Period-tripling subharmonic oscillations in a driven superconducting resonator

Abstract

We have observed period-tripling subharmonic oscillations in a driven superconducting coplanar waveguide resonator operated in the quantum regime, kBTω. 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, ω/2π∼5GHz, when driving the resonator with a current at 3ω, with amplitude exceeding an instability threshold. We observed three stable radiative states with equal amplitudes, phase shifted by 2π/3 rad, red detuned from the fundamental mode. The down-conversion from 3ω to ω is strongly enhanced by near-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.