Variable coupling between the inductively isolated current-biased Josephson junction qubit and the current bias leads

We examined the behavior of inductively isolated Josephson junction qubits in which the coupling to the bias leads could be varied in situ. The variable coupling was achieved by using a second Josephson junction and an inductor that act as an inductive current divider. The coupling between the current bias leads and the qubit was varied by changing the current through the second junction, altering its Josephson inductance. We measured the tunneling escape rates of Al/Al$O_x$/Al and Nb/Al$O_x$/Nb junctions with continuous or pulsed microwave power, showing the allowed energy transitions and coherent Rabi oscillations. We found that $T_2$, $T_2^*$ and $T_1$ did not change significantly as the coupling to the current bias leads was varied.