Dipolar Interacting Systems: Quantum Thermalization and Turbulence – DISQuTT

We propose to use two complementary experimental ultracold-gas setups with strongly magnetic dysprosium and chromium atoms, in order to explore what general laws drive the dynamics of a long-range interacting closed quantum system. In both cases, the system will first be set out of equilibrium, and we will then study the intriguing processes that take place during its way to equilibrium under the influence of dipole-dipole interactions. Our project will thus allow studying quantum thermalization from two complementary perspectives. Firstly, our experiment on dysprosium atoms will be a continuous fluid in tailored geometries, polarized in a well-defined Zeeman state. In that case, thermalization will be studied in the wake of quantum turbulence. Secondly, our experiment with chromium realizes a lattice-spin model for which thermalization occurs through spin entanglement. Raising the question of thermalization in these two systems will allow us to reach a comprehensive understanding on how long-range interacting systems find their equilibrium, and on the role of quantum correlations in the dynamics of continuous and lattice systems.
This collaboration will particularly benefit from strong technical synergies between both experimental groups, who will achieve simultaneously similar experimental developments, building on each other’s expertise. The first goal will be to improve the production stability of dipolar quantum gases, with high-resolution imaging and stabilization of the external magnetic field. These improvements aim at overcoming important bottlenecks associated with measurement and coherent control, in order to characterize emergent quantum properties. A second series of improvements will be to implement atom manipulation based on detuned light in order to engineer the Hamiltonian and optimize various excitation protocols.
With all these knobs at disposal, we will be able to track fundamental aspects of quantum thermalization in long range-systems, in close relation to the Eigenstate Thermalisation Hypothesis. A key ingredient will be the possibility to tune the gas geometry - which is known to have a very large impact for long-range interacting dipolar systems – in order to tune both the symmetries of the system and the total energy of the initial state. Besides, we plan to use matter wave optics to improve the characterization of local structures that will arise during dynamics. We will then track the growth of quantum correlations. This will be achieved through spatial and momentum first order correlators in the Dy experiment. For the Cr experiment, our focus will be to characterize quantum correlations through entanglement witnesses, based on spin squeezing like inequalities, or on Dicke-squeezing, depending on the initial engineered state.
A second major possibility that we will jointly explore is to bring the systems close to phase transitions before the excitation protocol is performed. For this, we will tune the strength of interactions relative to motion in our systems, by either magnetic field control or by modifying the mobility of particles when tuning a lattice depth - which will allow studying phases that are either spatially disordered (superfluid phase) or ordered (Mott insulator or supersolid phases). We will study quantum thermalization, cruising over these phase diagrams separating ordered, disordered, integrable or chaotic systems. Our aim is to derive general rules connecting quantum thermalization of long-range interacting systems to the underlying steady-state phase diagram, close to a phase transition.
We thus expect that this project can significantly advance a field of research that has barely been touched experimentally.