One difficulty the researchers had to overcome to achieve Bose-Einstein condensation was to avoid ordinary condensation, something like when water vapour cools and forms drops. To this end, they had to make the gas extremely cold, i.e. the particles had to move very slowly, with large de Broglie wavelengths, and the gas had to stay dilute so that the particles were kept apart. Efficient cooling can be achieved with laser light. Also, ”traps” can be set, using optical and magnetic forces to keep the cold atoms together in a little cloud.