We have completed and published the two major separate work packages.
1. ``Anisotropic Expansion of a Thermal Dipolar Bose Gas'', Physical Review Letters 117, 155301 (2016); ``Anisotropic collisions of dipolar Bose-Einstein condensates in the universal regime'', New Journal of Physics 18, 113004 (2016); see also the accompanying “perspective article” by Igor Ferrier-Barbut, New J. Phys. 18, 111004 (2016) and our explanatory video at
https://youtu.be/t3Oj_-WhbBo(si apre in una nuova finestra)In the first article we develop a complete quantitative theory of the free-expansion of a dipolar gas after it is released from a trap. The theory expresses the post-expansion aspect ratio (related to the difference of apparent temperatures along different directions, see Figure attached) in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. These results extend the utility of expansion imaging by providing accurate thermometry for dipolar Bose gases. Furthermore, this provides a simple and efficient method to determine scattering lengths in dipolar Bose gases, including near a Fano-Feshbach resonance, through the observation of thermal gas expansion. In the second paper we demonstrated and further develop the simulation capabilities of the dipolar-direct-simulation-Monte-Carlo method. We have performed large-scale numerical simulations of a collision between two Bose-condensed clouds with strong dipolar interactions and compared the results to experimental data from the group of Benjamin Lev at Stanford University. We describe a novel regime of quantum scattering, relevant to dipolar interactions, in which a large number of angular momentum states become coupled during the collision. The comparison between theory and experiment was excellent and contributes strongly to the foundations of understanding in strongly dipolar gases.
2. ``Two- and three-body problem with Floquet-driven zero-range interactions'', Physical Review A 95, 062705 (2017).
Here we have studied few-body physics with temporally manipulated interactions, in particular, sinusoidally driven. A complete theory of this scenario is developed. The main results include the discovery of a family of curves in the drive-parameter space wherein the effective scattering amplitude is resonantly enhanced, thereby creating a strongly interacting system. The resonance width along these curves changes from narrow to wide, thereby providing a novel and new experimental tool for tuning resonance width in Bose gases. In addition, the inelastic scattering on these resonance curves vanishes, thereby eliminating heating. We have also considered the three-body problem of two heavy particles and one light particle. We have shown that the Floquet driving can be used to tune the three-body and inelasticity parameters.
