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Dead-Time Mitigation and QBER Reduction in Photon Detection Using Timer-Redirected and Multi-Detector Models

Ramya Jothikumar

Published Oct 30, 2025• 0 citations
Publisher

Abstract

This paper presents a simulation-based performance analysis of photon detection systems employing a multi-detector array and a timer-redirected single-photon detector under various operational conditions. The model incorporates practical parameters such as detector dead time, quantum efficiency, and dark count probability, with photon arrivals characterized by a Poisson process at a rate of 1 GHz. Two detection schemes are analyzed: (1) a parallel multi-detector array, which enables concurrent photon detection, and (2) a timer-redirected single-detector configuration, which utilizes a loop delay mechanism to recover photon events lost during dead time. To evaluate detection fidelity, the Quantum Bit Error Rate (QBER) is computed and compared across both models. Simulation results reveal that increasing the number of detectors in the array significantly reduces QBER; however, the timer-redirected single-detector model offers a costeffective alternative with notable performance improvements. These findings provide valuable insights for optimizing detector architectures in quantum communication systems and high-speed photon-counting applications.

DOI
10.36227/techrxiv.176185798.88850046/v1

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This paper presents a simulation-based performance analysis of photon detection systems employing a multi-detector array and a timer-redirected single-photon detector under various operational conditions. The model incorporates practical parameters such as detector dead time, quantum efficiency, and dark count probability, with photon arrivals characterized by a Poisson process at a rate of 1 GHz. Two detection schemes are analyzed: (1) a parallel multi-detector array, which enables concurrent photon detection, and (2) a timer-redirected single-detector configuration, which utilizes a loop delay mechanism to recover photon events lost during dead time. To evaluate detection fidelity, the Quantum Bit Error Rate (QBER) is computed and compared across both models. Simulation results reveal that increasing the number of detectors in the array significantly reduces QBER; however, the timer-redirected single-detector model offers a costeffective alternative with notable performance improvements. These findings provide valuable insights for optimizing detector architectures in quantum communication systems and high-speed photon-counting applications.
There has been growing research interest in quantum technology in general and in quantum key distribution (QKD) in particular. However, the key generation rate of QKD systems is still limited by the quantum channel losses as well as the practical limitations of the quantum sources and detectors. Here, we focus on one of these limitations, namely, the quantum detector's dead time effect, which happens after each photon detection, limiting the maximum quantum bit transmission rate and consequently the key generation rate of QKD systems. Qubit transmission at the sub-dead-time regime (i.e., faster than the reciprocal of dead time) can introduce different security loopholes. In this paper, we propose the use of a detector array instead of a single detector to measure the quantum state of individual photons in discrete variable QKD systems, showing that it can significantly alleviate the limitations induced by detectors' dead time. A dead-time compensated BB84 scheme is introduced, allowing qubit transmission at the sub-dead-time regime. AnM−M-M−dimensional Markov chain model is used to describe the impact of dead time on the operation of the proposed BB84 system, employing detector arrays of sizeMMM. Consequently, novel analytical expressions can be derived for the sifted bit rate (SBR) and secrecy key rate (SKR) of the proposed QKD system, showing excellent match with the Monte Carlo simulation results. A remarkable gain is observed for the BB84 system employing detector arrays, showing a potentialMMM-fold improvement of SBR at high qubit transmission rates.
Quantum random number generators (QRNGs) produce true random numbers with significant applications in quantum communication and numerical computation, where high-rate random number generation is critical. Photon detection-based quantum random-number generation methods have been widely studied. However, the generation rate is constrained by the count rate of single-photon detectors. This study proposes an efficient method that enhances random number generation by simultaneously detecting photons in temporal and spatial dimensions. We achieved simultaneous detection of photon arrival time and spatial position by employing a laboratory-developed 5 × 5 single-photon detector array and a high-saturation count rate multichannel time-to-digital converter. The maximum efficiency of the method was 21.1 bits per event and it maintained a consistent efficiency of 17.6 bits per event while achieving a random number generation rate of 2.1 Gbps. The proposed QRNG approach offers a promising pathway for significantly increasing random number generation rates, benefiting applications that require secure and high-speed random number sequences.
