Transportable strontium lattice clock with $4 \times 10^{-19}$ blackbody radiation shift uncertainty

TL;DR

This paper presents a transportable strontium optical lattice clock with extremely low blackbody radiation shift uncertainty, demonstrating high stability and accuracy suitable for geodetic and inter-institutional frequency measurements.

Contribution

The development of a transportable strontium lattice clock with a record-low blackbody radiation shift uncertainty of 4.0×10⁻¹⁹ and verified high stability and accuracy.

Findings

Blackbody radiation shift controlled at 4.0×10⁻¹⁹

Clock frequency measured with 1.9×10⁻¹⁶ fractional uncertainty

Successful transport and operation at multiple locations

Abstract

We describe a transportable optical lattice clock based on the $^1\mathrm{S}_0 \rightarrow {^3\mathrm{P}_0}$ transition of lattice-trapped $^{87}$Sr atoms with a total systematic uncertainty of $2.1 \times 10^{-18}$. The blackbody radiation shift, which is the leading systematic effect in many strontium lattice clocks, is controlled at the level of $4.0 \times 10^{-19}$, as the atoms are interrogated inside a well-characterised, cold thermal shield. Using a transportable clock laser, the clock reaches a frequency instability of about $5 \times 10^{-16}/\sqrt{\tau/\mathrm{s}}$, which enables fast reevaluations of systematic effects. By comparing this clock to the primary caesium fountain clocks CSF1 and CSF2 at Physikalisch-Technische Bundesanstalt, we measure the clock transition frequency with a fractional uncertainty of $1.9\times 10^{-16}$, in agreement with previous results. The clock was successfully transported and operated at different locations. It holds the potential to be used for geodetic measurements with centimetre-level or better height resolution and for accurate inter-institute frequency comparisons.