Bose–Einstein condensate

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for matter to reatch the state of Bose–Einstein condensate i hase to be cooled to the the absoulute zero witch means 0 kalvin and 0 gravity t' ill all the particalles are in a virtuale stop, i am wondring can you reach that state by aplaying presure to it t ill the point that the particules have no space to move and stop and reach the state of Bose–Einstein condensate in riverse , without the need to cool it?
 

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  • #2
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i know it s not necessarie but you have to be very close , that' s not the essue here , the thing is when partucales slow down there presure drop and there tempature drop , i m saying maybe you can reach that state with applaying enought pressure that the particules have no where to move t ill eventially they vertually stop and reach Bose–Einstein condensate state in reverse?
 
  • #3
SpectraCat
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for matter to reatch the state of Bose–Einstein condensate i hase to be cooled to the the absoulute zero witch means 0 kalvin and 0 gravity t' ill all the particalles are in a virtuale stop, i am wondring can you reach that state by aplaying presure to it t ill the point that the particules have no space to move and stop and reach the state of Bose–Einstein condensate in riverse , without the need to cool it?
No .. in order for a BEC to be realized, the interparticle interactions have to be weak .. if you localize the particles by application of a large external pressure, you will necessarily induce very large interparticle interactions. So what you get will be a dense solid, rather than a BEC.
 
  • #4
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interesting . than it means ther is a limit of force that you can apply to any thing and the last transformation af any mater is a very heavy solid no matter what force you apply to it ? thank for the reply
 
  • #5
Cthugha
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No .. in order for a BEC to be realized, the interparticle interactions have to be weak .. if you localize the particles by application of a large external pressure, you will necessarily induce very large interparticle interactions.
Well, the meaning of "large" is somewhat unclear here. If you consider He4 in the superfluid state, the particle interactions are quite high and nevertheless you can have a rather large condensed fraction.

Apart from that I am a bit puzzled by this answer because creating local strain traps by applying pressure is one of the standard ways when trying to create quasiparticle BECs. This has been used e.g. for polaritons in "Bose-Einstein Condensation of Microcavity Polaritons in a Trap" by Balili et al. (Science 316, pp. 1007-1010 (2007) and is also quite a common strategy when trying to find a condensate of the yellow exciton in cuprous oxide (which is, however, extremely difficult to achieve). Applying some pressure to get a localized trap is completely ok, but is usually only sensible for particles or quasiparticles in solid state surroundings. For atomic gases it is more sensible to create local potentials in terms of laser traps or something like that.
 
  • #6
SpectraCat
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Well, the meaning of "large" is somewhat unclear here. If you consider He4 in the superfluid state, the particle interactions are quite high and nevertheless you can have a rather large condensed fraction.
Well, large means "large enough to disrupt the coherent nature of the condensate". As I understand it, the reason that not more than 10% of bulk superfluid helium is in the BEC state at temperatures arbitrarily close to 0K, is that the density of the material is so large that there is a significant probability that He atoms will undergo "strong" interactions that multiple Bose-Einstein condensed states will be populated, rather than just the ground state as in a pure BEC. I also recall that extrapolation to zero density shows that the BEC fraction increases to unity, which would seem to support the interpretation given above (which I believe is the standard one, but it has been al ong time since I studied this stuff.)

Apart from that I am a bit puzzled by this answer because creating local strain traps by applying pressure is one of the standard ways when trying to create quasiparticle BECs. This has been used e.g. for polaritons in "Bose-Einstein Condensation of Microcavity Polaritons in a Trap" by Balili et al. (Science 316, pp. 1007-1010 (2007) and is also quite a common strategy when trying to find a condensate of the yellow exciton in cuprous oxide (which is, however, extremely difficult to achieve). Applying some pressure to get a localized trap is completely ok, but is usually only sensible for particles or quasiparticles in solid state surroundings. For atomic gases it is more sensible to create local potentials in terms of laser traps or something like that.
Well, the reason my answer did not consider such quasiparticle BEC's is simply because I was unaware of their existence .. thanks for the citations .. I am interested to read those papers. However, I believe the statements I made are correct for experiments with real massive particles like atoms.
 
