title: Decay of Loschmidt echo enhanced by quantum criticality.
abstract: We study the transition of a quantum system from a pure state to a mixed one, which is induced by the quantum criticality of the surrounding system E coupled to it. To characterize this transition quantitatively, we carefully examine the behavior of the Loschmidt echo (LE) of E modeled as an Ising model in a transverse field, which behaves as a measuring apparatus in quantum measurement. It is found that the quantum critical behavior of E strongly affects its capability of enhancing the decay of LE: near the critical value of the transverse field entailing the happening of quantum phase transition, the off-diagonal elements of the reduced density matrix describing S vanish sharply.
authors.affiliation: Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: H T
authors.initials: HT
authors.lastname: Quan
authors.forename: Z
authors.initials: Z
authors.lastname: Song
authors.forename: X F
authors.initials: XF
authors.lastname: Liu
authors.forename: P
authors.initials: P
authors.lastname: Zanardi
authors.forename: C P
authors.initials: CP
authors.lastname: Sun