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!

# Theory Scientific News

Category for scientific news related to the theory group.

## 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]

## Review article now published in Nature Physics!

Our review on the quantum many-body physics in ultracold magnetic lanthanides is now published in Nature Physics!

Take a look here: Developments in atomic control using ultracold magnetic lanthanides

## Two-dimensional supersolidity in a circular trap

Dipolar condensates were recently coaxed into supersolid phases supporting both superfluid and crystal excitations. The first dipolar supersolids consisted of one dimensional droplet arrays, and a recent experiment here achieved two dimensional supersolidity, observing the transition from a linear chain to a zig-zag configuration of droplets.

In this work, in collaboration with Prof. Luis Santos from the Leibniz University Hannover, we show that while one-dimensional supersolids may be prepared from condensates via a roton instability, such a procedure in two dimensions tends to destabilise the supersolid. By evaporatively cooling directly into the supersolid phase–hence bypassing the roton instability–we experimentally produce a 2D supersolid in a near-circular trap, an observation verified through state-of-the-art finite temperature simulations. We show that 2D roton modes have little in common with the supersolid configuration, instead, unstable rotons produce a small number of central droplets, which triggers a nonlinear process of crystal growth. We calculate excitations for a 2D supersolid ground state, and make comparisons with 1D arrays using the static structure factor. These results provide insight into the process of supersolid formation in 2D, and define a realistic path to the formation of large two-dimensional supersolid arrays.

This work is on the arXiv, and a PDF can be found here.

## Phase coherence in out-of-equilibrium supersolid states of ultracold dipolar atoms

Supersolids are fluid and solid at the same time. In jointly collaboration work, together with Thierry Giamarchi, theoretical physicist from the University of Geneva, we have for the first time investigated what happens when such a state is brought out of balance.

## Supersolidity in an elongated dipolar condensate

**Now in Physical Review Research!**

Lauriane and Francesca, together with Blair Blakie and Danny Bailly (Otago University), theoretically studied the supersolid phase diagram of dipolar quantum Bose gases in cylindrical geometries. The work is now published in Physical Review Research.