What is the role of extreme cold in achieving Bose-Einstein Condensation?

In summary, the lack of heat in a BEC causes the atoms to fall to the lowest possible state, which is the ground state. The critical speed, Vc, is determined by the properties of the superfluid. If the kinetic energy of the particles in the superfluid is over Vc^2/2, they will feel the influence of other particles and become excited, leading to the breakdown of the superfluid state.
  • #1
PRodQuanta
342
0
I grasp the idea. The only thing I don't get, is why do the atoms have to be frozen? How does the lack of heat effect the state of which the atoms are in? And once the state of superfluidity is achieved, why must the liquid not have a viscosity?
Paden Roder
wanderingand asking aimlessly to gain knowledge.
 
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  • #2
Well, generally heat is a type of energy. The less energy available to something, the less it moves, and so the more it tends to fall to the lowest state possible due to the 1st law of thermodynamics. If the object was hotter than the surrounding environment, it has a tendency to radiate away the heat, and hence lose energy, thereby going to the lowest state it can.
 
  • #3
Thermal excitation gives some of the atoms enough energy to be in states above the ground state.

In addition, the term "frozen" refers to the solid state of matter. Superfluids like liquid He-4 are not frozen; they are just very cold.

- Warren
 
  • #4
A BEC can not have viscosity because most of the atoms are in the absolute groundstate. Therefore they can not loose energy anymore, and as you know viscosity arises because of friction/dissipation. Something that can't loose energy can't dissipate.
 
  • #5
superfluid with finite speed

As we all know,material in superfluid phase has a critical speed,Vc,under which superfluid can be achieved.Particles constituting the material are all in groundstate.They are almost independent without any effect on others.But if their kinetic energy is over m*Vc^2/2,maybe they will feel others' influence,which is the origin of viscosity.
 
  • #6
^ when an object in a superfluid exceeds the Vc (which, I think, is determined by the properties of the superfluid), the phonon generated by its movement has sufficient energy to excite the particles in the superfluid into various non-ground states. So, the superfluid state breaks down.
 
  • #7
And if that doesn't blow your mind's fuses, light slows down to car speeds as it passes through one of those miniature black holes or whatever they call them.
 
  • #8
Originally posted by jammieg
And if that doesn't blow your mind's fuses, light slows down to car speeds as it passes through one of those miniature black holes or whatever they call them.

They are not miniature black holes. The reason they can appearently slow light down is that the laser imparts its properties onto the chilled atoms and those atoms can be coaxed into releasing photons identical in wavelength and energy by using another laser as a primer to change the spin conditions of the atoms.
 
  • #9
To 30mph? Seems a bit much to assume "black holes" I admit perhaps I should have said it is something that can do almost what a black hole does in one respect.
 
  • #10
Originally posted by jammieg
To 30mph? Seems a bit much to assume "black holes" I admit perhaps I should have said it is something that can do almost what a black hole does in one respect.

You misunderstand. The propagation of the signal representing light inside the BEC is moving at 30 mph. I'll say it again. Light doesn't slow down! It's appearent velocity in the BEC is. But that is just the effect of having the signal that represents the photons' properties move slower...or completely stopped.
 
  • #11
I agree neutroncount that light isn't actually being slowed and I make the same mistake as others, but manipulated would be a better word and it's difficult to communicate that becuase of all the physics involved I forgot exactly how light works and so I agree that a less appropriate word was choosen and is misleading. To a layperson it wouldn't make any difference if one said slowed or compressed because it's still kind of true, as if someone compressed millions of miles of air into a tiny spot of gas it is giving the illusion of slowing light but actually it is more increasing the distance light has to travel through this process of refraction and photons absorbtions and reimmisions all adding to the illusion of lagging light but during some processes light isn't really light, but how it so dramatically increases these processes still seems mysterious to me, and no doubt Bose around 100 years ago seemed like a fool to most people at the time telling them that light could be manipulated in such ways. My point is black holes are black because they don't let much of anything go, and it seems that very high refractive indexes do to, and such high indexes are related to extremely cold atoms, but still a somewhat wild deducing on my part, and without explaining myself it's the sort of thing that contributes to the plague of overhyping.

Here are some sources I looked over:

http://news.bbc.co.uk/1/hi/sci/tech/655518.stm
http://ee.tamu.edu/Publications/Hemmer/CrystalStopsLight.pdf[/URL]
http://cua.mit.edu/ketterle_group/Introduction_to_BEC.htm
http://www.nature.com/nsu/990225/990225-5.html
[url]http://www.fenrir.com/free_stuff/columns/science/sci-119.htm[/url]
 
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What is Bose-Einstein Condensation?

Bose-Einstein Condensation is a phenomenon in which a large number of particles with integer spin, such as atoms, become confined to the same quantum state at very low temperatures. This creates a unique state of matter with properties different from those of a gas, liquid, or solid.

What is the significance of Bose-Einstein Condensation?

Bose-Einstein Condensation is significant because it allows scientists to study and observe quantum mechanical effects on a macroscopic scale. It also has potential applications in fields such as superconductivity, superfluidity, and quantum computing.

How does Bose-Einstein Condensation occur?

Bose-Einstein Condensation occurs when a gas of particles is cooled to a temperature close to absolute zero (0 Kelvin or -273.15 degrees Celsius). At this temperature, the particles' thermal energy is low enough for them to "condense" into the same quantum state, forming a Bose-Einstein Condensate.

What are the properties of a Bose-Einstein Condensate?

A Bose-Einstein Condensate has several unique properties, including superfluidity (the ability to flow without friction), coherence (all particles have the same phase and behave as a single quantum entity), and the ability to exhibit interference patterns similar to those seen in light waves.

How is Bose-Einstein Condensation related to the Bose-Einstein statistics?

Bose-Einstein Condensation is a result of the Bose-Einstein statistics, which describe the behavior of particles with integer spin. These statistics predict that at low temperatures, a large number of particles will occupy the lowest energy state, leading to the formation of a Bose-Einstein Condensate.

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