Advancements in Photon-Number Resolution for Quantum Information Technology

Quantum information technology heavily relies on the use of single photons as qubits. In order to ensure accuracy in quantum systems such as quantum computation, quantum communication, and quantum metrology, it is crucial to accurately determine the number of photons. Photon-number-resolving detectors (PNRDs) play a vital role in achieving this accuracy by providing two main performance indicators: resolving fidelity and dynamic range. However, existing PNRDs based on superconducting nanostrip single-photon detectors (SNSPDs) have faced challenges in finding a balance between fidelity and dynamic range.

Challenges with SNSPD-based PNRDs

SNSPDs are considered the leading technology for single-photon detection due to their near-perfect efficiency and high-speed performance. However, when it comes to photon-number resolution, these detectors have struggled. Existing array-style SNSPDs, which divide incident photons among a limited number of pixels, face fidelity constraints and are therefore referred to as quasi-PNRDs. The inability to accurately resolve a high number of photons poses limitations on the dynamic range of these detectors.

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 of the detectors, 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, ultimately enhancing readout fidelity.

The researchers widened the superconducting strip to a micrometer scale, leading to the development of the superconducting microstrip single-photon detector (SMSPD). Surprisingly, even without the use of cryogenic amplifiers, the SMSPD successfully achieved true-photon-number resolution up to 10. The readout fidelity reached an impressive 98 percent for 4-photon events and 90 percent for 6-photon events. These advancements in SMSPDs increase the potential for high-fidelity and large-dynamic-range photon-number resolution.

In addition to the enhanced photon-number resolution, the researchers proposed a dual-channel timing setup that enabled real-time photon-number readout. This approach significantly reduced data acquisition requirements and simplified the readout setup, making it more efficient.

The utility of the SMSPD system was demonstrated 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 ability to generate quantum random numbers is a significant advancement in the field of PNRDs, opening up possibilities for various optical quantum information applications.

With further improvement in the detection efficiency of SMSPDs, this technology could become readily accessible for a wide range of optical quantum information applications. The advancements made by the researchers from SIMIT highlight the potential of SNSPDs or SMSPDs to achieve high-fidelity and large-dynamic-range photon-number resolution.

Accurate photon-number resolution is crucial in various quantum systems, and SNSPD-based PNRDs have faced challenges in finding a balance between fidelity and dynamic range. However, recent advancements in the photon-number-resolving capability of SNSPDs, specifically the introduction of SMSPDs, have shown promising results. The widening of the superconducting strip, combined with improvements in readout electronics, has led to the first observation of true-photon-number resolution up to 10. The readout fidelity achieved by SMSPDs is significantly higher than previous technologies. Additionally, the researchers’ proposed dual-channel timing setup enables real-time photon-number readout, simplifying the readout setup and reducing data acquisition requirements. The utility of SMSPDs has been demonstrated in quantum information technology, showcasing their potential in various optical quantum information applications. As further advancements are made, SMSPDs could become readily accessible and contribute to the development of high-fidelity and large-dynamic-range photon-number resolution.


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