Nondegenerate parametric oscillations in a tunable superconducting resonator

TL;DR

This paper demonstrates nondegenerate parametric oscillations in a superconducting resonator with a SQUID, showing phase correlations, linewidth control, and four-mode amplification, advancing understanding of quantum microwave systems.

Contribution

It introduces a tunable superconducting resonator system exhibiting nondegenerate parametric oscillations with phase control and four-mode amplification, supported by experimental and theoretical analysis.

Findings

Self-sustained oscillations above threshold

Phase correlations with strong fluctuations

Observation of four-mode amplification and squeezing

Abstract

We investigate nondegenerate parametric oscillations in a multimode superconducting microwave resonator that is terminated by a SQUID. The parametric effect is achieved by modulating magnetic flux through the SQUID at a frequency close to the sum of two resonator-mode frequencies. For modulation amplitudes exceeding an instability threshold, self-sustained oscillations are observed in both modes. The amplitudes of these oscillations show good quantitative agreement with a theoretical model. The oscillation phases are found to be correlated and exhibit strong fluctuations which broaden the oscillation spectral linewidths. These linewidths are significantly reduced by applying a weak on-resonance tone, which also suppresses the phase fluctuations. When the weak tone is detuned, we observe synchronization of the oscillation frequency with the frequency of the input. For the detuned input, we also observe an emergence of three idlers in the output. This observation is in agreement with theory indicating four-mode amplification and squeezing of a coherent input.