Imaging and Cooling a single Cs atom trapped in an optical tweezer with a narrow 6S_1/2- 5D_5/2 quadrupole transition

Alkali atoms are widely used in atomic physics due to their simple structure, having a single electron in the outermost shell, which makes them ideal for laser cooling and trapping experiments. On the other hand, alkaline earth atoms possess narrow-line transitions that offer distinct advantages for precision laser cooling. In this work, we harness the best of both worlds by using a narrow-line electric quadrupole (E2) transition in cesium to image and cool a single atom in an optical tweezer.

Cesium, being the industry standard for cold-atom and atomic-clock experiments, offers the 6S_1/2 - 5D_5/2 transition with a linewidth of approximately 120 kHz. This linewidth is comparable to the trapping frequencies of tightly confined alkali atoms, making it ideal for high-fidelity control. We employ a spatial light modulator (SLM) to generate beams with different orbital angular momentum (OAM) modes, including vortex and Gaussian profiles. By controlling the beam polarization, we demonstrate ± 2 (OAM + spin) selection rules across the entire MF​ manifold for the Fg = 4 → Fe = 6 transition, thereby transferring two units of angular momentum using a single photon. Also this transition primarily decays through the 6P_3/2​ state, emitting a photon at 852 nm (D2​ line), which allows for background-free imaging by filtering out the excitation wavelength at 685 nm, potentially enhancing the imaging fidelity.

In this talk, I will present the experimental methods and results for achieving polarization-tuned, magic-wavelength trapping and cooling. I will also describe how we explore both attractive and repulsive Sisyphus cooling regimes under these conditions. Furthermore, simulations reveal that the gradient of the electric field governs the interaction with the atom, while the gradient of the field's gradient drives the cooling mechanism. This transition offers a promising approach for background-free imaging and single photon-sideband cooling in single-atom experiments, potentially paving the way for a more efficient approach to cooling down till motional ground state of the tweezer for QIS applications.