The Invisible Sea of Quantum Particles Has Taken Shape ⚡ экспресс
The Pauli principle compels fermions to occupy distinct quantum states, forming at low temperatures a filled region in momentum space — the Fermi sea, whose topology determines the response to perturbations and the character of correlation functions. Theory predicted that for non-interacting fermions, the Euler characteristic of a D-dimensional Fermi sea (a topological invariant describing its shape) is encoded in (D+1)-point density correlations. This work demonstrates it experimentally in a two-dimensional degenerate gas of neutral ⁶Li atoms via single-atom detection. By measuring connected three- and four-point density correlations in real space, topological invariants, including the Euler characteristic, were directly extracted. The results are in striking agreement with the ideal gas model, despite significant interactions, and open a new path for probing many-body topology through correlation methods.
The law discovered by Wolfgang Pauli forbids identical particles from occupying the same spot. Hence, in cold matter, a Fermi sea is born: particles, like water, fill energy levels from bottom to top. The shape of the sea's surface — including 'islands' of emptiness — dictates the properties of the whole system. Experimenters cooled lithium atoms nearly to absolute zero and, using a microscope, tracked how they gather into triplets and quartets. The pattern of these groups, like ripples on water, revealed the topography of the dark depths.
Now this method will probe Fermi seas in liquid helium-3 and even in the unimaginable crush of neutron stars.
🎯 Without the Pauli principle, electrons in atoms would roll down to the lowest level, and all chemical elements would become indistinguishable — the world would turn into a homogeneous mixture.