When a classical device suddenly perturbs a degenerate Fermi gas a coherent Fermi state arises. Coherent Fermi states involve an infinite superposition of particles and holes arranged in such a manner that there are no holes in the Fermi sea but the Fermi level depends on time and space - a Fermi-surf. Fermi distribution and other features of a Fermi-surf has a universal nature. It is described by Airy functions regardless of details of a perturbation.
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