Discrete time translation symmetry breaking in a Josephson junction laser

TL;DR

This paper investigates how a Josephson junction laser can spontaneously break discrete time translation symmetry through nonlinear interactions driven by a voltage bias, revealing conditions for this transition.

Contribution

It introduces a classical model to analyze the conditions under which time symmetry breaking occurs in a Josephson junction laser system.

Findings

Transition occurs via an instability in a subset of cavity modes.

Certain mode and voltage combinations facilitate the symmetry-breaking transition.

Critical drive strength can be analytically derived in specific cases.

Abstract

A Josephson junction laser is realised when a microwave cavity is driven by a voltage-biased Josephson junction. Through the ac Josephson effect, a dc voltage generates a periodic drive that acts on the cavity and generates interactions between its modes. A sufficiently strong drive enables processes that down-convert a drive resonant with a high harmonic into photons at the cavity fundamental frequency, breaking the discrete time translation symmetry set by the Josephson frequency. Using a classical model, we determine when and how this transition occurs as a function of the bias voltage and the number of cavity modes. We find that certain combinations of mode number and voltage tend to facilitate the transition which emerges via an instability within a subset of the modes. Despite the complexity of the system, there are cases in which the critical drive strength can be obtained analytically.