Quantum Noise in the Interferometer Detector

Abstract

In this paper I will examine the quantum noise sources in a laser interferometer detection system for gravitational radiation. The quantum noise sources will be of two basic forms — that due to the quantum nature of the light itself and that due to the damping in the mirror masses used as reflectors in the interferometers. We will find that the quantum nature of the light is the dominant source of noise and contributes via two mechanisms — directly as what has been called the photon counting noise and indirectly via the fluctuating force the light exerts on the mirrors. It will be shown that by setting up the initial state of the field entering the input port of the interferometer not being used by the laser in a generalised squeezed state, the effect of both of these noise sources can be made as small as desired. (The possibility for reducing the direct noise by a similar technique was shown by Caves for a simple single mode interferometer model). The noise introduced by the damping of the motion of the mirror masses will contribute significantly only if one does squeeze the state of the light beam and if the laser power is sufficiently large.