Optical Backaction-Evading Measurement of a Mechanical Oscillator

TL;DR

This paper demonstrates a two-tone backaction-evading measurement technique in the optical domain, reducing measurement noise in a GHz mechanical mode of a nanobeam, advancing quantum-limited sensing capabilities.

Contribution

It is the first implementation of optical backaction-evading measurement on a nanomechanical resonator, achieving noise reduction and showing potential for ultrasensitive force detection.

Findings

Achieved up to 0.67 dB noise reduction

Demonstrated transition from conventional to backaction-evading measurement

Validated the technique's viability for ultrasensitive motion detection

Abstract

Quantum mechanics imposes a limit on the precision of a continuous position measurement of a harmonic oscillator, as a result of quantum backaction arising from quantum fluctuations in the measurement field. A variety of techniques to surpass this standard quantum limit have been proposed, such as variational measurements, stroboscopic quantum non-demolition and two tone backaction-evading (BAE) measurements. The latter proceed by monitoring only one of the two non-commuting quadratures of the motion. This technique, originally proposed in the context of gravitational wave detection, has not been implemented using optical interferometers to date. Here we demonstrate continuous two-tone backaction-evading measurement in the optical domain of a localized GHz frequency mechanical mode of a photonic crystal nanobeam cryogenically and optomechanically cooled in a $^3$He buffer gas cryostat close to the ground state. Employing quantum-limited optical heterodyne detection, we explicitly show the transition from conventional to backaction-evading measurement. We observe up to 0.67 dB (14%) reduction of total measurement noise, thereby demonstrating the viability of BAE measurements for optical ultrasensitive measurements of motion and force in nanomechanical resonators.