Period tripling due to parametric down-conversion in circuit QED

TL;DR

This paper demonstrates that quantum vacuum fluctuations can induce period tripling in circuit QED systems, revealing a non-equilibrium phase transition driven by parametric down-conversion.

Contribution

It introduces a novel mechanism for period multiplication via quantum vacuum fluctuations in circuit QED, expanding understanding of time-translation symmetry breaking.

Findings

Observation of period tripling induced by quantum fluctuations

Identification of a non-equilibrium phase transition

Proposal of a microwave experimental setup

Abstract

Discrete time-translation symmetry breaking can be observed in periodically-driven systems oscillating at a fraction of the frequency of the driving force. However, with the exception of the parametric instability in period-doubling, multi-periodic driving does not lead to an instability threshold. In this paper, we point out that quantum vacuum fluctuations can be generically employed to induce period multiplication. In particular, we discuss the period-tripled states in circuit QED and propose a microwave setup. We show that for weak dissipation or strong driving, the system exhibits a non-equilibrium phase transition in the sense that the time scale over which the period-tripled state is generated can be arbitrarily separated from the time-scale of the subsequent dephasing.