Propagation of light through small clouds of cold interacting atoms

TL;DR

This paper experimentally demonstrates that small clouds of cold atoms can induce significant group delays and phase shifts on laser pulses, enabling potential applications in quantum technologies.

Contribution

The study shows large group delays and phase shifts in light passing through tiny cold atom clouds, revealing new possibilities for quantum optical applications.

Findings

Large group delays up to -10 ns observed

Negative group velocities as low as -300 m/s demonstrated

Moderate extinction with significant phase shifts achieved

Abstract

We demonstrate experimentally that a cloud of cold atoms with a size comparable to the wavelength of light can induce large group delays on a laser pulse when the laser is tightly focused on it and is close to an atomic resonance. Delays as large as -10 ns are observed, corresponding to "superluminal" propagation with negative group velocities as low as -300 m/s. Strikingly, this large delay is associated with a moderate extinction owing to the very small size of the cloud and to the light-induced interactions between atoms. It implies that a large phase shift is imprinted on the continuous laser beam, and opens interesting perspectives for applications to quantum technologies.