OBSERVATION OF THE RESONANT-TUNNELING OF COOPER PAIRS

We demonstrate how the Coulomb blockade of tunneling and the coherent Josephson tunneling of electron pairs can coexist in the same experime nt. Measurements were made on a circuit consisting of two dc SQUIDs co nnected in series, with a gate capacitively coupled to the center elec trode. Peaks in the current as a function of bias voltage shifted posi tion with gate voltage in agreement with the theory of resonant Cooper pair tunneling.