Quantum vortices in a dipolar gas!

We report on the observation of vortices in a dysprosium quantum gas! Together with Dr. Giacomo Lamporesi from the University of Trento, we investigate one of the most fundamental phenomenon of superfluidity: quantized vorticity. We exploit the anisotropic nature of the dipole-dipole interaction to induce angular symmetry breaking in an otherwise cylindrically symmetric pancake-shaped trap. Tilting the magnetic field towards the radial plane deforms the cloud into an ellipsoid through magnetostriction, which is then set into rotation. At stirring frequencies approaching the radial trap frequency, we observe the generation of dynamically unstable surface excitations, which cause angular momentum to be pumped into the system through vortices. In the image above, if we keep the magnetic field tilted whilst rotating the vortices arrange into a stripe configuration along the field–in close corroboration with simulations–realizing a long sought-after prediction for dipolar vortices. Tilting the field back up the vortices lose this alignment, and become isotropic in shape.

Check out the pre-print here: arXiv

Determination of the scattering length of erbium atoms

Now published in PRA with collaborators from JILA, Boulder (Colorado, USA), we accurately determine the scattering length for the four bosonic erbium isotopes with highest abundance in the magnetic field range from 0G to 5G. We use the cross-dimensional thermalization technique and extract the scattering length by applying a fit of the complete Enskog equations of change and by utilizing an analytic formula for the so-called number of collisions per re-thermalization. We benchmark our results with the very accurate but experimentally more demanding lattice modulation spectroscopy, confirming the accuracy of our experimental protocol.

The paper can be accessed here: Phys. Rev. A, and the pre-print here: arXiv

Welcome to Antonio!

At the beginning of May, Antonio Ortu joined our team as Post-Doc in the T-REQS lab, after completing the Ph.D. at the University of Geneva in Switzerland under the supervision of Mikael Afzelius. Welcome to Innsbruck, Antonio!

Bloch oscillations and matter-wave localization in erbium!

In our new pre-print, we study Er atoms in a one-dimensional lattice. We use Bloch oscillations to evaluate the role played by the different interaction terms, and in particular by the quantum fluctuations. We additionally observe a transition–driven by interactions–to a state localized to a single lattice plane. To benchmark our results, we developed a discrete one-dimensional extended Gross-Pitaevskii theory. This model is in quantitative agreement with the experiment, additionally revealing, in our parameter regime, the existence of many different phases: macrodroplets occupying single or many lattice sites and two-dimensional bright solitons.

See the pre-print here: arXiv:2205.03280

Domain supersolids in binary dipolar condensates

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

Inter-species interactions in an Er-Dy condensate

We present a first study of the influence of the dipole-dipole interaction on the total inter-species interaction in our erbium-dysprosium mixture. In collaboration with M. Modugno from the University of the Basque Country, we develop a model for our heteronuclear mixture, which describes qualitatively well our system and allows us to predict a lower and an upper bound for the inter-species scattering length. With this work, we make the first steps toward the study of the experimentally unexplored miscibility-immiscibility phase diagram and the realization of quantum droplets and supersolid states in heteronuclear dipolar mixtures.

This work is now published as the editors’ suggestion in Phys. Rev. A [paper] [arXiv]