INFLUENCE OF CONTROLLED QUANTUM-MECHANICAL CHARGE AND PHASE FLUCTUATIONS ON JOSEPHSON TUNNELING

We study the interplay of controlled quantum-mechanical charge and pha se fluctuations by measuring their influence on the supercurrent throu gh a small superconducting grain. The grain is connected to leads by t wo small Josephson tunnel junctions. The phase fluctuations are contro lled by the magnetic flux threading a SQUID that connects the grain to a large superconductor. The charge fluctuations are modulated by a vo ltage on a gate capacitor. As a function of gate voltage we observe a broadening of the Coulomb resonance of the supercurrent for decreasing phase fluctuations, in agreement with theoretical predictions.