement learning is one of the fastest growing areas in machine learning,and has obtained great achievements in biomedicine,Internet of Things(IoT),logistics,robotic control,etc.However,there are still many chal...Reinforcement learning is one of the fastest growing areas in machine learning,and has obtained great achievements in biomedicine,Internet of Things(IoT),logistics,robotic control,etc.However,there are still many challenges for engineering applications,such as how to speed up the learning process,how to balance the trade-of between exploration and exploitation.Quantum technology,which can solve complex problems faster than classical methods,especially in supercomputers,provides us a new paradigm to overcome these challenges in reinforcement learning.In this paper,a quantum-enhanced reinforcement learning is pictured for optimal control.In this algorithm,the states and actions of reinforcement learning are quantized by quantum technology.And then,a probability amplifcation method,which can efectively avoid the trade-of between exploration and exploitation via quantized technology,is presented.Finally,the optimal control policy is learnt during the process of reinforcement learning.The performance of this quantized algorithm is demonstrated in both MountainCar reinforcement learning environment and CartPole reinforcement learning environment—one kind of classical control reinforcement learning environment in the OpenAI Gym.The preliminary study results validate that,compared with Q-learning,this quantized reinforcement learning method has better control performance without considering the trade-of between exploration and exploitation.The learning performance of this new algorithm is stable with diferent learning rates from 0.01 to 0.10,which means it is promising to be employed in unknown dynamics systems.展开更多
This paper proposes a method of generating multipartite entanglement through using d.c. superconducting quan- tum interference devices （SQUID） inside a standing wave cavity. In this scheme, the d.c. SQUID works in t...This paper proposes a method of generating multipartite entanglement through using d.c. superconducting quan- tum interference devices （SQUID） inside a standing wave cavity. In this scheme, the d.c. SQUID works in the charge region. It is shown that, a large number of important multipartite entangled states can be generated by a controllable interaction between a cavity field and qubits. It is even possible to produce entangled states involving different cavity modes based on the measurement of charge qubits states. After such superpositions states are created, the interaction can be switched off by the classical magnetic field through the SQUID, and there is no information transfer between the cavity field and the charge qubits.展开更多
The analysis of accuracy for superposition of squeezed states （SSSs） in lossless and loss case has been performed in this study. In lossless case, time accuracies of SSSs with mean photon number ns have a scaling of...The analysis of accuracy for superposition of squeezed states （SSSs） in lossless and loss case has been performed in this study. In lossless case, time accuracies of SSSs with mean photon number ns have a scaling of ns-2 in two limits of large and small squeezing. With the help of photon loss model, the dissipative channel will degrade accuracies has been proved. In the limit of large squeezing, the accuracy will slowly decrease with the reduction of transmittance η. In the limit of small squeezing, time accuracy scales as 1/（η4n2） and will decrease much faster along with η decreases.展开更多
Using the principles of quantum state superposition and entanglement,quantum computing has been proven to be able to tackle problems that are hard for state-of-the-art supercomputers.Thirty years ago,when Shor’s algo...Using the principles of quantum state superposition and entanglement,quantum computing has been proven to be able to tackle problems that are hard for state-of-the-art supercomputers.Thirty years ago,when Shor’s algorithm and Grover’s algorithm were proposed and proven to have great acceleration on solving some problems,including factoring and searching,quantum computing was only a beautiful scientific dream.Today,quantum computing is advancing at an incredible pace.Over 10 years ago,Devoret and Schoelkopf said something similar in their review1.展开更多
基金supported by the NSF of China(Grant No.11405100)the Natural Science Basic Research Program in Shaanxi Province of China(Grant Nos.2020JM-507 and 2019JM-332)。
文摘The fractional shortcut to adiabaticity(f-STA)for the production of quantum superposition states is proposed firstly via a three-level system with aΛ-type linkage pattern and a four-level system with a tripod structure.The fast and robust production of the coherent superposition states is studied by comparing the populations for the f-STA and the fractional stimulated Raman adiabatic passage(f-STIRAP).The states with equal proportions can be produced by fixing the controllable parameters of the driving pulses at the final moment of the whole process.The effects of the pulse intensity and the time delay of the pulses on the production process are discussed by monitoring the populations on all of the quantum states.In particular,the spontaneous emission arising from the intermediate state is investigated by the quantum master equation.The result reveals that the f-STA exhibits superior advantages over the f-STIRAP in producing the superposition states.
