How small can you make an electric motor? Today, Alexey Ponomarev from the University of Augsburg in Germany and a couple of pals describe how to do it with just two atoms. Yep, an electric motor made of just two ultracold atoms.

Their motor consists of one neutral atom and one charged atom trapped in a ring-shaped optical lattice. The atoms jump from one site in the lattice to the next as they travel round the ring. Placing this ring in an alternating magnetic field creates the conditions necessary to keep the charged atom moving round the the ring.

However, starting the motor is another matter. Kickstarting the motor requires some kind of asymmetry which is provided by a combination of a symmetry-breaking driving field and the presence of the neutral atom, which the charged atom effectively pushes off against.

The result is a quantum electric ac-motor which Ponomarev and co go on to prove can do useful work.

Their paper is the first detailed analysis of how such a motor works and under what conditions it best works but curiously, it turns out that a team from the University of Glasgow in the UK actually built one of these quantum motors back in 2007, which they called an optical ferris wheel for ultracold atoms.

The next step say Ponomarev and co is to attach the motor to a nanoscopic resonator, such as a spring board or nanomushroom, and make it vibrate. If you can do that, they say, you’d be powering a classical object using a quantum motor. Now there’s a trick.

Ref: arxiv.org/abs/0909.2813: Quantum Machine Using Cold Atoms