News: BEC on a chip in Amsterdam
On Tuesday April 25, 2006 we observed our first Bose-Einstein condensate (BEC) on a chip in the "CELSIUS" experiment. The signature was the sudden appearance of an anisotropically expanding cloud when smoothly increasing the phase-space density through forced evaporative cooling.
Since then, we have optimized our evaporation trajectory and made various other improvements. Now we routinely reach Bose-Einstein condensation at a temperature of around Tc = 1.5 µK, with 105 atoms (87Rb), in a cylindrically symmetric harmonic trap. Further evaporative cooling results in a nearly pure condensate of about twenty thousand atoms. The images below (taken in August 2006) show a cloud just above the critical temperature (left), a partially condensed cloud (middle), and a nearly pure condensate (right) respectively.
Our chip consists of a silicon substrate with gold current-carrying wires on it created using vapor deposition. In our initial experiments, we mainly use a single on-chip wire, with a Z-like shape, in combination with a 'macroscopic' wire underneath the chip, for additional axial confinement.
A more detailed description can be found here on the home page of the CELSIUS experiment.