Single-photon induced instabilities in a cavity electromechanical device

TL;DR

This paper demonstrates a cavity electromechanical system with enhanced single-photon coupling, revealing instabilities and frequency combs at the quantum level, which could advance quantum control and sensing technologies.

Contribution

It introduces a strongly coupled flux-tunable transmon-cavity system achieving high single-photon coupling and observes instabilities and frequency combs at the single-photon level.

Findings

Achieved a single-photon coupling rate of 160 kHz, nearly 4% of the mechanical frequency.

Observed microwave frequency combs at sub-single photon levels.

Identified regimes governed by optomechanical backaction and electromagnetic nonlinearity.

Abstract

Cavity-electromechanical systems are extensively used for sensing and controlling the vibrations of mechanical resonators down to their quantum limit. The nonlinear radiation-pressure interaction in these systems could result in an unstable response of the mechanical resonator showing features such as frequency-combs, period-doubling bifurcations and chaos. However, due to weak light-matter interaction, typically these effects appear at very high driving strengths. By using polariton modes formed by a strongly coupled flux-tunable transmon and a microwave cavity, here we demonstrate an electromechanical device and achieve a single-photon coupling rate $g_0/2\pi$ of $160~$kHz, which is nearly 4\% of the mechanical frequency $\omega_m$. Due to large $g_0/\omega_m$ ratio, the device shows an unstable mechanical response resulting in frequency combs in sub-single photon limit. We systematically investigate the boundary of the unstable response and identify two important regimes governed by the optomechanical backaction and the nonlinearity of the electromagnetic mode. Such an improvement in the single-photon coupling rate and the observations of microwave frequency combs at single-photon levels may have applications in the quantum control of the motional states and critical parametric sensing. Our experiments strongly suggest the requirement of newer approaches to understand instabilities.