How to Cool Light to Quantum Order ⚡ экспресс
Stimulated cooling of a non-equilibrium Bose-Einstein condensate of weakly interacting exciton-polaritons from ~300 K to 20 K has been experimentally realized. Energy-momentum spectroscopy and interferometric measurements allowed separation of the condensate from thermalized particles macroscopically occupying excited states. Contrary to existing analytical theories, a segmentation of particle density into two fractions along the excited states is observed; both fractions obey Bose-Einstein statistics with different effective temperatures and chemical potentials. It is established that the temperature of a weakly interacting Bose gas is universally determined by the density-dependent chemical potential, revealing a fundamental property of non-equilibrium BECs. The stimulated nature of cooling directly governs the onset of quantum coherence and the dissipative properties of excited states.
Cooling usually brings order: water freezes into ice. But in the quantum world, order takes unexpected forms. Experimenters cooled polaritons — particles that are both light and matter — to near absolute zero. Instead of simple freezing, the cloud began to 'dance,' synchronizing the oscillations of all particles into a single rhythm. But then the dance split: the cloud broke into two 'dance floors' with different tempos, each obeying the laws discovered by Bose and Einstein. Most strikingly, the temperature of these regions turned out to be not a result of heating, but a direct reflection of the number of particles in each clump. The tighter the crowd, the hotter the dance. This unexpected principle is universal for quantum systems far from equilibrium and may find application in future devices operating at the edge of quantum effects.
🎯 Polaritons are billions of times lighter than atoms, so cooling them takes just moments even at temperatures relatively 'high' for the quantum world.