Accurate photon number state resolution is critical for photonic quantum computing architectures to ensure high-fidelity computational outputs [1]. To address this challenge, we have developed a spatially-multiplexed array of waveguide-integrated superconducting-nanowire single-photon detectors (SNSPDs).
We report a 16-pixel (4×4) superconducting nanowire single-photon detector (SNSPD) array featuring pixel-level photon-number-resolving capability. This multidimensional sensing is enabled by integrating a compact four-element series nanowire architecture into each spatial pixel, allowing direct discrimination of one to four photons. Under single-mode fiber illumination, the device achieves a total system detection efficiency of 41.5%, given the array geometrical fill factor of 53%. Across all channels, the device exhibits reliable multiphoton discrimination, maintaining minimum readout fidelities of 96%, 89%, 73%, and 77% for one- to four-photon states, respectively. Furthermore, independent channel evaluations reveal low timing jitter and negligible inter-channel crosstalk (<0.1 % ). By implementing differentiating pulse shaping for high-flux operation, a maximum single-channel −3 dB count rate of 984 MHz is achieved, establishing an aggregated array bandwidth potential of 8.9 GHz. This sensing architecture may provide a viable pathway toward high-flux single-photon imaging, offering potential applications in quantum optics and light detection and ranging (LiDAR) systems.
Superconducting nanowire single-photon detectors (SNSPDs) have abstracted widespread attention in the fields of quantum information and quantum photonics due to their high detection efficiency and low dark count rates (DCR). However, single-pixel SNSPDs exist the notable limitations in detection speed and photon number resolution (PNR) capabilities, which pose challenges for practical applications. In this study, we propose a design of a series four-pixel SNSPD that incorporates a SPICE circuit simulation model to achieve PNR and spatial resolution of the four photons in an ideal state, and then determine the optical cavity structure of the detector at the highest light absorption of up to 97% through optical simulation. This design provides a theoretical foundation for the subsequent fabrication of large-area SNSPD with PNR and spatial resolution, significantly improving the flexibility and adaptability of SNSPDs to meet diverse detection requirements. Furthermore, our work also lays a research foundation for multi-photon detection in quantum communication and quantum computing.
Detecting spatial and temporal information of individual photons is a crucial technology in today's quantum information science. Among the existing single-photon detectors, superconducting nanowire single-photon detectors (SNSPDs) have been demonstrated with a sub-50 ps timing jitter, near unity detection efficiency1, wide response spectrum from visible to infrared and ~10 ns reset time. However, to gain spatial sensitivity, multiple SNSPDs have to be integrated into an array, whose spatial and temporal resolutions are limited by the multiplexing circuit. Here, we add spatial sensitivity to a single nanowire while preserving the temporal resolution from an SNSPD, thereby turning an SNSPD into a superconducting nanowire single-photon imager (SNSPI). To achieve an SNSPI, we modify a nanowire's electrical behavior from a lumped inductor to a transmission line, where the signal velocity is slowed down to 0.02c (where c is the speed of light). Consequently, we are able to simultaneously read out the landing locations and arrival times of the photons from the output electrical pulses using only two connections. We have demonstrated single-photon imaging by using a 19.7 mm long SNSPI, which is meandered into an imaging area of 286 {\mu}m*193 {\mu}m. The nanowire has a temporal resolution of 50 ps for detecting 1.5 {\mu}m photons. The 2D spatial resolution is 13.0 {\mu}m in the vertical direction and 5.6 {\mu}m in the horizontal direction. The maximum number of resolvable locations (i.e., the effective number of pixels) in such a long nanowire is calculated to be 590. Rather than operating an individual detector in a scanning mode or using SPD arrays, this SNSPI gives an alternative approach to taking large-scale single-photon images and measuring temporal and spatial correlation.
Superconducting nanowire single-photon detectors (SNSPDs) have enabled the realization of several quantum optics technologies thanks to their high system detection efficiency (SDE), low dark counts, and fast recovery time. However, the widespread use of linear optical quantum computing, quasi-deterministic single-photon sources, and quantum repeaters requires even faster detectors that can also distinguish between different photon-number states. Here, we present an SNSPD array composed of 14 independent pixels, achieving an SDE of 90% in the telecommunications band. By reading each pixel of the array independently, we show detection of telecommunication photons at 1.5 GHz with 45% absolute SDE. We exploit the dynamic photon-number resolution of the array to demonstrate accurate state reconstruction for a wide range of light inputs, including operation with long-duration light pulses, as obtained with some cavity-based sources. We show two-photon and three-photon fidelities of 74% and 57%, respectively, which represent state-of-the-art results for fiber-coupled SNSPDs.
Photonic integrated circuits serve as essential platforms in quantum science, particularly in quantum communication and quantum computing, where linear high-performance single-photon detector arrays are required. Superconducting nanowire single-photon detectors (SNSPDs) are known for their outstanding overall performance and compatibility with on-chip integration, making them the preferred choice for quantum photonic applications. However, conventional SNSPD arrays face challenges such as increased readout complexity or reduced detection speed. Herein, we present an amplitude-encoded SNSPD array featuring single-channel readout and high-speed detection capabilities, demonstrating high-quality discrimination of 12 pixels. This detector can readily achieve proof-of-concept quantum random number generation, underscoring its promise for advanced quantum information applications.