In this thesis ultimate sensitive measurement for weak force imposed on a suspended mirror is
performed with the help of a laser and an optical cavity for the development of
gravitational-wave detectors. According to the Heisenberg uncertainty principle such
measurements are subject to a fundamental noise called quantum noise which arises from the
quantum nature of a probe (light) and a measured object (mirror). One of the sources of quantum
noise is the quantum back-action which arises from the vacuum fluctuation of the light. It
sways the mirror via the momentum transferred to the mirror upon its reflection for the
measurement. The author discusses a fundamental trade-off between sensitivity and stability in
the macroscopic system and suggests using a triangular cavity that can avoid this trade-off.
The development of an optical triangular cavity is described and its characterization of the
optomechanical effect in the triangular cavity is demonstrated. As a result for the first time
in the world the quantum back-action imposed on the 5-mg suspended mirror is significantly
evaluated. This work contributes to overcoming the standard quantum limit in the future.
