Current to frequency conversion in a Josephson circuit

TL;DR

This paper demonstrates current-to-frequency conversion in a complex Josephson circuit, the quantronium, showing potential for precise metrological applications through microwave spectrum analysis.

Contribution

It introduces a novel current-to-frequency conversion method in the quantronium circuit, extending Josephson-based standards beyond simple junctions.

Findings

Oscillations at frequency fB=I/2e observed in the quantronium.

Detection of sidebands in microwave spectrum up to 100 pA currents.

Potential application in precise current to frequency conversion for metrology.

Abstract

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.