  We study the complex-valued resonance spectrum of a dc-SQUID coupled to a
flux qubit, where the former is treated in the cubic and the latter in the
two-level approximation. It is shown that this spectrum is well-defined and
contains most of the relevant information on the escape process. Thus, the
language of resonance states is precise and well-adapted to switching- (or
trigger-) type qubit readout, and a worthwhile complement to the various
descriptions of continuous qubit measurement. Initial progress is analytic, but
nonperturbative numerical methods have been formulated and should soon yield
accurate results for all parameter values.
