Do Bose-Einstein condensates literally collapse?

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Offline Atomic-S

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Do Bose-Einstein condensates literally collapse?
« on: 18/12/2014 23:48:26 »
It was recently reported on television that if sodium is cooled to around 10-9K, its atoms assume a wave state and become delocalized.  The suggestion was that this is an oceanlike state. However, if so, does the material literally melt?  On the other hand, if it retains its shape, how do atoms that have no definite position hold into any kind of a shape?


Offline JohnDuffield

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Re: Do Bose-Einstein condensates literally collapse?
« Reply #1 on: 19/12/2014 10:58:32 »
IMHO the Bose-Einstein condensate isn't really understood. Heck, even electrons aren't really understood. They have a wave nature, and so do protons, and neutrons. We can diffract 'em. And you can arrange things such that a bunch of atoms all behave as if they're like one wave, like one particle. They don't "melt", it's more like they spread out and overlap. Only I'm not sure if that's right. And then there's the Bosenova:

"A bosenova or bose supernova is a very small, supernova-like explosion, which can be induced in a Bose–Einstein condensate (BEC) by changing the magnetic field in which the BEC is located, so that the BEC quantum wavefunction's self-interaction becomes attractive.[1] In the particular experiment when a bosenova was first detected, this procedure caused the BEC to implode and shrink beyond detection, and then suddenly explode. In this explosion, about half of the atoms in the condensate seem to have disappeared from the experiment altogether, remaining undetected either in the cold particle remnants or in the expanding gas cloud produced."

I can't explain it. But I have a hunch it could be very important.


Offline evan_au

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Re: Do Bose-Einstein condensates literally collapse?
« Reply #2 on: 19/12/2014 21:53:31 »
Quote from: Atomic-S
this is an oceanlike state
To extend this classical analogy, the surface of the ocean can be represented as a wavefunction, with sinusoidal waves.
If you crash a meteorite into the ocean, this periodic wave characteristic is disrupted.
A Bose-Einstein Condensate exposed to room temperatures is bombarded by photons and phonons and the BEC behaviour disappears. This is like bombarding every square meter of the ocean with another meteorite every second - there will be no measurable sinusoidal wave structure.

However, if so, does the material literally melt?
Sodium is a solid below 98C (just below the boiling point of water). Near absolute zero, it will remain a solid. So, no, I don't expect solid sodium to melt*.

An object like a Sodium atom has a wave nature at room temperature, but the continual bombardment from our ambient environment prevents us from detecting this effect.

However, at sufficiently low temperatures, the atoms are sufficiently isolated from these external influences that their wave nature can influence the bulk properties of the material - the wave functions can get "in sync", and it will behave like a wave in a container, which will have some wavelengths which are favoured, and others which are not favoured.

These properties are not directly useful to us at room temperature, because as soon as we warm up the BEC, the effect disappears.

* There are ways to suspend atoms so that they are separated, even at low temperature (such techniques have been attempted for quantum computers). In this case, the atoms are effectively a low-temperature gas. Because the atoms are separated in space, you would need very low temperatures before the wavefunctions could overlap to any measurable extent.