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Boffins receive quantum key from moving plane

Alice and Bob play catch

Array of multicoloured LEDs reminiscent of the matrix

A group of German researchers has taken a step closer to achieving quantum key distribution with satellites, receiving quantum keys transmitted by a moving airplane.

The experiment is described in this paper (PDF) presented to the QCrypt conference in Singapore last week.

Led by Sebastian Nauerth at the Ludwig Maximilian University of Munich, the researchers achieved a stable connection over 20 Km for ten minutes, and in that time achieved a key rate of 145 bits/s. While that’s far too slow for a data channel, this only refers to the rate at which the keys are transmitted.

However, if the system were to be made secure against eavesdropping, the authors note, the key exchange rate would fall to 5 bits/second.

The experiment was conducted just after sunset at Munich’s Oberpfaenhofen airport to avoid errors that could be introduced by sunlight. The researchers also had to create a mechanism of moving mirrors to compensate for the movement of the aircraft.

The qubits were encoded on the polarization of the beam transmitted from the aircraft (Alice) to the ground (Bob).

The kit the researchers used included a free-space laser terminal developed by the German Aerospace Centre (DLR), modified to implement the QKD transmitter communicating with a ground-based receiver on a DLR building. ®

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