Researchers at the Georgia Institute of Technology have demonstrated the first storage ring that is able to confine and guide the flow of ultracold neutral atoms in a circular path. Called the nano-electron-volt neutral-atom storage ring (Nevatron) the ring measures just 2 cm across.
In general, storage rings not only store particles but also serve to define an energy and trajectory in so far as the particles are guided round a prescribed track by some kind of magnet system. Particles with the wrong energy would fly away. Normally the ring's magnets exert themselves by acting on the particles' electric charge. Neutral atoms do not have a net charge but they can possess a net dipole moment that, if the atom is moving slowly enough, is sufficient for guidance. The Nevatron is a circular waveguide that uses magnetic fields from tiny electrical wires to direct low-energy atoms.
In contrast with high-energy particle storage rings, in which the goal is to increase the energy of the confined particles up to and beyond the tera-electron-volt scale, the researchers at Georgia Tech are interested in the opposite - using ultracold atoms with nano-electron-volt energies. Their experiment takes place within a vacuum chamber. First, a standard magneto-optical trap uses a combination of magnetic fields and intense laser beams to confine a few million atoms of rubidium while reducing their speed to a crawl less than 10 cm/s.
When the atoms in the trap reach the appropriate temperature - about 3 µK - the magnetic fields and laser beams confining them are switched off. That allows the cold atoms to flow by gravity into a "funnel" made up of two current-carrying wires about 1 mm apart. The funnel guides the atoms into the storage ring where they are confined by magnetic fields created by parallel wires, each of which carries a few amps of electric current.
So far, swarms of 1 million rubidium atoms have made as many as seven circuits around the ring, moving at speeds of 1 m/s. It is early days yet, but the ultimate goal of the Georgia Tech team is to do for uncharged atoms what optical fibre has done for light. In one potential application, the 2 cm storage ring could serve as the foundation for a miniaturized atom interferometer that would improve the accuracy of inertial guidance systems used in commercial aircraft.