Well, I'll give you a bit to start with. If you take a bucket of liquid helium and cool it down to within a few degrees of absolute zero, it undergoes a phase transition called Bose-Einstein condensation. All the atoms hurry to enter the same quantum state, because that minimizes their total energy. So you wind up with a bucket full of atoms that have all agreed to be in the same state. What happens when you try to use it like a normal fluid?
Well, you'll notice it flows without viscosity. That's right, it flows without resistance through even the very smallest pores in your container, and through even the smallest pipettes. Why? Because all the atoms are already in their lowest energy state. Since they're all doing the same thing, though, the walls of a pipette can't smack them around too much -- you can't smack around one, you have to smack around every single last trillion of them.
Superfluids also will only permit certain values of angular momentum, e.g. 3 or 5 or 7 rotations per second. Even if you spin the bucket at 4 rotations per second from now to eternity, the helium atoms won't care. Angular momentum is quantized for their collective quantum state, and they'll only rotate at 3, 5, or 7, and never, ever at 4.
And the list goes on. You can basically consider a bucketful of liquid helium to be like one giant macroscopic quantum object.
- Warren
