title: Ansatz for the quantum phase transition in a dissipative two-qubit system.
abstract: By means of a unitary transformation, we propose an ansatz to study quantum phase transitions in the ground state of a two-qubit system interacting with a dissipative reservoir. First, the ground-state phase diagram is analyzed in the presence of the Ohmic and sub-Ohmic bath using an analytic ground-state wave function that takes into account the competition between intrasite tunneling and intersite correlation. The quantum critical point is determined as the transition point from a nondegenerate to a degenerate ground state, and our calculated critical coupling strength α(c) agrees with that from the numerical renormalization-group method. Moreover, by computing the entanglement entropy between the qubits and the bath as well as the qubit-qubit correlation function in the ground state, we explore the nature of the quantum phase transition between the delocalized and localized states.
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: Hang
authors.initials: H
authors.lastname: Zheng
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: Zhiguo
authors.initials: Z
authors.lastname: Lü
authors.affiliation: Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhao