Broadband Dichromatic Variational Measurement

TL;DR

This paper introduces a broadband back action avoiding measurement technique using dichromatic optical probing in an opto-mechanical interferometer, enabling force detection beyond the Standard Quantum Limit across a broad frequency range.

Contribution

The paper presents a novel dichromatic probing method that cancels quantum back action in broadband force measurements on a mechanical oscillator.

Findings

Achieves force sensitivity surpassing SQL over a broad frequency band.

Uses dichromatic optical probe resonant with interferometer modes.

Enables continuous broadband back action evasion.

Abstract

Standard Quantum Limit (SQL) of a classical mechanical force detection results from quantum back action impinged by the meter on a probe mechanical transducer perturbed by the force of interest. In this paper we introduce a technique of continuous \vy{broadband} back action avoiding measurements for the case of a resonant signal force acting on a linear mechanical oscillator supporting one of mirrors of an optical Michelson-Sagnac Interferometer (MSI). The interferometer with the movable mirror is an opto-mechanical transducer able to support polychromatic probe field. The method involves a dichromatic optical probe resonant with the MSI modes and having frequency separation equal to the mechanical frequency. We show that analyzing each of the harmonics of the probe reflected from the mechanical system separately and postprocessing the measurement results allows excluding the back action in a broad frequency band and measuring the force with sensitivity better than SQL.