Torquing the Condensate: Angular Momentum Transport in Bose-Einstein Condensates by Solitonic "Corkscrew"

TL;DR

This paper theoretically investigates how angular momentum is transferred in Bose-Einstein condensates through a solitonic corkscrew interface, revealing a novel, vortex-independent mechanism of angular momentum exchange.

Contribution

It introduces a new mechanism involving a solitonic corkscrew that facilitates angular momentum transfer in BECs without vortex motion, expanding understanding of quantum fluid dynamics.

Findings

Rapid angular momentum transfer proportional to initial density

Transfer occurs without vortex advection or drift

Solitonic corkscrew exerts torque to transfer angular momentum

Abstract

When rotating classical fluid drops merge together, angular momentum can be advected from one to another due to the viscous shear flow at the drop interface. It remains elusive what the corresponding mechanism is in inviscid quantum fluids such as Bose-Einstein condensates (BECs). Here we report our theoretical study of an initially static BEC merging with a rotating BEC in three-dimensional space along the rotational axis. We show that a soliton sheet resembling a "corkscrew" spontaneously emerges at the interface. Rapid angular momentum transfer at a constant rate universally proportional to the initial angular momentum density is observed. Strikingly, this transfer does not necessarily involve fluid advection or drifting of the quantized vortices. We reveal that the solitonic corkscrew can exert a torque that directly creates angular momentum in the static BEC and annihilates angular momentum in the rotating BEC. Uncovering this intriguing angular momentum transport mechanism may benefit our understanding of various coherent matter-wave systems, spanning from atomtronics on chips to dark matter BECs at cosmic scales.