Echo in the Fermi Sea: How a Heavy Atom Responds to Light
In an ultracold cloud of 180,000 lithium atoms, about a thousand cesium atoms drift. They are 22 times heavier than their neighbors, which makes them nearly motionless among the fast-moving particles. When such a heavy atom absorbs light, it starts oscillating between two states, and the rate of these oscillations is called the Rabi frequency.