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.

• Received 22 December 1993

DOI:https://doi.org/10.1103/PhysRevLett.73.1541