Photon Bose-Einstein Condensates Follow Regression Theorem in Groundbreaking Study

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Researchers at the University of Bonn have demonstrated that photon Bose-Einstein condensates, an exotic quantum state where thousands of light particles (photons) merge into a "super photon," adhere to a fundamental physics theorem known as the regression theorem. This discovery, published in Nature Communications, opens up new possibilities for measuring the properties of photon Bose-Einstein condensates, which are typically difficult to observe.

Photon Bose-Einstein condensates are created when photons are cooled to extremely low temperatures using dye molecules, which absorb "hot" photons and emit them at lower temperatures. The experiment trapped photons in a tiny, highly reflective container filled with a dye solution. As the photons repeatedly collided with the dye molecules, they cooled down and eventually condensed into a quantum gas, forming the super photon. This quantum gas, however, is not static; it flickers as photons are continuously absorbed and re-emitted by the dye molecules.

The researchers used this flickering to test whether the regression theorem applies to quantum gases. The theorem predicts that the response of a system to a perturbation, such as a controlled increase in brightness (akin to blowing air into a campfire), should mirror the system's natural fluctuations. To test this, the researchers briefly fired a laser at the super photon, causing it to flare up before gradually returning to its original state. They found that the super photon’s response to this controlled perturbation followed the same dynamics as its natural flickering, confirming that the regression theorem holds true even in this exotic quantum system.

These findings have significant implications for fundamental research in photonic quantum gases. By controlling perturbations and observing the system's response, scientists can now explore the properties of photon Bose-Einstein condensates more precisely, paving the way for new discoveries in quantum physics and the development of novel photonic materials.