Fluctuation-Dissipation Relations of a Tunnel Junction Driven by a Quantum Circuit

TL;DR

This paper establishes fluctuation-dissipation relations for a quantum-driven tunnel junction, showing classical relations hold with quantum corrections, and demonstrates their validity through experimental measurements of current, admittance, and noise.

Contribution

It introduces a framework for understanding fluctuation-dissipation in quantum circuits, incorporating quantum fluctuations into classical relations and validating them experimentally.

Findings

Classical fluctuation-dissipation relations are valid with quantum corrections.

Quantum fluctuations modify the nonlinear I(V) characteristics.

Experimental measurements confirm theoretical predictions.

Abstract

We derive fluctuation-dissipation relations for a tunnel junction driven by a high impedance microwave resonator, displaying strong quantum fluctuations. We find that the fluctuation-dissipation relations derived for classical forces hold, provided the effect of the circuit's quantum fluctuations is incorporated into a modified non-linear $I(V)$ curve. We also demonstrate that all quantities measured under a coherent time dependent bias can be reconstructed from their dc counterpart with a photo-assisted tunneling relation. We confirm these predictions by implementing the circuit and measuring the dc current through the junction, its high frequency admittance and its current noise at the frequency of the resonator.