This is why we are using a different approach: We want to send the signals via satellite, and then the light quanta can spread out almost completely undisturbed in the atmosphere and space. Use of this method for communication from Europe to the US, for example, is not possible. But this has a disadvantage – the range of operation thus far is limited to a few hundred kilometres. The photons are sent through fibre-optic cables when these devices are used. ![]() Such devices are currently available for purchase, and some banks are probably already using them for their internal communications. ![]() Is quantum cryptography currently being used? After all, we are living in a time in which demand for tap-free data communication is higher than it ever was before. Then the system knows that it has an eavesdropper on the line and can react accordingly. He disrupts the quantum characteristics of the photons, and the recipient inevitably becomes aware of this. A cunning selection of polarisation conditions guarantees that an eavesdropper who intercepts these photons shall invariably insert errors when he forwards the photons after listening in. The key is created through an exchange of individual photons, individual light quanta, which we polarise in different ways each time – meaning, we change their direction of vibration. Should an eavesdropping offence actually be confirmed, the transmission can be interrupted and the most significant data are not transferred at all – and the data thief is left empty-handed. With this method, one can find out on the basis of physical laws whether or not an eavesdropper is listening in during key distribution. But the situation is different when quantum cryptography is used. The danger that transmission of an encryption key could be tapped without being noticed when using conventional methods is omnipresent. To put it briefly: tap-proof exchange of information. In this project, the research team focussed on a new method called quantum cryptography. German Aerospace Center (DLR) engineer Florian Moll describes the principle to us. They were successful in exchanging a quantum key between a research aircraft and a ground station – a significant step towards development of tap-proof data communication. ![]() The prize for 2015 goes to physicists from the Ludwig-Maximilian University (LMU) in Munich and engineers from the German Aerospace Center (DLR) in Oberpfaffenhofen. With the scientific award from the Stifterverband – the Erwin Schrödinger Prize – the Helmholtz Association and the Stifterverband honour a research team every year that combines various subject areas, thus creating special innovations.
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