Resonance phenomena in the interaction of a many-photon wave packet and a qubit

We demonstrate that a highly excited quantum electromagnetic mode strongly interacting with a single qubit exhibits several distinct resonances in addition to the one identified and studied by Bloch and Siegert in the interaction with classical radiation. The resonance phenomena are associated with non-classical effects: the collapse of Rabi oscillations, splitting of the photon wave packet and field-qubit entanglement. The analysis is based on a semiclassical phase-space flow of 2 × 2 matrices and becomes exact when the photon number tends to infinity. The flow equations are solved perturbatively and numerically, showing that the resonant detuning of the field and qubit frequencies lies on two branches in the leading order, which further split into distinct curves in higher orders.