Quantum fluids

A quantum fluid is a fluid where the mean distance between the particles is less than or comparable to the thermal de Broglie wavelength

$\Lambda =h/{\sqrt {(2\pi mkT)}}$,

where

$\,h$ is Planck's constant

$\,m$ is the mass of the particles of the fluid

$\,k$ is the Boltzmann constant and

$\,T$ is the absolute temperature.

In such a case there is a strong overlap of wave functions of adjacent particles and hence quantum statistics (Bose-Einstein or Fermi-Dirac) is applicable. This often results in unusual observable macroscopic phenomena, such as superfluidity, superconductivity and other 'super' transport phenomena.

Reference

• The extraordinary phases of liquid $^{3}$He. Nobel lecture by D.M.Lee.