  We report measurements of macroscopic resonant tunneling between the two
lowest energy states of a pair of magnetically coupled rf-SQUID flux qubits.
This technique provides a direct means of observing two-qubit dynamics and a
probe of the environment coupled to the pair of qubits. Measurements of the
tunneling rate as a function of qubit flux bias show a Gaussian line shape that
is well matched to theoretical predictions. Moreover, the peak widths indicate
that each qubit is coupled to a local environment whose fluctuations are
uncorrelated with that of the other qubit.
