German Researchers Take Next Step In Quantum Communications
April 3, 2013

Germans Successfully Transmit Quantum Security Key Over Long Distance

Brett Smith for - Your Universe Online

Quantum-based communications is still in its infancy, but the technology is widely expected to become used as the next generation of secure data transfer.

According to a new report in Nature Photonics, a group of German physicists has announced the successful transmission of a quantum security key from an aircraft to a ground station via laser, overcoming one of the technology´s biggest hurdles: the ability to transmit and receive quantum-based data over long distances.

“We didn´t know how well this would work; it had never been done before. But we were able to create absolutely stable reception with good tracking for several minutes. It was great to experience,” co-author Florian Moll“¯told

One of the most promising aspects of quantum communication — which uses photons to transmit information — is its potential for data security.“¯Heisenberg´s uncertainty principle makes it difficult to determine the exact position and momentum of a quantum particle. However, this principle can also be exploited for secure quantum communications.

Like conventional secure data transfer, quantum cryptography calls for both the sender and receiver to have a shared key with which they can encode and decode messages. Unlike current protocols, quantum communication guarantees the security of its keys by its very nature. Quantum states are very fragile and interception of a security key will alter the behavior of the photons, making any security loss easily detectable.

One of the biggest problems with the technology is that it can only be transmitted through fiber optic cable or over distances of less than 125 miles between stationary transmitters, as the potential for signal loss is very high.

In an effort to take the next step in the evolution of quantum communications, scientists from the Ludwig Maximilian University of Munich (LMU) and German Center for Aeronautics and Space Research (DLR) wanted to see if the technology can also be used with fast-moving transmitters and be integrated into existing optical communications systems. These two elements of a quantum-based communications system would be necessary for creating a worldwide quantum network based on satellites.

For their experiment, the German team fitted an aircraft with a laser system and combining a data transmitter with a second transmitter for the quantum cryptography. They were then able to transmit the quantum security key through the laser beam, from the aircraft and to a ground station, where it was recorded.

“This demonstrates that quantum cryptography can be implemented as an extension to existing systems,” said lead author Sebastian Nauerth of LMU.

“With the aid of rapidly movable mirrors, a targeting precision of less than 3 m over a distance of 20 km was achieved,” added Moll.

The team noted that the rate of signal loss due to air turbulence was comparable to that expected for transmission via satellite.

The researchers say that the results bode well for the future of quantum communications. They said they expect to use the results in new research and for future developments.

“We obviously want to make our technology applicable for satellites as well,” Moll said.