Noise modelling of waveguide based squeezed light sources

Abstract

Squeezed states of light are used for precision metrology and quantum-enhanced measurements, with applications spanning communication and sensing. State-of-the-art squeezed-light sources typically rely on optical cavities to achieve high, usable levels of squeezing. Recently, waveguide-based squeezed-light sources have demonstrated significant improvements in achievable squeezing, with performance currently limited by fabrication-induced losses. In this work, we present a detailed analysis of waveguide-based squeezers, examining the effects of phase noise, multiple loss mechanisms, and fundamental light leakage seeding the squeezer. We further investigate a cascaded squeezer architecture, in which a second waveguide operates as a phase-sensitive amplifier to mitigate out-coupling and detection losses. Owing to their ease of integration, robustness to high pump powers, and low intrinsic phase noise, we propose waveguide-based squeezed-light sources as a promising alternative for quantum noise reduction in future gravitational wave detectors, such as the Einstein Telescope.

Figures (6)

• Figure 1: A contour plot of the maximum squeezing as a function of loss and phase noise. The red dots show current squeezers used at the LIGO and VIRGO detectorsLIGOSqueezersVirgosqueezer, accounting only for injection losses. The red dashed line gives current Einstein Telescope (ET) requirements of effective squeezingETDocs, whilst the star is a suggested squeezer for ETETDocsETSqueezer. The red square is the current best waveguide squeezerhirotaGeneration10dBSqueezed2025. At lower squeezing levels, losses are the dominant limiting factor, while at higher squeezing levels, minimizing phase noise becomes equally critical.
• Figure 2: Plot showing the effects of in-coupling, out-coupling, detection, and propagation efficiencies on squeezing. Out-coupling and detection losses have an identical effect. Black dots indicate typical values of out-coupling, propagation, and in-coupling losses from kashiwazakiOver8dBSqueezedLight2023.
• Figure 3: Sketch of the integrated squeezer architecture with the two waveguides connected by fibre to the continuous wave (CW) source and detection. Highlighted are the key analysis parameters described in the text: $\alpha_{\text{SHG}}$, $\alpha_{\text{OPA}}$, $\epsilon$, $\eta_{\text{in}}$, $\eta_{\text{prop}}$, $\eta_{\text{det}}$, $\eta_{\text{out}}$, $\eta_{\text{BS}}$, $\theta_{\text{rms}}$.
• Figure 4: Squeezing as a function of leakage level, $\epsilon$, for varying levels of BS ratios. The ideal case is for a 50/50 BS and the squeezing is worsened for greater leakage levels and imperfect BS ratios.
• Figure 5: A schematic of the cascaded squeezing architecture, which can be used to mitigate losses after the sensor using a second OPA to amplify the signal and vacuum state.