Frequency Measurement of an Optical Lattice Clock

A frequency measurement system is developed away from a National Metrological Institute with a frequency link to International Atomic Time (TAI). The absolute frequency of the
¹
S
₀
-
³
P
₀
clock transition of the
⁸⁷
Sr lattice clock is determined to be 429,228,004,229,875(4) Hz. The frequency measurement system is being further improved by introducing an optical fiber link and by upgrading the GPS link.