I Maximum practical size of a BEC

[Davephaelon]

It's technically very difficult to create BEC's of atoms, using lasers to cool the atoms to near absolute zero, in a vacuum chamber, and it was only first accomplished in 1995, despite being predicted many decades before that. The atom, or molecule, BEC's so far created are, from what I've read, just big enough to be seen by the naked eye, with a little optical magnification. I didn't actually check what the maximum width achieved so far with BEC's, but is there any practical limit to how large an atom, or molecule, BEC could be? If technology wasn't an issue could it be an inch across, a foot, or even 100 feet? I do understand that a BEC entails overlapping de Broglie waves of the individual Bosonic entities. So presumably if one could attain matter wavelengths of the individual bosons of say a foot, that BEC's multiple feet across might be possible.

 

[Davephaelon]

I should have said maximum "theoretical" size of a BEC in my post title, as current technological limitations probably restrict atom BEC's to a few thousand individual atoms.

 

[PeterDonis]

I do understand that a BEC entails overlapping de Broglie waves of the individual Bosonic entities

That's not really a good description. A better description is that a BEC entails multiple bosons being in the same state: because of the way Bose-Einstein statistics work, the presence of bosons in a particular state makes it more likely for other bosons to be in the same state (whereas with fermions, no two fermions can be in the same state). The potential size of a BEC is limited only by the "size" of the state that all the bosons are to occupy; doing it with atoms as the bosons probably does restrict the potential size because of limits to how much the quantum states of atoms can "spread out".

 

[Mentz114]

I should have said maximum "theoretical" size of a BEC in my post title, as current technological limitations probably restrict atom BEC's to a few thousand individual atoms.

It's a fascinating subject. Here are links to two PhD theses which give gruesome detail of the engineering challenges. I think the numbers are around 2 to 3 million atoms/ions now.

https://www2.physics.ox.ac.uk/sites/default/files/2013-01-19/giuseppe_pdf_75967.pdf
http://jilawww.colorado.edu/bec/CornellGroup/theses/ensher_thesis.pdf

 

[Davephaelon]

Thanks for the responses, and links. In the meantime, I found this very nice slideshow that encapsulates the astonishing achievement of creating a BEC by the Cornell/Wieman group in 1995. An earlier version of their containment system is at the Smithsonian Institution, definitely a must-see whenever I visit that museum.

http://www.colorado.edu/physics/EducationIssues/ModernPhysics/Lecture_Notes/CSMSP11_Lecture27_BEC(asgiven).pdf

 

[DrClaude]

I do understand that a BEC entails overlapping de Broglie waves of the individual Bosonic entities. So presumably if one could attain matter wavelengths of the individual bosons of say a foot, that BEC's multiple feet across might be possible.

The de Broglie wavelength of the individual bosons does not extend over the entire condensate. What is important for condensation is for the de Broglie wavelength to be commensurate with the inter-particle distance.