Quantum theory has an increasing importance in the computing and telecommunication technology. These techniques promise high encryption security in optical telecommunication. The practical realization of the principles needs reliable and robust quantum optical devices. The goal of this research topic is to develop optical systems and measurement techniques for quantum telecommunication experiments. We are focusing on special light sources producing quantum entangled photon pairs. These entangled photons form the basis, as an example, of quantum key distribution. The 1550 nm wavelength band is applied so as to be compatible with the classical fiber optic communication. Photon pairs can be efficiently produced in this wavelength range by the spontaneous parametric down conversion (SPDC) effect.

The goal of this PhD project is to develop an entangled photon pair source for the telecom wavelength band. The SPDC process should be realized in a periodically poled potassium titanyl phosphate (ppKTP) crystal. The candidate has to develop measurement techniques to qualify the entanglement and the spectral properties of the produced photons. Low photon number detection techniques and quantum tomography methods are applied for the investigation.

The candidate has to invent new optical design to enhance the photon flux, the entanglement quality and the robustness of the photon pair production. Simultaneously with the photon source development, polarization controlling and photon detection techniques have to be improved as well. The new inventions have to be integrated in an experimental quantum telecommunication system to demonstrate quantum key distribution between separately located endpoints.