Observation of squeezed light in the 2 $\mathrm{\mu m}$ region

TL;DR

This paper reports the successful generation and detection of squeezed light at 2 micrometers, demonstrating significant quantum noise reduction crucial for advanced gravitational-wave detectors.

Contribution

The work is the first to generate and measure squeezed light at 2 μm using a novel experimental setup with a thulium fibre laser and PPKTP crystal.

Findings

Measured 4.0 dB of squeezing in the 2 μm region

Achieved 10.5 dB of anti-squeezing relative to shot noise

Inferred 10.7 dB of squeezing after accounting for losses

Abstract

We present the generation and detection of squeezed light in the 2 $\mathrm{\mu m}$ wavelength region. This experiment is a crucial step in realising the quantum noise reduction techniques that will be required for future generations of gravitational-wave detectors. Squeezed vacuum is generated via degenerate optical parametric oscillation from a periodically-poled potassium titanyl phosphate crystal, in a dual resonant cavity. The experiment uses a frequency stabilised 1984 nm thulium fibre laser, and squeezing is detected using balanced homodyne detection with extended InGaAs photodiodes. We have measured $4.0 \pm 0.1$ dB of squeezing and $10.5 \pm 0.5$ dB of anti-squeezing relative to the shot noise level in the audio frequency band, limited by photodiode quantum efficiency. The inferred squeezing level directly after the optical parametric oscillator, after accounting for known losses and phase noise, is 10.7 dB.