  We replace the Josephson junction defining a three-junction flux qubit's
properties with a tunable direct current superconducting quantum interference
devices (DC-SQUID) in order to tune the qubit gap during the experiment. We
observe different gaps as a function of the external magnetic pre-biasing field
and the local magnetic field through the DC-SQUID controlled by high-bandwidth
on chip control lines. The persistent current and gap behavior correspond to
numerical simulation results. We set the sensitivity of the gap on the control
lines during the sample design stage. With a tuning range of several GHz on a
qubit dynamics timescale, we observe coherent system dynamics at the degeneracy
point.
