DOI: 10.7795/720.20250926
title: Additional data for the publication "Transportable strontium lattice clock with 4 x 10^-19 blackbody radiation shift uncertainty"

description: We describe a transportable optical lattice clock based on the 1S0 -&gt; 3P0 transition of lattice-trapped 87Sr atoms with a total systematic uncertainty of 2.1 x 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 x 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 x 10^-16 (tau/s)^-0.5, 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 x 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.
description: **Figure_2a.tsv**: Data shown in figure 2 (a) of the manuscript. State populations are measured as described in the manuscript.
 Columns 1-2 (3-4) contain the frequency offset of the clock laser from a centre frequency that is arbitray but close to resonance and the fraction of atoms detected in the 3P0 state after interrogation where atoms are initially prepared in the magnetic substate m_F = -9/2 (+9/2) of the 3P0 state.
 format: "text/tsv"
 recommended software: [Python](https://www.python.org/)

**Figure_2b.tsv**: Source data of the Allan deviation shown in figure 2 (b) of the manuscript.
 Deviation of the fractional frequency difference between the transportable clock Sr4 and the stationary clock Sr3 from its mean value, on a one-second grid.
 Optical beat frequency between clock lasers recorded by dead-time-free counters.
 Timestamps and gaps removed.
 format: "text/tsv"
 recommended software: [Python](https://www.python.org/)

**Figure_4.tsv**: Data shown in figures 4 (a) and (b) of the manuscript.
 Fractional frequency differences between atoms moved by a variable distance and atoms at the centre of the BBR shield, with the difference in second-order Zeeman shift removed as described in the manuscript.
 Columns 1-4 contain the moving distance, the measured fractional frequency difference, the deviation thereof from the expected differential BBR shift, and the measurement uncertainty.
 format: "text/tsv"
 recommended software: [Python](https://www.python.org/)

**Figure_B1.tsv**: Data shown in figure B1 of the manuscript.
 Radii of the holes 1 and 2 of the BBR shield as measured at the outer edges for different angles of orientation, before and after coating and assembly of the parts.
 Measured with a measuring microscope.
 Corrected for an offset measured with a coordinate measuring machine, as described in the manuscript.
 Colummn 1 contains the angle of orientation, columns 2-5 the measured radii of the holes as stated in the header.
 format: "text/tsv"
 recommended software: [Python](https://www.python.org/)

**Figure_E1.tsv**: Data shown in figure E1 of the manuscript.
 Allan deviation values of the frequency ratio between the hydrogen maser used in the absolute frequency measurements and either the transportable clock (Sr4) or the stationary clock (Sr3).
 Columns 1-5 contain the averaging times and Allan deviation values of the measurements in the order shown in figure E1, as also stated by the column headers.
 Computed from experimental data
 format: "text/tsv"
 recommended software: [Python](https://www.python.org/)
description: We acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy -- EXC-2123 QuantumFrontiers -- Project-ID 3908379.67.
We acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under SFB 1464 TerraQ -- Project-ID 434617780 -- within projects A04 and A05.
This work was partially supported by the Max Planck-RIKEN-PTB Center for Time, Constants and Fundamental Symmetries.
This work has received funding from the European Partnership on Metrology, co-financed by the European Union's Horizon Europe Research and Innovation Programme and by the Participating States, under grant number 22IEM01 TOCK.