Photon-number-resolving detectors (PNRDs) are essential for accurate determination of the number of photons in various quantum systems. Two key performance indicators for PNRDs are resolving fidelity and dynamic range. Superconducting nanostrip single-photon detectors (SNSPDs) are considered the leading technology for single-photon detection due to their high efficiency and speed. However, SNSPD-based PNRDs have faced challenges in achieving a balance between fidelity and dynamic range.

Researchers from the Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, have made significant progress in enhancing the photon-number-resolving capability of SNSPDs. By increasing the strip width or total inductance, they were able to overcome bandwidth limitations and timing jitter in readout electronics. This led to stretched rising edges and improved signal-to-noise ratio in the response pulses, resulting in enhanced readout fidelity.

By widening the superconducting strip to a micrometer scale, the researchers introduced the superconducting microstrip single-photon detector (SMSPD) and achieved true-photon-number resolution up to 10 without the use of cryogenic amplifiers. The readout fidelity reached an impressive 98 percent for 4-photon events and 90 percent for 6-photon events. Additionally, the researchers proposed a dual-channel timing setup for real-time photon-number readout, reducing data acquisition requirements significantly and simplifying the readout setup.

The researchers demonstrated the utility of the enhanced SNSPDs in quantum information technology by creating a quantum random-number generator based on sampling the parity of a coherent state. This technology ensures unbiasedness, robustness against experimental imperfections and environmental noise, and resistance to eavesdropping. The advancements in photon-number resolution using SNSPDs or SMSPDs represent a significant breakthrough in the field of PNRDs and hold great potential for various optical quantum information applications. With further improvements in the detection efficiency of SMSPDs, this technology could become widely accessible in the near future.


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