  We study analytically the dynamic behaviors of quantum correlation measured
by quantum discord between two uncoupled qubits, which are immersed in a common
Ohmic environment. We show that the quantum discord of the two noninteracting
qubits can be greatly amplified or protected for certain initially prepared
$X$-type states in the time evolution. Especially, it is found that there does
exist the stable amplification of the quantum discord 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
there does exist a sudden change of the quantum discord in the time evolution
at a critic time point $t_c$, and the discord amplification and protection may
occur only in the time interval $0<t\leq t_c$ for certain $X$-type states. This
sheds new light on the creation and protection of quantum correlation.

Quantum Physics