An ion crystal quantum repeater – Niels Bohr Institute - University of Copenhagen

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An ion crystal quantum repeater

The further development of quantum information science is dependent on reliable quantum communication. To send and recieve quantum states over reasonably long distances is an immense challenge given the rapid decoherence of quantum systems. A possible way forward is to use so-called ”quantum repeaters” which – instead of transmitting the actual quantum state – establish entanglement between the sender and the reciever. When entanglement is established it is then possible to do quantum communication with the transmission of only classical information.


In this colloquium we shall detail the workings of such a quantum repeater scheme and describe the hitherto most promising proposal for an actual realisation – the DLZC repeater (1) which is implemented in ensembles of freely moving neutral atoms. Finally, we explore one specific system that might be an improvement on the DLZC repeater: Using an ion crystal. These crystals are made of several thousand ions that are cooled by lasers and trapped in an electric trap where they form periodic structures. The control of the geometry of such a crystal is very good and the lifetime exceptionally long. A further advantage is that the crystal is located in a high finesse cavity which allows for strong coupling to light. The experimental work is done in Aarhus in the group lead by M. Drewsen.


The intended audience is fellow students of physics familiar with the undergraduate curriculum - in particular optics and quantum mechanics. No knowledge of quantum information science is assumed.


In collaboration with:  Post. Doc. D. Witthaut.

Supervisor:   A. S. Sørensen.


(1) L.-M. Duan, M. D. Lukin, J. I. Cirac, and P. Zoller: Long-distance quantum communication with atomic ensembles and linear optics, Nature 414, 413 (2001).