Quantum Ratchet Made Using an Optical Lattice

A ratchet is a device that produces a net forward motion of an object from a periodic (or random) driving force. Although ratchets are common in watches and in cells (see Focus: Stalling a Molecular Motor), they are hard to make for quantum systems. Now researchers demonstrate a quantum ratchet for a collection of cold atoms trapped in an optical lattice [1]. By varying the lattice’s light fields in a time-dependent way, the researchers show that they canmove the atoms coherently from one lattice site to the next without disturbing the atoms’ quantum states.