基金supported by National Key Research and Development Program of China(Grant No.2020YFA0309702)the National Natural Science Foundation of China(Grant No.61502526)+1 种基金NSAF(Grant No.U2130205)the Natural Science Foundation of Henan Province,China(Grant Nos.202300410532 and 252300421818)。
文摘Preparing quantum superposition states is a crucial step in realizing quantum algorithms,which demands substantial resources.In this paper,we propose a new method for preparing quantum uniform superposition states via quantum measurement,and design the bitwise implementation circuit,which only contains Hadamard,CNOT,and π/8 phase gates.Compared to the Shukla–Vedula method,the number of quantum gates required by both methods scales the same,while,the new method offers stronger fault tolerance,and the ancillary qubits employed during the implementation process can be reused,making it more suitable for implementation on real quantum computers.As an application,we provide the circuit for Shor's discrete logarithm quantum algorithm,based on the new method,demonstrating its technical advantage for implementation of quantum algorithms.
基金Supported by the National Natural Science Foundation of China under Grant Nos.61475197,61590932,11274178the Natural Science Foundation of the Jiangsu Higher Education Institutions under Grant No.15KJA120002+1 种基金the Outstanding Youth Project of Jiangsu Province under Grant No.BK20150039the Priority Academic Program Development of Jiangsu Higher Education Institutions under Grant No.YX002001
文摘We present a simple method on the generation of any bi-photon superposition state using only linear optics.In this scheme, the input states, a two-mode squeezed state and a bi-photon state, meet on a beam-splitter and the output states are post-selected with two threshold single-photon detectors. We carry out corresponding numerical simulations by accounting for practical experimental conditions, calculating both the Wigner function and the state fidelity of those generated bi-photon superposition states. Our simulation results demonstrate that not only distinct nonclassical characteristics but also very high state fidelities can be achieved even under imperfect experimental conditions.
基金Supported by the National Natural Science Foundation of China under Grant Nos.61671280,11771009,and 11847101the Natural Science Basic Research Plan in Shaanxi Province of China under Grant No.2017KJXX-92+1 种基金the Fundamental Research Funds for the Central Universities under Grant No.GK201902007the Funded Projects for the Academic Leaders and Academic Backbones,Shaanxi Normal University under Grant No.16QNGG013
文摘We find tight upper bound on the coherence of a superposition of two states in terms of the coherence of the two states constituting the superposition with l1-norm of coherence.Our upper bound is tighter than the one presented by Liu,et al.[Quantum Inf.Process.15(2016)4209.]We also generalize the results to the case that the superposition is constituted with more than two states in high dimension,and we give the corresponding upper bounds.
文摘A powerful approach to generate multilevel superposition state in A-type manifold of levels is proposed. In the analysis, we introduce a group of rotations to transform the coupled system to a simpler form, which involves one coupled and several decoupled, dark states in the ground state manifold. Then an arbitrary superposition state of initial and final states can be created. In particular, when the Rabi frequencies of the Stokes pulses have equal magnitudes, a superposition state （equal population of the （n - 2） superposition states） will be generated. A numerical simulation of coherence generation is given. It is shown that a small transient population in metastable state decreases as the intensity of Stokes pulses increases. Experimental implementation in Neon atom is given.
基金Project supported by the Natural Science Foundation of Fujian Province,China (Grant No T0650013)
文摘In this paper the superpositions of two arbitrary coherent states ｜ψ〉 = α ｜β｜ ＋ be^iψ ｜mβe^iδ〉 are constructed by using the superposition principle of quantum mechanics. The entropic squeezing effects of the quantum states are studied. The numerical results indicate that the amplitudes, the ratio between the amplitudes of two coherent states, the phase difference between the two components and the relative phase of the two coefficients play important roles in the squeezing effects of the position entropy and momentum entropy.
文摘A scheme for creating an arbitrary coherent superposition of two atomic states in serial multi-A-type system is proposed. This technique with the application of a control field is based on the existence of two degenerate dark states and their interaction. The mixing of the dark states can be controlled by changing the relative delay time of the control pulse. One can get any desired superposition by changing the delay time of the control pulse.
