物理学报2017，Vol.66Issue(1)：19-26,8.DOI:10.7498/aps.66.010301
弱测量对四个量子比特量子态的保护
The protection of qudit states by weak measurement
摘要
Abstract
Liao Xiang-Ping et al.(Chin.Phys.B 23 020304,2014) pointed out that the method of weak measurement and quantum weak measurement reversal can protect entanglement and improve the fidelity of three-qubit quantum state.We generalize the method of weak measurement to the case of qudit state in this paper.By using the operation of weak measurement and quantum weak measurement reversal,we investigate the evolution dynamics of fidelity and fidelity improvement for qudit state under amplitude damping decoherence.We compare two kinds of operations:one is to let the input qudit state cross the amplitude damping decoherence directly,and the other one is that we first make a weak measurement operation on the input qudit state,then through the amplitude damping decoherence,finally an operation of quantum weak measurement reversal is done with the output qudit state.We discuss the GHZ state,W state,CL state and some special separable states exactly and obtain the analytic expressions of fidelity and fidelity improvement for qudit state before and after the weak measurement and quantum weak measurement reversal operation.According to the analytic expressions we plot the evolution curves against its corresponding parameters.The effects of corresponding parameters are discussed and a susceptible protection region of the qudit state is also given in the context.The results show that the structure of qudit state is the determined factor to the effect of weak measurement and quantum weak measurement reversal.There are some different effects on the different structured qudit states.For entangled state,the fidelity of qudit GHZ state can be protected in a relatively big evolution region,most part of the fidelity improvement is in the upper part of the zero reference plane.While the fidelity of qudit W state can be improved effectively in the whole evolution region,which is a perfect protection.The evolution regulations of qudit CL state and Dick state are between evolution regulations of the GHZ state and W state.When we input some special separable qudit states which have similar structures to W state,their fidelity and fidelity improvement are almost the same as W state's.It is demonstrated that the structure of qudit state is important for the weak measurement in a step.This work is meaningful for the quantum information process.关键词
弱测量/四量子比特/振幅阻尼/保真度Key words
weak measurement/qudit/amplitude/fidelity引用本文复制引用
黄江..弱测量对四个量子比特量子态的保护[J].物理学报,2017,66(1):19-26,8.基金项目
Project supported by the natural science foundation of Guangdong province(Grant No.2015A030310354),and the Foundation of Excellent-Young-Backbone Teacher of Guangdong Ocean University,China.广东省自然科学基金(批准号:2015A030310354)和广东海洋大学优秀青年骨干教师基金资助的课题. （Grant No.2015A030310354）
