Description
Optical lattice clocks have progressed swiftly over the past decade, now outperforming state-of-the-art microwave clocks by more than two orders of magnitude in both stability and accuracy, reaching a level of control of the frequency of 18 digits or better. This opens up new applications in fundamental physics, astronomy and Earth science. In this context, LTE initiated the development of a transportable 171Yb lattice clock in 2021 to explore the coupling of the atoms to the Earth’s gravitational potential. The scientific objective is to build an instrument that can be connected to some of the ~60 outputs of the French research infrastructure REFIMEVE, which disseminates a 1542 nm ultrastable carrier throughout the country. This will allow remote comparisons to the ~12 operational European optical clocks and therefore give access to geopotential variations (in space and time), especially in places where abrupt changes occur (coastal/mountainous areas). As the control over 18 digits allows resolving 1 cm height differences, our approach will complement existing geodesy techniques based on spirit levelling and satellites, and help further constrain models describing the Geoid.
We present the status of the transportable optical lattice clock ROYMAGE. Its design aims at trapping a large number of atoms (>104) in less than 100ms, to reduce the dead-time of the clock and thereby improve its stability. We present the successive bricks we have developed to allow this ultrafast loading: a 399 nm source providing 1 W of power, an ytterbium oven featuring a flux of 4e11 atoms/s, a transverse molasses collimating the atomic beam so that the flux is preserved down the trapping region, a Zeeman slower bringing the atoms from 300 m/s to 30 m/s, a speed at which they are captured in a 3D Magneto-Optical Trap (MOT). We also introduce the atomic loader RAZPOUTYNE, which combines a 2D MOT and a Zeeman slower in a compact geometry, and has already demonstrated the trapping of 7e8 ytterbium atoms.
The next steps are a second cooling stage MOT at 556 nm, then loading the atoms into an optical lattice deep enough (Lamb-Dicke regime) to cancel the first-order Doppler effect and the recoil shift. This will pave the road towards transportation of the instrument along the REFIMEVE network and towards participation in a refined realization of the Geoid.