Period-tripling subharmonic oscillations in a driven superconducting resonator

TL;DR

This paper reports the experimental observation of period-tripling subharmonic oscillations in a driven superconducting resonator operating in the quantum regime, revealing stable phase-shifted states and resonant downconversion phenomena.

Contribution

It demonstrates the first observation of period-tripling oscillations in a superconducting resonator with a tunable Kerr nonlinearity, supported by a quantitative theoretical model.

Findings

Three stable radiative states with 120° phase shifts

Enhanced downconversion via second mode resonance

Quantitative agreement with driven mode dynamics model

Abstract

We have observed period-tripling subharmonic oscillations, in a superconducting coplanar waveguide resonator operated in the quantum regime, $k_B T \ll \hbar\omega$. The resonator is terminated by a tunable inductance that provides a Kerr-type nonlinearity. We detected the output field quadratures at frequencies near the fundamental mode, $\omega/2\pi \sim 5\,$GHz, when the resonator was driven by a current at $3\omega$ with an amplitude exceeding an instability threshold. The output radiation was red-detuned from the fundamental mode. We observed three stable radiative states with equal amplitudes and phase-shifted by $120^\circ$. The downconversion from $3\omega$ to $\omega$ is strongly enhanced by resonant excitation of the second mode of the resonator, and the cross-Kerr effect. Our experimental results are in quantitative agreement with a model for the driven dynamics of two coupled modes.