Observation of the Resonant Tunneling of Cooper Pairs

Abstract
We demonstrate how the Coulomb blockade of tunneling and the coherent Josephson tunneling of electron pairs can coexist in the same experiment. Measurements were made on a circuit consisting of two dc SQUIDs connected in series, with a gate capacitively coupled to the center electrode. Peaks in the current as a function of bias voltage shifted position with gate voltage in agreement with the theory of resonant Cooper pair tunneling.