基金supported by the National Key Basic Research Program of China(Grant Nos.2013CB921800,and 2014CB848700)the National Natural Science Foundation of China(Grant Nos.11425523,11375167,11575173,and 11227901)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB01030400)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDY-SSW-SLH004)
文摘Quantum superposition is a fundamental principle of quantum mechanics, so it is not surprising that equal superposition states(ESS) serve as powerful resources for quantum information processing. In this work, we propose a quantum circuit that creates an arbitrary dimensional ESS. The circuit construction is efficient as the number of required elementary gates scales polynomially with the number of required qubits. For experimental realization of the method, we use techniques of nuclear magnetic resonance(NMR). We have succeeded in preparing a 9-dimensional ESS on a 4-qubit NMR quantum register. The full tomography indicates that the fidelity of our prepared state with respect to the ideal 9-dimensional ESS is over 96%. We also prove the prepared state is pseudo-entangled by directly measuring an entanglement witness operator. Our result can be useful for the implementation of those quantum algorithms that require an ESS as an input state.
文摘Special kinds of generalized superposition states, superposition coherent states, are studied in this paper. These states can be produced by superposing a pair of coherent states ｜ α 〉 and ｜- α 〉. Their quantum statistical properties, the fluctuations of field and squeezing have been discussed in detail. These properties are dependent on superposition phase. We also describe the squeezing regions in phase space for these states.
基金supported by the National Natural Science Foundation of China (Grant Nos 10674038 and 10604042)National Basic Research Program of China (Grant No 2006CB302901)
文摘This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately π/2, 3π/2, and π1, as well as for the superposition state of two pseudoclassical states. According to the analysis, it is found that the superposition state of two coherent states with their phase differences π/2 and 3π/2, and the superposition state of two pseudoclassical states both do exhibit the amplitude-squared squeezing. Also, some specific states are found to exhibit even stronger squeezing effects when relative phase of the superposition is equal to the average photon number. Amplitude-squared squeezing is dependent on the difference in phase between two coherent states.
基金Project supported by the National Natural Science Foundation of China (Grant No 10674025)the Doctoral Foundation of the Ministry of Education of China (Grant No 20070386002)
文摘This paper proposes a scheme for generation of superpositions of coherent states of the effective bosonic mode in a collection of atoms. In the scheme an atomic sample interacts with a slightly detuned cavity mode and a resonant strong classical field. Under ceitain conditions the atomic system evolves from a coherent state to a superposition of coherent states.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10674025)the Doctoral Foundation of the Ministry of Education of China (Grant No. 20070386002)
文摘This paper proposes a scheme for generating arbitrary superpositions of several coherent states along a straight line for a cavity mode. In the scheme, several atoms are sent through a cavity initially in a strong coherent state. The superposition of several coherent states with desired coefficients may be generated if each atom is detected in the excited state after it exits the cavity. The scheme is based on resonant atom-cavity interaction and no classical field is required during and after the atom cavity interaction. Thus, the scheme is very simple and the interaction time is very short, which is important in view of decoherence.
基金教育部霍英东教育基金，the National Natural Science Foundation of China under，Funds from Fuzhou University
文摘We propose a method for the generation of superpositions of two-mode coherent states for the center-of-mass and relative vibrational modes of two trapped ions. In the scheme the ions are driven by a single travelling-wave laser field tuned to the carrier. Then a measurement of the internal states collapses the vibrational modes to the entangled coherent state.
文摘The present study delves into the application of investigating quantum state behaviour,particularly focusing on coherent and superposition states.These states,characterized by their remarkable stability and precision,have found extensive utility in various domains of quantum mechanics and quantum information processing.Coherent states are valuable for manipulating quantum systems with accuracy.Superposition states allow quantum systems to exist in numerous configurations at the same time,which paves the way for quantum computing’s capacity for parallel processing.The research accentuates the crucial role of quantum error correction(QEC)in ensuring the stability and reliability of quantum information processing systems.Quantum systems are prone to errors from decoherence and environmental noise,making QEC essential for ensuring accurate results by employing the Shor code,an error-correcting code devised by Peter Shor,it becomes feasible to detect and rectify errors that may arise during quantum computations.The Shor code detects and corrects both bit-flip and phase-flip errors,greatly enhancing the robustness of quantum information systems.This research offers insights into the multifaceted utility of MZI(Mach-Zehnder interferometer)and its relevance in the advancement of quantum technology.By integrating QEC with the capabilities of MZI,this study offers a holistic approach to advancing the precision and reliability of quantum technologies.
