Dilute Alkali BEC Critical Velocity Bound: A Theoretical Perspective

Michael Crescimanno, R. L. Walsworth

Seok Jin Choi, N. P. Bigelow

There exists a large body of experimental and theoretical work carried out on Bose–Einstein condensates (BECs) of dilute alkali atoms since their first creation some ten years ago. Much of this work, although not stated explicitly, involves exciting initial steps for the quantum control of coherent matter waves. In this paper, we shall discuss some examples of the experimental and theoretical work on BECs from the perspective of quantum control.

Chao Feng

This thesis examines the manifestation of the critical velocity for superfluidity in dilute gas Bose-Einstein condensates (BECs). Superfluidity is a macroscopic quantum phenomenon characterised by unique properties such as frictionless flow, high thermal conductivity and the presence of quantised vortices. Our study focuses on what is arguably the most well-known attribute: the ability for an object to move through a superfluid without experiencing a drag force when travelling below a threshold critical velocity.The Landau criterion for superfluidity predicts the critical velocity in a BEC is equal to the speed of sound, and this conclusion is supported by a large body of theoretical work. However, a number of experiments have observed lower critical velocities than theory predicts. In the first part of this thesis, we numerically model experiments on the superfluid critical velocity of an elongated, harmonically trapped Bose-Einstein condensate as reported by [P. Engels and C. Atherton, Phys. Rev. Lett. 99, 160405 (2007)]. These experiments swept a repulsive obstacle, formed by a optical dipole potential, through the long axis of a condensate at constant velocity. Their results found an increase in the resulting density fluctuations of the condensate above an obstacle velocity of v _ 0:3 mm s

Jonas Siegl, Wolf Weimer, Kai Morgener +3 more

Jelena Stajic

Quantum Fluids In recent years, quantum fluids have been studied largely in gaseous form, such as the Bose-Einstein condensates (BECs) of alkali atoms and related species. Quantum liquids, other than liquid helium, have been comparatively more difficult to come by. Cabrera et al. combined two BECs and manipulated the atomic interactions to create droplets of a quantum liquid (see the Perspective by Ferrier-Barbut and Pfau). Because the interactions were not directional, the droplets had a roughly round shape. The simplicity of this dilute system makes it amenable to theoretical modeling, enabling a better understanding of quantum fluids. Science , this issue p. [301][1]; see also p. [274][2] [1]: /lookup/doi/10.1126/science.aao5686 [2]: /lookup/doi/10.1126/science.aar3785

Mark Edwards