Bright and dark states of light: The quantum origin of classical interference

Celso J. Villas-Boas, Carlos E. Máximo, Paulo P. de Souza, Romain Bachelard, Gerhard Rempe

Published 2021-12-10, updated 2024-03-12Version 2

Classical theory asserts that several electromagnetic waves cannot interact with matter if they interfere destructively to zero, whereas quantum mechanics predicts a nontrivial light-matter dynamics even when the average electric field vanishes. Here we show that in quantum optics classical interference emerges from collective bright and dark states of light, \textit{i.e.}, entangled superpositions of multi-mode photon-number states. This makes it possible to explain wave interference using the particle description of light and the superposition principle for linear systems.