Nonclassical light sources, which emit individual photons in a pre-defined quantum state (as opposed to lasers which emit many photons in a collective coherent state), play a basic role in quantum information processing. Efficient quantum communication protocols, as well as many metrology applications, are based on single-photon or twin-photon sources.
Natural atoms and artificial atoms, such as nitrogen-vacancy centres in diamond, or point defects in semiconductor crystals in general, are fundamental building blocks of quantum information processing: they can represent quantum information. As they interact with photons, they also form an interface to the most fundamental implementation of quantum information carriers. Our aim is to use the variety of quantum resonances of atoms for nonlinear optical interactions, in order to coherently transfer quantum information between optical and microwave photons.
One of the main obstacles of widespread application of quantum communication is the lack of quantum memory devices which can be coupled to communication channels. Such devices should accept information from “flying quantum bits” (quantum bits travelling in communication channels), store it, and reconvert it into flying quantum bits on demand. Furthermore, quantum memory devices with the capability to manipulate quantum information are key components of distributed quantum computing. The experimental know-how gained in the process of developing prototype quantum information devices also contributes to the development of devices based on new principles to increase the efficiency of processing classical information.