Erlangen 2022 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 60: Quantum Information II

Q 60.22: Poster

Thursday, March 17, 2022, 16:30–18:30, P

Quantum repeater node for unconditionally secure quantum key distribution — Stefan Langenfeld, •Philip Thomas, Olivier Morin, and Gerhard Rempe — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching

In classical communications a measure-and-resend strategy is used to amplify signals and overcome the exponential losses in optical fibers. In the quantum case this does not work due to the no-cloning theorem. An alternative concept which became known as the quantum repeater [1] aims at dividing a link into shorter segments across which entanglement is created independently. This leads to an effective increase in attenuation length by a factor equal to the number of segments.

Here, we demonstrate an elementary quantum repeater link consisting of a single repeater node and two classical end nodes, Alice and Bob. The repeater node is realized using two ⁸⁷Rb atoms in a high-finesse optical cavity [2]. Photons which are entangled with atom A are sent to Alice until she registers a detection event. Then, the same procedure is carried out on atom B and Bob, while the qubit on atom A is being stored. When Bob registers a photon, a Bell-state measurement is performed for entanglement swapping. We show an enhanced rate vs. distance scaling and thus the key signature of a quantum repeater. Furthermore, we demonstrate an error rate below 11 % which is essential for unconditional security in quantum key distribution protocols.

[1] H.-J. Briegel et al., Phys. Rev. Lett. 81, 5932 (1998)

[2] S. Langenfeld et al., Phys. Rev. Lett. 126, 230506 (2021)