Semi-classical evaporative cooling: classical and quantum distributions

Abstract

We develop a semiclassical thermodynamic framework for the evaporative cooling of trapped atomic gases that treats Maxwell--Boltzmann, Bose--Einstein, and Fermi--Dirac statistics on equal footing across box, harmonic, mixed, and linear-quadrupole potentials. Using the global thermodynamic variables of inhomogeneous confinement, we show that all geometries are unified by a single parameter $s$, which fixes the polylogarithm order, the density of states exponent, and the number of degrees of freedom $2s$. Modeling evaporation as a recursive sequence of energy truncation and rethermalization, we derive closed-form recurrence relations for the particle number and internal energy that track the full thermodynamic state, with the classical energy budget set by a virial factor $C_{\mathrm{trap}} = 1 + 3/(2s)$. Quantum degeneracy emerges not as a singularity in the global susceptibilities, but as a smooth, geometry-dependent crossover in which bosons and fermions display opposite thermodynamic signatures. The results provide a versatile theoretical tool for modeling evaporative cooling across experimentally relevant geometries and offer quantitative guidance for optimizing the cooling process in ultracold atomic systems.