[′lən·dən ‚sü·pər‚flü′id·əd·ē ‚thē·ə·rē] (cryogenics) A theory, based on the fact that helium-4 obeys Bose-Einstein statistics, in which helium-4 is treated as an ideal Bose-Einstein gas, and its superfluid component is equated with the finite fraction of the atoms of such a gas which are in the ground state at very low temperatures.