Towards Ultimate Squeezed Light Generation in Thin-Film Lithium Niobate

Abstract

Squeezed light is a crucial quantum resource with applications in quantum sensing, quantum networking, and quantum computing. The recently developed thin-film lithium niobate (TFLN) platform promises to outperform conventional platforms for squeezed light generation due to its nonlinear strength, scalability, and capability for squeezed light manipulation. In this dissertation, we first demonstrate broadband squeezed light with 0.6 dB measured and 2.6 dB inferred using single-pass TFLN waveguides. We also identify and address three major issues that limit the generation of ultra-high squeezing levels: 1) low nonlinear efficiency, 2) chip coupling loss, and 3) propagation loss. To address the issue of low nonlinear efficiency, we demonstrate a second-order nonlinear efficiency of 104 %/W by overcoming the limitations imposed by nanoscale inhomogeneity. This was achieved through the development of an adapted poling approach, which eliminates the impact of nanoscale inhomogeneity. To tackle the issue of chip coupling losses, we developed a three-dimensional forward-taper mode converter that enlarges the optical mode. The forward taper edge coupler features ultra-low loss, ultra-wide bandwidth, and polarization insensitivity. Finally, we propose a simulation model that links propagation loss with arbitrary-shape waveguide surface roughness to provide a clear direction for optimizing propagation loss. With these three major issues resolved, we expect to achieve unprecedented levels of squeezing soon.