题 目：Pointer States of Decoherence and Non-canonical Equilibrium Statistics: Role of System-bath Coupling
报告人：Prof. Jiangbin Gong (National University of Singapore)
In real physical situations, such as light-harvesting systems, super-conducting qubits, and atom-cavity systems, a weak system-bath coupling (SBC) assumption may be invalid. In this talk, I shall discuss some features shared by two seemingly unrelated issues, namely, pointer states of decoherence and non-canonical equilibrium statistics, by considering the role of SBC that is no longer weak. Pointer states of decoherence are a representation in which decoherence quickly turns a superposition state to an incoherent mixture. For weak or strong SBC, the behavior of pointer states is well known. Using a simple dynamical model, I show that even for intermediate SBC, approximate pointer states may still emerge and they can continuously deform to expected limits for weak or strong SBC. Thus, superposition states of pointer states are rapidly destroyed by decoherence but pointer states themselves can be rich superposition states for intermediate SBC.
As equilibrium statistics is a long-time outcome of quantum dissipation, we expect system's noncanonical statistics, as characterized by the diagonal representation of the reduced density matrix (which is no longer the energy representation of the system), to behave similarly as the pointer states of decoherence. This is confirmed in a spin-boson model with super-ohmic spectral density. We exploit both polaron transformation and perturbation theory to analytically obtain non-canonical statistics of a two-level system at arbitrary temperature and for arbitrary SBC strength, with results in agreement with exact Monte-carlo simulations. It is also found that irrespective of SBC strength, non-canonical statistics enhances as temperature decreases but may completely vanish at high temperature.
1. Wen-ge Wang, Lewei He, and Jiangbin Gong, "Preferred States of Decoherence under Intermediate System-Environment Coupling", Phys. Rev. Lett. 108, 070403 (2012).
2. Chee Kong Lee, Jianshu Cao, and Jiangbin Gong, "Non-Canonical Statistics of an Open Quantum System: Theory and Exact Monte-Carlo Simulations", submitted.
Prof. Jiangbin Gong’s main research interests include quantum control, nonlinear physics, and fundamental issues in open quantum systems. He obtained his B. Sc in theoretical physics from Nanjing University in 1993. Subsequently he obtained his Ph.D in theoretical chemical physics from the University of Toronto in 2001. During 2001-2005 he was a Henry-Croft Postdoctoral Fellow at the University of Toronto and a Postdoctoral Research Associate at the James Franck Institute, University of Chicago. In 2006 he joined the Department of Physics, National University of Singapore (NUS) as an Assistant Professor. Since 2010, he has been an Associate Professor at NUS. In 2011 he was awarded NUS Dean’s Chair Professorship with a three-year term.