(ORDO NEWS) — German physicists discovered a previously unknown phase transition in a Bose – Einstein optical condensate and a new state of light quanta – an overdamped phase. The results, according to the authors, may in the future be important for the implementation of secure quantum communication. The research is published in the journal Science.
In 2010, researchers at the University of Bonn under the leadership of Professor Martin Weitz (Martin Weitz) first received a completely new light source – a single “superphoton” consisting of many thousands of individual light particles – a kind of Bose-Einstein condensate of light particles.
Bose – Einstein condensate is an extreme aggregate state of matter that occurs only at temperatures close to absolute zero. This state is characterized by the fact that the particles in such a system are no longer distinguishable and are predominantly in a quantum-mechanical state, that is, they behave like one giant “superparticle”, the state of which can be described by a wave function.
In the new experiment, the scientists used the same setup they did ten years ago: they trapped light particles in a resonator consisting of two curved mirrors spaced a little more than a micrometer apart, which reflect a fast, reciprocating beam of light. The space between the mirrors is filled with a liquid dye solution that cools the photons. This is achieved due to the fact that the dye molecules first “swallow” the photons, and then “spit out” them again, bringing them to the temperature of the dye solution – the equivalent of room temperature.
At some point, the researchers were able to detect a phase transition in a system of captured light particles. The authors explain this transition as follows: semitransparent mirrors cause loss and replacement of photons, creating a disequilibrium that causes the system to oscillate. As a result, two separated phases are formed: the oscillation phase and the damping phase. In the latter, the vibration amplitude gradually decreases.
“The super-damping phase we are observing corresponds to a new state of the light field,” the first author of the article, Fahri Emre Öztürk, a graduate student of the Institute of Applied Physics, quoted in a university press release.
The authors note that usually the action of a laser is not separated from the effect of the Bose – Einstein condensate by a phase transition and there is no clearly defined boundary between these two states. However, in this experiment, the superdamping state of the Bose – Einstein optical condensate was separated by a phase transition from both the vibrational state and the light of a standard laser.
“This shows that we are dealing with two separate phases of a Bose-Einstein optical condensate,” says study leader Professor Martin Weitz.
Scientists plan to use the results obtained for further research to search for new states of the light field in multiple coupled light condensates that arise in optical systems. They hope that in the future their discovery will be used in the field of quantum communication.
“If suitable quantum-mechanically entangled states arise in bound light condensates, it could be interesting for the transmission of quantum-encrypted messages,” Oztürk notes.
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