March 1, 2024

Expanded superconducting strips for greater precision in photon counting

Superconducting microstrip photon number resolution detector. Credit: Kong (SIMIT).

Using single photons as qubits has become a prominent strategy in quantum information technology. Accurately determining the number of photons is crucial in several quantum systems, including quantum computing, quantum communication, and quantum metrology.

Photon number resolution detectors (PNRDs) play a vital role in achieving this precision and have two key performance indicators: resolution fidelity, which measures the probability of accurately recording the number of incident photons, and dynamic range, which describes the maximum resolvable photon. number.

Superconducting nanoribbon single-photon detectors (SNSPDs) are considered the leading technology for single-photon detection. They offer near-perfect efficiency and high-speed performance.

However, regarding photon number resolution, SNSPD-based PNRDs have struggled to find a balance between fidelity and dynamic range. Existing array-style SNSPDs, which split incident photons among a limited number of pixels, face fidelity constraints. These detectors are therefore called quasi-PNRDs.

SNSPDs operate by breaking the local superconductivity of a narrow band, cooled and current-polarized when a photon is absorbed. This creates a local resistive region called a hotspot, and the resulting current is shunted through a load resistor, generating a detectable voltage pulse.

Therefore, an SNSPD with a sufficiently long superconducting range can be viewed as a cascade of thousands of elements, and n-photons simultaneously activating different elements should generate n non-overlapping access points. However, conventional SNSPDs combined with modified cryogenic readouts can only resolve numbers of 3-4 photons, resulting in a low dynamic range.

Unlocking Quantum Precision: Expanded Superconducting Strips for Greater Photon Counting Accuracy

Photon number resolution in an SMSPD: (a) Histograms (dots) and Gaussian fit (lines) of the rising edge time of response pulses under pulsed laser illumination with a mean effective number of photons at 2.5 and 5.1 . The colored areas represent the decomposed Gaussian functions. (b) Confusion matrix illustrating the probabilities of assigning n detected photons to reported photons, where the diagonal terms represent the fidelity of the photon number reading. (c) Photon count statistics reconstructed from pulse rising edge time distributions at different mean effective photon numbers ranging from 0.05 to 5. Measured photon count statistics (color bars) align closely with the Poisson statistics of the coherent source (dashed lines). Credit: Kong, Zhang, et al., doi 10.1117/1.AP.6.1.016004,

As reported in Advanced PhotonicsResearchers at the Shanghai Institute of Microsystems and Information Technology (SIMIT) of the Chinese Academy of Sciences have made progress in improving the photon number resolution 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 resulted in stretched rising edges and better signal-to-noise ratio in the response pulses and therefore higher reading fidelity.

By extending the superconducting range to a micrometer scale, researchers presented the first observation of true photon number resolution down to 10 using the superconducting microstrip single photon detector (SMSPD). Surprisingly, they achieved these results even without the use of cryogenic amplifiers. Reading fidelity reached an impressive 98% for 4-photon events and 90% for 6-photon events.

Additionally, the researchers proposed a dual-channel timing setup to enable real-time photon number reading. This approach significantly reduced data acquisition requirements by three orders of magnitude and simplified readout setup. They also demonstrated the usefulness of their system in quantum information technology, creating a quantum random number generator based on sampling the parity of a coherent state.

This technology guarantees impartiality, robustness against experimental imperfections and environmental noise, and resistance to eavesdropping.

This research represents a significant advance in the field of PNRDs. With further improvements in the detection efficiency of SMSPDs, this technology could become readily accessible for various optical quantum information applications. These results highlight the potential of SNSPDs or SMSPDs to achieve high-fidelity photon number resolution and large dynamic range.

More information:
Ling-Dong Kong et al, Large inductance superconducting microstrip photon detector enabling resolution of 10 photon numbers, Advanced Photonics (2024). DOI: 10.1117/1.AP.6.1.016004

Quote: Unlocking Quantum Precision: Expanded Superconducting Strips for Greater Photon Counting Accuracy (2024, February 9) retrieved February 9, 2024 from https://phys.org/news/2024-02-quantum-precision-superconducting -photon-accuracy.html

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