# Trapping of Bose-Einstein condensates in a three-dimensional dark focus generated by conical refraction

## TL;DR

This paper introduces a highly efficient three-dimensional dark-focus optical trap for Bose-Einstein condensates using conical refraction, enabling improved confinement with simple setup modifications.

## Contribution

It demonstrates a novel optical trapping method utilizing conical refraction to create a 3D dark-focus potential with near 100% efficiency, applicable to ultracold atoms.

## Key findings

- Achieved near 100% conversion efficiency from Gaussian to bottle beam.
- Successfully confined a $^{87}$Rb Bose-Einstein condensate in the trap.
- Measured trap shape, vibrational frequencies, and atom lifetime.

## Abstract

We present an efficient three-dimensional dark-focus optical trapping potential for neutral atoms and Bose-Einstein condensates. This "optical bottle" is created by a single blue-detuned light field exploiting the phenomenon of conical refraction occurring in biaxial crystals. The conversion of a Gaussian input beam to the bottle beam has an efficiency of close to 100 % and the optical setup requires the addition of the biaxial crystal and a circular polarizer only. Based on the conical-refraction theory, we derive the general form of the potential, the trapping frequencies, and the potential barrier heights. We present experiments on confining a $^{87}$Rb Bose-Einstein condensate in three dimensions. We determine the trap shape, the vibrational frequencies along the weak axis, as well as the lifetime of ultracold atoms in this type of potential.