Following our recent experimental observation of vortices in Bose-Einstein condensates comprised of atoms with inherent long-range dipole-dipole interactions [Nat. Phys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the three-dimensional dominantly dipolar regime, where beyond-mean-field effects are crucial for stability, and investigate the interplay between trap geometry and magnetic field tilt angle. Last year, Jean Dalibard was awarded with the most prestigious French prize for physicists, the CNRS Gold medal, and this work is our contribution to a Special Issue honouring his many contributions to the field of ultracold atoms, and in particular his work on quantum vortices. See the full collection here: CNRS Gold Medal Jean Dalibard (academie-sciences.fr).

See the pre-print here: arXiv:2303.13263

# Theory Scientific News

Category for scientific news related to the theory group.

## Anti-dipolar supersolids are anti-boring!

By rapidly rotating the dipole moment in an ultracold Bose gas it is possible to tune the dipole-dipole interaction. Rotating dipoles around the origin of the x-y plane, for example, gives a time averaged interaction that is equivalent to *anti-dipoles* oriented along the z axis! This means that the effective interaction is opposite: head-to-tail anti-dipoles repel, and side-by-side anti-dipoles attract! In an infinite tube of anti-dipoles, this means that the possible supersolid states have cylindrical symmetry around the x-y axis, which we utilize to facilitate analytic predictions, and faster numerical simulations, of two-component antidipolar supersolids!

See the pre-print here: arXiv:2301.08007

## Review of recent experiments with dipolar gases

The last 15 years has seen tremendous experimental progress for the manipulation and control of ultracold atoms with sizeable dipole-dipole interactions. In this review, together with other group leaders who first condensed dysprosium and chromium, we review the discoveries made so far, and lay out the future perspectives for this exciting field!

The paper can be found here: Dipolar physics: a review of experiments with magnetic quantum gases – IOPscience

## Double the supersolid, double the fun?

Here in Innsbruck, and in Stuttgart and Pisa, clouds of ultracold dipolar atoms have recently been observed in the long-sought after supersolid state, in which there exists global phase coherence and crystalline density structure in the superfluid. Two-component dipolar gases are also now experimentally producible, with our erbium and dysprosium mixtures, however the fate of the supersolid state remains largely unknown.

Together with researchers from Hanover, we predict the existence of a binary supersolid state in which the two components form a series of alternating domains, producing an immiscible double supersolid. Remarkably, we find that a dipolar component can even induce supersolidity in a nondipolar component. In stark contrast to single-component supersolids, the number of crystal sites is not strictly limited by the condensate populations, and the density is hence substantially lower. Our results are applicable to a wide range of dipole moment combinations, marking an important step towards long-lived bulk-supersolidity.

See the pre-print here: arXiv:2203.11119, and the now published paper here: PhysRevA.106.053322

## Supersolids go round!

In recent years a new state of matter has appeared on the scene: the supersolid. This has both the crystal structure of a solid and the properties of a superfluid, a quantum fluid that can flow without friction. We show that an established method for forming supersolids in a one-dimensional crystal–by tuning how the particles interact with one another–fails to reach supersolidity in two dimensions. However, by developing a new theoretical technique we demonstrate that cooling a gas of magnetic atoms directly into the supersolid regime is a viable method for creating two-dimensional supersolids in round, pancake-shaped traps. This leads us to the experimental observation of the first supersolid in a round trap, and opens the door to future theoretical studies of the crystal growth.

You can find out more about this in our paper.

## New Openings 2022 for PhD and Master-Students!

It is now an exciting time to work with ultracold highly-magnetic quantum gases, thrived by the rapid developments of quantum science based on lanthanide species. We are continually searching for outstanding Master and PhD Students!