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中国物理学会期刊

中间测量对受驱单量子比特统计复杂度的影响

CSTR: 32037.14.aps.69.20200802

Influence of intermediated measurements on quantum statistical complexity of single driven qubit

CSTR: 32037.14.aps.69.20200802
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  • 最近, 基于量子信息理论的统计复杂度引起了人们的关注. 在噪声环境下, 一个受外界驱动的单量子比特系统具有丰富的动力学行为. 本文利用Lindblad方程, 在Born-Markov近似下, 研究N次中间量子测量后, 在系统演化的最后时刻\tau, 末态的统计复杂度C. 研究发现: 在\tau由0变大的过程中, C从0开始, 先增大到最大值, 然后减小, 直到再趋近于0; N 较小时, C伴随着明显的不规则振荡现象, 振幅随\tau逐渐减小; N越大, C\tau的变化趋势越接近无中间测量时的变化趋势. 研究结果给量子态的操控提供了一定的理论参考.

     

    Recently, quantum statistical complexity based quantum information theory has received much attraction. Quantum measurements can extract the information from a system and may change its state. At the same time, the method of measuring multiple quantum is an important quantum control technique in quantum information science and condensed matter physics. The main goal of this work is to investigate the influence of multiple quantum measurements on quantum statistical complexity.
    It is a fundamental problem to understand, characterize, and measure the complexity of a system. To address the issue, a damped and linearly driven two-level system (qubit) is taken for example. The driving amplitude and dephasing intensity are considered. By using the Lindblad equation and the Born-Markov approximation, the time evolution of the system can be obtained. Under multiple intermediated measurements, the system has a complex dynamic behavior. Quantum statistical complexity C at the last moment \tau is studied in detail. The results show that on the whole, C first increases from zero to a maximal value with \tau increasing, then decreases, and finally it approaches to zero. At first, the system is in a pure state and C=0. Finally, the system is in a maximally mixed state due to the interaction with the environment and C=0 again. When the number of measurements N is relatively small, C fluctuates with \tau increasing, but when N is relatively large, the fluctuations disappear. Due to the quantum Zeno effect, as N is larger, the variation of C with \tau is similar to that for the case of no intermediated measurement. Because of the quantum superposition principle, uncertainty principle, and quantum collapse, quantum measurement can disturb the system, so quantum statistical complexity C exhibits a complex behavior.
    In the quantum realm, the complexity of a system can be transformed into a resource. The quantum state needs creating, operating, or measuring. Therefore, all our results provide a theoretical reference for the optimal controlling of quantum information process and condensed matter physics. At the same time, the number of the degrees of freedom is two for the damped and linearly driven two-level system, so this system is simple and easy to study. The complexity of such a system can be tailored by properly tuning the driving strength. Therefore, the model can be used as a typical example to study the quantum statistical complexity.

     

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