Low-frequency Rabi spectroscopy for a dissipative two-level system

We have analyzed the interaction of a dissipative two-level quantum system with high- and low-frequency excitation. The system is continuously and simultaneously irradiated by these two waves. If the frequency of the first signal is close to the level separation, the response of the system exhibits undamped low-frequency oscillations whose amplitude has a clear resonance at the Rabi frequency with the width being dependent on the damping rates of the system. The method can be useful for low-frequency Rabi spectroscopy in various physical systems which are described by a two-level Hamiltonian, such as nuclei spins in NMR, double-well quantum dots, superconducting flux and charge qubits, etc. As examples, the application of the method to a nuclear spin and to the readout of a flux qubit are briefly discussed.