Multimode phononic correlations in a nondegenerate parametric amplifier

TL;DR

This paper demonstrates how nonlinear interactions in a mechanical nondegenerate parametric amplifier generate multimode phononic correlations, which vary with driving strength and have applications in quantum metrology and out-of-equilibrium physics.

Contribution

It introduces a mechanical system exhibiting multimode phononic correlations that change character across the parametric threshold, enabling new quantum measurement techniques.

Findings

Correlations manifest in combined quadrature below threshold.

Correlations manifest in amplitude difference above threshold.

System enables back-action evading measurements for weak force detection.

Abstract

We describe the realization of multimode phononic correlations that arise from nonlinear interactions in a mechanical nondegenerate parametric amplifier. The nature of these correlations differs qualitatively depending on the strength of the driving field in relation to the threshold for parametric instability. Below this threshold, the correlations are manifest in a combined quadrature of the coupled mechanical modes. In this regime, the system is amenable to back-action evading measurement schemes for the detection of weak forces. Above threshold, the correlations are manifest in the amplitude difference between the two mechanical modes, akin to intensity difference squeezing observed in optical parametric oscillators. We discuss the crossover of correlations between these two regimes and applications of this quantum-compatible mechanical system to nonlinear metrology and out-of-equilibrium dynamics.