Ergoregion instabilities and vortex stability in dilute Bose-Einstein condensates

Mikko Möttönen, Ville Pietilä, Suvi Mirjami Virtanen

Luca Giacomelli, Iacopo Carusotto

This paper shows that multiply quantized vortices in two-dimensional Bose-Einstein condensates display instabilities analogous to the ergoregion instabilities of rotating relativistic spacetimes. This implies that multiply quantized vortices are dynamically unstable in an otherwise uniform condensate.

Anna Berti, Luca Giacomelli, Iacopo Carusotto

We make use of an analog gravity perspective to obtain a physical understanding of hydrodynamic instabilities stemming from the presence of quantized vortices in two-component atomic condensates and of their relation to ergoregion instabilities of rotating massive objects in gravitation. In addition to the localized instabilities related to vortex splitting, configurations displaying dynamically unstable modes that extend well outside the vortex core are found. In this case, the superradiant scattering process involves phonon emission into the much wider ergoregion of spin modes, so the physics most closely resembles the one of rotating massive objects. Our results confirm the potential of two-component condensates as analog models of rotating space-times in different regimes of gravitational interest.

J.-P. Martikainen, Anna Sanpera, Kalle‐Antti Suominen

Luca Giacomelli, Iacopo Carusotto

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.