Quantum back action cancellation in the audio band

TL;DR

This paper demonstrates the cancellation of quantum back action noise in an optomechanical cavity within the audio frequency band, enhancing measurement sensitivity and potentially benefiting gravitational wave detection.

Contribution

It introduces a method to cancel quantum back action noise in the audio band using transmission measurements and cross-correlation techniques, a novel approach in optomechanics.

Findings

Back action noise was canceled between 1 kHz and 50 kHz.

Transmission measurement with cross correlation removes shot noise.

Enhanced sensitivity in microresonator displacement measurement.

Abstract

We report on the cancellation of quantum back action noise in an optomechanical cavity. We perform two measurements of the displacement of the microresonator, one in reflection of the cavity, and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light in transmission of the optomechanical cavity allows us to cancel the back action noise between 1 kHz and 50 kHz, and obtain a more sensitive measurement of the microresonator's position. To confirm that the back action is eliminated, we measure the noise in the transmission signal as a function of circulating power. By splitting the transmitted light onto two photodetectors and cross correlating the two signals, we remove the contributon from shot noise and measure a quantum noise free thermal noise spectrum. Eliminating the effects of back action in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of back action in interferometric gravitational wave detectors such as Advanced LIGO.