In this laboratory INRiM maintains the Italian primary frequency standard, based on a nitrogen-cooled cesium fountain clock operating at 89 K. Cryogenic operation reduces key systematic effects and helps achieve an accuracy at the level of 2×10⁻¹⁶, placing the standard among the best microwave realizations of the second.
The fountain’s measurements are used to support and calibrate the generation of the national time scale UTC(IT). By providing a primary reference, the fountain constrains long-term drifts and biases of the commercial ensemble used for continuous operation and ensures traceability of UTC(IT) to the SI second.
INRiM periodically transmits evaluated frequency data to the Bureau International des Poids et Mesures (BIPM) for the computation of International Atomic Time (TAI) and the reference UTC, thereby contributing to the international time-keeping process. The fountain will continue to underpin UTC(IT) accuracy and to support routine reporting for TAI/UTC, in coordination with the increasing operational use of optical standards.
Beyond time scale support, the fountain provides a reference for high-resolution measurements in atomic and molecular physics and for the characterization of advanced oscillators. The standard is disseminated through optical fiber links to external laboratories, allowing users to perform frequency measurements with traceability and resolution that are difficult to achieve with local references.
The laboratory develops and validates the subsystems that determine the clock performance, laser cooling and state preparation, microwave interrogation and synthesis chains, magnetic and thermal control, detection and data analysis. Systematic shifts are continuously evaluated and documented, so that the uncertainty budget remains transparent and improvements can be implemented methodically. It also provides a metrological anchor for comparisons with optical clocks and for long-haul dissemination experiments, where a primary microwave reference is essential to validate the full traceability chain.