Bloch Oscillations in a Josephson Circuit

TL;DR

This paper reports the first direct observation of Bloch oscillations in a Josephson circuit called the quantronium, using microwave impedance modulation and spectral analysis, with implications for quantum metrology and mesoscopic physics.

Contribution

It demonstrates Bloch oscillations in the quantronium circuit, a novel experimental realization that extends previous theoretical predictions.

Findings

Bloch oscillations observed via microwave impedance modulation.

Spectral sidebands match theoretical predictions.

Implications for quantum metrology and mesoscopic physics.

Abstract

Bloch oscillations predicted to occur in current-biased single Josephson junctions have eluded direct observation up to now. Here, we demonstrate similar Bloch oscillations in a slightly richer Josephson circuit, the quantronium. The quantronium is a Bloch transistor with two small junctions in series, defining an island, in parallel with a larger junction. In the ground state, the microwave impedance of the device is modulated periodically with the charge on the gate capacitor coupled to the transistor island. When a current flows across this capacitor, the impedance modulation occurs at the Bloch frequency, which yields Bloch sidebands in the spectrum of a reflected continuous microwave signal. We have measured this spectrum, and compared it to predictions based on a simple model for the circuit. We discuss the interest of this experiment for metrology and for mesoscopic physics.