Measurement of quantum defect of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

This paper reports that ultracold atoms are populated into different $n$S and $n$D Rydberg states ($n$=25$\sim $52) by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes $n$S and $n$D states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of $n$S and $n$D states.