Topological quantum phase transition in the transverse Wen-plaquette model

In this paper we study the quantum phase transition between a quantum state with topological order and that without topological order (TQPT) in the transverse Wen-plaquette model. By mapping the transverse Wen-plaquette model onto the d = 1 Ising model in a transverse field, some exact results of the TQPT are obtained. The transverse Wen-plaquette model undergoes a continuous TQPT which is characterized in terms of the expectation values of string operators. In particular, the duality relationship between open-string and closed-string is explored -the expectation value of closed-string operator and that of open-string operator play the role of order parameter and disorder order parameter of the topological order, respectively. At the critical point the condensation of both Z(2) vortex and Z(2) charge indicates that the TQPT is a new type of phase transition beyond the Landau-Ginzburg-Wilson paradigm. Copyright (C) EPLA, 2008