Merging of rotating Bose condensates

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• Prof. Wei Guo, National High Magneic Field Laboratory & Florida State University, Tallahassee, United States
• Friday 18 October 2019, 14:00-15:00
• Physics East 217.

If you have a question about this talk, please contact m.chung.

It has been known that when rotating classical fluids merge together, the viscous shear flow at the interface can lead to the formation of vortical structures due to the Kelvin-Helmholtz instability. Angular momentum can be advected from one fluid body to another, accompanied by the drifting of these vortical structures. However, for invisid quantum fluids such as Bose-Einstein condensates (BECs), little is known on what flow structures may form at the interface and how the angular momentum transfer is achieved between merging rotating BECs. Here we report our recent numerical study of the merging dynamics of two rotating atomic BECs with different phase topology in both two dimensional (2D) space and three dimensional (3D) space. We observe the spontaneous emergence of spiral dark soliton lines (2D case) or helical soliton sheets (3D case) that enable the transfer of angular momentum between the condensates without even involving fluid advection or drifting of the quantized vortices. A close examination of the flow field around the solitons reveals that their sharp endpoints (2D case) or edge lines (3D case) can induce flows like vortex points or vortex lines but effectively with a fraction of a quantized circulation. The angular momentum transfer is achieved because these solitonic structures can exert a torque that directly creates angular momentum in the initially static BEC and annihilates angular momentum in the rotating BEC . Uncovering this intriguing mechanism may have a far-reaching impact due to its relevance to the dynamical evolution of various rotating coherent matter-wave systems, such as the merging of spinning neutron stars that consist of neutron-pair superfluid and the collision of revolving galactic dark matter halos that form BECs.

Relevant publications:

[1] T. Kanai, W. Guo†, and M. Tsubota, “Flows with fractional quantum circulation in Bose-Einstein condensates induced by nontopological phase defects”, Phys. Rev. A 97 , 013612 (2018). [2] T. Kanai, W. Guo†, and M. Tsubota, “Merging of rotating Bose-Einstein condensates”, J. Low Temp. Phys., 195, 37-50 (2019). [3] T. Kanai, W. Guo†, M. Tsubota, and D. Jin, “Angular Momentum Transport in Bose-Einstein Condensates by Solitonic Corkscrew, submitted to Phys. Rev. (2019), arxiv:1909.08086.

This talk is part of the Condensed Matter Physics Seminars series.

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