title: A variational master equation approach to quantum dynamics with off-diagonal coupling in a sub-Ohmic environment.
abstract: A master equation approach based on an optimized polaron transformation is adopted for dynamics simulation with simultaneous diagonal and off-diagonal spin-boson coupling. Two types of bath spectral density functions are considered, the Ohmic and the sub-Ohmic. The off-diagonal coupling leads asymptotically to a thermal equilibrium with a nonzero population difference Pz(t → ∞) ≠ 0, which implies localization of the system, and it also plays a role in restraining coherent dynamics for the sub-Ohmic case. Since the new method can extend to the stronger coupling regime, we can investigate the coherent-incoherent transition in the sub-Ohmic environment. Relevant phase diagrams are obtained for different temperatures. It is found that the sub-Ohmic environment allows coherent dynamics at a higher temperature than the Ohmic environment.
authors.affiliation: School of Science, Hangzhou Dianzi University, Hangzhou 310018, China.
authors.forename: Ke-Wei
authors.initials: KW
authors.lastname: Sun
authors.affiliation: Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Fujihashi
authors.affiliation: Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan.
authors.forename: Akihito
authors.initials: A
authors.lastname: Ishizaki
authors.affiliation: Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhao