Photon number resolving detectors as evidence for the corpuscular nature of light

TL;DR

This paper questions whether photon-number-resolving detectors truly prove light's particle nature, showing that existing detectors' results can be explained by classical wave models and are limited by low signal-to-noise ratios.

Contribution

The paper offers a classical wave interpretation of PNR detector outputs and demonstrates that current low SNR detectors do not provide conclusive evidence for light's corpuscular nature.

Findings

Classical wave model explains PNR detector results

Existing PNR detectors have insufficient SNR for definitive conclusions

Experimental data aligns with classical amplitude threshold detection

Abstract

We consider the question of whether photon-number-resolving (PNR) detectors provide compelling evidence for the discrete nature of light; i.e., whether they indicate the prior presence of a certain number of discrete photons. To answer this question, we reveal the insufficient signal-to-noise ratio (SNR) of existing PNR detectors, and propose an alternative interpretation for the analysis of PNR detector output that is consistent with a wave picture of light and does not rely on the presumption of light particles. This interpretation is based on the aggregation of correlated or accidentally coincident detections within a given detector coincidence window. Our interpretation accounts for the arbitrary character of detector coincidence windows and includes connections to established treatments of intensity interferometers. To validate our interpretation, we performed an experiment on a multiplexed PNR detector and examined the dependence of photon number on the coincidence window via post-processing. These observations were then compared to a fully classical wave model based on amplitude threshold detection, and the results were found to be in excellent agreement. We find that results from low SNR PNR detectors, such as those existing in the literature, are able to be described by classical descriptions, and therefore do not demonstrate evidence for the discrete nature of light.