LNOI wafer+Quantum squeezing in an all-resonant periodically poled lithium niobate microresonator

The article demonstrates the generation of broadband squeezed light using a thin-film lithium niobate (TFLN) microresonator with dual-resonant, periodically poled lithium niobate (PPLN) technology. This work achieves quantum squeezing below the shot-noise limit, providing significant advancements in quantum sensing and metrology. The squeezed light was generated at 1587 nm by a pump wavelength of 793.5 nm, utilizing a χ(2) parametric process. The system operates in the continuous-wave (CW) regime and achieves squeezing with unprecedented low pump power.

Key findings include:

1. Device Design and Fabrication: The device uses a TFLN microresonator that incorporates near-full-depth domain inversion and over-coupled resonances. These features result in high intrinsic quality factors (2.6 million for the PPLN cavity) and high escape efficiency (91.5%), crucial for efficient squeezed light generation.

2. Squeezing and Anti-Squeezing Measurements: With a pump power of only 27 mW, the device achieves squeezing of −0.81 dB ± 0.04 dB and anti-squeezing of +4.29 dB ± 0.10 dB. Inferred on-chip squeezing levels are −7.52 dB ± 0.22 dB, surpassing the performance of other integrated squeezed-light devices.

3. Squeezed Light Spectrum: The generated squeezed light exhibits a broadband spectrum with a bandwidth exceeding 10.3 THz, spanning 244 mode pairs. This is enabled by high escape efficiency, low group velocity dispersion, and a compact poling length in the PPLN resonator.

4. Experimental Setup and Characterization: The squeezed light was characterized using a balanced homodyne detector and phase modulator, allowing precise measurements of the squeezed and anti-squeezed quadratures. The high visibility (91.5%) and relative phase stability (17 milliradians) of the setup further ensure accurate quantum measurements.

5. Comparison to Other Platforms: The proposed TFLN-based device operates at a much lower pump power than other platforms based on χ(3) nonlinearities. It achieves the highest squeezing ratio and broadest spectral bandwidth reported for χ(2)-based devices, with a small footprint of 0.6 mm².

6. Potential for Scalable Quantum Photonics: This work provides a path toward fully integrated, power-efficient squeezed-light sources. The use of dual-resonant cavities allows for independent control of resonant conditions, which helps maintain optimal pump enhancement while reducing the need for high pump power. The platform is also compatible with electro-optic phase control, enabling fast modulation and stabilization.

In conclusion, this study represents a significant breakthrough in the field of integrated quantum photonics, offering a highly efficient and scalable route to broadband squeezed light sources for quantum-enhanced sensing and metrology applications.