Physicists at the Max Planck Institute of Quantum Optics have constructed a mirror by arranging a few hundred atoms in a two-dimensional optical lattice of interfering laser beams. The quantum mirror is the first example of a system in which an ordered ensemble of atoms interacts collectively with incident light. This new form of interaction between light and matter opens up a new field in basic research, but also opens up new applications in quantum information processing.
Mirrors usually consist of carefully polished metal surfaces or specially coated glass. However, physicists at the Max Planck Institute have now shown for the first time that even a single layer of 200 atoms can reflect light very well. As the atoms are arranged at a much greater distance from each other than in a metal surface, they have a very low density. The Garching researchers have thus constructed what could be described as the lightest mirror in the world. With a diameter of around seven micrometers and a thickness of a few tens of nanometers, which corresponds to the range of movement of the atoms in the optical lattice, the mirror itself is far too small to be seen with the naked eye. However, its reflection is visible to the naked eye because the atomic ensemble reflects light extremely effectively.
Over a thousand individual optical components, which together weigh around two tons, are needed to trap the atoms of the mirror in an optical lattice of crossed laser beams, generate the flashes of light that it is supposed to reflect and analyse the reflected light. The new material will therefore hardly replace conventional mirrors. However, quantum physicists could use it to conduct many more experiments in the future.
