Bloch Oscillations

By letting an erbium quantum droplet fall under gravity through an optical lattice, it is possible to understand the inter-atomic interactions and quantum fluctuations through variations of the Bloch oscillation.

 

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 paper in Nature Physics here: Nat. Phys. The paper is also twinned with a nice write-up from Prof. Zoran Hadzibabic from the University of Cambridge, titled “When ultracold magnets swirl

Bloch oscillations and matter-wave localization in erbium!

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 open access paper here: Commun. Phys. 5, 227 (2022)

Heating a liquid into a… solid?!

 

Raising the temperature of a material enhances the thermal motion of particles. Such an increase in thermal energy commonly leads to the melting of a solid into a fluid and eventually vaporises the liquid into a gaseous phase of matter. Here, together with theorists from Aarhus, Denmark, we study the finite-temperature physics of dipolar quantum fluids and find surprising deviations from this general phenomenology. In particular, we describe how heating a dipolar superfluid from near-zero temperatures can induce a phase transition to a supersolid state with a broken translational symmetry. The predicted effect agrees with our experimental measurements from the Er-Dy, which opens the door for exploring the unusual thermodynamics of dipolar quantum fluids.



See the pre-print here: arXiv:2209.00335