Current to frequency conversion in a Josephson circuit

F. Nguyen, N. Boulant, G. Ithier, P. Bertet, H. Pothier, D. Vion, D. Esteve

Published 2007-09-26Version 1

The voltage oscillations which occur in an ideally current-biased Josephson junction, were proposed to make a current standard for metrology. We demonstrate similar oscillations in a more complex Josephson circuit derived from the Cooper pair box: the quantronium. When a constant current I is injected in the gate capacitor of this device, oscillations develop at the frequency fB=I/2e, with e the electron charge. We detect these oscillations through the sidebands induced at multiples of fB in the spectrum of a microwave signal reflected on the circuit, up to currents I exceeding 100 pA. We discuss the potential interest of this current to frequency conversion experiment for metrology.