September 19, 2018 / Department of Physics

Milestones for secure quantum communication

The University of Stuttgart is funded with 1.6 million Euro for building a quantum repeater

In the modern, digital world quantum cryptography is a promising solution to ensure that private data can be reliable encrypted and is tamper proof. Unfortunately, the transfer rates of secret bits are still limited. This is caused by technical issues such as optical loss in fiber connections. The 3rd and 4th Physics Institute and the IHFG (Institut für Halbleiteroptik und Funktionelle Grenzflächen) of the university in Stuttgart will now implement a so-called quantum repeater, which increases the accessible distance and the rates of quantum cryptography. The project Q.Link.X is funded by the BMBF.

Quantum cryptography realizes a maximal secure communication based on physical principles. This is a crucial advantage against classical encryption methods which rely on hard mathematical problems which can still be solved with a big computational effort. The physical base of quantum cryptography is that a single quanta, such as a single photon, can only be measured once. If now a key is transferred via a distance, a certain error and loss rate signal to a user if a key is trustworthy or not. Only if the security is guaranteed, a secret message is subsequently transferred.

The fundamentals of this technique are researched at the University of Stuttgart for a long time. Still an optical and simultaneously secure optical interlink over large distances is not yet possible. The loss in optical fibers implies that over hundreds of kilometers a transfer can only be realized with relay stations – which intrinsically hold a security risk, since the the (secret) information is there accessible as a clear text.

The alternative is to implement relay stations, which do not measure the quantum state, but which interlink to remote quantum systems to a larger one. This are so-called quantum repeaters. Such signal extenders will be implemented in the coming years at the University of Stuttgart in the joint project “Quanten-Link-Extension” (Q.Link.X). The federal ministry of education and research (BMBF, Geramny) has now granted 1.6 million Euro to the University of Stuttgart for this ambitious goal. Q.Link.X will implement fiber-based communication with quantum security and increase the accessible distances and transfer rates.

25 partners in science and industry

Since such a quantum repeater relies on specialized optical and electronic components, multiple partners are involved in the realization of the different building blocks. The 3rd and 4th Physics Institute and the IHFG (Institut für Halbleiteroptik und Funktionelle Grenzflächen) will optimize the individual parts and will also realize a fully-functional demonstrator. Additionally, 20 academic partners and three industry partners and start-ups are involved in the collaboration.

The researchers are confident that the development of quantum repeaters will expedite a development of long-distance quantum communication. The core components will also be part of the coming cluster “Quantenwissenschaften von den Grundlagen zur Anwendung: Entwicklung von Quanteninstrumenten der Zukunft” which is a part of the excellence strategy of the University of Stuttgart.

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