| （英） |
Homodyne detection is widely used as a means of measuring the quadrature-phase amplitude of light, and a broadband balanced detector operating at the quantum noise limit is needed to speed up continuous-variable quantum information processing. In this study, we evaluate a custom-developed low-noise balanced detector by measuring the quadrature-phase amplitudes of the vacuum states. In the frequency domain evaluation using a spectrum analyzer, the noise clearance (the increase of the quantum noise relative to the detector noise power) of 10 dB at 3 GHz is achieved, indicating that a broadband low-noise homodyne detector is realized. The measured noise powers, when the detector noise is subtracted, are proportional to the optical power of the local oscillator light at all frequencies, confirming a linear response of the custom balanced detector. We also perform the time-domain evaluation using a high-speed digitizer, and confirm the low noise and linear operation of the detector. |