  • #7
Cthugha
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Well, large means "large enough to disrupt the coherent nature of the condensate". As I understand it, the reason that not more than 10% of bulk superfluid helium is in the BEC state at temperatures arbitrarily close to 0K, is that the density of the material is so large that there is a significant probability that He atoms will undergo "strong" interactions that multiple Bose-Einstein condensed states will be populated, rather than just the ground state as in a pure BEC. I also recall that extrapolation to zero density shows that the BEC fraction increases to unity, which would seem to support the interpretation given above (which I believe is the standard one, but it has been a long time since I studied this stuff.)
Ah, I see the point. Indeed the condensate fraction will only be on the order of 10% for superfluids. However, in some respect the term "condensate fraction" is somewhat ill chosen because it does not really measure anything like that, but just the ground state occupancy and both the condensate fraction and the population of the excitation spectrum give the superfluid fraction which is the fraction not in the "normal" state. However, whether one should call just the ground state population condensed or the whole non-normal fraction seems more like a matter of taste. To what degree the coherent nature of the condensate is disrupted by having the excitation spectrum populated is also not easy to define. The transport associated with a superfluid is usually coherent, but there may be fluctuations between the ground state and the excitation spectrum which may cause the ground state intensity correlation functions to show deviations from unity. It is all a matter of definition, I suppose.

There was also some discussion about that difference in some earlier thread in these forums:https://www.physicsforums.com/showpost.php?p=3049361&postcount=10"
 
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  • #8
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for matter to reatch the state of Bose–Einstein condensate i hase to be cooled to the the absoulute zero witch means 0 kalvin and 0 gravity t' ill all the particalles are in a virtuale stop, i am wondring can you reach that state by aplaying presure to it t ill the point that the particules have no space to move and stop and reach the state of Bose–Einstein condensate in riverse , without the need to cool it?

BEC is a matter with very high density and very low temperature. so i dont think it is possible to reach BEC without the need to cool it.
 
  • #9
SpectraCat
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BEC is a matter with very high density and very low temperature. so i dont think it is possible to reach BEC without the need to cool it.
Actually, BEC's have very low densities compared to normal condensed matter. This is because in order to get Bose condensation, the interactions between the particles have to be fairly weak, certainly they must be weaker than the interparticle interactions responsible for normal condensation.

As for cooling .. that is correct .. since they are at very low temperature by definition, you must do considerable work to cool the atoms to the point where a BEC can be formed.
 
  • #10
M@2
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BEC is a matter with very high density and very low temperature. so i dont think it is possible to reach BEC without the need to cool it.
The solid, for example crystal lattice, is much more condensate, than BEC, but it remains solid at a rather high temperature.
 
  • #11
M@2
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for matter to reatch the state of Bose–Einstein condensate i hase to be cooled to the the absoulute zero witch means 0 kalvin and 0 gravity t' ill all the particalles are in a virtuale stop, i am wondring can you reach that state by aplaying presure to it t ill the point that the particules have no space to move and stop and reach the state of Bose–Einstein condensate in riverse , without the need to cool it?
Yes. See at solid He4. It is crystalline at pressure >25atm.

And solid He4 can be made supersolid.
:)
 
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  • #12
M@2
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I think, in future we shall discover many interesting things in BEC, unknown now. Let me quote Nobel Prize winner in 2003 Leggett for research of quantum liduids:
Book: Leggett_Quantum Liquids_ Bose Condensation and Cooper Pairing in Condensed-Matter Systems(2006).pdf (page 46)
To conclude this section, let us inquire whether we can say anything rigorous about
the occurrence or not of (simple) BEC in an extended system in thermodynamic
equilibrium, or failing that at least about the condensate fraction as a function of
the system parameters (density n, temperature T, . . .). Actually, results in this area
are rather few. More than 40 years ago, Gavoret and Nozi`eres (1964) showed in a
classic paper that BEC persists in an interacting gas in three-dimensional free space
at T = 0 provided that perturbation theory in the interaction converges (a premise
which excludes solid 4He as a counterexample); however, this method cannot be used to
set a nontrivial limit on the transition temperature Tc, nor on the condensate fraction
at T = 0. More recently Kennedy et al. (1988) proved the existence, at T = 0, of BEC
in a “lattice gas” at half filling without relying on perturbation theory. However, the
existence of BEC has not been proven even at T = 0, to my knowledge, for any other
extended system with short-range interactions.
Let me stress the words: "Actually, results in this area are rather few"... "the existence of BEC has not been proven even at T = 0, to my knowledge, for any other extended system with short-range interactions".
 

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