All-Optical Formation of an Atomic Bose-Einstein Condensate

TLDR

The experiment uses a quasielectrostatic dipole trap formed by two crossed CO₂ laser beams, with evaporative cooling achieved by reducing the beam power over about 2 s. A 87Rb Bose–Einstein condensate was produced directly in this optical trap, starting from a sub‑Doppler cooled cloud with an initial phase‑space density of ~1/200, resulting in spin‑1 condensates of ~3.5 × 10⁴ atoms distributed among mF = –1, 0, 1 states.

Abstract

We have created a Bose-Einstein condensate (BEC) of ${}^{87}\mathrm{Rb}$ atoms directly in an optical trap. We employ a quasielectrostatic dipole force trap formed by two crossed ${\mathrm{CO}}_{2}$ laser beams. Loading directly from a sub-Doppler laser-cooled cloud of atoms results in initial phase space densities of $\ensuremath{\sim}1/200$. Evaporatively cooling through the BEC transition is achieved by lowering the power in the trapping beams over $\ensuremath{\sim}2\mathrm{s}$. The resulting condensates are $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ spinors with $3.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms distributed between the ${m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}1,0,1)$ states.