Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discr...Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement （POVM）. We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.展开更多
An efficient multipaxty quantum secret sharing scheme is proposed, in which the secret is a quantum state, and the dealer encodes the secret by performing the operations of quantum-controlled-not and Hadamard gate. Th...An efficient multipaxty quantum secret sharing scheme is proposed, in which the secret is a quantum state, and the dealer encodes the secret by performing the operations of quantum-controlled-not and Hadamard gate. The participants perform the single-particle measurements on their particles, and then can cooperate to recover the original quantum state. In our scheme, both the dealer and the participants do not need to perform the entanglement measurement. Compared with the existing schemes, our scheme is simpler and more efficient.展开更多
We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single st...We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single standing-wave laser pulse whose carrier frequency is tuned to the ions transition. In the scheme each ion does not need to be exactly positioned at the node of the standing wave, which is very important from viewpoint of experiment, Furthermore, our scheme may allow the generation of a superposition of coherent states with large mean phonon number for a large number of trapped ions in a fast way by choosing suitable laser intensity. We show that it can also be used to generate maximally entangled states of multiple trapped ions.展开更多
量子非局域性作为一种极具价值的量子资源,在诸多量子信息处理任务中扮演着不可或缺的关键角色.对非局域性进行精准表征与有效探测,始终是量子信息理论研究与实验探索中非常有挑战性的重要课题.如何在结构复杂的多体量子系统里准确识别...量子非局域性作为一种极具价值的量子资源,在诸多量子信息处理任务中扮演着不可或缺的关键角色.对非局域性进行精准表征与有效探测,始终是量子信息理论研究与实验探索中非常有挑战性的重要课题.如何在结构复杂的多体量子系统里准确识别并验证量子非局域性现象,如何设计出更为高效的非局域性探测方法,已成为亟待解决的重要科学问题.本文致力于多体量子非局域性的探测问题,着重探究如何借助Svetlichny不等式来实现多体量子非局域性的探测.首先探讨了Svetlichny不等式的最大量子违背,构造了达到Svetlichny不等式的最大量子违背的量子态与可观测量集,展示了如何构造其他的量子态与可观测量集来实现其最大量子违背,以此阐明了实现Svetlichny不等式最大量子违背的量子态和可观测量集是不唯一的.其次,为了寻找更多违背Svetlichny不等式的量子态和可观测量集,借助量子态的神经网络表示构建了神经网络量子态,通过优化算法对网络参数进行优化来实现Svetlichny不等式的违背,进而探测到非局域态.通过与经典的Nelder-Mead单纯形法对比,发现量子变分蒙特卡罗(variational Monte Carlo,VMC)方法在效率与精度上更适配基于神经网络量子态的非局域性探测,并在不同哈密顿量下成功实现了借助神经网络量子态与VMC方法对多体量子纯态非局域性的探测.本研究不仅证实了基于神经网络量子态与VMC方法的多体量子非局域性探测在理论上与技术上的可行性,同时也为非局域性探测领域提供了颇具价值的研究新见解,更为借助神经网络解决复杂的量子多体问题开拓了全新的研究思路.展开更多
基金Project supported by the Natural Science Foundation of Guangdong Province,China(Grant Nos06029431and020127)the Natural Science Foundation of the Education Bureau of Guangdong Province,China(Grant No Z02069)
文摘Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement （POVM）. We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.
文摘An efficient multipaxty quantum secret sharing scheme is proposed, in which the secret is a quantum state, and the dealer encodes the secret by performing the operations of quantum-controlled-not and Hadamard gate. The participants perform the single-particle measurements on their particles, and then can cooperate to recover the original quantum state. In our scheme, both the dealer and the participants do not need to perform the entanglement measurement. Compared with the existing schemes, our scheme is simpler and more efficient.
基金The project partially supported by National Fundamental Research Program of China under Grant No. 2005CB724508 and National Natural Science Foundation of China under Grant Nos. 60478029, 90503010, and 10575040 . We would like to thank Prof. Ying Wu for many enlightening discussions.
文摘We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single standing-wave laser pulse whose carrier frequency is tuned to the ions transition. In the scheme each ion does not need to be exactly positioned at the node of the standing wave, which is very important from viewpoint of experiment, Furthermore, our scheme may allow the generation of a superposition of coherent states with large mean phonon number for a large number of trapped ions in a fast way by choosing suitable laser intensity. We show that it can also be used to generate maximally entangled states of multiple trapped ions.
文摘量子非局域性作为一种极具价值的量子资源,在诸多量子信息处理任务中扮演着不可或缺的关键角色.对非局域性进行精准表征与有效探测,始终是量子信息理论研究与实验探索中非常有挑战性的重要课题.如何在结构复杂的多体量子系统里准确识别并验证量子非局域性现象,如何设计出更为高效的非局域性探测方法,已成为亟待解决的重要科学问题.本文致力于多体量子非局域性的探测问题,着重探究如何借助Svetlichny不等式来实现多体量子非局域性的探测.首先探讨了Svetlichny不等式的最大量子违背,构造了达到Svetlichny不等式的最大量子违背的量子态与可观测量集,展示了如何构造其他的量子态与可观测量集来实现其最大量子违背,以此阐明了实现Svetlichny不等式最大量子违背的量子态和可观测量集是不唯一的.其次,为了寻找更多违背Svetlichny不等式的量子态和可观测量集,借助量子态的神经网络表示构建了神经网络量子态,通过优化算法对网络参数进行优化来实现Svetlichny不等式的违背,进而探测到非局域态.通过与经典的Nelder-Mead单纯形法对比,发现量子变分蒙特卡罗(variational Monte Carlo,VMC)方法在效率与精度上更适配基于神经网络量子态的非局域性探测,并在不同哈密顿量下成功实现了借助神经网络量子态与VMC方法对多体量子纯态非局域性的探测.本研究不仅证实了基于神经网络量子态与VMC方法的多体量子非局域性探测在理论上与技术上的可行性,同时也为非局域性探测领域提供了颇具价值的研究新见解,更为借助神经网络解决复杂的量子多体问题开拓了全新的研究思路.
