The absolute frequency of the 87Sr optical clock transition

TL;DR

This paper reports an extremely precise measurement of the 87Sr optical clock transition frequency, achieving one of the highest accuracies for atomic transition measurements, with implications for redefining time standards.

Contribution

The study provides a highly accurate measurement of the 87Sr clock transition frequency with detailed systematic uncertainty analysis and advanced frequency comparison techniques.

Findings

Measured the 87Sr transition frequency as 429228004229873.65 Hz

Achieved a fractional uncertainty of 8.6x10^-16

Reduced systematic uncertainty to 1.5x10^-16

Abstract

The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6x10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5x10-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fiber transfer scheme to compare the remotely located clock signals.