Amplification of quantum discord between two uncoupled qubits in a common environment by phase decoherence

We study analytically the dynamic behaviours of quantum correlation measured by a quantum discord between two uncoupled qubits, which are immersed in a common Ohmic environment. We show that the quantum discord of the two non-interacting qubits can be greatly amplified or protected for certain initially prepared X-type states in the time evolution. In particular, it is found that stable amplification of the quantum discord exists for the case of two identical qubits, and the quantum discord can be protected for the case of two different qubits with a large detuning. It is also indicated that in general a sudden change of the quantum discord occurs in the time evolution at a critical time point tc, and the discord amplification and protection may occur only in the time interval 0<t≤tc for certain X-type states. This sheds new light on the creation and protection of quantum correlation.