  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 and the second one is tuned to the Rabi
frequency, it is shown that the response of the system exhibits an undamped low
frequency oscillation. 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 an example, the application of
the method to the readout of a flux qubit is considered.
