Comment on `Simulation of Bell states with incoherent thermal light'

TL;DR

This paper demonstrates that the quantum interference patterns observed in simulating Bell states with pseudothermal light can be explained by semiclassical theory and are observable at high flux using photocurrent cross-correlation, challenging the quantum interpretation.

Contribution

It shows that the experimental results of Bell state simulation with pseudothermal light are explainable by semiclassical photodetection theory and can be observed at high flux levels.

Findings

Photon-coincidence counting experiments are explained by semiclassical theory.

Quantum interference patterns are observable at high flux with photocurrent cross-correlation.

Classical electromagnetic waves can simulate quantum interference in this setup.

Abstract

Recently, Chen \em et al\rm.\ [New J. Phys. {\bf 13} (2011) 083018] presented experimental results, accompanied by quantum-mechanical analysis, showing that the quantum interference behavior of Bell states could be simulated in a modified Mach-Zehnder interferometer whose inputs are pseudothermal light beams obtained by passing laser light through a rotating ground-glass diffuser. Their experiments and their theory presumed low-flux operation in which the simulated quantum interference is observed via photon-coincidence counting. We first show that the Chen \em et al\rm.\ photon-coincidence counting experiments can be fully explained with semiclassical photodetection theory, in which light is taken to be a classical electromagnetic wave, and the discreteness of the electron charge leads to shot noise as the fundamental photodetection noise. We then use semiclassical photodetection theory to show that the \em same\rm\ simulated quantum interference pattern can be observed in high-flux operation, when photocurrent cross-correlation is used instead of photon-coincidence counting.