Laguerre-Gaussian shaped lattices for a strontium optical clock

Optical lattice clocks (OLCs) have achieved an unprecedented relative systematic uncertainty of about 10⁻¹⁹, establishing them as candidates for the upcoming redefinition of the second in the International System of Units (SI). Currently, the accuracy of OLCs is primarily limited by black body radiation (BBR), cold collisions, and lattice light shift effects. Various strategies are being explored to mitigate these limitations, including using cryogenic environments to manage BBR and using new trapping geometries to control atomic distributions and interactions.

In this project, we propose a new OLC setup that aims to characterize BBR and density effects below the 10⁻¹⁸ level. To achieve this goal, we have developed a copper science chamber that is placed inside a primary vacuum chamber. This configuration minimizes temperature inhomogeneities around the atoms to within a few tens of millikelvin (mK). The system features an adaptable one-dimensional (1D) optical lattice shaped with Laguerre-Gaussian LG_0ℓ modes to increase the number of trapping sites while reducing atomic occupancy per site. We created shaped lattices with values of ℓ from 0 to 4 whose trap depths were compatible with clock operation. We trapped thousands of Strontium atoms in TEM₀₀, LG₀₁ and LG₀₂ shaped lattices and performed low-resolution clock spectroscopy on bosonic ⁸⁸Sr, yielding 100 Hz-wide transitions.

To investigate cold collision effects, we plan to implement a second cooling stage using the ¹S₀ → ³P₁ intercombination transition in strontium. This will increase atomic density, enhancing observable collision effects and enabling the detection of motional sidebands. These measurements will provide insight into the anharmonicity of LG-shaped lattices and help validate the lattice light shift model under varying trap conditions. Finally, the clock setup is still under construction. Current work focuses on enclosing the interrogation chamber within the primary vacuum to improve the thermal homogeneity and reduce the uncertainty related to BBR, and at the same time, the instrumentation required for high-resolution spectroscopy is currently being installed.

atomic clock, optical lattice clock, optical lattice, light shift, systematic effects, blackbody radiation, cold collisions, Laguerre-Gaussian modes.

Full document (EN) : HAL-TEL-05556321