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26 Apr 2018: Spin-orbit coupling induced quantum droplet in ultracold Bose-Fermi mixtures

For Thursday 26 April 2018 we will discuss:

  • X. Cui: Spin-orbit coupling induced quantum droplet in ultracold Bose-Fermi mixtures [arXiv:1804.04552]

    Quantum droplets have intrigued much attention recently in view of their successful observations in the ultracold homonuclear atoms. In this work, we demonstrate a new mechanism for the formation of quantum droplet in heteronuclear atomic systems, i.e., by applying the synthetic spin-orbit coupling(SOC). Take the Bose-Fermi mixture for example, we show that by imposing a Rashba SOC between the spin states of fermions, the greatly suppressed Fermi pressure can enable the formation of Bose-Fermi droplets even for very weak boson-fermion attractions, which are insufficient to bound a droplet if without SOC. In such SOC-induced quantum droplets, the boson/fermion density ratio universally depends on the SOC strength, and they occur in the mean-field collapsing regime but with a negative fluctuation energy, distinct from the interaction-induced droplets found in literature. The accessibility of these Bose-Fermi droplets in ultracold Cs-Li and Rb-K mixtures is also discussed. Our results shed light on the droplet formation in a vast class of heteronuclear atomic systems through the manipulation of single-particle physics.

19 Apr 2018: Anisotropic Critical Velocity of a Dipolar Superfluid

For Thursday 19 April 2018 we will discuss:

  • M. Wenzel et al: Anisotropic Critical Velocity of a Dipolar Superfluid [arXiv:1804.04552]

    We present transport measurements on a dipolar superfluid using a Bose-Einstein condensate of 162^Dy with strong magnetic dipole-dipole interactions. By moving an attractive laser beam through the condensate we observe an anisotropic critical velocity for the breakdown of dissipationless flow, which, in the spirit of the Landau criterion, can directly be connected to the anisotropy of the underlying dipolar excitation spectrum. In addition, the heating rate above this critical velocity reflects the same anisotropy. Our observations are in excellent agreement with simulations based on the Gross-Pitaevskii equation and highlight the effect of dipolar interactions on macroscopic transport properties, rendering dissipation anisotropic.

5 Apr 2018: Shockwaves in the UFG

For Thursday 5 April 2018 we will discuss the following article:

TALuS 3/22/2018

Welcome back from spring break!  We’ll be meeting again at the regular time and place to discuss astronomy and gravitational physics.