Longhi Stefano
Dipartimento di Fisica, Politecnico di Milano and Istituto di Fotonica e Nanotecnologie del Consiglio Nazionale delle Ricerche, Piazza L. da Vinci 32, I-20133 Milano, Italy.
Sci Bull (Beijing). 2017 Jun 30;62(12):869-874. doi: 10.1016/j.scib.2017.05.012. Epub 2017 May 15.
Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of time reversal of a subsystem of discrete states coupled to an external environment characterized by a continuum of states, into which they generally decay. It is shown that, by flipping the discrete-continuum coupling from an Hermitian to a non-Hermitian interaction, thus resulting in a non unitary dynamics, time reversal of the subsystem of discrete states can be achieved, while the continuum of states is not reversed. Exact time reversal requires frequency degeneracy of the discrete states, or large frequency mismatch among the discrete states as compared to the strength of indirect coupling mediated by the continuum. Interestingly, periodic and frequent switch of the discrete-continuum coupling results in a frozen dynamics of the subsystem of discrete states.
由厄米哈密顿量描述的量子或经典系统中的时间反演是一个物理上允许的过程，原则上这需要反转哈密顿量的符号。在这里，我们考虑一个与具有连续态的外部环境耦合的离散态子系统的时间反演问题，离散态通常会衰变到该连续态中。结果表明，通过将离散 - 连续态耦合从厄米相互作用翻转到非厄米相互作用，从而导致非幺正动力学，可以实现离散态子系统的时间反演，而连续态并不反转。精确的时间反演需要离散态的频率简并，或者与由连续态介导的间接耦合强度相比，离散态之间存在大的频率失配。有趣的是，离散 - 连续态耦合的周期性和频繁切换会导致离散态子系统的动力学冻结。
