Precision measurement of the energy levels and quantum defects of Cs

Precise measurements of Cs energy levels and quantum defects are important for understanding atomic structure, and are recently attracting more attention due to the development of quantum sensors, such as Rydberg electric field sensors, and quantum simulators. Here, we present absolute-frequency measurements for transitions from the |6S_1/2, F = 3〉 hyperfine ground state of ¹³³Cs to nS_1/2 (n = 28 − 140), nD_3/2 (n = 27 − 90), and nD_5/2 (n = 27 − 90) Rydberg states. The spectra are obtained using two-photon laser excitation in ultra-cold Cs. The lasers used to excite the Rydberg states are both locked to a GPS referenced frequency comb, resulting in laser linewidths of less than 200 Hz and absolute frequency stability of 2×10^-12/√Hz. By globally fitting the absolute-frequency measurements to the extended Ritz formula, we determine the quantum defects of the nS_1/2, nD_3/2, and nD_5/2 series. The fits are also used to extract the Cs ionization energy. With the improved quantum defects, we can rigorously calculate the polarizabilities of Rydberg states of Cs at high principal quantum numbers. The theoretical calculations of the polarizabilities are compared with Stark spectroscopy measurements. The results are used to generate a new model potential for the Cs atom.