Multiplexed nanowire detectors count photons to sub-photon uncertainty up to 276

A team at Paderborn University in Germany has built a detection system that counts photons across a range from zero to more than 9,000. Combining superconducting nanowire single-photon detectors (SNSPDs) with multiplexing, the researchers measured pulses of up to 276 photons with an uncertainty below one photon. The work is reported in Optica.

The counting problem

Photon counting becomes harder as photon numbers rise. Avalanche photodiodes, a common choice for single-photon work, mostly indicate whether light is present or absent rather than how many photons arrived. Detectors designed for bright light, such as photodiodes, suffer from electrical noise that hides the photon number. This leaves a gap between single-photon measurements and the optical power meters used for bright beams.

SNSPDs are valued for high efficiency, very fine timing resolution and low noise. They can also resolve a small number of photons arriving together. Multiplexing, which spreads light over many detector elements, can imitate photon-number resolution. According to the researchers, the two ideas had each been studied separately but not combined at this scale, and the new system is an order of magnitude larger than earlier multiplexed single-photon counters.

How the system works

Each light pulse is first divided into 128 smaller pulses separated in time. These are then distributed over eight detectors, giving 1,024 detection bins. The original photons are shared among the bins, and low-loss optical components keep the distribution even while preserving photon-number information in each one.

Precision also depends on a detector model that the group previously developed with Mariia Sidorova of PTB in Germany. The model describes the behaviour of each individual detector element, so the response of the whole system can be interpreted accurately rather than treated as an ideal bank of identical counters.

Results

The team tested the device with laser pulses whose average photon number ranged from one to 15,000. This allowed them to examine how the detector responds under different conditions and how precisely it can determine photon number. With the model in place, they counted up to 276 photons with uncertainty below a single photon.

The authors report that a conventional multiplexed system would need about 37,000 detector elements for comparable precision, against the 1,024 bins used here. The title of the paper refers to beating the Poisson noise limit, the shot-noise floor that normally constrains measurements of laser light.

Why it matters

Large-scale photon measurement underpins photonic quantum computing and single-photon-level imaging. Tim Bartley of Paderborn University said the technology should reveal how photonic quantum computers and single-photon-sensitive cameras can be scaled up. A detector that bridges single-photon counting and power metering could also help with precision optical measurement more broadly.

Limitations and next steps

The study used only laser pulses, which have well-understood statistics. The researchers plan to apply the approach to bright quantum states of light, where non-classical effects at large photon numbers could be probed. Precise counting of up to 276 photons is also well below the full 9,000-photon range over which the system operates, so the sub-photon uncertainty applies to the narrower window. The team says further improvements in SNSPD technology could extend the system's usefulness across a range of sensitive sensing applications.

The paper is by Timon Schapeler and colleagues: Macroscopic photon counting beating the Poisson noise limit, Optica (2026), DOI 10.1364/optica.604389.

Source: Multiplexed detector system precisely counts more than 9,000 photons (Phys.org, 13 November 2026).

Image: AI-generated illustration.