There is so much literature out there on Bose Condensates, that it is literally all about the cooling of a gas.

But I am interested in the physics of the condensate heating up - can someone explain what happens? I suspect there is a phase transition from a liquid to a gas state, but what would we see, what physical processes are going on?

Thank you!

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    $\begingroup$ The discussions typically focus on the equilibrium thermodynamic properties (and assume quasi-static changes to the parameters), so things just happen in reverse when heating instead of cooling the gas. Please clarify whether your question is instead about (fast) non-equilibrium dynamics, such as quenching the confinement. $\endgroup$ – Sebastian Riese Jan 27 at 10:58
  • $\begingroup$ You're way ahead of me, I was wanting to know what physical effects are going on. The cooling of a gas, in reverse, would suggest a Gibbs-helmholtz phase change from a liquid to vapor state? I read that cooling a gas down releases energy, what about the reverse? Is any of that wrong? $\endgroup$ – Gareth Meredith Jan 27 at 11:02
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    $\begingroup$ Since the equilibrium properties are defined by just the macroscopic parameters (depending on the ensemble, for example, the temperature and the particle number), the reverse process will give the reverse process quantities (such as heat). However, liquid and vapour state are not relevant phase distinctions for BEC. In the case of BEC of ultracold trapped atoms, a gaseous state makes a phase transition to the BEC state. (In the case of Helium 4 there are two liquid phases: a normal fluid below $4.2\,\mathrm{K}$ and a superfluid phase below $2.2\,\mathrm{K}$.) $\endgroup$ – Sebastian Riese Jan 27 at 11:18
  • $\begingroup$ Ok now this interests me... why can you not describe a Bose Einstein condensate as a phase transition? Because, I am surprised by this considering there is a distinct change from a liquid to a vapor state and requires only one parameter, a differential volume. $\endgroup$ – Gareth Meredith Jan 27 at 11:21
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    $\begingroup$ The transition to BEC is a phase transition, but a phase transition need not be a vapour/liquid transition and a BEC transition is fundamentally different from a vapour/liquid transition – if you have a question regarding phase transitions and the BEC transition as a phase transition in particular, I suggest you ask a separate question. (Note that liquid and vapour can be transformed to on another without a phase transition, by going around the critical point in the $T$ $p$ parameter space.) $\endgroup$ – Sebastian Riese Jan 27 at 11:25

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