Researchers have found a way to get around the initial limitations of laser cooling, to cool atoms into Bose Einstein condensates using laser light from start to finish — a much faster, atom-conserving approach that has been a dream among physicists in the field. “What we invented was a new twist on the method to make it work at high [atomic] densities,” Vuletić says.
1. Use conventional laser cooling techniques to cool a cloud of rubidium atoms down to just above the point at which atoms become so compressed that photons start to heat up the sample.
2. Switch over to a method known as Raman cooling, in which they used a set of two laser beams to cool the atoms further. They tuned the first beam so that its photons, when absorbed by atoms, turned the atoms’ kinetic energy into magnetic energy. The atoms, in response, slowed down and cooled further, while still maintaining their original total energy.
3. Then aim a second laser at the much-compressed cloud, which was tuned in such a way that the photons, when absorbed by the slower atoms, removed the atoms’ total energy, cooling them even further.
Instead of only having 10,000 atoms after starting with one million using the old cooling method, they keep 70% of the atoms.
Using the new laser cooling technique, they were able to cool rubidium atoms from 200 microkelvin to 1 microkelvin in just 0.1 seconds, in a process that is 100 times faster than the conventional method. The final sample of Bose-Einstein condensates contained 1,400 atoms, from an original cloud of 2,000, conserving a much larger fraction of condensed atoms compared with existing methods.
They believe they can make 1,000-times-larger condensates in the future.