Noise-reducing quantum key distribution

Quantum key distribution (QKD) is a swiftly advancing field with the great potential to be ubiquitously adopted in quantum communication applications, attributed to its unique capability to offer ultimate end-to-end theoretical security. However, when transitioning QKD from theory to practice, environmental noise presents a significant impediment, often undermining the real-time efficacy of secure key rates. To uphold the operation of QKD systems, a myriad of protocols and experimental designs have been proposed to counteract the effects of noises. Even with real-time variations, the primary component of environmental noise can be modeled as a unitary evolution or background noise, which can be compensated or reduced with various noise-reducing schemes. This review provides an overview of design strategies for reducing noises in practical QKD systems under various circumstances. These strategies are evaluated based on their principles and suitability in real-world applications. Through this review, we aim to provide readers with a clear understanding of the logic behind these noise-reducing QKD designs, facilitating a smoother start of research and engineering in this field.