Ultra-cold dipolar gases: quantum droplets, non-equilibrium lattice dynamics, and spin transport

Seminar

Speaker: Luis Santos
When: Feb. 18 2016 16:00
Where: Erwin-Schödinger-Saal, IQOQI

I will focus in this talk on three different scenarios in which the physics of dipolar gases differ significantly from that expected for non-dipolar counterparts. The first scenario [1] relates to recent surprising experiments in Stuttgart, in which destabilized dysprosium condensates do not collapse but rather form stable droplets due to an unknown stabilization mechanism. We show that this stabilization mechanism is provided by quantum fluctuations, which result in an effective repulsion at large densities. Quantum stabilization, which nicely accounts for the experimental results, is directly linked to the dipolar character of the dysprosium condensate, and hence should be relevant for all future experiments with strongly dipolar gases. In the second part I will focus on the non-equilibrium dynamics of isolated polar lattice gases [2], which is characterized by the formation of dynamically-bound on-site and inter-site clusters of two or more particles, and by an effective blockade repulsion. These effects combined with the controlled preparation of initial states available in cold gases experiments can be employed to create interesting out-of-equilibrium states. These include quasi-equilibrated effectively repulsive 1D gases for attractive dipolar interactions and dynamically-bound crystals. Furthermore, non-equilibrium polar lattice gases can offer a promising scenario for the study of quasi-many-body localization in the absence of quenched disorder. Finally, I will discuss dipole-induced spin transport [3], an issue of special relevance for frozen polar molecules in optical lattices, where spin may be encoded in rotational states. An imperfect lattice filling leads to a disorder spin transport in which lattice filling plays the role of the disorder strength. We study the transport properties for 1D, 2D and 3D systems by means of a combination of spectral and multi-fractal analysis. Whereas 1D spin excitations are always localized, 2D excitations present an effective localization-to-delocalization crossover for finite lattices around half-filling. Interestingly, 3D spin excitations are characterized by a transition between non-ergodic and ergodic delocalized eigenstates. [1] F. Wächtler and L. Santos, arXiv:1601.04501. [2] L. Barbiero, C. Menotti, A. Recati, and L. Santos, Phys. Rev. B 92, 180406(R) (2005). [3] X. Deng, B. Altshuler, G. V. Shlyapnikov, and L. Santos, in preparation.

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