LAUSR

Collective couplings of atomic dipoles to a shared electromagnetic environment produce a wide range of many-body phenomena. We report on the direct observation of resonant electric dipole-dipole interactions in a cubic array of atoms in the many-excitation limit. The interactions produce spatially dependent cooperative Lamb shifts when spectroscopically interrogating the millihertz-wide optical clock transition in strontium-87. We show that the ensemble-averaged shifts can be suppressed below the level of evaluated systematic uncertainties for optical atomic clocks. Additionally, we demonstrate that excitation of the atomic dipoles near a Bragg angle can enhance these effects by nearly an order of magnitude compared with nonresonant geometries. Our work demonstrates a platform for precise studies of the quantum many-body physics of spins with long-range interactions mediated by propagating photons. Editor’s summary A three-dimensional optical lattice filled with cold fermionic atoms is a powerful implementation of an optical atomic clock. Studying interactions in such systems can lead to both improved clock precision and insights into many-body physics. Hutson et al. investigated strontium-87 atoms placed in a cubic optical lattice and measured the effects of resonant dipole-dipole interactions. They found that the interactions caused a tiny clock shift, the magnitude of which could be controlled by varying the relative orientation of the probe light and the atomic dipoles. —Jelena Stajic Cold strontium-87 atoms placed in a cubic optical lattice were used to measure and control resonant dipole-dipole interactions.