What does weird quantum mechanics actually LOOK like?

submitted by gluonium
1 decade 7 years 7 months ago
This video is a clip from "Sonda", a Polish science program broadcast in 1980's. It beautifully demonstrates what superfluid helium (a Bose-Einstein condensate) actually looks like and how it behaves on a macroscopic level. This is exceptionally rare video, I have never seen video of a superfluid anywhere else, ever. The whole thing is in Polish and I can't understand a word but I think I can explain what the video shows anyway.
It opens with a shot of a quadruple walled transparent vacuum (dewar) flask with liquid helium in the inner flask jacketed by bubbling liquid nitrogen in the outer annular flask that acts as a cold shield. The outer flask is topped up with nitrogen at :10 and the view switches back to the full LN2 jacket with LHe in the inner flask until :48. At this point you see LHe in the inner flask in the normal liquid state and you see it boiling at 1:00 as the pressure above it is reduced and it is forced to cool even lower than its normal boiling point of 4.2 kelvin. At precisely 1:07 the liquid transitions into the superfluid state at 2.17K and all boiling immediately ceases as its viscosity drops to exactly ZERO, where the liquid becomes frictionless. Conventional boiling is forbidden in superfluids because the liquid acts, in a sense, like one single huge atom. All the individual atoms of helium in the flask now occupy a single, coherent, quantum mechanical wave function. Next, a small beaker with a ceramic bottom is filled with normal liquid helium (1:30) that, like all other liquids, cannot pass through its ultrafine pores. The liquid He is brought to the superfluid state at 1:42 and can thereafter flow freely through the ceramic since pore size is irrelevant if flow is frictionless. The weirdest phenomenon of all is shown at 2:25, a Rollin film, the ability of a superfluid to flow UP and out of its own container! The Large Hadron Collider will be completely bathed in this bizzare liquid when it turns on later this year.

12 Comments

10089says...

I registered just to correct this description:

There is a difference between superfluidity and a bose einstein condensate. The effect of superfluid Helium might be descriped by the BEC theory, but its far from a "real" one in the theoretical sense. (otherwise, the creation of those wouldnt have been worth a nobel price not too long ago)

The exact explanation is a bit to long for that comment-field, but lets say that the demands for a BEC are _much_ higher than for superfluidity.

To get all atoms to occupy the lowest quantum state, such crude ways like the shown double dewar wont do it.
In fact, normally you would use a penning-trap, and do laser and evaporation cooling to get a few 100k atoms at the end with temperatures in the microkelvin range.


But superfluidity in itself is cool enough: You can also use it as near perfect cooling liquid (and you DO, for example in the LHC): Superfluid helium has _no_ thermal resitance. Heat can spread in it with the speed of sound, allowing the transportation of heat for km with only a minimal temperature rise.
Otherwise, supplying all those magnets in the LHC-Tunnels would be next to impossible.

Kruposays...

Polish guy uses Celsius instead of your fancy Kelvins, but yeah.

The end part is hilarious - he says, it's "crying" because it itself doesn't know to what use it can be put. Awesome.

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