PACART · Free space photon atom coupling - the art of focusing

A conceptually simple but radically new approach will be explored and developed: the interaction of light with a single atom in free space. No experiment has yet come close to the highest possible coupling efficiency attainable in such a fundamental system. The usual way of enhancing light-matter coupling is to place an atom inside a cavity. Another approach involves setting the atom in the near field of a plasmonic antenna. The free space approach, however, is special: a light field matched to the atomic dipole provides many desired aspects of fully efficient coupling. The birth of this new research area was marked by the PI's pioneering publication in 2000 arguing that efficient coupling of an atom to a light field is possible in free space without modifying the density of modes of the light field such as in a cavity or having competing radiative or non-radiative decay channels such as in plasmonic enhancement. At the time of writing, the highest probability achieved for exciting a single atom with a single photon in free space is less than 1%. At the heart of the project proposed here is a deep diffraction-limited parabolic mirror, which can provide the required aberration-free focusing of a vectorial dipole wave over the full 4π solid angle – a true challenge to optics. Perfectly efficient free space coupling to a single quantum system will be a novel building block for numerous applications. In addition, the experimental set-up will allow for the studying of other open questions in the realm of classical and quantum optics related to full solid angle focusing.