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

# Theory Scientific News

Category for scientific news related to the theory group.

## 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!

## Maintaining supersolidity from one to two dimensions

Now published in Physical Review A, we theoretically investigate the role of trap geometry plays in determining the dimensionality of dipolar droplet arrays, which range from one-dimensional to zigzag, through to two-dimensional supersolids. Supersolidity is well established in one-dimensional arrays, and may be just as favorable in two-dimensional arrays provided that one appropriately scales the atom number to the trap volume. We develop a tractable variational model—which we benchmark against full numerical simulations—and use it to study droplet crystals and their excitations. We also outline how exotic ring and stripe states may be created with experimentally feasible parameters. Our work paves the way for future studies of two-dimensional dipolar supersolids in realistic settings.

You can see the paper here: E. Poli et al., Phys. Rev. A 104, 063307 (2021) [pdf] [arXiv]