Force on a moving object in an ideal quantum gas.

The article focuses on the kinetic force exerted on a heavy impurity object moving slowly through an ideal quantum gas in the regime of a large Knudsen number, where collisions with gas particles are elastic and characterized by a constant transport cross section. It derives expressions for the drag force using Bose–Einstein and Fermi–Dirac distribution functions, showing that at high temperatures the force scales with the square root of temperature (√T), consistent with classical behavior, while at low temperatures quantum statistics cause the force to scale with the square of temperature (T²). In an ideal Bose gas, the force vanishes at absolute zero due to the formation of a condensate, whereas in an ideal Fermi gas, the force remains finite at zero temperature because fermions near the Fermi surface contribute to momentum transfer. The study provides a semiclassical framework linking thermodynamic properties of quantum gases to the drag experienced by an embedded heavy particle.