Proc. Natl Acad. Sci. USA 109, 10811–10814 (2012)

A charge-carrying particle moving through a magnetic field feels a force perpendicular to its direction of motion. The resulting build-up of charge on one side of a material creates an electric potential that was first identified by Edwin Hall in 1879. Now, Lindsay LeBlanc and colleagues have seen a similar type of 'Hall effect' in an ultracold gas of neutral atoms.

LeBlanc et al. used lasers to trap and cool a rubidium cloud until it condensed to a superfluid. Despite the fact that the atoms are charge neutral, the team has previously shown that the effects of magnetic fields can be mimicked by firing in two more laser beams at a wavelength corresponding to a particular atomic transition. Now, they have observed the mass transport indicative of a Hall-like response by showing that the superfluid wobbles when the trapping strength is varied.

The conventional Hall effect has proved to be a useful and sensitive tool for investigating semiconductors. The superfluid Hall effect could soon play a similar role in better understanding Bose–Einstein condensation.