1State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China 2Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Abstract：Ultralong-range Cs$_2$ Rydberg-ground molecules ($nD_{5/2} + 6S_{1/2}F$) ($33 \leq n \leq 39$, $F=3$ or 4) are investigated by a two-photon photo-association spectroscopy of an ultracold Cs gas. Two vibrational ground molecular spectra of triplet $^{3}\!\varSigma$ and hyperfine mixed singlet-triplet $^{1,3}\!\varSigma$ molecular states and their corresponding binding energies are attained. The experimental observations are simulated by an effective Hamiltonian including low energy electron scattering pseudopotentials, the spin-orbit interaction of the Rydberg atom, and the hyperfine interaction of the ground-state atom. The zero-energy singlet and triplet s-wave scattering lengths are extracted by comparing the experimental observations and calculations. Dependences of the measured binding energies on the effective principal quantum number, $n_{\rm eff} = n - \delta_D$ ($\delta_D$ is the quantum defect of Rydberg $D$ state), yield the scaling of $n_{\rm eff}^{-5.60 \pm 0.16}(^{3}\!\varSigma,F=3)$, $n_{\rm eff}^{-5.62 \pm 0.16}(^{3}\!\varSigma,F=4)$ for deep triplet potential and $n_{\rm eff}^{-5.65 \pm 0.38}(^{1,3}\!\varSigma, F=3)$, $n_{\rm eff}^{-6.19 \pm 0.14}(^{1,3}\!\varSigma,F=4)$ for shallow mixed singlet-triplet potential well. The simulations of low-energy Rydberg electron scattering show agreement well with the experimental measurements.
2020, Vol. 37 
