Narrow-line electric quadrupole cooling and background-free imaging of a single Cs atom with spatially structured light

We demonstrate background-free imaging and sideband cooling of a single ^133Cs atom via the narrow-line 6S₁/₂5D₅/₂ electric quadrupole transition in a 1064 nm optical tweezer. The 5D₅/₂ state decays through the 6P₃/₂ state to the ground state, emitting an 852 nm wavelength photon that allows for background-free imaging. By encoding both spin and orbital angular momentum onto the 685 nm excitation light, we achieve background-free fluorescence histograms with 99. 58 (3) % imaging fidelity by positioning the atom at the dark center of a vortex beam. Tuning the tweezer polarization ellipticity realizes a magic trap for the stretched |F=4, m₅=4|F^'=6, m₅^'=6 cycling transition. Using a Gaussian beam, we cool to 50. 16em{0ex}K in a 1. 1 mK trap and outline a strategy for ground-state cooling. We compare cooling performance across different sideband regimes, while also exploring how the orbital angular momentum of structured light controls the selection rules for quadrupole transitions. These results expand the toolbox for high-fidelity quantum control and cooling in alkali-atom tweezer arrays.