Observation of Co-tunneling in Pairs of Coupled Flux Qubits

Understand

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.