Blue-detuned optical ring trap for Bose-Einstein condensates based on conical refraction

TL;DR

This paper introduces a new optical trapping method for ultra-cold atoms using conical refraction in biaxial crystals, creating a stable, blue-detuned ring trap for Bose-Einstein condensates with demonstrated theoretical and experimental validation.

Contribution

It presents a novel optical ring trap based on conical refraction, with analytical and numerical analysis of trapping potentials and frequencies for ultra-cold atoms.

Findings

Successful trapping of Bose-Einstein condensates in the Poggendorff ring

Analytical expressions for trapping frequencies and potential depths

Good agreement between simulations and experimental results

Abstract

We present a novel approach for the optical manipulation of neutral atoms in annular light structures produced by the phenomenon of conical refraction occurring in biaxial optical crystals. For a beam focused to a plane behind the crystal, the focal plane exhibits two concentric bright rings enclosing a ring of null intensity called the Poggendorff ring. We demonstrate both theoretically and experimentally that the Poggendorff dark ring of conical refraction is confined in three dimensions by regions of higher intensity. We derive the positions of the confining intensity maxima and minima and discuss the application of the Poggendorff ring for trapping ultra-cold atoms using the repulsive dipole force of blue-detuned light. We give analytical expressions for the trapping frequencies and potential depths along both the radial and the axial directions. Finally, we present realistic numerical simulations of the dynamics of a $^{87}$Rb Bose-Einstein condensate trapped inside the Poggendorff ring which are in good agreement with corresponding experimental results.