Low-noise Balanced Homodyne Detection with Superconducting Nanowire Single-Photon Detectors

TL;DR

This paper demonstrates that superconducting nanowire single-photon detectors can be effectively used for low-noise balanced homodyne detection of continuous-variable quantum states, achieving record shot-noise clearance and phase measurement capabilities.

Contribution

The work introduces a novel application of SNSPDs for continuous-variable quantum measurements, achieving high shot-noise clearance and phase sensitivity in homodyne detection.

Findings

Achieved a shot-noise clearance of 46.0 dB, the highest reported for balanced optical homodyne detection.

Demonstrated phase-dependent quadrature measurement of weak coherent states.

Achieved a CMRR of 22.4 dB in the homodyne detection setup.

Abstract

Superconducting nanowire single-photon detectors (SNSPDs) have been widely used to study the discrete nature of quantum states of light in the form of photon-counting experiments. We show that SNSPDs can also be used to study continuous variables of optical quantum states by performing homodyne detection at a bandwidth of $400~\mathrm{kHz}$. By measuring the interference of a continuous-wave field of a local oscillator with the field of the vacuum state using two SNSPDs, we show that the variance of the difference in count rates is linearly proportional to the photon flux of the local oscillator over almost five orders of magnitude. The resulting shot-noise clearance of $(46.0\pm1.1)~\mathrm{dB}$ is the highest reported clearance for a balanced optical homodyne detector, demonstrating their potential for measuring highly squeezed states in the continuous-wave regime. In addition, we measured a $\mathrm{CMRR}=22.4~\mathrm{dB}$. From the joint click counting statistics, we also measure the phase-dependent quadrature of a weak coherent state to demonstrate our device's functionality as a homodyne detector.