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arXiv:2610.06388

Value of spatially multiplexed SNSPDs with photon-number-resolving capabilities

Fabio Auriemma, Mikkel Ejrnaes

quant-phSubmitted Oct 5, 2026• Announced Oct 6, 2026• 0 citations
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Abstract

We develop a combinatorial and Bayesian framework to quantify the information gained by increasing the local photon-number resolution of multiplexed detection systems based on superconducting nanowire single-photon detectors (SNSPDs). Motivated by recent studies that attribute photon-number resolving capabilities to a single SNSPD overcoming the typical on/off detection mechanism, we generalize the existing formulation for the binary devices by deriving the probability response tensor of multiplexed systems based on SNSPDs with an arbitrary number of resolvable states. We include finite efficiency through binomial loss convolution and, separately, assess the impact of dark counts. From this response tensor we derive a generalized N-photon detector fidelity, a Bayesian photon-number reconstruction, and the corresponding reconstruction fidelity. We particularize this formulation to study 2-, 3- and 4-state multiplexed systems with different numbers of detectors and show that increasing local photon-number resolution systematically improves both detector fidelity and Bayesian photon-number reconstruction. This substantially relaxes the quadratic scaling between detector number and resolvable photon-number required by purely binary multiplexed arrays. These results provide a quantitative value-of-information assessment for multi-state photon-number-resolving detector arrays.

Comments
16 pages, 5 figures, 1 appendix

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We develop a combinatorial and Bayesian framework to quantify the information gained by increasing the local photon-number resolution of multiplexed detection systems based on superconducting nanowire single-photon detectors (SNSPDs). Motivated by recent studies that attribute photon-number resolving capabilities to a single SNSPD overcoming the typical on/off detection mechanism, we generalize the existing formulation for the binary devices by deriving the probability response tensor of multiplexed systems based on SNSPDs with an arbitrary number of resolvable states. We include finite efficiency through binomial loss convolution and, separately, assess the impact of dark counts. From this response tensor we derive a generalized N-photon detector fidelity, a Bayesian photon-number reconstruction, and the corresponding reconstruction fidelity. We particularize this formulation to study 2-, 3- and 4-state multiplexed systems with different numbers of detectors and show that increasing local photon-number resolution systematically improves both detector fidelity and Bayesian photon-number reconstruction. This substantially relaxes the quadratic scaling between detector number and resolvable photon-number required by purely binary multiplexed arrays. These results provide a quantitative value-of-information assessment for multi-state photon-number-resolving detector arrays.
Abstract We experimentally demonstrate high-fidelity detection of 0, 1- and 2-photon states in a commercial superconducting nanowire single photon detector (SNSPD) under 20 MHz pulsed coherent illumination. The arrival of a different number of photons induces distinct temporal dynamics in the disruption of the superconducting state of the detector. Therefore, specific features emerge in the arrival-time histograms, that we show are directly correlated with the photon-number state. We show that, across a broad range of time-averaged light intensities, the probabilities of detecting 1- and 2 + -photon events collapse onto the Poisson distribution of coherent light. We identify the voltage detection threshold as a critical factor for photon number resolving (PNR) capabilities. Even under demanding conditions of high repetition rate illumination, we found that a high trigger level significantly enhances total detection fidelity, achieving 0.920 and 0.845 for 1-photon and for 2-photon events. These results correspond to remarkably low conditional misidentification probabilities, 0.000 02 and 0.0013, describing the classification error among detected 1- and 2-photon events. We identify an inherent 39 ps latency difference between single- and multi-photon detection events. We show that the measured 2-photon conditional misidentification probability corresponds to the one of a multiplexed PNR detector with 730 pixels. We believe that our findings provide a framework for developing high/fidelity spatially multiplexed SNSPD by exploiting the intrinsic PNR capabilities of individual constituting elements.
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High Resolution Image Download MS PowerPoint Slide Efficiently distinguishing photon numbers is a crucial yet challenging technology for various quantum information and quantum metrology applications. While superconducting transition edge sensors offer good photon-number-resolving (PNR) capabilities, they are hampered by low detection speed, timing jitter, and complex cooling and readout requirements. In this work, we present a significant advancement toward achieving high-fidelity PNR single-photon detectors by combing high efficiency superconducting nanowire single-photon detector and spatial multiplexing technology. The unique twin-layer configuration of superconducting nanowire atop a dielectric mirror ensures the near-unity detection efficiency. The segmented design, where each section is shunted by a resistor, enables spatial multiplexing, establishing a mapping relationship between pulse amplitude and registered photons. The fabricated detector exhibits impressive performance metrics, including a single-photon system detection efficiency (SDE) of ∼98% at a dark count rate of 20 cps and photon-number resolution capability up to 32. Further characterization through detector tomography reveals high fidelities for two-, three-, and four-photon events, approximately 87%, 73%, and 40% respectively. Moreover, the detector operates at a high count rate of 41 MHz at 3 dB-SDE, with a low timing jitter of as low as 40 ps. With its near-unity efficiency, high photon-number resolution, low dark count rate, fast detection speed, and superior timing resolution, we expect significant interest in these detectors, promising substantial benefits for weak light detection and optical quantum information applications.