Quantum mechanical trick: The light pulse disappears in one atomic cloud and is revived in another. Image: SR Garner.
Reading American physicists have stopped the light of a laser in an extremely cold medium, stored it, and then released it from another medium at a distance of one-tenth of a millimeter. The researchers around Naomi Ginsberg were thus able to demonstrate one of the basic principles of quantum physics in experiments: the so-called indistinguishability, in which identical particles such as atoms or electrons can not be individually characterized, but can only ever be described in the totality of all existing particles they are also coupled to each other over certain distances. Through this coupling, the information of the laser pulse transmitted from one medium to the other, although both were far apart by quantum physical scales. As a storage medium for the laser light, the scientists used a so-called Bose-Einstein condensate. At this extreme manifestation of matter, at temperatures very close to the absolute zero of minus 273.15 degrees Celsius, all the atoms of a substance combine to form a kind of superatom. This means that the atoms, so to speak, move in lockstep and the same conditions prevail throughout the medium. In this condensate, the researchers sent a laser pulse, which influenced the beat of this same step. The information transmitted by the laser had thus been transferred to the Bose-Einstein condensate.

Until then, the course of the experiments was nothing unusual. However, the second part of the experiment was exciting for the physicists: Ginsberg and her colleagues were able to revive the laser impulse a split second later in a second Bose-Einstein condensate, more than a tenth of a millimeter away. Thus, the second condensate emitted a laser pulse that was exactly like the first one. Since the condensate consisted of the same type of atoms, ie the atoms were basically indistinguishable from the atoms of the first condensate and thus also coupled to each other, the information of the laser pulse passes from one medium to another.

The scientists see in their experiment not only a gimmick or the demonstration of quantum physical principles, but also practical applications: quantum effects could once be used in the transmission of encrypted data. Also, Bose-Einstein capacitors could be used to build highly sensitive instruments, for example, to measure gravitational force.

Naomi Ginsberg (Harvard University, Cambridge) et al .: Nature, Vol. 445, p. 623 ddp / science.de? Ulrich Dewald ad

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