Experiments with ‘superphotons’ for secure quantum communications

September 3 () –

Physicists have been able to shape a fusion of light particles into a kind of ‘superphoton’, with a simple reticular structure composed of four points of light arranged in a square shape.

In the future, these types of structures could be used in quantum networks so that the exchange of information between several participants is eavesdropping proofThe results have been published in the journal Physical Review Letters.

When a large number of light particles are cooled to a very low temperature and simultaneously confined in a compact space, they suddenly become indistinguishable and behave like a single superphoton. Physicists call this a Bose-Einstein condensate, and it typically resembles a fuzzy light particle.

“However, we have now succeeded in printing a simple lattice structure into the condensate,” he explains. in a statement Andreas Redmann, Institute of Applied Physics (IAP) at the University of Bonn.

IAP researchers create superphotons by filling a small container with a dye solution. The side walls of the container are reflective. If the dye molecules are excited with a laser, photons are generated that bounce back and forth between the reflective surfaces. These light particles start out relatively hot, but as they move between the reflective surfaces they repeatedly collide with the dye molecules. and cool until they finally condense to form a superphoton.

“Reflective surfaces are normally perfectly smooth,” explains Redmann. “We decided to deliberately add small indentations to them, which figuratively provide more space for the light to collect in them.” In this way, a structure is imprinted into the condensate, almost like when you press a mould with one closed side down into a sandbox: if you lift it up again, you can still see the imprint of the mold in the sand.

“In this way, we have managed to create four regions in which the condensate prefers to remain,” says Redmann. It is as if a bowl of water were divided into four cups arranged in a square shape.

Unlike water, however, the superphoton will not necessarily split into four smaller portions. If the cups are placed close enough to each other so that light particles can pass through them in a quantum mechanical manner, it will remain as a single condensate.

This property could be used, for example, to create so-called quantum entanglement. If the light in one cup changes state, it will also affect the light in the other cups. This quantum physical correlation between photons is a basic requirement for making information exchanges, such as secret conversations or transactions, between several participants eavesdropping-proof.

“If the shape of the reflecting surfaces is deliberately changed, it is theoretically possible to create Bose-Einstein condensates that split into 20, 30 or even more lattice sites,” explains Redmann.

“This would allow us to make communication between many participants in a discussion eavesdropping-proof. Our study has demonstrated for the first time how certain emission patterns can be deliberately created for use in a specific application. This makes the method extremely interesting for many different technological developments.“, he added.