Optical Torsional Spring

Abstract

One of the key milestones toward the SQL is the development of the mechanical oscillator driven by the quantum back-action. However, the quantum back-action acting on the massive objects beyond the Planck mass (${\sim }22\,{\upmu }$g) had not yet been observed because strong thermal fluctuating forces induced by the environment usually dominate measurements. To reduce the environmental noise, making the pendulum is suitable for allowing the mirror to be isolated from the environment. Although this isolation can largely reduce the noise, a stationary radiation pressure of the light exposes the free mass to instability if a linear optical cavity is used. This technical limitation had been a significant issue since there is a fundamental compromise between the technical limitation and the sensitivity; sufficient tolerance with firm suspension makes the mass differ from the free mass, which results in an increase of the thermal fluctuating force. In this chapter, we present how by using a triangular optical cavity it is possible to overcome this limitation. The relevant publication is Opt. Express 22 12915 (2014) (Matsumoto, Michimura and Aso, Opt. Express 22:12915, 2014, [1]).