Observation of Squeezed States of Light in Higher-Order Hermite-Gaussian Modes with a Quantum Noise Reduction of up to 10 dB

Experimental Demonstrations of Alignment and Mode Matching in Optical Cavities with Higher-Order Hermite-Gauss Modes

Higher-order spatial laser modes have recently been investigated as candidates for reducing test-mass thermal noise in ground-based gravitational-wave detectors such as advanced LIGO. In particular, higher-order Hermite-Gauss (HG) modes have gained attention within the community for their more robust behaviors against random test-mass surface deformations and stronger sensing and control capacities. In this Letter we offer experimental investigations on various aspects of HG mode interferometry. We have generated purified HG modes up to the twelfth order HG_{6,6} mode, with a power conversion efficiency of 38.8% and 27.7% for the HG_{3,3} and HG_{6,6} modes respectively. We demonstrate for the first time the misalignment and mode mismatch-induced power coupling loss measurements for HG modes up to the HG_{6,6}. We report an excellent agreement with the extended numerical power loss factors that in the "small power loss" region converge to 2n+1 or n^{2}+n+1 for a misaligned or mode mismatched HG_{n,n} mode. We also demonstrate the wavefront sensing (WFS) signal measurement for HG modes up to the HG_{6,6}. The measurement result is accurately in accordance with theoretical WFS gain β_{n,n-1}sqrt[n]+β_{n,n+1}sqrt[n+1] for an HG_{n,n} mode, with β_{n,n-1} being the beat coefficient of the adjacent HG_{n,n} and HG_{n-1,n} modes on a split photodetector.

10 dB Quantum-Enhanced Michelson Interferometer with Balanced Homodyne Detection

Future generations of gravitational-wave detectors (GWD) are targeting an effective quantum noise reduction of 10 dB via the application of squeezed states of light. In the last joint observation run O3, the advanced large-scale GWDs LIGO and Virgo already used the squeezing technology, albeit with a moderate efficiency. Here, we report on the first successful 10 dB sensitivity enhancement of a shot-noise limited tabletop Michelson interferometer via squeezed light in the fundamental Gaussian laser mode, where we also implement the balanced homodyne detection scheme that is planned for the third GWD generation. In addition, we achieved a similarly strong quantum noise reduction when the interferometer was operated in higher-order Hermite-Gaussian modes, which are discussed for the GWD thermal noise mitigation. Our results are an important step toward the targeted quantum noise level in future GWDs and, moreover, represent significant progress in the application of nonclassical states in higher-order modes for interferometry, increased spatial resolution, and multichannel sensing.

Generation of Higher-Order Hermite–Gaussian Modes via Cascaded Phase-Only Spatial Light Modulators

The spatial distribution of higher-order Hermite–Gaussian (HG) modes is more complicated than the fundamental mode, and the characteristics of different modes and their orthogonal characteristics have essential applications in the fields of measurement, imaging, and large-capacity communications. The main issue in future applications is how to efficiently generate higher-order HG modes. The spatial light modulator has high spatial resolution and excellent maneuverability, so it is a simple and effective way to generate higher-order HG modes. Here, the efficient generation of higher-order HG modes via cascaded spatial light modulators was experimentally investigated. For the HG90 mode, the conversion efficiency is 61%. The method with high conversion efficiency has promising application potentials in biophotonics, laser physics, and quantum information.