Quantum Simulation of SPAD in the Space Radiation Environment
Single-Photon Avalanche Diodes (SPADs) are critical components of emerging quantum communication networks that detect single photons. They are placed in satellites for long-distance communication and are susceptible to radiation-induced displacement damage in space. This degrades SPAD performance parameters, including reduced efficiency, increased thermal dark counts, damage to the Si crystal, and increased afterpulsing rate. This paper simulates SPAD in a space radiation environment by introducing a quantum simulation framework, modeling the SPAD detector as a three-level quantum system, ground state ($|g\rangle$), excited state ($|e\rangle$) and a trap state ($|t\rangle$). Furthermore, to model the photon as a quantum system, second quantization and Fock-space truncation are used. The interaction between the photon-SPAD closed system is simulated using the Jaynes-Cummings model, and the open-system dynamics is governed by the Lindblad master equation and Qiskit's gate-based noise channels. The key characteristics, such as the efficiency, timing jitter, thermal dark counts, and afterpulsing \& radiation effects, are obtained using quantum simulation of SPAD. This approach differs significantly from conventional TCAD simulations, which rely on semiclassical approximations that do not capture the discrete quantum statistics of single-photon interactions and the dynamics of trap states.