Entanglement sent over 50 km of optical fiber

Entanglement sent over 50 km of optical fiber
In a nonlinear crystal illuminated by a strong laser the photon wavelength is converted to the optimal value for long-distance travel. Credit: IQOQI Innsbruck/Harald Ritsch

The quantum internet promises absolutely tap-proof communication and powerful distributed sensor networks for new science and technology. However, because quantum information cannot be copied, it is not possible to send this information over a classical network. Quantum information must be transmitted by quantum particles, and special interfaces are required for this. The Innsbruck-based experimental physicist Ben Lanyon, who was awarded the Austrian START Prize in 2015 for his research, is investigating these important intersections of a future quantum Internet.

Now his team at the Department of Experimental Physics at the University of Innsbruck and at the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences has achieved a record for the transfer of quantum entanglement between matter and light. For the first time, a distance of 50 kilometers was covered using fiber optic cables. "This is two orders of magnitude further than was previously possible and is a practical distance to start building inter-city quantum networks," says Ben Lanyon.

Converted photon for transmission

Lanyon's team started the experiment with a calcium atom trapped in an . Using , the researchers write a onto the ion and simultaneously excite it to emit a in which is stored. As a result, the quantum states of the atom and the light particle are entangled. But the challenge is to transmit the photon over fiber optic cables. "The photon emitted by the calcium ion has a wavelength of 854 nanometers and is quickly absorbed by the optical fiber," says Ben Lanyon. His team therefore initially sends the light particle through a nonlinear crystal illuminated by a strong laser. Thereby the photon wavelength is converted to the optimal value for long-distance travel: the current telecommunications standard wavelength of 1550 nanometers. The researchers from Innsbruck then send this photon through a 50-kilometer-long optical fiber line. Their measurements show that atom and light particle are still entangled even after the wavelength conversion and this long journey.

Even greater distances in sight

As a next step, Lanyon and his team show that their methods would enable entanglement to be generated between ions 100 kilometers apart and more. Two nodes send each an entangled photon over a distance of 50 kilometers to an intersection where the light particles are measured in such a way that they lose their with the ions, which in turn would entangle them. With 100-kilometer node spacing now a possibility, one could therefore envisage building the world's first intercity light-matter quantum network in the coming years: only a handful of trapped ion-systems would be required on the way to establish a quantum internet between Innsbruck and Vienna, for example.

Lanyon's team is part of the Quantum Internet Alliance, an international project within the Quantum Flagship framework of the European Union. The current results have been published in the Nature journal Quantum Information.


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More information: V. Krutyanskiy et al, Light-matter entanglement over 50 km of optical fibre, npj Quantum Information (2019). DOI: 10.1038/s41534-019-0186-3
Citation: Entanglement sent over 50 km of optical fiber (2019, August 29) retrieved 19 September 2019 from https://phys.org/news/2019-08-entanglement-km-optical-fiber.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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User comments

Aug 30, 2019
Satellite based entangled pairs have been sent to receptors over 700 miles apart.
But that was through space, not fiber optic cables.
Just pointing out this is a record through refractory solids only, rather than an outright record.

Aug 30, 2019
I thought Quantum transmission would have Zero latency.

Aug 30, 2019
Doesn't all this laser driven quantum juggling, mix macro scale classical coherence with your quantum entanglement? Thereby making it amplify-able and copy-able and insecure.

( Not that any of this is secure if your quantum-repeaters have a back door fitted by the NSA, KGB or Huawei? )

Aug 30, 2019
I thought Quantum transmission would have Zero latency.


http://curious.as...rmediate

This is an awkward and simplified explanation, but it can lead to more in depth articles if the interest is there.

Aug 30, 2019
Thank you to the author of the article for not confusing information with quantum information.

Aug 31, 2019
Vienna, 21. April 2004
World Premiere: Bank Transfer via Quantum Cryptography Based
on Entangled Photons
Press conference and demonstration of the ground-breaking experiment:
21 April 2004, 11:30, Vienna City Hall – Steinsaal
A collaboration of:
group of Professor Anton Zeilinger, Vienna University; ARC Seibersdorf research
GmbH; City of Vienna; Wien Kanal Abwassertechnologien GmbH and Bank Austria –
Creditanstalt
Today, the Bank Austria Creditanstalt has, on behalf of the City of Vienna, performed the
World's first bank transfer encoded via quantum cryptography.
This novel technology was demonstrated by the group of Professor Anton Zeilinger, Vienna
University in collaboration with the group Quantum Technologies (Information Technologies
Division) of Seibersdorf research. The bank transfer was initiated by Vienna's Mayor Dr.
Michael Häupl, and executed by the Director of the Bank Austria Creditanstalt, Dr. Erich
Hampel. The information was sent via a glass fiber cable, laid by the com

Sep 14, 2019
Doesn't all this laser driven quantum juggling, mix macro scale classical coherence with your quantum entanglement? Thereby making it amplify-able and copy-able and insecure.

( Not that any of this is secure if your quantum-repeaters have a back door fitted by the NSA, KGB or Huawei? )

Just one observation, in your spot on ponderings, Comrade EyeNStein. Why would those guys come in through the back when they own the front door?

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