One-Atom Maser Confirms Planck’s Theory

Nearly a century after Max Planck explained changes in the spectra of hot radiating bodies in terms of quanta, a team from the Max Planck Institute for Quantum Optics and the University of Munich, both in Garching, Germany, have demonstrated the theory experimentally. The researchers, who described the results of their experiment in the Feb. 17 issue of Nature, produced radiation fields with a fixed photon number that can be described only by quantum physics.

The team excited rubidium atoms with a 297-nm frequency-doubled dye laser, and the atoms passed through the superconducting resonator of a one-atom maser, where they emitted and reabsorbed photons. The researchers measured the state of the atoms as they left the cavity, reducing the field inside to a pure number state, and found that they could store photons for up to 0.2 s.