A superconducting-nanowire single-photon camera with 400,000 pixels

For the last 50 years, superconducting detectors have offered exceptional sensitivity and speed for detecting faint electromagnetic signals in a wide range of applications. These detectors operate at very low temperatures and generate a minimum of excess noise, making them ideal for testing the non-local nature of reality, investigating dark matter, mapping the early universe, and performing quantum computation and communication. Despite their appealing properties, however, there are currently no large-scale superconducting cameras – even the largest demonstrations have never exceeded 20 thousand pixels. This is especially true for one of the most promising detector technologies, the superconducting nanowire single-photon detector (SNSPD). These detectors have been demonstrated with system detection efficiencies of 98.0%, sub-3-ps timing jitter, sensitivity from the ultraviolet (250 nm) to the mid-infrared (>10 μm), and dark count rates below 6.2×10−6 counts per second (cps), but despite more than two decades of development they have never achieved an array size larger than a kilopixel. Here, we report on the implementation and characterization of a 400,000 pixel SNSPD camera, a factor of 400 improvement over the previous state-of-the-art. The array spanned an area 4 × 2.5mm with a 5 × 5 μm resolution, reached unity quantum efficiency at wavelengths of 370nm and 635 nm, counted at a rate of 1.1 × 105 cps, and had a dark count rate of 1.0e−4 cps per detector (corresponding to 0.13 cps over the whole array). The imaging area contains no ancillary circuitry and the architecture is scalable well beyond the current demonstration, paving the way for large-format superconducting cameras with 100% fill factors and near-unity detection efficiencies across a vast range of the electromagnetic spectrum.

过去五十年来，超导探测器在各类应用场景中探测微弱电磁信号时，均展现出卓越的灵敏度与响应速度。这类探测器需在极低温环境下工作，且产生的额外噪声极低，因此十分适合用于验证现实的非局域性、研究暗物质、绘制早期宇宙图谱，以及开展量子计算与量子通信研究。尽管这类探测器拥有诸多优异特性，但目前仍缺乏大规模超导相机——即便最大的演示装置，像素规模也从未突破2万。这一点在极具应用前景的超导纳米线单光子探测器（superconducting nanowire single-photon detector, SNSPD）这一技术路线中尤为突出。该类探测器已实现98.0%的系统探测效率、小于3皮秒（ps）的计时抖动，以及从紫外波段（250纳米）到中红外波段（>10微米）的探测灵敏度，暗计数率低于6.2×10⁻⁶ 次每秒（cps）。尽管经过二十余年的研发，其阵列规模仍未突破千像素大关。本研究报道了一款拥有40万像素的SNSPD相机的研制与表征结果，相较此前的最高技术水平实现了400倍的性能提升。该阵列的有效面积为4×2.5毫米，分辨率为5×5微米，在370纳米与635纳米波长下达到了100%的量子效率，计数速率达1.1×10⁵ 次每秒，单探测器暗计数率为1.0×10⁻⁴ 次每秒（对应整个阵列的暗计数率为0.13次每秒）。该成像区域未设置任何辅助电路，且其架构具备远超本次演示装置的可扩展性，为实现具备100%填充因子、且在宽广电磁光谱范围内拥有近单位探测效率的大画幅超导相机铺平了道路。