Probing nS/nD Rydberg States via 6P_3/2 Intermediate Level Using Electromagnetically Induced Transparency in ⁸⁷Rb

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 $6P_{3/2},$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 (${\lambda }_p<{\lambda }_c$), 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.