Making Fermionic Condensates: Overcoming the Exclusion Principle

[p_branes]

My question is that how did people actually make a fermionic condensate? I would think this would be extremely difficult as the exclusion principle states that fermions cannot be in the same quantum state so how ebactly did people achieve this?

 

[ZapperZ]

My question is that how did people actually make a fermionic condensate? I would think this would be extremely difficult as the exclusion principle states that fermions cannot be in the same quantum state so how ebactly did people achieve this?

They can't be in the same quantum state. Remember that if you describe a free particle as plane waves, there are two quantum numbers, n and k, that describe such a system. You can have two fermions having the same n, but having k1 and -k1 quantum numbers, k2 and -k2, etc...

For Cooper pairs in conventional superconductors, this is exactly the case. Equal but opposite electrons k's for two electrons pair up forming a singlet state. So for example, you have one pair with k1 and -k1, another pair having k2 and -k2, etc... So essentially, each fermions are STILL uniquely different as far as their quantum numbers are concerned. If n1,k1 is already taken, another electron cannot scatter into that state.

The difficulty in understanding all this is that the "single-particle" statistics for fermions is still obeyed. However, when you consider a bound pair, you now have to consider the two-particle statistics, which can be very different if these particle are bosons (or composite bosons in this case).

Zz.

 

[chroot]

A fermionic condensate is actually composed of particles which can form pairs. The paired up fermions act as if they were collectively a boson, and then the bosons Bose-Einstein condense.

http://physicsweb.org/article/news/8/1/14

- Warren

 

[p_branes]

Thanks now i get it.

 

[garytse86]

i think they made fermionic condensate cos i saw it in "Focus" the other day

 

[ZapperZ]

Sometime things on here don't get followed up, or forgotten and another new string starts up asking the same thing all over again.

As a follow up to this, don't miss the new report on the further development of the saga of the Fermionic condensate. This time a pair of reports (still not out officially yet) have confirmed the occurrence of pairing in a fermionic gas upon condensation. This will be an analogous process occurring in superconductors with the formation of Cooper pairs.

http://physicsweb.org/article/news/8/7/12

The earlier report by the Deborah Jin's group only reported a condensation in a fermionic gas. They could not observe any pairing but hinted that it could happen. This new report seals the deal.

Zz.