Abstract
We investigate the stability of vortices in two-dimensional Bose--Einstein condensates. In analogy with rotating spacetimes and with a careful account of boundary conditions, we show that the dynamical instability of multiply quantized vortices in trapped condensates persists in untrapped, spatially homogeneous geometries and has an ergoregion nature with some modification due to the peculiar dispersion of Bogoliubov sound. Our results open new perspectives to the physics of vortices in trapped condensates, where multiply quantized vortices can be stabilized by interference effects and singly charged vortices can become unstable in suitably designed trap potentials. We show how superradiant scattering can be observed also in the short-time dynamics of dynamically unstable systems, providing an alternative point of view on dynamical (in)stability phenomena in spatially finite systems.
Highlights
Quantized vortices are one of the key features of superfluids and Bose–Einstein condensates (BECs) and have received a great deal of attention in the last decades, both theoretically and experimentally [1,2]
Quite recently, convincing evidence that doubly quantized vortex are unstable in a spatially uniform BEC was reported [11], while dynamical stability of such configurations had been previously claimed by several authors [7,12]
An interesting way to look at this paradigmatic problem of condensed-matter physics is the one offered by analog gravity [13], which relies on the fact that collective excitation modes on top of a moving medium are described by the same equations as a massless scalar field on a curved space-time
Summary
Quantized vortices are one of the key features of superfluids and Bose–Einstein condensates (BECs) and have received a great deal of attention in the last decades, both theoretically and experimentally [1,2]. We are here interested in quantized vortices in superfluids: their purely azimuthal vθ ∝ 1/r irrotational flow pattern becomes supersonic in the vicinity of the vortex core and corresponds to an analog rotating space-time with an ergoregion but no horizon. This naturally suggests the possibility of observing ergoregion instabilities in infinite condensates. Application of our formalism to singly quantized vortices brings the unexpected consequence that their celebrated dynamical stability is not a general fact, but a consequence of the spatially homogeneous or harmonic trap geometries usually considered in the literature: more complex configurations showing an inner density bump followed by a constant density plateau turn out to be dynamically unstable against the vortex spiralling out, even at zero temperature.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
