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IEEE Transactions on Applied Superconductivity

Superconducting Nanostrip Photon-Number-Resolving Detector for Photon Distribution Reconstruction

Pasquale Ercolano, A. Porzio, Mikkel Ejrnaes, Ciro Bruscino, Daniela Salvoni, Jia Huang, Martina Peluso, Chengjun Zhang, Hao Li, Lixing You, L. Parlato, Giovanni Piero Pepe

Published Mar 10, 2026• 1 citation
Publisher

Abstract

Single photon detectors based on superconducting nanostrips demonstrated high performance at 1550 nm, combining high efficiency and low noise. Arranged in arrays, these devices can implement photon-number resolution, expanding the range of applicability of superconducting detectors. A detector of this kind was used in our recent work to implement the annihilation operator and the characterization of quantum states in terms of their photon number distribution. The reconstructed distributions were consistent with the theoretical predictions, exhibiting fidelities higher than 99.9%. In this work, this procedure was repeated with each pixel singularly to define a detector fidelity matrix, evaluating the fidelity among all the possible pixel combinations. In this way, we introduce an additional tool that quantifies not only the quality of the reconstructed photon number distribution when compared to the theoretical expectation, but also the mutual fidelity when different pixels are chosen as independent, and then the fabrication uniformity.

DOI
10.1109/tasc.2026.3672096

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Single photon detectors based on superconducting nanostrips demonstrated high performance at 1550 nm, combining high efficiency and low noise. Arranged in arrays, these devices can implement photon-number resolution, expanding the range of applicability of superconducting detectors. A detector of this kind was used in our recent work to implement the annihilation operator and the characterization of quantum states in terms of their photon number distribution. The reconstructed distributions were consistent with the theoretical predictions, exhibiting fidelities higher than 99.9%. In this work, this procedure was repeated with each pixel singularly to define a detector fidelity matrix, evaluating the fidelity among all the possible pixel combinations. In this way, we introduce an additional tool that quantifies not only the quality of the reconstructed photon number distribution when compared to the theoretical expectation, but also the mutual fidelity when different pixels are chosen as independent, and then the fabrication uniformity.
Detectors capable of resolving the number of photons are essential in many applications, ranging from classic photonics to quantum optics and quantum communication. In particular, photon-number-resolving detectors based on arrays of superconducting nanostrips can offer a high detection efficiency, a low dark count rate and a recovery time of a few nanoseconds. In this work, we use a detector of this kind for the unbiased generation of random numbers by following two different methods based on the detection of photons. In the former, we exploit the property that the light is equally distributed on each strip of the entire detector, whereas in the latter we exploit the fact that, for a high average number of photons, the parity of the Poissonian distribution of the number of photons emitted by the laser tends to be zero. In addition, since these two methods are independent, it is possible to use them at the same time.
A photon number resolving detector (PNRD) is a device providing a different output depending on the number of incident photons in the single or few photons regime. This tool is crucial in several applications such as quantum communication, boson sampling, photon sources characterization and so on. PNRD are not new players in ultraviolet or visible wavelengths, but superconducting nanostrips provide a performing counterpart also in the near-infrared, where the aforementioned applications would like to operate. In this work we present a comprehensive description of the operation of an eight-pixel PNRD at the telecom wavelength of 1550 nm.
Superconducting nanostrip photon detectors have been used as single-photon detectors, which can discriminate only photons' presence or absence. It has recently been found that they can discriminate the number of photons by analyzing the output signal waveform, and they are expected to be used in various fields, especially in optical-quantum-information processing. Here, we improve the photon-number-resolving performance for light with a high-average photon number by pattern matching of the output signal waveform. Furthermore, we estimate the positive-operator-valued measure of the detector by a quantum detector tomography. The result shows that the device has photon-number-resolving performance up to five photons without any multiplexing or arraying, indicating that it is useful as a photon-number-resolving detector.
Efficient and precise photon-number-resolving detectors are essential for optical quantum information science. Despite this, very few detectors have been able to distinguish photon numbers with both high fidelity and a large dynamic range, all while maintaining high speed and high timing precision. Superconducting nanostrip-based detectors excel at counting single photons efficiently and rapidly, but face challenges in balancing dynamic range and fidelity. Here, we have pioneered the demonstration of 10 true photon-number resolution using a superconducting microstrip detector, with readout fidelity reaching an impressive 98% and 90% for 4-photon and 6-photon events, respectively. Furthermore, our proposed dual-channel timing setup drastically reduces the amount of data acquisition by 3 orders of magnitude, allowing for real-time photon-number readout. We then demonstrate the utility of our scheme by implementing a quantum random-number generator based on sampling the parity of a coherent state, which guarantees inherent unbiasedness, robustness against experimental imperfections and environmental noise, as well as invulnerability to eavesdropping. Our solution boasts high fidelity, a large dynamic range, and real-time characterization for photon-number resolution and simplicity with respect to device structure, fabrication, and readout, which may provide a promising avenue towards optical quantum information science.
Photon-number-resolving superconducting photon detectors promise to simplify detection schemes where only photon statistics matters in the few-photon regimes. Employed in one- and two-photon subtraction protocols, they allowed reconstruction of the photon number distribution for coherent and thermal states obtained from a pulsed laser at telecom wavelengths. The experimental setup is based on photon detection events recorded using a photon-number-resolving detector based on an array of eight superconducting NbN nanostrips working at 2.2 K. Photon subtraction was implemented using a low-reflectivity beam splitter and two superconducting nanostrip single photon detectors with an efficiency higher than 90% and a dark count rate of 1 cps. Our results confirm that our scheme accurately reproduces the theoretically expected effects of the annihilation operator on the states, achieving a fidelity higher than 99%.