Phys.org  January 27, 2024 Collective couplings of atomic dipoles to a shared electromagnetic environment produce a wide range of many-body phenomena. A team of researchers in the USA (University of Colorado, Colorado State University) reported on the direct observation of resonant electric dipole-dipole interactions in a cubic array of atoms in the many-excitation limit. The interactions produced spatially dependent cooperative Lamb shifts when spectroscopically interrogating the millihertz-wide optical clock transition in strontium-87. They showed that the ensemble-averaged shifts could be suppressed below the level of evaluated systematic uncertainties for optical atomic clocks. They demonstrated that excitation of the atomic dipoles […]