Long-Range Interactions with Rydberg Atoms

Ultracold atomic systems usually work with ground-state atoms, where the van der Waals interactions are short-range and can be modeled as contact potentials.  Rydberg atoms are atoms in a highly excited principal quantum number state (n > 20). Using an ultraviolet laser (230 nm), we directly couple our ground-state atoms to a Rydberg P-state. In this excited state, the valence electron is far away from the nucleus, so the atoms are highly polarizable. This leads to strong long-range interactions between the Rydberg atoms.  Previously, we used resonant excitation to a low-lying Rydberg state (23P) to study the quench dynamics of a two-dimensional quantum Ising spin system. Now, we are interested in realizing an itinerant atomic Fermi gas with strong long-range interactions. For this, we need to extend the short lifetime of the Rydberg state (~10 µs) by highly detuning the laser from the Rydberg transition, a method known as Rydberg dressing. In this limit, the ground state acquires a small admixture of the Rydberg state, greatly enhancing its lifetime to make it comparable to motional timescales, while reducing the strength of the interactions to allow competition with the kinetic energy of the gas. 

Probing the Quench Dynamics of Antiferromagnetic Correlations in a 2D Quantum Ising Spin System

Guardado-Sanchez, E., Brown, P., Mitra, D., Devakul, T., Huse, D. Schauss, P. & Bakr, W.
Phys. Rev. X 8, 021069 (2018) [Featured in “Physics”]

Simulating the real-time evolution of quantum spin systems far out of equilibrium poses a major theoretical challenge, especially in more than one dimension. We experimentally explore quench dynamics in a two-dimensional Ising spin system with transverse and longitudinal fields. We realize the system with a near unit-occupancy atomic array of over 200 atoms obtained by loading a spin-polarized band insulator of fermionic lithium into an optical lattice and induce short-range interactions by direct excitation to a low-lying Rydberg state. Using site-resolved microscopy, we probe antiferromagnetic correlations in the system after a sudden quench from a paramagnetic state and compare our measurements to numerical calculations using state-of-the-art techniques. We achieve many-body states with longer-range antiferromagnetic correlations by implementing a near-adiabatic quench of the longitudinal field and study the buildup of correlations as we vary the rate with which we change the field.