In order to determine velocity distribution of a Bose-Einstein condensate (BEC), it is common practice to release it from the trap, and after a period of free expansion its shadow is imaged onto a CCD via resonant absorption imaging. The recorded data is digitally processed to extract physical quantities such as the velocity distribution in the expanded cloud. But my question is whether there is a procedure that does not necessitate the expansion of a BEC. That is, if one wanted to obtain the kinetic energy as a function of time of a stirred BEC, is it possible to record the velocity distribution over a period of time without letting the BEC expand?
Inside a trap a BEC normally has no velocity distribution (apart from zero point motion) the expansion that is observed after release is driven by its mean field energy being converted into kinetic energy. If you are exciting your BEC in some way and want to measure the excitions in situ you could do it with a non-destructive imaging technique if you can achieve a high enough resolution. Alternatively, if your atomic species has a suitably narrow transition and you have some way to observe the signal in situ, you could observe the excitations as Doppler broadening of this spectrum. In this way we observed time-resolved sloshing of our BEC inside An optical dipole trap (see supplemental material of https://doi.org/10.1038/s41567-018-0242-5, or chapter 6, appendix B of my PhD thesis)
Hello and thanks for your answer. My BEC is excited by a spatially oscillating blue-detuned Gaussian laser beam. Indeed we are looking for a method to measure the excitations in situ. I will look into the documents you mentioned above, but where can I find your PhD thesis?
My thesis is available on RG: https://doi.org/10.13140/RG.2.2.20031.46244
What species are you using?
Thanks for sending the link. I should have mentioned that I am simulating these systems using the time-dependent Gross Pitaevskii equation. I am chiefly trying to make connections with experiments, to find methods for an experimental verification of our present results, and this is why I have asked the above question. That parameters I am using are for bosons in general as identified by an s-wave scattering length that arises in the mean-field interactions.
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