We have observed Bose-Einstein condensation of sodium atoms. The atoms were trapped in a novel trap that employed both magnetic and optical forces. Evaporative cooling increased the phase-space density by 6 orders of magnitude within seven seconds. Condensates contained up to 5×${10}^5$ atoms at densities exceeding ${10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ∼2μK. The distribution consisted of an isotropic thermal distribution and an elliptical core attributed to the expansion of a dense condensate.

• Received 17 October 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.3969

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Letters from the Past - A PRL Retrospective

2008 marked PRL’s 50th anniversary. As part of the celebrations a collection of milestone Letters was started. The collection contains Letters that have made long-lived contributions to physics, either by announcing significant discoveries, or by initiating new areas of research.