  We implemented experimentally an interferometer-type charge qubit consisting
of a single-Cooper-pair transistor closed by a superconducting loop that is in
flip-chip configuration inductively coupled to a radio frequency tank circuit.
The tank permits to readout the qubit state, acting as inductance measuring
apparatus. By applying continuous microwave power to the quantum device, we
observed inductance alterations caused by redistributions of the energy level
populations. From the measured data, we extracted the energy gap between ground
and upper levels as a function of the transistor quasicharge as well as the
Josephson phase across both junctions.
