Decay of Loschmidt echo enhanced by quantum criticality.
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.
Quan
H T
HT
Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080, China.
Song
Z
Z
Liu
X F
XF
Zanardi
P
P
Sun
C P
CP