(Top) Condensate atom cloud imaged in the IR with decreasing temperature. (Bottom) Temperature contour plot showing the atom cloud.
What is a Bose Einstein Condensate (BEC)
Transition from a particle to wave nature with decreasing temperature.
Formation of the Condensate
The process of laser cooling is summarized in the image below. The species of interest is exposed to a photon flux tuned to a particular resonance frequency. At resonance the photons impart momentum to the atoms. If the photon frequency is Doppler red-shifted from resonance then only atoms coming towards the laser beams will be affected. Those moving away from the laser will be unaffected by the photon flux. If laser beams are such that they are coming from all directions the atoms will be cooled from all directions. This laser cooling, lowers the atom population temperature to ~100 microKelvin, still above the condensate temperature.
Laser cooling:Formation of the condensate uses a combination of laser and evaporative cooling and adiabatic expansion.
The next stage of cooling is evaporative cooling with an applied Radio Frequency (RF) field. Another unique property of atoms is that for atoms above a certain energy level, when exposed to an RF field, they can be excited and essentially removed from the population, leaving behind only those at a lower energy and therefore population temperature. This is called evaporative cooling and brings the temperature of the population to much below one microKelvin.
The final stage of cooling is adiabatic expansion. The atoms are held and compressed on an integrated circuit with a precisely tuned magnetic field. When the field is turned off the cloud expands, and cools further. The final stage brings the population to below the nK range, and in the space environment, to the pK range. The condensate is formed and can live on the order of 20 seconds in microgravity where it can be exposed to other magnetic fields, electric fields, species of condensate, and imaged.