Quantum noise and vacuum fluctuations in balanced homodyne detections through ideal multi-mode detectors

Abstract The balanced homodyne detection as a readout scheme of gravitational-wave detectors is carefully examined from the quantum field theoretical point view. in specifies directly measured operator detection. This specification necessary when we apply recently developed measurement theory to detections. We examine two models measurement. One model which at photodetector Glauber’s photon number operator, and other power optical measured. These are regarded ideal photodetectors. first show these yield same expectation value Since it consensus community that vacuum fluctuations contribute noises detectors, also clarify contributions noise spectral density without using two-photon formulation used community. found conventional includes main interferometer but does not include those local oscillator. Although contribution oscillator theoretically yields difference between above densities, this negligible realistic situations.