Inducing Strong Non-Linearities in a Phonon Trapping Quartz Bulk Acoustic Wave Resonator Coupled to a Superconducting Quantum Interference Device

TL;DR

This paper demonstrates how coupling a high-Q quartz phonon resonator to a SQUID amplifier induces strong non-linearities, revealing complex spectral behaviors relevant for cryogenic quartz oscillators.

Contribution

It introduces a novel experimental setup coupling a quartz phonon resonator with a SQUID, exploring nonlinear effects in the strong signal regime.

Findings

Significant non-Duffing nonlinear response observed

Quasi-periodic spectral structures identified

Insights into future cryogenic quartz oscillator behavior

Abstract

A quartz Bulk Acoustic Wave resonator is designed to coherently trap phonons in a way that they are well confined and immune to suspension losses so they exhibit extremely high acoustic $Q$-factors at low temperature, with $Q\times f$ products of order $10^{18}$ Hz. In this work we couple such a resonator to a SQUID amplifier and investigate effects in the strong signal regime. Both parallel and series connection topologies of the system are investigated. The study reveals significant non-Duffing response that is associated with the nonlinear characteristics of Josephson junctions. The nonlinearity provides quasi-periodic structure of the spectrum in both incident power and frequency. The result gives an insight into the open loop behaviour of a future Cryogenic Quartz Oscillator in the strong signal regime.