Study of relaxation phenomena in strongly fluctuating quantum syetems

我们研究了出现在临界点以下有序态的亚稳态的弛豫现象。特别地，我们研究了在很低的温度下，没有预期的热涨落，系统处于经典意义上的冻结状态的情况。即使在这种情况下，系统仍然可以通过量子涨落来放松。为了阐明量子涨落引起这种相互作用的机制，我们发展了一种研究量子系统动力学性质的方法。例如，纯量子力学方法(薛定谔方程)、约化密度矩阵法等。研究包括量子隧道现象、朗道-齐纳过程等。对于量子隧穿现象，我们提出了一种直接的方法，它可以补充对最近流行的场论方法的理解。

We study relaxation phenomena from metastable states which appear in the ordered states below the critical points. In particular, we study the cases at very low temperatures where no thermal fluctuation are expected and the syatem is in freezing state in classical sense. Even in such cases, system still can relax through quantum fluctuations. In order to clarify mechanisms of such relazation by quantum fluctuation, we developed method to investigate dynamical property of quantum system. For example, purely quantum mechanical method (Schrodinger equation), reduced density matrix method, etc.The study includes quantum tunneling phenomena, Landau-Zener process. For quantum tunneling phenomena we proposed direct approach to the phenomana and it could give a complementary understanding of the phenomana to the field theoretical methods which are popular recently.