title: Entanglement evolution and quantum phase transition of biased s = 1/2 spin-boson model.
abstract: The ground state and the spectral structure of lower-lying excited states of a dissipative two-level system coupled to a sub-Ohmic bath (s = 1/2) with nonzero bias have been studied using the unitary transformation method. By calculating the ground-state entanglement entropy, the ground-state average of σ(z)(G), and the static susceptibility of the two-level system, we explore the nature of the transition (crossover) between the delocalized and localized state of the two-level system. Furthermore, we calculate the time-dependent expectation (σ(z)(t)) and the time evolution of the entanglement entropy to show that, when the system undergoes a transition (crossover) from the delocalized to the localized state, the time evolution of the two-level system changes from coherent to decoherent dynamics.
authors.affiliation: Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Chunjian
authors.initials: C
authors.lastname: Zhao
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Lü
authors.forename: Hang
authors.initials: H
authors.lastname: Zheng