OBSERVATION OF PARITY-INDUCED SUPPRESSION OF JOSEPHSON TUNNELING IN THE SUPERCONDUCTING SINGLE-ELECTRON TRANSISTOR

We have measured the supercurrent branch of a superconducting single e lectron transistor as a function of gate charge, temperature, and magn etic field. At low temperature and magnetic field, the switching curre nt goes from a minimum to a maximum when the gate charge is varied fro m 0 to e, as expected for an island in the ground state with an even e lectron number. When the odd electron number ground state becomes popu lated by an increase of temperature or field, the Josephson tunneling is strongly suppressed, in agreement with theoretical predictions.