Atom-photon Interactions

Bringing together different physical carriers of quantum information is one of the most exciting challenges in implementing quantum computing schemes. Different physical systems solve different problems. While photons are well-suited to the transport and read-out of quantum information, atoms are much better information carriers when it comes to implementing universal gate operations. A good interconnection between these two physical systems will be essential in processing devices such as quantum repeaters.

Research in this area at CQT follows different threads. The Microtraps group is investigating the interaction of photons in cavities with atoms and has demonstrated strong coupling. Such an interaction forms the basis for many proposals for implementing complex quantum information tasks (arXiv:1006.1644). We work with optical resonators of high finesse and innovative shapes, and have excellent control positioning atoms and ions in these resonators.

In another thread, CQT researchers are trying to interface atoms with “individual” photons, photons having localizable wave packets as we are used to from experiments based on single-photon counters or spontaneous emission from atoms. Here we engineer the spatial wave function of photons by strong focusing such that we can couple the photons very well to an electronic transition in a single atom. The observation of the shadow from a single atom (Nature Physics 4, 924 (2008)), and a significant phase shift induced in a light beam by a single atom (Phys. Rev. Lett. 103, 153601 (2009)) are two recent accomplishments here at CQT.

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