Different Types of Coherence: Young-type Interference versus Dicke Superradiance

TL;DR

This paper clarifies the distinction between Young-type interference from classical dipoles and Dicke superradiance, showing they are fundamentally different phenomena despite similar intensity patterns.

Contribution

The study reveals that Dicke superradiance and classical dipole interference arise from different types of coherence, resolving a longstanding paradox in quantum optics.

Findings

Dicke states produce superradiance without a dipole moment.

Separable states with dipoles show classical interference patterns.

Both configurations yield similar far-field intensity distributions.

Abstract

Dicke superradiance, i.e., the enhanced spontaneous emission of coherent radiation, is often attributed to radiation emitted by synchronized dipoles coherently oscillating in phase. At the same time, Dicke derived superradiance assuming atoms in entangled Dicke states which do not display any dipole moment. To shed light on this apparent paradox, we study the intensity distribution arising from two identical two-level atoms prepared either in an entangled Dicke state or in a separable atomic state with non-vanishing dipole moment. We find that the two configurations produce similar far field intensity patterns, however, stemming from fundamentally distinct types of coherence: while in the second case the atoms display coherence among the individual particles leading to Young-type interference as known from classical dipoles, atoms in Dicke states possess collective coherence leading to enhanced spontaneous emission. This demonstrates that the radiation generated by synchronized dipoles and Dicke superradiance are fundamentally distinct phenomena and have to be interpreted in different ways.