Moving plane exchanges quantum keys with Earth
September 17, 2012
A Do228 aircraft equipped with the flight terminal. One can see the optical dome underneath the fuselage (marker). (a) A closeup of this dome housing the coarse pointing assembly. (b) A schematic section view of the flight terminal. (Credit: Sebastian Nauerth et al.)
An airplane has beamed quantum encryption keys to a station on the ground, paving the way for an ultra-secure global communications network, New Scientist reports.
Quantum key distribution (QKD) uses photons polarized in two different ways to encode the1′s and 0′s of an encryption key.
Quantum keys had previously been exchanged between two land-based stations. Now Sebastian Nauerth at the Ludwig Maximilian University of Munich, Germany, and colleagues have extended the feat to an aircraft, a stepping stone to QKD via satellite, which could allow secure messages to be transmitted around the world.
Flying at a speed of nearly 300 km per hour, the challenge was to tightly align the infrared laser pulses transmitted by the aircraft with the receiving station on the ground over a distance of 20 km.
The transmission lasted for 10 minutes, amounting to a key long enough to encrypt 10 kilobytes of data. The team presented the work at the QCrypt conference in Singapore on September 12.
Optical ground station. (a) Telescope of the optical ground station located on the roof of
the DLR institute building next to the airport Oberpfaenhofen. ( b) Closeup of the optical breadboard
attached to the back of the main telescope mirror, indicating the signal path for the qubits (green) and
the beacon light (red). (Credit: Sebastian Nauerth et al.)
Comments (5)
by Timothy
The article said the distance was 20km, not the altitude. Since the transmission lasted 10 minutes, the plane was probably flying a wide slow circle around the transmitter. At an altitude of 5 km (16,250 feet) a plane 19.3 km downrange would be 20 km away, and still well above the horizon.
by Timothy
Sorry, I guess I read the artlcle after the fix.
by Editor
Right, a circle at fixed altitude and max distance would be optimal (only azimuth tracking, not Az-El).
by Gorden Russell
That altitude just didn’t look right so I clicked over to Wolfram Alpha and converted 20 kilometers into feet and got the answer of 65,617 feet. That plane has turboprops that can’t possibly get that high. This has got to be a misquote.
by Editor
Good catch! Fixed. A New Scientist error, but my bad for not reading carefully. The 20 km is obviously slant range, both because of the altitude envelope and to achieve reduced delta-f (doppler effects) and stationkeeping problems.