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A step towards the Quantum Internet: Building networks from quantum-memory satellites

Satellit Hylas-1

Satellit Hylas-1
Image Credit: ESA – J. Huart

Using multiple satellites to connect distant groud stations.

Using multiple satellites to connect distant groud stations.
Image Credit: Wallnöfer et. al. / AG Eisert

Quantum physicists from an inter-institutional project around Prof. Jens Eisert (Freie Universität Berlin) were able to show that information transfer could indeed take place over intercontinental distances with the help of quantum memory satellites and with a quantum repeater strategy. The results of the work were published in "Nature: Communication Physics."

The members of the Dahlem Center for Complex Quantum Systems who have contributed to the work are Julius Wallnöfer, Frederik Hahn, Fabian Wiesner, Nathan Walk and Jens Eisert.

News from Aug 31, 2022

Establishing functional long-distance quantum networks is a central challenge and a focus of active research in modern quantum physics. People are dreaming these days about what is called the quantum internet - a communication network that lets many entities interact and communicate, but at enormous security levels: The security of such schemes is based on basic physical laws and can in principle even be unconditional. This gives rise to a challenging prescription, but an exciting one at the same time. The quantum internet is the blueprint of communication networks of tomorrow, and unsurprisingly, large consortia all over the world are aiming at realizing such communication networks.

As the quantum internet of the future will be based around far-reaching quantum links, physicists around the world are keen on investigating how these networks may function. A joint group of researchers from the Freie Universität Berlin and Humboldt Universität zu Berlin, the German Aerospace Center (DLR), the University of Strathclyde and the Fraunhofer Heinrich-Hertz-Institute have now been able to demonstrate that intercontinental distances may indeed be reached using satellites with quantum memories employing a quantum repeater strategy.

Quantum information technology is about utilising the properties of quantum systems to improve how information is processed. A core issue one has to face when implementing a strategy to transfer quantum information is data noise and imperfections. Photons get lost rather frequently when sent through an optical fiber. Especially for long-distance communication, this poses a challenge.

Naturally, any quantum network becomes much more useful if it connects spatially separated parties – classical networks certainly would not be such a crucial technology either, if they were constrained to a single room. Imperfections at the classical level can be alleviated by simply making copies of the original information and resending them over and over again. However, the same method does not work for quantum information as the no-cloning theorem prohibits the creation of perfect copies at the quantum level. Another approach is necessary: the quantum repeater strategy.

Just like one would use a wireless repeater to amplify the network signal in a big house, a quantum repeater allows to extend the range of quantum connections and, thus, provides a means to circumvent the no-cloning problem. At the heart of the strategy lies a core concept of quantum information technology – entanglement. Entangled quantum systems interact with one another in a unique way as you would only find in the quantum realm. A process called entanglement swapping enables the establishment of long-distance connections over multiple intermediate segments, for example, with the use of so-called quantum memories.

"While the quantum repeater protocol is a well-established approach for long-distance quantum communication, there are many open theoretical questions once you deviate a little from the standard cases", says Julius Wallnöfer, first author of the recent work published in Communications Physics, a journal of the Nature group. What was lacking until now was a solid computational basis to assess this form of connection, especially with regards to employing multiple satellites. This is one of the crucial results of the project: Using a code written by Wallnöfer, the researchers were able to develop a state-of-the-art simulation to analyse quantum-repeater setups and strategies across very long distances. Satellites are an attractive option for long-range communication in comparison to typically data loss afflicted optical fibers. In particular, the work shows that by putting quantum memories on satellites, reaching intercontinental distances is not only feasible but can easily outperform approaches without quantum memories.

The results of the project centred around the work group of Jens Eisert of the Freie Universität critically further our understanding of how quantum networks may function in the future. Especially with efforts underway to build the first actual quantum networks, the question of which technologies will be used for a quantum internet of tomorrow is clearly one of imminent importance. Many questions remain to be settled until we have established quantum communication systems covering the entire planet. This work can be seen as a small stepping stone towards this goal.

Publication in Nature: Communication Physics

DOI: https://doi.org/10.1038/s42005-022-00945-9

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  • AG Eisert
  • communications physics
  • entanglement
  • intercontinental
  • Julius Wallnöfer
  • nature
  • quantum communication systems
  • quantum information technology
  • quantum internet
  • quantum networks
  • quantum repeater protocol
  • quantum-memory
  • satellites