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Quantum Simulation of the Thermal Dark Counts of the SPAD Detector for Space Applications

Kavita Lalwani, Durgesh Tinker

Published Mar 23, 2026• 0 citations
Publisher

Abstract

Single-Photon Avalanche Diodes (SPADs) are widely employed in spacebased photon detection systems for applications such as deep-space communication, LIDAR, and radiation monitoring. However, their performance is fundamentally limited by thermal dark counts, which are spurious detection events arising from temperature-induced carrier excitations. In this work, we present a quantum-mechanical modelling framework in which the SPAD is represented as a quantized two-level system |g> , |e> corresponding to the ground and excited (avalanche-triggering) states. Thermal effects are incorporated through open quantum system dynamics using the Lindblad master equation, enabling a physically consistent description of temperature-driven carrier generation and relaxation processes. To enable scalable and hardware-relevant analysis, we implement the model within a gate-based quantum simulation framework, where quantum state transitions emulate thermally induced carrier excitation events. The time evolution of the excitation probability is computed to extract the theoretical dark count rate under varying thermal conditions relevant to space environments. This approach establishes a quantum simulation platform for predicting SPAD noise behaviour in temperature-variable environments, providing a foundation for optimizing detector design and improving photon-counting reliability in space applications.

DOI
10.1051/epjconf/202636001026/pdf

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Single-Photon Avalanche Diodes (SPADs) are widely employed in spacebased photon detection systems for applications such as deep-space communication, LIDAR, and radiation monitoring. However, their performance is fundamentally limited by thermal dark counts, which are spurious detection events arising from temperature-induced carrier excitations. In this work, we present a quantum-mechanical modelling framework in which the SPAD is represented as a quantized two-level system |g> , |e> corresponding to the ground and excited (avalanche-triggering) states. Thermal effects are incorporated through open quantum system dynamics using the Lindblad master equation, enabling a physically consistent description of temperature-driven carrier generation and relaxation processes. To enable scalable and hardware-relevant analysis, we implement the model within a gate-based quantum simulation framework, where quantum state transitions emulate thermally induced carrier excitation events. The time evolution of the excitation probability is computed to extract the theoretical dark count rate under varying thermal conditions relevant to space environments. This approach establishes a quantum simulation platform for predicting SPAD noise behaviour in temperature-variable environments, providing a foundation for optimizing detector design and improving photon-counting reliability in space applications.
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⟩|g\rangle∣g⟩), excited state (∣e⟩|e\rangle∣e⟩) and a trap state (∣t⟩|t\rangle∣t⟩). 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.
Single-Photon Avalanche Diodes (SPADs) are critical components of emerging quantum communication networks, used to detect single photon. They are placed in satellites for longdistance communication and are susceptible to radiation-induced displacement damage in the space environment. This degrades their performance. In this work, SPAD is simulated in a space environment by introducing a quantum simulation framework that leverages second quantization and Fock space truncation to model the SPAD as a two-level (|g⟩,|e⟩), incorporating radiation damage through Lindblad open system dynamics. This approach differs significantly from conventional TCAD simulations, which rely on semiclassical approximations that fail to capture the discrete quantum statistics of single-photon interactions and the dynamics of trap states. In this work, Photon Detection Efficiency and timing jitter, in ideal and damping environments, are simulated as expectation values.
InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.
Single-photon detection concept is the most crucial factor that determines the performance of quantum key distribution (QKD) systems. In this paper, a simulator with time domain visualizers and configurable parameters using continuous time simulation approach is presented for modeling and investigating the performance of single-photon detectors operating in Gieger mode at the wavelength of 830 nm. The widely used C30921S silicon avalanche photodiode was modeled in terms of avalanche pulse, the effect of experiment conditions such as excess voltage, temperature and average photon number on the photon detection efficiency, dark count rate and afterpulse probability. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result emerged from the simulated data generated and detected by commercial devices is that the modeling process provides guidance for single-photon detectors design and characterization. The validation and testing results of the single-photon avalanche detectors (SPAD) simulator showed acceptable results with the theoretical and experimental results reported in related references and the device's data sheets.
A Single-Photon Avalanche Diode (SPAD) is a specialized optoelectronic device designed for the detection of single photons. It can discern the presence or absence of photons as well as their reception frequency. A significant challenge associated with SPADs is the generation of unintended pulses, which manifest in two primary categories: Dark Count Rate (DCR) and Afterpulse Probability (PAP). Dark counting refers to the occurrence of output pulses in the absence of photon detection, while afterpulse are undesirable outputs resulting from the trapping of carrier’s post-avalanche event within the detector. These trapped carriers are subsequently accelerated by the activation field applied to the detector, causing another avalanche breakdown known as an afterpulse. Both the afterpulse effect and dark counting are considered detrimental phenomena in SPADs, which are commonly utilized in Quantum Key Distribution (QKD) systems. Quantum Key Distribution is a cryptographic method for securely distributing secret keys, leveraging principles of quantum mechanics. Moreover, this method ensures that an eavesdropper cannot intercept or regenerate photon states. In this study, a novel approach is proposed to detect errors induced by these undesirable pulses in a quantum key distribution system. The proposed method, designed to mitigate the effects of unwanted pulses in QKD using the BB84 protocol, employs two quantum channels for photon transmission and a classical channel for coordination between the communicating parties and filtering the secret key (sifting). This method preserves the secure key rate when compared to the traditional BB84 protocol. The reduction of undesirable pulses in the proposed method is contingent upon factors such as the probability of afterpulse occurrence, dark count events, and the efficiency of the single-photon detector, with the reduction being computed in direct proportion to these parameters.
A Single-Photon Avalanche Diode (SPAD) is a specialized optoelectronic device designed for the detection of single photons. It can discern the presence or absence of photons as well as their reception frequency. A significant challenge associated with SPADs is the generation of unintended pulses, which manifest in two primary categories: Dark Count Rate (DCR) and Afterpulse Probability (PAP). Dark counting refers to the occurrence of output pulses in the absence of photon detection, while afterpulse are undesirable outputs resulting from the trapping of carrier’s post-avalanche event within the detector. These trapped carriers are subsequently accelerated by the activation field applied to the detector, causing another avalanche breakdown known as an afterpulse. Both the afterpulse effect and dark counting are considered detrimental phenomena in SPADs, which are commonly utilized in Quantum Key Distribution (QKD) systems. Quantum Key Distribution is a cryptographic method for securely distributing secret keys, leveraging principles of quantum mechanics. Moreover, this method ensures that an eavesdropper cannot intercept or regenerate photon states. In this study, a novel approach is proposed to detect errors induced by these undesirable pulses in a quantum key distribution system. The proposed method, designed to mitigate the effects of unwanted pulses in QKD using the BB84 protocol, employs two quantum channels for photon transmission and a classical channel for coordination between the communicating parties and filtering the secret key (sifting). This method preserves the secure key rate when compared to the traditional BB84 protocol. The reduction of undesirable pulses in the proposed method is contingent upon factors such as the probability of afterpulse occurrence, dark count events, and the efficiency of the single-photon detector, with the reduction being computed in direct proportion to these parameters.