CRM: Centro De Giorgi
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Quantum Information and Many-Body Quantum Systems

seminar: Atom-Photon Entanglement and Remote Preparation of an Atomic Quantum Memory

speaker: Markus Weber (Department für Physik, Ludwig-Maximilians-Universität München)

abstract: Entanglement is a key element of quantum information and communication. Especially for future applications like the quantum repeater 1 and quantum networks, entanglement between different species like atoms and photons is necessary 2,3, thereby interfacing photonic quantum communication channels and matter-based quantum memories and processors. Considered applications of atom-photon entanglement in long-distance quantum communication are quantum teleportation from light to matter and its generalization the so-called remote state preparation 4. Both techniques allow to transfer an arbitrary quantum state of a photonic qubit to an atomic quantum memory. However for quantum networks or the quantum repeater it is mandatory to generate also entanglement between separated quantum processors. Therefore two atoms at remote locations are first entangled with a photon each. The two photons are brought together and then are subject to a Bell-state measurement, which serves to swap the entanglement to the atoms 5,6. In our experiment a single optically trapped 87Rb atom is excited to a state which has two decay channels. Due to conservation of angular momentum in the following spontaneous decay the atomic spin-state gets entangled with the polarization of the emitted photon. On the basis of our recently demonstrated high-fidelity atom-photon entanglement 3 we prepared an arbitrary state of a distant atomic quantum memory. By applying a quantum teleportation protocol on a locally prepared state of a photonic qubit, we realized this so-called remote state preparation on a single optically trapped 87Rb atom. We evaluated the performance of this scheme by the full tomography of the prepared atomic states, reaching an average fidelity of 82% 4. So far atom-photon entanglement was observed over a distance of few meter. However for future applications like the quantum repeater the spatial separation has to be extended to macroscopic distances. Together with the implementation of a new improved single photon source – based on a single trapped 87Rb atom – this opens up the possibility to perform “real-world” quantum teleportation from light to matter qubits and finally also to entangle distant atoms via entanglement swapping 5,6. Beside the observation of atom-photon entanglement and the remote-state preparation of an atomic quantum memory, here I will report on first experimental steps towards long-distance quantum teleportation from light to matter qubits. 1 H.-J. Briegel, W. Dür, J. I. Cirac, and P. Zoller, Phys. Rev. Lett. 81, 5932 (1998). 2 B. B. Blinov, D. L. Moehring, L.-M. Duan, and C. Monroe, Nature (London) 428, 153 (2004). 3 J. Volz & M. Weber et al., Phys. Rev. Lett. 96, 030404 (2006). 4 W. Rosenfeld, S. Berner, J. Volz, M. Weber, and H. Weinfurter, quant-ph0608229, accepted for publ. in Phys. Rev. Lett. (2007). 5 M. Zukowski, A. Zeilinger, M.A. Horne, and A. K. Ekert, Phys. Rev. Lett. 71, 4287 (1993). 6 C. Simon and W. T. M. Irvine, Phys. Rev. Lett. 91, 110405 (2003).


timetable:
Fri 30 Mar, 15:00 - 15:30, Aula Dini
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