Speckle intensity correlations of photons scattered by cold atoms

TL;DR

This paper investigates how internal Zeeman degeneracy in cold atoms affects speckle intensity correlations, revealing that such degeneracy causes decoherence and reduces correlations exponentially in optically thick clouds.

Contribution

It demonstrates that internal atomic states limit speckle correlations, extending previous work by analyzing the impact of Zeeman degeneracy on mesoscopic scattering.

Findings

Speckle correlations cannot surpass the Rayleigh law.

Internal degeneracy causes strong decoherence of speckle correlations.

Correlations decay exponentially in diffusive regimes for thick clouds.

Abstract

The irradiation of a dilute cloud of cold atoms with a coherent light field produces a random intensity distribution known as laser speckle. Its statistical fluctuations contain information about the mesoscopic scattering processes at work inside the disordered medium. Following up on earlier work by Assaf and Akkermans [Phys.\ Rev.\ Lett.\ \textbf{98}, 083601 (2007)], we analyze how static speckle intensity correlations are affected by an internal Zeeman degeneracy of the scattering atoms. It is proven on general grounds that the speckle correlations cannot exceed the standard Rayleigh law. On the contrary, because which-path information is stored in the internal atomic states, the intensity correlations suffer from strong decoherence and become exponentially small in the diffusive regime applicable to an optically thick cloud.