Deterministic entanglement swapping with an ion-trap quantum computer

Entanglement—once only a subject of disputes about the foundation of quantum mechanics—has today become an essential issue in the emerging field of quantum information processing, promising

a number of applications, including secure communication, teleportation and powerful quantum computation. Therefore, a focus of current experimental work in the field of quantum information

is the creation and manipulation of entangled quantum systems. Here, we present our results on entangling two qubits in an ion-trap quantum processor not through a direct interaction of the

ion qubits but instead through the action of a protocol known as entanglement swapping1. Our ion-trap system enables us to implement all steps of the entanglement swapping protocol in a

fully deterministic way. Thus, two ion qubits can be prepared on demand in a well-defined entangled state. This particular feature may facilitate the implementation of quantum repeaters2 or

aid in distributing entangled states in ion-trap quantum computers3.

We gratefully acknowledge support by the Austrian Science Fund (FWF), the European Commission (SCALA, CONQUEST networks) and the Institut für Quanteninformation GmbH. This material is based

on work supported in part by the U.S. Army Research Office.

Present address: Current addresses: Department of Physics and Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA (K.K.); Institute of Optics, Information and

Photonics, Max Planck Research Group, University of Erlangen-Nuernberg, Staudtstrasse 7/B2, 91058 Erlangen, Germany (A.S.V.),

Institut für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

M. Riebe, T. Monz, K. Kim, P. Schindler, M. Chwalla, M. Hennrich & R. Blatt

Institut für Quantenoptik und Quanteninformation, Österreichische Akademie der Wissenschaften, Technikerstr. 21A, A-6020 Innsbruck, Austria

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