A minimal theoretical model for Superconducting nanowire single-photon detectors

Superconducting nanowire single-photon detectors (SNSPDs) convert single-photon absorption into voltage pulses through nonequilibrium superconducting dynamics and are capable of achieving an instrument response within less than 50 ps. Applications of such devices ranges from fast and high rate telecommunications, instruments for dark energy searches, and astornomical applications (e.g., intensity interferometry). Within a BCS-based framework including electron-photon interaction, we model the nanowire as a kinetic-inductance circuit coupled to a transient resistive hotspot. The interplay between gap suppression, quasiparticle diffusion, phonon escape, and photon-induced pair breaking governs the transient response. This condensed-matter approach links microscopic BCS dynamics and light-matter coupling to macroscopic observables such as jitter, recovery time, and detection efficiency. From first principle fundamentals we modelled detectors and propose new insights how to improve their quantum efficiecy and applicability.