Single trapped atoms are greatly valued in quantum technology. They are ideal standards because they are the same everywhere in the world, they make extraordinary sensors and clocks, and they can be used as nodes in quantum information networks and quantum computing. Because an atom is a truly tiny quantity of matter, special techniques must be used to interface them even to ordinary laser beams. In these works, we approached the problem of strongly coupling a single trapped atom to individual photons and to photon pairs. We built an optical system of four high numerical-aperture lenses around a single 87Rb atom held in an “optical tweezer” trap. This allowed us to shape the photons’ wave-fronts to match the atom’s radiation pattern, to ensure both efficient absorption of single photons by a single atom, and efficient collection of photons emitted by the atom. At the same time, we developed the world’s first source of entangled photon pairs, both of which are resonant to optical transitions in the 87Rb atom. These new technologies enable study of light-matter interactions at the level of individual quanta, of interest to both quantum technologies and other technologies based on light mattter interactions, e.g. super-resolution imaging.
Reference
Bruno N, Bianchet LC, Prakash V, Li N, Alves N, Mitchell MW 2019, ‘Maltese cross coupling to individual cold atoms in free space’, Optics Express, vol. 27, no. 21, p. 31042.
Prakash V, Bianchet LC, Cuairan MT, Gomez P, Bruno N & Mitchell MW 2019, ‘Narrowband photon pairs with independent frequency tuning for quantum light-matter interactions’, Optics Express, vol. 27 , no. 26, pp. 38463.
“Maltese cross” geometry for strongly coupling single photons to a single atom. Atom (not visible) sits at the centre of the cross, at the focus of four beams formed by the four lenses around the perimeter.
