Physics of Squeezed and Entangled Light: A Review of Progress in Quantum Resource Generation and Applications in Quantum Communication

Abstract

This article provides a detailed analysis of the theoretical foundations and cutting-edge experimental progress concerning squeezed light and entangled light, two indispensable quantum resources for next-generation communication technologies. We commence by establishing the rigorous quantum mechanical description of these non-classical states, detailing the fundamental mechanism of variance reduction in squeezed states below the Standard Quantum Limit (SQL), and elucidating the strong quantum correlations inherent in entangled photon pairs. Subsequently, we critically review the primary experimental techniques for generating these resources, including spontaneous parametric down-conversion (SPDC), four-wave mixing (FWM), and cavity-enhanced parametric oscillators (OPOs), with a focus on recent advancements in efficiency, spectral purity, and bandwidth. The core of this review explores the pivotal role of squeezed and entangled light in advanced quantum communication applications, such as Quantum Key Distribution (QKD)—specifically Continuous-Variable QKD (CV-QKD) and Discrete-Variable QKD (DV-QKD)—quantum teleportation, and the development of quantum repeaters. We discuss the persistent challenges related to decoherence, transmission losses, and scaling, alongside critical future perspectives, including the imperative of chip-scale photonic integration (IQP) and the utilization of satellite-based quantum links for intercontinental communication.