A 'pause button' for light particles
How do you stop something that is faster than anything else, intangible and always in motion by nature? A team led by physicists Dr. Thorsten Peters and Professor Thomas Halfmann is doing the seemingly impossible: stopping light for tiny fractions of a second. They then end the stopover at the push of a button letting the light pulse continue its journey. The researchers are even stopping individual light particles.
What sounds like a physical gimmick could be of use for future applications. So-called quantum technology attempts to use bizarre effects of quantum physics for faster computers, more precise sensors and bug-proof communications. Photons, which are used in quantum technology as information carriers, play a decisive role in this.
To this end, physicists, for example, require light sources that emit individual photons at the push of a button. To process the information stored on light particles, it would also be important for individual photons to interact, which they do not usually do. In future quantum computers, photons will for example have to transfer their information to atoms and vice versa. To this end too, the interaction between the two types of particles must be intensified, which the photons stopped by the group from the TU Darmstadt could make possible.
How does this emergency stop for light work? For some time now it has been possible to freeze photons and re-emit them on command. However, whilst they are stopped, the photons do not exist as such. They are swallowed by an atomic cloud, which then assumes a so-called excited state and stores the photon as information. Only upon receipt of a signal does the excitation change back into a photon, which then continues on. The researchers in Darmstadt are doing it in a similar manner, but with one crucial difference: their photons are actually preserved.