文摘In this paper, we analytically solve the master equation for Jaynes-Cummings model in the dispersive regime including phase damping and the field is assumed to be initially in a superposition of coherent states. Using an established entanglement measure based on the negativity of the eigenvalues of the partially transposed density matrix we find a very strong sensitivity of the maximally generated entanglement to the amount of phase damping. Qualitatively this behavior is also reflected in alternative entanglement measures, but the quantitative agreement between different measures depends on the chosen noise model The phase decoherence for this model results in monotonic increase in the total entropy while the atomic sub-entropy keeps its periodic behaviour without any effect.
基金supported by the National Natural Science Foundation of China under Grants No. 11775075No.1143011 and No. 11935006。
文摘We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on impurity atoms. It is found that the nonclassicality of MQSSs can be manipulated by changing the number of the impurities and their interaction with the BEC. It is shown that the BEC matter-wave field exhibits a collapse and revival phenomenon which reveals the quantum nature of the BEC matter-wave field. We investigate the micro-macro entanglement between the impurities and the BEC, and find enhancement of the micro-macro entanglement induced by the initial quantum coherence of the impurity atoms.
文摘Reinforcement learning is one of the fastest growing areas in machine learning,and has obtained great achievements in biomedicine,Internet of Things(IoT),logistics,robotic control,etc.However,there are still many challenges for engineering applications,such as how to speed up the learning process,how to balance the trade-of between exploration and exploitation.Quantum technology,which can solve complex problems faster than classical methods,especially in supercomputers,provides us a new paradigm to overcome these challenges in reinforcement learning.In this paper,a quantum-enhanced reinforcement learning is pictured for optimal control.In this algorithm,the states and actions of reinforcement learning are quantized by quantum technology.And then,a probability amplifcation method,which can efectively avoid the trade-of between exploration and exploitation via quantized technology,is presented.Finally,the optimal control policy is learnt during the process of reinforcement learning.The performance of this quantized algorithm is demonstrated in both MountainCar reinforcement learning environment and CartPole reinforcement learning environment—one kind of classical control reinforcement learning environment in the OpenAI Gym.The preliminary study results validate that,compared with Q-learning,this quantized reinforcement learning method has better control performance without considering the trade-of between exploration and exploitation.The learning performance of this new algorithm is stable with diferent learning rates from 0.01 to 0.10,which means it is promising to be employed in unknown dynamics systems.
基金Project supported by Hunan Provincial Natural Science Foundation of China （Grant No 06jj50014）.
文摘This paper proposes a method of generating multipartite entanglement through using d.c. superconducting quan- tum interference devices （SQUID） inside a standing wave cavity. In this scheme, the d.c. SQUID works in the charge region. It is shown that, a large number of important multipartite entangled states can be generated by a controllable interaction between a cavity field and qubits. It is even possible to produce entangled states involving different cavity modes based on the measurement of charge qubits states. After such superpositions states are created, the interaction can be switched off by the classical magnetic field through the SQUID, and there is no information transfer between the cavity field and the charge qubits.
基金supported by the National Natural Science Foundation of China (Grant No. 61075014)the Science Foundation of Xi’an University of Posts and Telecommunications for Young Teachers (Grant No.ZL2010-11)the Science Foundation of Shaanxi Provincial Department of Education (Grant No. 11JK0902)
文摘The analysis of accuracy for superposition of squeezed states （SSSs） in lossless and loss case has been performed in this study. In lossless case, time accuracies of SSSs with mean photon number ns have a scaling of ns-2 in two limits of large and small squeezing. With the help of photon loss model, the dissipative channel will degrade accuracies has been proved. In the limit of large squeezing, the accuracy will slowly decrease with the reduction of transmittance η. In the limit of small squeezing, time accuracy scales as 1/（η4n2） and will decrease much faster along with η decreases.
文摘Using the principles of quantum state superposition and entanglement,quantum computing has been proven to be able to tackle problems that are hard for state-of-the-art supercomputers.Thirty years ago,when Shor’s algorithm and Grover’s algorithm were proposed and proven to have great acceleration on solving some problems,including factoring and searching,quantum computing was only a beautiful scientific dream.Today,quantum computing is advancing at an incredible pace.Over 10 years ago,Devoret and Schoelkopf said something similar in their review1.
