Physicists at the California Institute of Technology have built a laser with a single atom by trapping a cold caesium atom in an optical cavity. The laser produces nonclassical light that could be used in quantum computing.
After cooling and trapping the single caesium atom in a tiny optical resonant cavity, the Caltech team used a laser is used to excite the caesium atom, causing it to decay to an intermediate state and emit a photon. Strong coupling between the atom and cavity means the photon is almost always emitted into a laser cavity mode rather than free space. Then another laser transfers the atom to another excited state and it then decays back to the ground state – and the whole process to be repeated.
The emitted light shows a quantum effect called photon antibunching. This makes it have more ordered light than conventional lasers but the single-atom laser has a very small flux - less than 100 000 photons per second. It also only operates for about a second.