Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Final Activity Report Summary - PHOTONICENTANGLEMENT (Experimental manipulation of photonic entanglement for linear optics quantum information processing)

Photonic entanglement plays a crucial role both in fundamental tests of quantum mechanics and in quantum information processing (QIP). Remarkably, recent theoretical and experimental advances have shown the possibility to exploit multi-photon entanglement for efficient QIP using only linear optics together with projective measurement. Building on our long experience in research on entanglement from spontaneous parametric down-conversion, the main purpose of the present project is to perform a number of significant experiments in the field of QIP with particular emphasis on linear optics quantum computation, long-distance quantum communication and new test of multi-party quantum locality. Within the project, we plan to experimentally investigate the potential application of a photonic logic gate in fault-tolerant quantum computation; we plan to exploit free-space entanglement distribution to perform long-distance quantum communication on the order of ten kilometres; we plan both to exploit multi-qubit code to experimentally investigate the possibility to overcome the decoherence caused by the channel noise and, to exploit entanglement swapping to investigate the possibility to solve the photon loss in the quantum channel; moreover, we also plan to realise and exploit two-photon four-dimensional entanglement for efficient QIP such as quantum key distribution and quantum computation; and finally we plan to exploit a high-quality high-dimensional multi-photon entanglement source to perform large-scale quantum communication and simulation.

The main results of the project are two folds: First, six Ph.D. students and two Post-Doc were trained efficiently during the project. Second, during the project we have achieved a number of significant experimental and theoretical results and have published 28 peer-reviewed scientific articles (including one article under preparation, three articles submitted, one in Nature, two in Nature Physics, thirteen in Physical Review Letters (PRL) and eight in Physical Review A). The most significant scientific achievements in the present project include

- We report the world-first experimental demonstration of quantum teleportation of a two-qubit composite system (Nature Physics 2, 678 (2006)). On this basis, we managed to achieve the world-first experimental realisation of a teleportation-based CNOT gate for fault-tolerant quantum computation (submitted to Science (2008))

- We report the world-first free-space entanglement distribution over the effective thickness of the aerosphere (PRL 94, 150501(2005)). On this basis, we managed to achieve long-distance quantum teleportation in free space over a distance of 16 km (in preparation for Nature Physics (2008)).

- We exploit multi-qubit code to experimentally demonstrate the possibility to overcome the decoherence caused by the channel noise (PRL 96, 220504 (2006)). Using a similar setup we also managed to report an experimental violation of Bell's Inequality beyond Tsirelson's Bound for test of quantum nonlocality (PRL 97, 170408 (2006)).

- We developed and exploited a two-photon, four-dimensional entanglement source to report an all-versus-nothing violation of local realism (PRL 95, 240406 (2005)). On this basis, we developed a two-photon four-qubit cluster state to report an experimental realisation of one-way quantum computation (PRL 99, 120503 (2007)).

- We developed a robust atom-photon entanglement source for quantum repeaters (PRL 99, 180505 (2007)). On this basis we managed to report the world-first experimental demonstration of entanglement swapping with storage and retrieval of light (to appear in Nature (2008)). Moreover, we also managed to report the world-first experimental demonstration of multi-stage entanglement swapping (to appear in PRL (2008))

In summary, we have successfully realised both the training and scientific objectives of the project. The present project is leading edge in linear optics QIP and the techniques that were developed in the above experiments will lay the basis for future large scale realisations of linear optical QIP.

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