Capture velocity

[Louis]

Hi!

Has someone tried to contrast the capture velocity simulation with actual results? 

Best,

L.

[Louis]

I would like to update my comment on this branch: I tried the capture velocity code and it does not work as I think it is supposed to do: capture velocity is reduced as B' increases. In theory the capture velocity should increase initially with B' and eventually decrease. Has someone else seen this and solved it? I'm on it, not successful yet.

Best,

L.

[Barker, Daniel S. (Fed)]

Hi L.,

 

How the capture velocity changes with magnetic field depends on both the functional form of the field and on the laser beam geometry. So, the answer to this question depends on what you’re simulating. For a Zeeman slower, the capture velocity increases with “entrance” magnetic field, but this is not the case for a MOT.

 

According to this much under-cited result from Haubrich et al. (https://www.sciencedirect.com/science/article/pii/003040189390387K), the capture velocity (for a MOT) should decrease as the magnetic field gradient is increased (roughly as dB^-2/3). The observation of decreasing atom number with gradient actually predates the theoretical work (e.g. https://journals.aps.org/pra/pdf/10.1103/PhysRevA.46.4082).

 

I think the most detailed studies of capture velocity have used 2D MOTs to load 3D MOTs, since the push beam gives a lot of control on the velocity of the atomic beam. For example: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.80.013409 or https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.13.014013. Thus far, I don’t know of quantitative experiment/theory comparisons of capture velocities using pylcp. We have published two papers with simulations of capture/escape dynamics (https://iopscience.iop.org/article/10.1088/1681-7575/aadbe4/meta, https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.11.064023 [this one compares with experiment, but there’s a fit parameter]), but they both used prerelease versions of the package that eventually became pylcp (and may not be simulating exactly what you’re looking for in any case).

 

Let us know if you have any more questions!

 

Daniel

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[Louis]

Dear Daniel,

Thank you very much for all your help! After going through the literature I checked my code and I found the problem. Now the results make sense.

Best, 

L.