Characterizing light shift of an open optical Zeeman transition with a single cesium atom in an optical tweezer

Characterizing the trap-light-induced frequency shifts of optical Zeeman transitions is essential for the precise control of the interacting dynamics between optically trapped single atoms and external light fields. The closed hyperfine transition, for example, 6S_1/2 | F = 4〉 → 6P_3/2 | F' = 5〉 of the cesium (Cs) atom, is commonly used because of its high transition strength. However, within this hyperfine transition line, different Zeeman transitions experience distinct light shifts due to diverse susceptibilities to the light field, which are usually sorted as dynamic scalar, vector, and tensor polarizabilities. Here, we report an efficient method for measuring the light shifts of optical Zeeman transitions using single neutral atoms confined in an optical tweezer (OT). The method employs a weak probe beam together with an auxiliary optical pumping beam to manipulate the atomic population in ground states. In this way, population changes in a specific Zeeman state are mapped onto a different ground-state hyperfine manifold, allowing the optical spectrum of the Zeeman transition to be reconstructed through standard state-detection techniques. By using the method, we demonstrate the spectrum measurement of the open Zeeman transition 6S_1/2 | F = 4, m_F = 4〉 → 6P_3/2 | F' = 5, m_F' = 3〉 for a single Cs atom trapped in a π polarized OT. We further perform a systematic characterization of the tweezer-induced light shifts for both this open transition and the closed Zeeman transition 6S_1/2 | F = 4, m_F = 4〉 → 6P_3/2 | F' = 5, m_F' = 5〉 over a wide range of trap depths. The influence of the tensor polarizability in deep trap depths is experimentally observed.