Tunable spin-motion dynamics with polar molecules*

Ultracold molecules in optical lattices offer a versatile platform for investigating quantum many-body physics due to their strong, long-range, and tunable dipolar interactions. We will present recent results from realizing generalized t-J models and a range of XXZ and XYZ spin models using ultracold KRb molecules [1, 2, 3]. Confining the molecules to two dimensions provides further control of the spatial anisotropy of their dipolar interactions, and a low-entropy sample allows exploration of qualitatively new physics in these spin-motion systems. We discuss our progress towards creating such a deeply degenerate 2D Fermi gas of ground state polar molecules, building on our previous work of selecting [4] and evaporating [5] molecules in individual layers of 2D optical traps. We compress an atomic mixture of K and Rb to a quasi-2D geometry using an optical lattice of variable spacing, and transfer the mixture to a fixed-spacing lattice. We then create ground state molecules and leverage the greater vertical confinement provided by the fixed-spacing lattice to perform dipolar evaporation [5]. Reaching deep degeneracy for these 2D samples will allow us to explore the rich quantum phases and dynamics of various spin-motion models.

[1] Tunable itinerant spin dynamics with polar molecules, J. Li et al., Nature 614, p. 70–74 (2023)

[2] Observation of Generalized t-J Spin Dynamics with Tunable Dipolar Interactions, A. N. Carroll et al., arXiv:2404.18916 (2024)

[3] Two-axis twisting using Floquet-engineered XYZ spin models with polar molecules, C. Miller et al., Nature 633, p. 332–337 (2024)

[4] Reactions between layer-resolved molecules mediated by dipolar spin exchange, W. Tobias et al., Science 375, p. 1299-1303 (2022).

[5] Dipolar evaporation of reactive molecules to below the Fermi temperature, G. Valtolina et al., Nature 588, p. 239–243 (2020)