Rapid switch for light particles
If somebody sends a payment instruction while Internet banking this is encrypted behind the scenes. Before the receiving bank can process the transaction it must first of all know which key can be used to decipher the information. These keys are therefore highly attractive prey for people with bad intentions.
Future quantum computers will be capable of transmitting uncrackable keys via a quantum network. Quantum cryptography makes use of light particles, which have specific quantum mechanical properties. As soon as you look at these light particles you change the properties. The intended receiver then knows immediately that somebody else has looked at the light particles during their transmission.
As these light particles are so sensitive for each potential manipulation, it must be possible to rapidly and remotely switch on and off the light sources that transmit the particles. NanoNextNL researchers at Eindhoven University of Technology have now succeeded in doing that. The speed is crucial in this, says project leader Andrea Fiore. ‘Compare it with the shutter time of a camera that needs to be very short to photograph something moving really fast. The speed that we control the transmission of the light particles with allows us to realise a very efficient exchange of particles. And that is important for the future quantum Internet.’
By aiming a laser at the right-hand section, the light source at the left can be switched on and off (image: Yan Liang – L2Molecule.com)
Laser pulse as switch
The researchers used miniscule light sources that spontaneously emit individual light particles as a consequence of atomic processes. Around these they etched a special structure that conducts the light. By using a brief laser pulse at a relatively large distance from the light source to disrupt the refractive index of the surrounding structure, it becomes easier or more difficult to produce light particles. Using this approach the spontaneous emission of light by the light source can be switched on and off at will, and then on a timescale of 200 billionths of a second.
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