  We present investigations of Josephson charge-phase qubits inductively
coupled to a radio-frequency driven tank-circuit enabling the readout of the
states by measuring the Josephson inductance of the qubit. The circuits
including junctions with linear dimensions of 60 nm and 80 nm are fabricated
from Nb trilayer and allowing the determination of relevant sample parameters
at liquid helium temperature. The observed partial suppression of the
circulating supercurrent at 4.2 K is explained in the framework of a quantum
statistical model. We have probed the ground-state properties of qubit
structures with different ratios of the Josephson coupling to Coulomb charging
energy at 20 mK, demonstrating both the magnetic control of phase and the
electrostatic control of charge on the qubit island.
