inverted two-photon Rydberg excitation, electromagnetically induced transparency, ionization energy, quantum defect, Applied optics. Photonics, TA1501-1820

We perform precise measurements of the 87Rb Rydberg excitation spectrum by using electromagnetically induced transparency (EIT) in a ladder system. We utilize a two-photon excitation configuration with the probe and control lasers at 420 nm and 1013 nm, respectively. In this work, we employ 6P3/2,F′ = 3 as an intermediate state to excite the high-lying Rydberg states of the nS and nD series, with principal quantum numbers ranging from n=35 to n=70. To improve the signal-to-noise ratio (SNR) in this inverted level scheme (λp<λc), we apply a 100 kHz chopping to the control beam, which is followed by a demodulation operated with a lock-in amplifier. Additionally, we verify the ionization energies and determine the quantum defects for the nS and nD series, respectively. Our work offers a database for applications of large-scale quantum simulation and quantum computation with the 87Rb atom array.