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Quantum communications with photons and atoms

Final Activity Report Summary - QUANTCOM (Quantum Communications with Photons and Atoms)

Quantum mechanics allows for the realisation of computation or communication tasks that are difficult or impossible with traditional methods of information processing. The field of quantum information has thus blossomed over the past years, driven by the prospect of exploiting capabilities from the quantum realm to accomplish such tasks.

In particular, quantum communication aims to transmit quantum states between distant locations. Entanglement, which is related to the non-classical correlations that are possible between separated quantum states, is the main source to achieve such a purpose. Having at disposal nearly perfect entangled states between two distant sites opens the possibility to perform quantum cryptography or realise the faithful transfer of quantum states via quantum teleportation.

Since long-distance communication would almost certainly be accomplished by a photonic channel the degree of entanglement, and thus the communication fidelity, decreased exponentially with the channel length due to unavoidable losses. The concept of quantum repeaters, which consisted of dividing the channel into many segments and operating cascaded entanglement connections, allowed overcoming of the exponential increase of resource and only led to a polynomial growth. Significantly, the required asynchronous preparation of the segment required efficient light-matter interfacing.

This project led to the first experimental demonstration of a rudimentary segment of a quantum repeater and demonstrated for the first time the reversible mapping of photonic entanglement in and out of a quantum memory, which was a powerful ability for the quantum information science.