It鈥檚 a big boom, only on a miniature scale. When waves build up in a quantum fluid of ultracold caesium atoms, they can cause the atoms to ripple outwards in a starburst shape, creating beautiful, tiny, fireworks.
The fireworks occur in a Bose-Einstein condensate, (BEC), a quantum gas made of particles called bosons cooled to near absolute zero. Caesium atoms are bosons, so Han Fu at the University of Chicago and her colleagues placed a highly cooled gas of these atoms in a disc-shaped trap formed by lasers, which held the atoms in place. The whole thing was only 26 micrometres across, the size of some bacteria, because large BECs are hard to make.
The team suffused the trap with a magnetic field of changing strength. This pumps energy into the system, exciting the atoms to higher energy states. 鈥淏osons are copycats: they like to be in the same state,鈥� says Fu. 鈥淥nce a few caesium atoms are excited, more will want to join them.鈥�
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Fu found that this follow-the-leader behaviour creates a self-amplifying effect, with ripples of atoms getting ever more energetic. Eventually, they can bust out of the trap like waves splashing over a levee. The result is a celebratory firework of frozen caesium
Physical Review Letters
