WHY THIS MATTERS IN BRIEF

Quantum communication networks are seen as the future gold standard of unhackable communications networks and now they’re functioning over greater distances.

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As we continue to see breakthrough after breakthrough in quantum technologies we have to remember that many of the things we’re witnessing today have their origins in the deep past. A quarter century ago, theoretical physicists at the University of Innsbruck made the first proposal on how to transmit quantum information via quantum repeaters over long distances, which would open the door to the construction of a worldwide quantum information network.

Now, a new generation of Innsbruck researchers has built a quantum repeater node for the standard wavelength of telecommunication networks and transmitted quantum information over tens of kilometers which opens the door for global scale quantum communications networks that will be largely unhackable. The study is published in the journal Physical Review Letters.

The Future of Communications, by keynote Matthew Griffin

Quantum networks connect quantum processors or quantum sensors with each other. This allows tap-proof communication and high-performance distributed sensor networks. Between network nodes, quantum information is exchanged by photons that travel through optical waveguides. Over long distances, however, the likelihood of photons being lost increases dramatically.

As quantum information cannot simply be copied and amplified, 25 years ago Hans Briegel, Wolfgang Dür, Ignacio Cirac and Peter Zoller, then all at the University of Innsbruck, provided the blueprints for a quantum repeater. These featured light-matter entanglement sources and memories to create entanglement in independent network links that are connected between them by a so-called entanglement swap to finally distribute entanglement over long distances.

Quantum physicists led by Ben Lanyon from the Department of Experimental Physics at the University of Innsbruck have now succeeded in building the core parts of a quantum repeater – a fully functioning network node made with two single matter systems enabling entanglement creation with a photon at the standard frequency of the telecommunications network and entanglement swapping operations.

The repeater node consists of two calcium ions captured in an ion trap within an optical resonator as well as single photon conversion to the telecom wavelength. The scientists thus demonstrated the transfer of quantum information over a 50-kilometer-long optical fiber, with the quantum repeater placed exactly halfway between starting and end point.

The researchers were also able to calculate which improvements of this design would be necessary to make transmission over 800 kilometers possible, which would allow them to connect Innsbruck to Vienna.