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Dynamic process and Uhlmann process: Incompatibility and dynamic phase of mixed quantum states

机译:动态过程和Uhlmann过程:混合量子态的不相容性和动态相位

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摘要

While a pure quantum state may accumulate both the Berry phase and dynamic phase as it undergoes a cyclic path in the parameter space, the situation is more complicated when mixed quantum states are considered. From the Ulhmann bundle, a mixed quantum state can accumulate the Ulhmann phase if the parallel-transport condition is satisfied. However, we show that the Ulhmann process is in general not compatible with the evolution equation of the density matrix governed by the Hamiltonian. Thus a mixed quantum state usually accumulates a dynamic phase during its time evolution. We present the expression of the dynamic phase for mixed quantum states. In examples of one-dimensional two-band models and simple harmonic oscillator, the dynamic phase can take multiple discrete values in cyclic, quasistatic processes at infinitely high temperature due to the resonant points. However, the behavior differs if the energy spectrum is continuous without a band gap. Moreover, there is no natural analog of the dynamic phase in classical systems.
机译:当纯量子态在参数空间中经历循环路径时,可能会同时累积Berry相和动态相,但考虑混合量子态时,情况就更加复杂了。如果满足平行传输条件,则从Ulhmann束中,混合量子态可以累积Ulhmann相。但是,我们表明,Ulhmann过程通常与哈密顿量控制的密度矩阵的演化方程不兼容。因此,混合量子态通常在其时间演化过程中累积一个动态相位。我们提出了混合量子态的动态相位表达。在一维两频带模型和简单谐波振荡器的示例中,由于谐振点,动态相位在无限高温下的循环准静态过程中可能会具有多个离散值。但是,如果能谱是连续的而没有带隙,则行为会有所不同。而且,在经典系统中没有动态阶段的自然模拟。

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  • 来源
    《Physical review》 |2020年第10期|104310.1-104310.15|共15页
  • 作者单位

    Department of Physics Southeast University Jiulonghu Campus Nanjing 211189 China;

    School of Physics Sichuan University Chengdu Sichuan 610064 China;

    Department of Physics University of California Merced California 95343 USA;

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