Detecting single photons is not always necessary to evidence interference of photon probability amplitudes

TL;DR

This paper demonstrates that in certain quantum optics experiments, subtracting accidental coincidences does not alter measurement results, allowing classical correlation analysis to replicate quantum effects like interference and bunching.

Contribution

It shows that for zero mean Gaussian states, removing accidental coincidences reproduces quantum effects in correlation measurements, challenging the necessity of photon-level detection.

Findings

Accidental coincidence subtraction yields the same results for squeezed vacuum states.

Quantum effects like interference are observable through macroscopic fluctuation correlations.

The correspondence has limitations in Bell tests, multimode scenarios, and higher-order correlations.

Abstract

Subtracting accidental coincidences is a common practice quantum optics experiments. For zero mean Gaussian states, such as squeezed vacuum, we show that if one removes accidental coincidences the measurement results are quantitatively the same, both for photon coincidences at very low flux and for intensity covariances. Consequently, pure quantum effects at the photon level, like interference of photon wave functions or photon bunching, are reproduced in the correlation of fluctuations of macroscopic beams issued from spontaneous down conversion. This is true both in experiment if the detection resolution is smaller than the coherence cell (size of the mode), and in stochastic simulations based on sampling the Wigner function. We discuss the limitations of this correspondence, such as Bell inequalities (for which one cannot substract accidental coincidences), highly multimode situations such as quantum imaging, and higher order correlations.