  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 the examples, the application of the method to a nuclear spin and to
the readout of a flux qubit are briefly discussed.
