Quantum noise in current biased Josephson junction

TL;DR

This paper investigates quantum fluctuations in a current biased Josephson junction using the RCSJ model, focusing on voltage and phase noise induced by equilibrium current fluctuations, and calculates the widths of Josephson radiation lines.

Contribution

It introduces a quantum Langevin equation approach to analyze quantum noise in Josephson junctions beyond perturbation theory.

Findings

Calculated widths of Josephson radiation lines.

Analyzed voltage and phase fluctuations at low temperatures.

Extended understanding of quantum noise in nonlinear superconducting devices.

Abstract

Quantum fluctuations in a current biased Josephson junction, described in terms of the RCSJ-model, are considered. The fluctuations of the voltage and phase across the junction are assumed to be initiated by equilibrium current fluctuations in the shunting resistor. This corresponds to low enough temperatures, when fluctuations of the normal current in the junction itself can be neglected. We used the quantum Langevin equation in terms of random variables related to the limit cycle of the nonlinear Josephson oscillator. This allows to go beyond the perturbation theory and calculate the widths of the Josephson radiation lines.