Bose–Einstein condensation in the blink of an eye

It’s been more than two decades since Carl Wieman and Eric Cornell created the first Bose–Einstein condensate (BEC), confirming the counterintuitive prediction that a macroscopic population of atoms can pile into a single quantum ground state if cooled below some critical temperature. In all those years, the recipe for creating the condensates has hardly changed: Laser Doppler cooling chills the cloud of atoms as close to the critical temperature as possible; when that technique can go no further, evaporative cooling does the rest. But the evaporative cooling step is inefficient. It works by jettisoning most of a cloud’s atoms in order to cool the remaining few—a relatively slow process that can take a minute or more. Now MIT researchers led by Vladan Vuletić have come up with an alternative approach that allows them to create BECs in a fraction of the time.

The team dispensed with evaporative cooling and instead used Raman sideband cooling, a laser technique that exploits an optical cycle—specifically, a one-two combination of hyperfine and electron transitions—to extract kinetic energy from atoms one quantum at a time. Invented in the 1990s, the method can easily cool a trapped, isolated atom to its motional ground state. In atomic clouds, however, the pump light that initiates the electron transition inevitably leads to scattering and molecular excitations, both of which generate unintended heat. Vuletić and his colleagues discovered that if they detuned the pump laser to frequencies far below that of the electron transition, they could largely avoid the unwanted effects. The researchers used the cooling strategy to create a dense BEC of rubidium atoms in just 300 ms—with minimal atomic losses. Aside from potential applications in precision metrology and quantum-gas microscopy, the new approach could also make it easier to create and study BECs in space. (J. Hu et al., Science 358, 1078, 2017 .)