We discuss the difficulties of photon-counting at extremely high rates and introduce a scheme for a photon-counting detection system that addresses these difficulties. The method uses an array of N detectors and a 1-by-N optical switch with a control circuit to direct input light to live detectors. We compare performance of our system to other, passive detection systems and show that our detection system can handle incident photon rates higher than otherwise possible by suppressing the effects of detector deadtime. To support this claim, we present results of theoretical analysis and a proof-of- concept experiment. In particular, both calculations and the experiment prove that a group of intelligently managed N detectors provides an improvement in operation rate that can exceed the improvement that would be obtained by either a single detector with deadtime reduced by 1/N, even if it were feasible to produce a single detector with such a large improvement in deadtime, or a passive beamsplitter tree system with N detectors. In addition to deadtime reduction, our scheme reduces afterpulsing as well as background counts (such as dark counts). We conclude that an intelligent active management of a group of N detectors is the best arrangement of photon-counting detectors to handle high photon rates, an important technological challenge for fast developing quantum metrology and quantum key distribution applications.
A photon-number-resolving detector based on a four-element superconducting nanowire single photon detector is demonstrated to have sub-30-ps resolution in measuring the arrival time of individual photons. This detector can be used to characterise the photon statistics of non-pulsed light sources and to mitigate dead-time effects in high-speed photon counting applications. Furthermore, a 25% system detection efficiency at 1550 nm was demonstrated, making the detector useful for both low-flux source characterization and high-speed photon counting and quantum communication applications. The design, fabrication, and testing of this detector are described, and a comparison between the measured and the theoretical performance is presented.
In quantum communication systems, the precise estimation of the detector´s response to the incoming light is necessary to avoid security breaches. The typical working regime uses a free-running single-photon avalanche diode in combination with attenuated laser pulses at telecom wavelength for encoding information. We demonstrate the validity of an analytical model for this regime that considers the effects of dark counts and dead time on the measured count rate. For the purpose of gaining a better understanding of these effects, the photon detections were separated from the dark counts via a software-induced gating mechanism. The model was verified by experimental data for mean photon numbers covering three orders of magnitude as well as for laser repetition frequencies below and above the inverse dead time. Consequently, our model would be of interest for predicting the detector response not only in the field of quantum communications, but also in any other quantum physics experiment where high detection rates are needed.
Detector dead time is typically treated as a fixed parameter in quantum key distribution (QKD) security analyses. In practice, however, the effective recovery time of single-photon avalanche photodiodes (SPADs) depends on the incident count rate. In this work, we demonstrate that this count-rate-dependent recovery nonlinearity constitutes a distinct attack primitive. We experimentally characterize the dead time shift of a free-running SPAD under controlled broadband loading and observe a substantial increase in effective recovery time as the detected rate rises into the high photon count regime. We show that recovery-induced availability reduction can be modeled as an adversarial erasure channel and derive a conservative bound on the signal detection probability under loading. Unlike previously studied detector-control or efficiency mismatch attacks, the proposed mechanism does not rely on deterministic blinding or timing discrimination. Instead, count-rate-dependent recovery asymmetry induces basis-dependent suppression of detection probabilities (p⊥<p∥p_\perp<p_\parallelp⊥​<p∥​), converting mismatch-induced errors into loss. Particularly, we show in active-basis BBM92 systems, this effect reduces the observed quantum bit error rate (QBER) below the abort threshold while increasing erasure probability. Using experimentally measured detector recovery data, we quantify the parameter regime in which such stealth suppression is achievable. These results establish count-rate-dependent detector recovery as a security-relevant vulnerability and show that countermeasures designed for timing-based efficiency mismatch do not directly address recovery-induced erasure (RIE) attack. Our findings underscore the need to incorporate detector recovery dynamics explicitly into practical QKD security models.