Protecting backaction-evading measurements from parametric instability

TL;DR

This paper proposes a detuning method to stabilize backaction-evading measurements in parametrically coupled oscillators, overcoming instability caused by higher-order processes and enabling high-cooperativity quantum measurements.

Contribution

It introduces a detuning strategy that stabilizes BAE measurements, allowing operation at higher cooperativities and improving measurement performance.

Findings

Detuning stabilizes the system against parametric instabilities.

The technique enables operation at higher cooperativities.

Detuning was key to achieving acceleration in a recent weak signal detection experiment.

Abstract

Noiseless measurement of a single quadrature in systems of parametrically coupled oscillators is theoretically possible by pumping at the sum and difference frequencies of the two oscillators, realizing a backaction-evading (BAE) scheme. Although this would hold true in the simplest scenario for a system with pure three-wave mixing, implementations of this scheme are hindered by unwanted higher-order parametric processes that destabilize the system and add noise. We show analytically that detuning the two pumps from the sum and difference frequencies can stabilize the system and fully recover the BAE performance, enabling operation at otherwise inaccessible cooperativities. We also show that the acceleration demonstrated in a weak signal detection experiment [PRX QUANTUM 4, 020302 (2023)] was only achievable because of this detuning technique.