Strontium (Sr) optical lattice clocks are among the most widely adopted optical frequency standards and have demonstrated outstanding stability and accuracy, with reproducibility at the 10⁻¹⁷ level. Their frequency comparisons have been used to test gravitational theories and are expected to enable relativistic geodesy, where height differences are inferred from gravitational red-shift.
INRiM has assembled its own Sr optical lattice clock, implementing original solutions aimed at combining ultra-high stability with metrological accuracy. The apparatus employs a 2D-MOT loaded atomic beam, which helps suppress black-body-radiation (BBR) shifts originating from the atomic oven. An optical shutter for the Sr beam is used to suppress background-collision shifts, improving long-term accuracy and repeatability.
The current plan foresees the installation and characterization of a new quantum-enhanced spectroscopy chamber for the Sr clock. The objective is to enable advanced interrogation schemes and improved performance, including routes toward quantum-enhanced stability.
The Sr clock complements INRiM’s other standards (microwave and optical with Yb) by enabling optical-to-optical and optical-to-microwave comparisons, frequency-ratio measurements and cross-checks of systematic effects. These measurements are central to the international roadmap toward a redefinition of the second and to the validation of optical standards across laboratories.
When connected to fiber-based dissemination, the Sr clock can be compared with remote standards with very low added uncertainty. This capability supports participation in international comparison campaigns and provides a traceable reference for experiments that require ultra-stable optical frequencies and accurate time stamps. The laboratory maintains the laser stabilization, vacuum, magnetic shielding and data analysis chain needed to operate the clock reliably and to document its uncertainty budget.