Hahn Thilo, Wigger Daniel, Kuhn Tilmann
Institut für Festköpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10 48149 Münster, Germany.
Entropy (Basel). 2020 Feb 29;22(3):286. doi: 10.3390/e22030286.
In quantum physics, two prototypical model systems stand out due to their wide range of applications. These are the two-level system (TLS) and the harmonic oscillator. The former is often an ideal model for confined charge or spin systems and the latter for lattice vibrations, i.e., phonons. Here, we couple these two systems, which leads to numerous fascinating physical phenomena. Practically, we consider different optical excitations and decay scenarios of a TLS, focusing on the generated dynamics of a single phonon mode that couples to the TLS. Special emphasis is placed on the entropy of the different parts of the system, predominantly the phonons. While, without any decay, the entire system is always in a pure state, resulting in a vanishing entropy, the complex interplay between the single parts results in non-vanishing respective entanglement entropies and non-trivial dynamics of them. Taking a decay of the TLS into account leads to a non-vanishing entropy of the full system and additional aspects in its dynamics. We demonstrate that all aspects of the entropy's behavior can be traced back to the purity of the states and are illustrated by phonon Wigner functions in phase space.
在量子物理学中，有两个典型的模型系统因其广泛的应用而脱颖而出。它们是二能级系统（TLS）和谐振子。前者通常是受限电荷或自旋系统的理想模型，后者则用于晶格振动，即声子。在这里，我们将这两个系统耦合起来，这会导致许多引人入胜的物理现象。实际上，我们考虑了TLS的不同光学激发和衰变情况，重点关注与TLS耦合的单个声子模式所产生的动力学。特别强调的是系统不同部分的熵，主要是声子的熵。虽然在没有任何衰变的情况下，整个系统始终处于纯态，导致熵为零，但各个部分之间复杂的相互作用会导致各自的纠缠熵不为零以及它们的非平凡动力学。考虑TLS的衰变会导致整个系统的熵不为零，并在其动力学中产生其他方面的影响。我们证明，熵行为的所有方面都可以追溯到态的纯度，并通过相空间中的声子维格纳函数来说明。
