Pulse Control of Decoherence in a Qubit Coupled with a Quantum Environment

We study the time evolution of a qubit linearly coupled with a quantum environment under a sequence of short π pulses.Our attention is focused on the case where qubit-environment interactions induce the decoherence with population decay.We assume that the environment consists of a set of bosonic excitations.The time evolution of the reduced density matrix for the qubit is calculated in the presence of periodic short π pulses.We confirm that the decoherence is suppressed if the pulse interval is shorter than the correlation time for qubit-environment interactions.