German researchers successfully transmit a quantum key from a fast-moving object

Researchers at the German Aerospace Center (DLR) have managed to transmit a quantum key from a fast-moving object, opening up new possibilities in cryptography. The quantum data was sent from an aircraft to a ground station via a laser beam.

“Key exchange based on quantum mechanics is considered to be absolutely secure against eavesdropping,” said a news release from the DLR, which conducted the experiment with the Ludwig-Maximilians-Universität in Munich. “The quantum mechanical states of individual photons are used for the encryption; attempts at interception disturb the behavior of the particles and so can be detected immediately.

“However, quantum cryptography has only been put to limited use so far – the data is usually transmitted via glass fiber so that only limited distances can be bridged. The current flight experiment now proves that the encryption technology can also be used with fast-moving objects and can be integrated into existing optical communications systems. In the future, quantum data might also be distributed globally via satellite in this way.

The quantum key transmission experiment took place in Oberpfaffenhofen—which is where the DLR controls the European-built Columbus module for the International Space Station—using the optical ground station at the DLR Institute for Communications and Navigation and a DLR Dornier Do 228-212 research aircraft.

The aircraft was fitted with a laser system for the experiment, combining a transmitter for data communication with a second transmitter for the quantum cryptography. The laser beam sent from the aircraft was received by the ground station, recorded with specially developed measuring equipment and analyzed. The detailed assessments have been published in the journal Nature Photonics.

The particular challenge with the experiment was directing the light signals precisely onto the ground station telescope, stated the DLR news release. To do this, the researchers managed to achieve a targeting accuracy of thousandths of a degree while flying.

"We didn't know how well this would work; it had never been done before,” reports Florian Moll from the DLR Institute of Communications and Navigation, as quoted in the release. “But we were able to create absolutely stable reception with good tracking for several minutes. It was great to experience.”

A group led by LMU physicist Harald Weinfurter developed the laser used for the quantum cryptography specifically for this experiment. Using this system, it is possible to generate extremely weak laser pulses and thus exploit the quantum properties of individual photons, according to the DLR. “This forms the basis for encryption technology that cannot be intercepted,” it said.