title: Statistical description of small quantum systems beyond the weak-coupling limit.
abstract: An explicit expression is derived for the statistical description of small quantum systems, which are relatively weakly and directly coupled to only small parts of their environments. The derived expression has a canonical form, but is given by a renormalized self-Hamiltonian of the studied system, which appropriately takes into account the influence of the system-environment interaction. In the case that the system has a narrow spectrum and the environment is sufficiently large, the modification to the self-Hamiltonian usually has a mean-field feature, given by an environmental average of the interaction Hamiltonian. In other cases, the modification may be beyond the mean-field approximation.
authors.affiliation: Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China. wgwang@ustc.edu.cn
authors.forename: Wen-ge
authors.initials: WG
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008956:Models, Chemical; D015233:Models, Statistical; D011789:Quantum Theory