An optically trapped mirror for reaching the standard quantum limit

TL;DR

This paper demonstrates a novel optical cavity design that uses a triangular configuration to optically trap a mirror's motion, enhancing stability and sensitivity for quantum-limited force measurements.

Contribution

It introduces a triangular optical cavity that enables optical trapping of a mirror’s yaw motion, overcoming limitations of traditional suspended mirror systems for reaching the SQL.

Findings

Triangular cavity provides a positive torsional spring effect.

Demonstrated measurement of radiation pressure-induced torsional spring.

Enhanced stability and sensitivity in optomechanical systems.

Abstract

The preparation of a mechanical oscillator driven by quantum back-action is a fundamental requirement to reach the standard quantum limit (SQL) for force measurement, in optomechanical systems. However, thermal fluctuating force generally dominates a disturbance on the oscillator. In the macroscopic scale, an optical linear cavity including a suspended mirror has been used for the weak force measurement, such as gravitational-wave detectors. This configuration has the advantages of reducing the dissipation of the pendulum (i.e., suspension thermal noise) due to a gravitational dilution by using a thin wire, and of increasing the circulating laser power. However, the use of the thin wire is weak for an optical torsional anti-spring effect in the cavity, due to the low mechanical restoring force of the wire. Thus, there is the trade-off between the stability of the system and the sensitivity. Here, we describe using a triangular optical cavity to overcome this limitation for reaching the SQL. The triangular cavity can provide a sensitive and stable system, because it can optically trap the mirror's motion of the yaw, through an optical positive torsional spring effect. To show this, we demonstrate a measurement of the torsional spring effect caused by radiation pressure forces.