Scientists at the Australian National University observed for the first time the effect of depletion of the Bose-Einstein condensate - a special state of aggregation of matter in which quantum effects manifest themselves at the macrolevel. Mysterious ghost particles have been recorded that are pushed out of the condensate and whose behavior is inexplicable in the framework of modern ideas. This was announced in a press release on Phys.org.
To observe the elusive "runaway" particles, the researchers created a Bose condensate consisting of polaritons - quasiparticles that arise when photons interact with the excitation quanta of the medium (phonons, excitons, plasmons, and others). The condensate was emitting light that was blocked by the edge of the blade, similar to how the Moon obscures the Sun during a solar eclipse. This allowed scientists to detect previously invisible particles that were "expelled" from the condensate due to quantum fluctuations.
The properties of exciton-polariton condensates, which are a nonequilibrium quantum liquid, can vary from more material to "light-like". In the first case, they behaved as the theory describes for condensates under thermal equilibrium conditions. However, the behavior of "light-like" condensates did not fit into any of the modern theories.
The Bose-Einstein condensate is a phase state of matter formed by bosons - particles that can be in the same quantum state (roughly speaking, they cannot be fundamentally distinguished from one another even by their position in space). This distinguishes bosons from fermions (eg electrons), which are subject to the Pauli exclusion principle. Bose condensates can behave like liquids whose quantum properties (such as superfluidity) are visible to the naked eye.