Can Helium 3 & 4 really be frozen?

Sep 2019
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Azores
Yep. The only thing I can think of is orbital electron photoabsorption and reemission, which is fully reversible, but if you do that, the behaviour of the state you're probing is now the excited state, which is definitely not absolute zero, even if the initial and final temperatures were both at absolute zero.
How is that if the orbital electron was in its ground state, and absorbs a photon raising to a higher energy level, before reemitting the photon. does it not return to its ground state. The total energy of the electron and photon before the absorption and after its emission must the the same. If not and a photon with the same energy is emitted where would the extra energy come from
 

topsquark

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Apr 2008
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On the dance floor, baby!
How is that if the orbital electron was in its ground state, and absorbs a photon raising to a higher energy level, before reemitting the photon. does it not return to its ground state. The total energy of the electron and photon before the absorption and after its emission must the the same. If not and a photon with the same energy is emitted where would the extra energy come from
That assumes that the electron falls back down into the ground state all in one go.

For example, a "semi-stable state" of an electron in an atom is a state that is relatively long lived. Optical pumping in lasers and in some cryogenic systems are a good example of the use of a semi-stable state.

So let's go ahead and talk about 2 excited states for the electron. Call the ground state electron GS, the first excited state FE, and second excited state SE. We are going to introduce a photon with energy SE - GS, which will promote an electron from the ground state to the SE state. This electron can now decay in one of two modes: directly back to the GS or to the FE state. If the FE state is a semi-stable state then the electon emits a photon with an energy of SE - FE. It is the SE - FE energy that is the goal in building lasers, etc.

The diagram is a bit rough. I couldn't find a good graphic for it and this idiotic version of MS Paint is even worse than the old one!

-Dan
 

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Sep 2019
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Lasers cooling is getting close to zero kelvin. Superfluids, Bose Einstein condensates have some weird properties What Does Absolute Zero Mean? | DiscoverMagazine.com

A BEC consisting of multiple particles is considered to behave as one particle. Am I correct in assuming there is only one field in a condensate not multiple interacting fields?

In QFT all things are Fields.
Once the condensate is heated it breaks up into its separate disconnected fields. BUT During the period the condensate exists, are the individual particles in the condensate considered entangled or not.
 
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Lasers cooling is getting close to zero kelvin. Superfluids, Bose Einstein condensates have some weird properties What Does Absolute Zero Mean? | DiscoverMagazine.com
Yep. You basically use a laser to pop off the particles that have the highest energy in the distribution, leaving behind only those particles with the lowest energy and cooling the system overall.

A BEC consisting of multiple particles is considered to behave as one particle. Am I correct in assuming there is only one field in a condensate not multiple interacting fields?
A Bose-Einstein Condensate is just best described by considering the whole thing as a single quantum system using a Bose-Einstein distribution. Wave functions and probability density functions (PDFs) that describe quantum systems are not fields, at least in the way we normally describe things as fields...

In QFT all things are Fields.
Once the condensate is heated it breaks up into its separate disconnected fields. BUT During the period the condensate exists, are the individual particles in the condensate considered entangled or not.
I don't know anything about QFT (I bought a textbook on it recently and I still need to work through it!), but in general the physics of a BEC requires the modeller to consider it as a single quantum system to get the best results.

Entanglement is a specific phenomenon involving two photons where they are considered to belong to the same quantum system, so it's loosely related, I guess... but I wouldn't call atoms in a BEC entangled just because they can also be described using a single quantum system.

A car can be described as a vehicle and so can a boat, but that doesn't necessarily mean that the way a car can be described can also be applied to a boat.
 
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Sep 2019
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(I bought a textbook on it recently and I still need to work through it!), but in general the physics of a BEC requires the modeller to consider it as a single quantum system to get the best results.

Entanglement is a specific phenomenon involving two photons where they are considered to belong to the same quantum system, so it's loosely related, I guess... but I wouldn't call atoms in a BEC entangled just because they can also be described using a single quantum system.
I bought quantum field theory for the gifted amateur some time ago, by Lancaster and Blundell, It is heavy going, and Ive decided I aint gifted. But I am getting there slowly.

The similarities between a BEC and entanglement have caused me to do a bit of a trawl of the internet.

Some researchers claim a BEC is a form of entanglement. Others state some of the particles are entangled in the condensate, I am not convinced either way. Here is one link https://www.iqoqi-vienna.at/news-events/events/news-detail/article/quantum-entanglement-achieved-between-the-two-clouds-of-atoms-starting-from-a-single-bose-einstein-c/

The researchers have taken a BEC separated it into the two clouds, and found the two clouds still remain entangled.

Spooky, the quantum fields must be as one on the spooky plane
 
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