Researchers have investigated the isotopic effect on the broadening and shifting of mercury (Hg) atomic clock transitions due to collisions with ultracold rubidium (Rb) atoms. This work is crucial for improving the precision of Hg atomic clocks, which are promising candidates for next-generation optical clocks. Current optical clocks surpass the precision of microwave clocks and are fundamental for the redefinition of the second, as well as for applications in navigation, fundamental metrology, and the search for new physics.

The study focused on the 6s² ¹S₀ – 6s6p ³P₀ clock transition of Hg, using different mercury isotopes (¹⁹⁸Hg, ¹⁹⁹Hg, ²⁰⁰Hg, ²⁰¹Hg, ²⁰²Hg, and ²⁰⁴Hg) in the presence of an ultracold Rb gas. It was observed that collisional interactions between Hg and Rb cause broadening and shifting of the transition frequency. These effects depend on the mass and nuclear structure of the Hg isotopes, known as the isotopic effect. A detailed understanding of these interactions is vital for mitigating their contributions to error in atomic clocks.

The results show that the isotopic effect is significant, with variations in the broadening and shifting coefficients for different Hg isotopes. These data provide an experimental basis for validating theoretical models of interatomic interactions at low temperatures and are directly applicable to the design and optimization of future mercury-based optical clocks. The ability to predict and control these collisional effects is a step forward towards building atomic clocks with even greater stability and precision, opening the door to new tests of fundamental physics and advanced technologies.