摘要
退相干抑制是量子系统控制中一项重要的控制任务.受到经典控制理论中的前馈控制的启发,本文借助弱测量和环境辅助测量提出一种新的退相干抑制方案,并将其推广到一般的N量子比特情形.所提方案的核心思想是:在退相干通道前,借助弱测量算符和前馈控制算符将量子比特转移到一个对环境噪声更鲁棒的状态上;在退相干通道中,对与被保护的量子比特耦合的环境进行测量;在退相干通道后,再借助相应的反转算符恢复初始状态.所提方案适用于具有至少一个可逆的Kraus算符的任意退相干通道下的量子状态保护.假设所考虑的振幅阻尼或相位阻尼退相干通道的特性是完全已知的,那么所提方案即便是在重阻尼情况下也能取得100%的保真度,这是所提方案的最大优势.以2量子比特纠缠态的并发度增强和噪声环境下量子隐形传态的保真度提高为例设计了两组数值仿真实验,推导了性能指标的解析表达式,并通过与无保护方案对比凸显出所提方案的优越性.
All open quantum systems are affected by environmental noises due to their interactions with the external environment and inevitably suffer from decoherence. Hence, it is fundamentally important and necessary to investigate decoherence suppression for open quantum systems via proper control strategies. Inspired by feedforward control in the classical control theory, this paper proposes a novel decoherence suppression scheme via weak measurement and environment-assisted measurement. We first take the single-qubit system as an example to illustrate steps of the proposed scheme. To be specific, the single-qubit system is transferred to a state that is more robust to environmental noises via pre-weak measurement operators and feed-forward control operators before the decoherence channel, a measurement is performed on the environment coupled to the protected qubit during the decoherence channel, and the initial state is recovered via reversed feed-forward control operators and post-weak measurement operators after the decoherence channel. The optimum post-weak measurement strength is derived by setting the normalized final state equal to the initial state. By considering the optimum post-weak measurement strength, analytical formulas of the total success probability and the total fidelity are deduced. The proposed scheme is applicable for protecting quantum states from arbitrary decoherence channels with at least one invertible Kraus operator although only the amplitude damping channel and the phase damping channel are taken into account. Provided that the decay rate of the amplitude or phase damping channel is completely known, one can always achieve unit fidelity even for heavy damping cases, which is the biggest advantage of the proposed scheme. Influences of several parameters including strengths of weak measurements, the initial state and the decay rate of the decoherence channel on the performance of decoherence suppression are analyzed, and detailed procedures of a single-qubit pure and mixed state protection a
作者
张骄阳
丛爽
王驰
Sajede Harraz
Zhang Jiao-Yang;Cong Shuang;Wang Chi;Sajede Harraz(Department of Automation,University of Science and Technology of China,Hefei 230027,China)
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第22期33-46,共14页
Acta Physica Sinica
基金
国家自然科学基金(批准号:61973290)资助的课题。
关键词
退相干抑制
量子前馈控制
弱测量
环境辅助测量
decoherence suppression
quantum feed-forward control
weak measurement
environment-assisted measurement
