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Title:  Quantum communication: towards real-world application
Author:  Jeroen A.W. van Houwelingen
As Contributor:   (not claimed)
Type: Ph.D.
Field: Physics
  • Quantum Physics
Approach: Experimental
Degree granting institution:  Université de Genève
Supervisor(s): Nicolas Gisin
Defense date:  2008-04-15


This thesis is devoted to the development and study of quantum optical tech- niques that allow the use of quantum communication protocols such as a quantum repeater in out-of-the-lab conditions. Up until now almost all experiments in this research field were inside the laboratory. The experiments performed in this the- sis aimed to overcome the particular problems that can arise from non-laboratory environments and investigate if there are unexpected complications involved in this. The first experiment we performed was an entanglement swapping experiment inside the laboratory, but using systems that we believe are suitable for out-of-the- lab use. In order to provide a proof of principle of the employed techniques we used standard single mode optical fibers to simulate a `real world' telecommunication environment. The results of this experiment showed that indeed the chosen systems work in such situations. In our second experiment we investigated a new technique of performing Bell state measurements. The technique was found to work but the usefulness for real world experiments is hindered by the added losses with regards to more basic Bell state measurements. The technique might have applications in quantum information protocols that require more than one Bell state to be measured. Next we performed the first teleportation experiment that was performed out of the lab that uses prior entanglement distribution. A qubit was teleported from the laboratory to a Swisscom switching station located 500m away from the lab. For this experiment the qubit was created by a dfferent laser pulse than the entangled pair. This experiment again showed the robustness of our systems in real world environments and effectively dealt with some of the problems that arise from using multiple sites. The only remaining non real-world part of this experiment is that all photons were created in the same lab. The final part of this work shows the progress made in developing photon-pair sources that can be separated by significant distances. This is required to make a true quantum relay or repeater in which every link is located at a different location. Some other contributions made during this thesis are tests of a new type of semi- conductor photon-pair sources. Also some fundamental Bell test were performed that test some alternative theories to explain correlations found in experiments. The overall conclusion of this thesis is that the techniques developed are useful for long distance quantum communication in general and specifically for out-of-the-lab application.

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