Sub-shot-noise terahertz measurement with electric field amplitude modulation via Rydberg atoms

The terahertz (THz) band (0.1−10 THz) is widely applied in imaging, communications, and spectroscopy. Optics-based terahertz measurement techniques using coherent light as the probe field are limited by the standard quantum shot-noise limit. This study presents an experimental demonstration of quantum-enhanced terahertz electromagnetic field measurement below the shot-noise limit based on a quantum measurement model utilizing squeezed light. By leveraging amplitude-modulation techniques and employing squeezed light as the probe field, we achieve field-strength measurement at 0.14 THz and further conduct terahertz absorption characterization experiments and theoretical simulations for various dielectric samples. The results show that squeezed light improves the signal-to-noise ratio by approximately 1.5 dB. This work validates the feasibility of squeezed light based Rydberg atom optical measurements for high-sensitivity THz detection and establishes a viable technical pathway for quantum THz spectroscopic characterization of diverse dielectric materials.