Coherent evolution of superexchange interaction in seconds-long optical clock spectroscopy.

Scaling up the performance of atomic clocks requires understanding complex many-body Hamiltonians to ensure meaningful gains for metrological applications. Here we use a degenerate Fermi gas loaded into a three-dimensional optical lattice to study the effect of a tunable Fermi-Hubbard Hamiltonian. The clock laser introduces a spin-orbit coupling spiral phase and breaks the isotropy of superexchange interactions, leading to XXZ-type spin anisotropy. By tuning the lattice confinement and applying imaging spectroscopy, we map out favorable atomic coherence regimes. We transition through various interaction regimes and observe coherent superexchange, tunable through on-site interaction and site-to-site energy shift, affecting the Ramsey fringe contrast over timescales >1 second. This study lays the groundwork for using a three-dimensional optical lattice clock to probe quantum magnetism and spin entanglement. Editor's summary: Three-dimensional optical lattice atomic clocks are a promising tool for both quantum metrology and simulation. To fully realize this potential, understanding and controlling the interactions between the atoms is crucial. Milner et al. loaded a three-dimensional lattice with tunable confinement with a degenerate Fermi gas of strontium-87 atoms. Using Ramsey spectroscopy, the researchers measured the interaction effects as they varied the lattice confinement parameters. —Jelena Stajic [ABSTRACT FROM AUTHOR]