Bright and Dark States of Light: The quantum Origin of Classical Interference

TL;DR

This paper explains how classical interference arises from quantum superpositions of photon states, revealing that even when the average electric field is zero, quantum light exhibits nontrivial interactions with matter.

Contribution

It introduces a quantum framework based on bright and dark states to explain classical interference phenomena in terms of entangled photon states.

Findings

Classical interference can be derived from quantum superpositions of multi-mode photon states.

Quantum light exhibits nontrivial matter interactions even with zero average electric field.

The superposition principle explains wave interference from a particle perspective.

Abstract

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.