# Why aren't all quantum systems superfluids

Simply I was just wandering why aren't all quantum systems (F-D and BE condensates) superfluids at low temp like He 3 and 4?

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Out of curiosity, could you expand on why you might think they should be in your question? Also, are you really referring to ALL quantum systems or just FD/BE condensates? Strictly speaking as far as we know everything in the universe can be regarded as a quantum system... – joshphysics Feb 25 at 23:22
well why aren't all Bose-Einstein condensates super-fluids at low types, i.e why is it only He 3 and 4, not say argon for example that become super fluids at low temps? – user21119 Feb 25 at 23:28

Fermi-Dirac and Bose-Einstein condensates do indeed share many of the striking features of superfluids like liquid helium, though as wikipedia will tell you the concepts overlap but are not identical.

My favourite superfluid aspect of atom clouds is the formation of quantized vortices when they are spun: the angular momentum will go into creating many $L=\hbar$ vortices instead of the whole thing rotating together.

Isn't that just fantastic? (note also that it took until 2006 to visualize quantized vortices in helium.)

Other features make less sense. Rollin film creeping, for example, makes little sense for a typical cloud of cold atoms, as it's trapped by light and there is no container to get out of. Filtering through porous materials would destroy a cloud condensate by heating alone.

Seen from the other side, why is only helium superfluid when cooled sufficiently? There I'm less sure, but all (most?) other materials will solidify before that; I understand that helium will not freeze at low pressures as the zero-point energy of the lattice would be enough to melt it. (Wikipedia confirms this.)

Other than that, it depends on exactly what you mean by your question.

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