Decoherence of interacting qubits in contact with a common environment

Decoherence of interacting two qubits placed under the influence of a common environment is studied by means of the quantum master equation, where the two qubits interact with each other via the XY-coupling and the two-qubit system has the dephasing coupling with the environment. It is shown that when the asymmetry of the interaction between the two-qubit system and environment is not small, the qubit-qubit interaction significantly affects the dephasing of the two-qubit system. To examine such an interaction effect, the decay of two-qubit entanglement is calculated. It is found that the qubit-qubit interaction makes not only the decay of entanglement small but also the period of the oscillatory behaviour short.