How a superfluid flows may depend on its history.
The Bose-Einstein condensate variety of superfluids are made from atoms cooled to a few billionths of a degree above absolute zero, a temperature so cold that the atoms pack together and act as one superatom. Stirring the superatom when it is already moving can make it stop, and the speed to stop the stirring motion is slower than what was needed to set the fluid spinning in the first place. This shows that what happens to the current state of the superatom depends on what the material has already experienced.
It is the first time this type of memory effect has been observed in superfluid Bose-Einstein condensates, researchers report February 12 in Nature. The result may help scientists in their attempt to develop devices where atoms take on an equal role to electrons in electronic devices.