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Quantum Computing, Communication, and Simulation

Compact 64-channel time-resolved single-photon detection system for quantum photonics applications

Piergiorgio Daniele, Francesco Di Lena, Gennaro Fratta, Ivan Giuseppe Labanca, Giulia Acconcia, Fabrizio Sgobba, Danilo Triggiani, Andrea Andrisani, Cosmo Lupo, Luigi Santamaria Amato, Ivan Rech

Published Mar 5, 2026• 0 citations
Publisher

Abstract

We introduce a compact 64-channel detection system tailored for high-precision, time-resolved single-photon measurements in quantum photonic applications such as Boson Sampling and Hong-Ou-Mandel interferometry. The system integrates an 8×8 SPAD array (30 µm active area, 75 µm pitch) with microlenses, achieving a 76% fill-factor, <100 ps jitter, and low dark count rates. Two acquisition boards—each featuring four TACs with four channels—provide 32 timing channels, with a 2:1 multiplexing scheme enabling full array coverage. Time tags are generated via FPGA and transferred through USB 3.0 at rates up to 700 MB/s. This system will support upcoming multi-photon experiments at the Italian Space Agency (ASI).

DOI
10.1117/12.3079732

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•Jan 1, 2026•0 citations
We introduce a compact 64-channel detection system tailored for high-precision, time-resolved single-photon measurements in quantum photonic applications such as Boson Sampling and Hong-Ou-Mandel interferometry. The system integrates an 8×8 SPAD array (30 µm active area, 75 µm pitch) with microlenses, achieving a 76% fill-factor, <100 ps jitter, and low dark count rates. Two acquisition boards—each featuring four TACs with four channels—provide 32 timing channels, with a 2:1 multiplexing scheme enabling full array coverage. Time tags are generated via FPGA and transferred through USB 3.0 at rates up to 700 MB/s. This system will support upcoming multi-photon experiments at the Italian Space Agency (ASI).
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Real-time analysis of single-photon coincidence is critical in photonic quantum computing. The large channel number and high counting rate foreseen in such experiments pose a big challenge for the conventional time tagged method and coincidence instruments. Here we propose a real-time time-tagged coincidence method and a data filtering solution, demonstrated by a 32-channel coincidence counting unit that has been implemented successfully on a field-programmable gate array system. The unit provides high counting rates, a tunable coincidence window, and a timing resolution of 390 ps. Beyond that, it is feasible to be scaled up to 104 channels and is thus ideally suited for channel consuming applications such as boson sampling. Based on the versatility and scalability the unit has shown, we believe that it is the turn-key solution for many single-photon coincidence counting applications in photonic quantum computing.
Quantum communication is a fast-growing field that takes advantage of the quantum physics laws to protect and secure sensitive data. This work takes part of the European project UNIQORN (Affordable Quantum Communication for Everyone: Revolutionizing the Ecosystem from Fabrication to Application) whose aim is to develop a Quantum System on Chip (QSoC) for telecom application. The Integrated Circuit (IC) designed contributes in the QRNG block of the system, tailored to communicate with the integrated non-linear optics circuit. Such detector is a 32×1 linear array based on Single-Photon Avalanche-Diode (SPAD) detectors for the generation of a raw random number, by revealing the position on the array of the single photon impinging on it, realized in a BCD 0.16 μm technology. The linear array architecture consists of 32 pixels, pitched at 125 μm, each made by 4 SPADs with different diameter (5 μm, 10 μm, 20 μm, 50 μm). Two operation modes are implemented: Single-Hit Mode, needed to reveal the (5-bit) position of the pixel triggered by a single photon, representing a random number, in a time window synchronous with the laser emission. Multi Hit Mode, used to identify a coincidence of a certain number of photons(more than one, two, three or four) detected within a specified time window, thanks to a multi threshold coincidence detection logic.
The implementation and commercialization of quantum cryptography technologies have to face some challenges related to the development of single-photon detectors operating at 1550 nm. The main requirements are: i) high detection efficiency; ii) low noise; iii) high count rate; iv) low timing jitter. Different technologies are currently available for single-photon detection at 1550 nm, but semiconductor devices (like Single-Photon Avalanche Diode, SPAD) offer a photon detection efficiency that is inherently higher than any photocathode employed in vacuum tube detectors. Additionally InGaAs/InP SPADs can detect single photons at 1550 nm with low noise when moderately cooled by means of thermo-electric coolers. Consequently, InGaAs/InP SPAD can be the enabling technology of practical quantum key distribution (QKD) systems, provided that the maximum count rate is increased above 1 Mcps. The main limit is the afterpulsing effect that usually sets too long (< 10 μs) a hold-off time after each avalanche ignition. We present the developments achieved in InGaAs/InP SPAD device design, fabrication technology and front-end electronics, aimed at decreasing the afterpulsing effect, while not impairing photon detection efficiency and timing jitter. The new InGaAs/InP SPADs provide count rates higher than 1 Mcps and temporal response with 60 ps Full-Width at Half Maximum and very short (30 ps time constant) tail. The front-end electronics includes a wide-band pulse generator able to gate the SPAD up to 133 MHz repetition rate. Eventually, a fast avalanche-quenching scheme minimizes quenching time to less than 1 ns, thus effectively reducing afterpulsing by decreasing the total charge flowing through the junction.
Superconducting nanowire single-photon detectors are an enabling technology for modern quantum information science and are gaining attractiveness for the most demanding photon counting tasks in other fields. Embedding such detectors in photonic integrated circuits enables additional counting capabilities through nanophotonic functionalization. Here, we show how a scalable number of waveguide-integrated superconducting nanowire single-photon detectors can be interfaced with independent fiber optic channels on the same chip. Our plug-and-play detector package is hosted inside a compact and portable closed-cycle cryostat providing cryogenic signal amplification for up to 64 channels. We demonstrate state-of-the-art multi-channel photon counting performance with average system detection efficiency of (40.5 ± 9.4)% and dark count rate of (123 ± 34) Hz for 32 individually addressable detectors at minimal noise-equivalent power of (5.1 ± 1.2) · 10−18 W/Hz. Our detectors achieve timing jitter as low as 26 ps, which increases to (114 ± 17) ps for high-speed multi-channel operation using dedicated time-correlated single photon counting electronics. Our multi-channel single photon receiver offers exciting measurement capabilities for future quantum communication, remote sensing, and imaging applications.
We developed a SPAD detector implementing an array structure to achieve short deadtime and high detection efficiency, to be employed in ground-based optical receivers for enhancing key rates in Quantum Key Distribution (QKD) channels at 800 nm. The device detects over 2 billion photons per second, thus enabling transmission rates beyond 2 GHz. The detector features two 8 × 8 SPAD arrays, named Trial A and Trial B, sharing 4 outputs. Trial A combines its 64 SPADs’ outputs in an OR-tree connected to a frequency divider, distributing the pulses to the 4 outputs. Trial B has 4 independent quadrants, each with its own OR-tree feeding a toggle flip-flop and connected to a single output. A pulse shrinker reduces the pile-up effect. The detector exhibits a Photon Detection Efficiency (PDE) of 39.6% at 800 nm, a median Dark Count Rate (DCR) of 300 cps/pixel, afterpulsing probability below 0.1% and a 230 ps Full-Width at Half-Maximum (FWHM) jitter per SPAD.