量子关联引起的能量异常流动

Abnormal Flow of Heat Caused by Quantum Correlations

量子关联是量子体系区别于经典的重要特征之一,如何量化与利用量子关联不仅是量子信息论中的核心问题,也是量子热力学中比较关心的话题。对于经典体系来说,能量总是自发从高温物体流向低温物体,即封闭系统的熵只能增加或保持,永远不会减少,同时随着时间增加,能量耗散增加,但整个体系始终未表现出较强的关联性。在量子体系下,子系统间往往存在关联,在此情况下,上述结论并不总是成立,甚至由于整体熵值减小导致能量反向流动,这种非经典的特性表明仅使用冯·诺依曼熵表征系统熵的变化是不完备的,因此需要对经典热力学第二定律进行完善。基于该定律,本文研究了在孤立体系下,量子关联与能量、熵之间的关系,表明子系统间的量子关联会导致能量反向流动或加速能量正向流动,可以视为制冷或热加速过程,初始时不同的关联决定了之后的能量流动情况,两者高度相关。为了解释这种现象,引入了相对熵等热力学参量来解释关联对量子系统热力学性质的影响,结果表明,当相干项不为零时,表征系统关联的互信息总是随着演化先降低再增加,因而导致了与经典不同的特性。基于以上现象,提出了基于光学体系的实验方案,用来验证理论的正确性。

The presence of correlations in physical systems can be a significant characteristic that distinguishes quantum systems from classics. The quantification and utilization of quantum correlations are not only considered as core issues in quantum information theory, but also attract much attention of quantum thermodynamics community. For classical thermodynamics, heat spontaneously flows from hot to cold without showing a strong correlation for the isolated system. The entropy of a closed system tends to increase with time and this phenomenon can be regarded as the thermodynamics arrow of time. As a system advances through time, energy dissipation occurs, and it becomes more statically disordered. However, the above conclusions are not always valid in quantum area, due to the correlations between subsystems, even leading to the reverse flow of energy. This means that the formula of the second law of classical thermodynamics needs to be revised and using more physical quantities other than von Neumann entropy to show this non-classical quality. We here propose that quantum correlations between the subsystems can cause the energy to flow backward or accelerate the forward flow of energy. For explaining such phenomenon, we introduce the relative entropy and other thermodynamic parameters to quantitatively characterize the influence of correlations on the thermodynamic properties of quantum systems. These results show that the mutual information that characterizes the system correlations always decreases during evolution and then increases again when there exists a nonzero correlation terms among subsystems. Thus, we propose an experimental scheme based on the optical system to verify the correctness of the theory.