A strontium lattice clock with $3 \times 10^{-17}$ inaccuracy and its frequency

Understand

We have measured the absolute frequency of the optical lattice clock based on $^{87}$Sr at PTB with an uncertainty of $3.9\times 10^{-16}$ using two caesium fountain clocks.

• This is close to the accuracy of today's best realizations of the SI second.
• The absolute frequency of the 5s$^2$ $^1$S$_0$-5s5p $^3$P$_0$ transition in $^{87}$Sr is 429,228,004,229,873.13(17) Hz.
• Our result is in excellent agreement with recent measurements performed in different laboratories worldwide.