Emission spectrum of the driven nonlinear oscillator

TL;DR

This paper analyzes the emission spectrum of driven nonlinear resonators in circuit QED, revealing higher harmonics and noise-induced fluctuations that highlight the system's nonlinearity.

Contribution

It provides a theoretical analysis of the emission spectrum of driven nonlinear resonators using a master equation approach, identifying higher harmonics as signatures of nonlinearity.

Findings

Detection of second-order peaks in emission spectrum

Identification of higher harmonics in noise fluctuations

Signature of nonlinearity in circuit QED resonators

Abstract

Motivated by recent "circuit QED" experiments we investigate the noise properties of coherently driven nonlinear resonators. By using Josephson junctions in superconducting circuits, strong nonlinearities can be engineered, which lead to the appearance of pronounced effects already for a low number of photons in the resonator. Based on a master equation approach we determine the emission spectrum and observe for typical circuit QED parameters, in addition to the primary Raman-type peaks, second-order peaks. These peaks describe higher harmonics in the slow noise-induced fluctuations of the oscillation amplitude of the resonator and provide a clear signature of the nonlinear nature of the system.