Entangled Subspaces for Two Coupled Qubits in a Normal Environment

Abstract

By investigating the effect of environmental perturbations on two initially coupled qubits, we find that the interactions between the qubits and between the qubits and the environment are not only the source of decoherence, but also the power of avoiding disentanglement. It is shown that there are the entangled subspaces for four kinds of different coupling ways between the qubits, in which the qubits preserve entanglement all the time. Thus, any new coherent source does not be introduced to preserve entanglement in the entangled subspaces.