Phys. Rev. Lett. 107, 230401 (2011)

Interfering laser beams can reflect particles — a phenomenon now demonstrated by Charlotte Fabre and colleagues, who have created a matter mirror by crossing two infrared beams.

Optical interference creates a periodic energy potential where the two laser beams meet. By launching a cloud of rubidium atoms towards this mirror and then imaging the atoms after they had interacted with the laser light, Fabre et al. were able to measure what fraction of the incident cloud was reflected, and how many atoms were transmitted. The reflectivity of the mirror could be controlled by increasing the laser power.

Periodic mirrors are already well known in optics, where they are called distributed Bragg reflectors. Alternating layers of high- and low-refractive-index materials can trap photons in cavities, to construct lasers, for example, or guide light propagation, as in optical fibres. The development of distributed Bragg reflectors for matter waves will aid the translation of these concepts from light to matter.