Physical processes in the nanoscale are often governed by rules of quantum mechanics. To study these quantum processes or transfer them between distant systems, photons are possibly the most promising and most credible candidates because they interact weekly with matter and it is possible to send them over long distances through optical fibers or free space. For addressing the microscopic quantum processes with photons, the interaction between light and the nanoscale system has to be optimized and also faithfully transfer the quantum information.

In technical terms, the interaction should preserve quantum coherence. Sanli Faez and his collaborators at the Max-Planck institute in Erlangen, Germany, have built a new platform for coherent interaction between photons and single molecules. Their system consists of an ensemble of organic dye molecules that are embedded inside the tight optical mode of a waveguide made of another organic material inside a glass capillary. With a careful choice of materials and the fabrication process, each dye molecule acts similar to a perfect quantum two-level system with a very high degree of coherence. They have measured the transmission of photons through this waveguide, which is readily coupled to an optical fiber, and have seen that each time the frequency of the laser matches the narrow optical transition of the molecules there is a dip of a few percent. Because the interaction between each molecule and light is elastic the quantum coherence is preserved. The special advantage of this platform, over other schemes of enhance light-matter interaction such as cavities, is the possibility of coupling several dye molecules to the same mode of light. Meanwhile, the frequency of each molecule can be externally tuned. These two possibilities, together, allow for studying many-body quantum interactions in a controlled fashion. Furthermore, the small dye molecules can be used as local quantum reporters for other quantum processes in their local environment, for example tunneling of electrons.

Sanli Faez,(1,2) Pierre Türschmann, (1) Harald R. Haakh, (1) Stephan Götzinger,(3,1) and Vahid Sandoghdar (1,3): Coherent Interaction of Light and Single Molecules in a Dielectric Nanoguide. http://arxiv.org/abs/1407.2846  
(1)Max Planck Institute for the Science of Light (MPL), D-91058 Erlangen, Germany
(2)Leiden Institute of Physics, PO Box 9504, 2300 RA Leiden, The Netherlands
(3)Department of Physics, Friedrich Alexander University of Erlangen-Nürnberg, D-91058 Erlangen, Germany

(The article will soon appear in Physical Review Letters)