Decoherence and relaxation of a quantum bit in the presence of Rabi oscillations

The dissipative dynamics of a quantum bit driven by a strong resonant field and interacting with a heat bath is investigated. We derive generalized Bloch equations and find modifications of the qubit's damping rates caused by Rabi oscillations. The nonequilibrium decoherence and relaxation of a phase qubit inductively coupled to a resonant tank circuit is considered as an illustration of the general results.