State Mixing Of Ultracold Rydberg Atoms In External Electric Fields

Rydberg atom is the highly excited atom with a high principal quantum number n. Compared to the ground state atom, Rydberg atom has many features. For examples: Rydberg atoms have strong long-range Van der Waals interactions and dipole interactions, which offers many facilities in search of the dipole blockade effect and achievement of the excitation of a single Rydberg atom; Rydberg atoms have a large polarizability and very sensitive to an external electric field, leading to Stark effect; Rydberg atoms also have a long lifetime, large electric dipole moment and giant orbit radius, which make Rydberg an idea candidate of the quantum gate and being the hot topic in the research of the atomic and molecular physics.In this paper, we study the electric fields induced Stark effect and state-mixing effect between initially nS state and (n-4) stark manifolds.In our experiments, we choose alkali metal cesium atoms as the research sample. The ultracold cesium atoms are excited to Rydberg states via 6S1/2â†'6P3/2â†'nD/nS two-photon transition in a standard magnetic trap. The state selective field ionization is employed to ionize prepared Rydberg atoms and released ions are detected with a calibrated macro channel plate detector.Firstly, according to the theoretical calculation of Rydberg stark structure, we obtain the parameters of the avoided crossings, such as center field and energy gap. The ion spectroscopy near the avoided crossing is experimentally measured, which is agree well with the calculations.Secondly, after preparing the nS Rydberg atoms in the MOT, we apply an external electric field and obtain high-1 state when electric field through the avoided crossing formed between the nS and near (n-4) Stark state. We have measured the transfer rate as a function of the amplitude of the electric field and investigated the transfer mechanism. The results show that the measured transfer rate of high-1 is creasing as the electric field and get to the maximum, after that begin to decrease.we we measure the transferred high-l Stark states as a function of the strength of electric-field pulse. The measured signal of high-l Stark states increased to saturated then decreased with electric field increase. We think the strong interaction between high-l Rydberg atoms causes penning ionization and m-mixing effect.Finaly, we focus on a specific single avoid crossing to investigate the adiabatic/diabatic passage when the electric field ramp through the selected avoided crossing. We change the ramp time and delay time and measured the high-1 state, which shows that the m-mixing effect has an important role in the detection of the high-1 state. The free ions due to the interaction between Rydberg atoms are also measured as a function of the delay time, which proves the existence of m-mixing effect.The innovations of this work are shown two aspects as followed:1.We have studied the avoiding crossing of Rydberg atom’s energy level in the condition of the electric field and got the value of electric field in the center of avoiding crossing. The state mixing and transfer through avoided crossing have being obtained experimentally and the measurement is consistent with the theoretical simulation.2. The transformation of high-l state with the electric field have been investigated. We find that the transfer rate of high-l state increase to saturation and after that shown decrease trend with the increase of electric field, which is attributed to the m-mixing effect. The strong interaction between high-l Rydberg atoms caused penning ionization and to form the plasma.