Claudio ELIGIO CALOSSO : Seminar

Claudio ELIGIO CALOSSO will give a seminar for the 150th anniversary of the BIPM at salle TRANSFERT1 (0.82.19) SUPMICROTECH ENSMM on Wednesday April 2th, 11 am : "Understanding an si second with more clocks"

Abstract : Since 1967 the duration of the SI second is defined by the radio frequency of 9,192,631,770 Hz that drives the transition between two specific states of atomic cesium. This transition is highly shielded from external influences, allowing for an exceptionally precise frequency determination. It has proven difficult to establish a definition that is more elegantly connected to fundamental constants while achieving similar accuracy. No such proposal has matched the performance of the best cesium fountain clocks, which realize the SI second with an uncertainty close to 10⁻¹⁶. However, in the last two decades optical clocks have made amazing advancements. Clocks that utilize lasers to probe transitions in aluminum, strontium, and ytterbium now report measurement uncertainties as low as 10⁻¹⁸. In response, the International Committee on Weights and Measures now aims to update the definition of the SI second at the General Conference for Weights and Measures in 2030. The longevity of the cesium second has set a high standard for this redefinition, and identifying the best new standard has proven challenging. Each candidate clock represents decades of research, and all continue to advance the boundaries of metrology.