Qubit decoherence with an initial correlation

Decoherence of a qubit system interacting with a bosonic reservoir is considered when there is at most one excitation in the whole system and there is an initial correlation with the reservoir. An exact time-evolution of the system is obtained and the effect of the initial correlation on the time-evolution is examined in detail.

► Exact reduced dynamics with an initial correlation is obtained for a qubit system.
► Both of individual reservoirs and common reservoir are considered.
► The effect of an initial correlation on the decay of coherence and entanglement are examined.