  The dissipation-induced relaxation (T_1) time of a macroscopic quantum system
- a \{lambda}-type three-level rf SQUID flux qubit weakly coupled to control
and readout circuitry (CRC) - is investigated via time-domain measurement. The
measured interwell relaxation time of the qubit's first excited state,
T_1=3.45+/-0.06 \{mu}s, corresponds to an effective damping resistance of the
flux qubit R=1.6+/-0.1 M\{omega} which is much lower than the intrinsic
quasiparticle resistance of the Josephson tunnel junction. An analysis of the
system shows that although the CRC is very weakly coupled to the qubit it is
the primary source of damping. This type of damping can be significantly
reduced by the use of more sophisticated circuit design to allow coherent
manipulation of qubit states.
