Long-range Interaction Of Ultracold Ns Cs Rydberg Atoms

Rydberg atoms are the ones whose outer electrons are excited to very high excited states of atoms which have the large principal quantum numbers. Compared with the atoms in the ground state, they have many unique characteristics, for example, long lifetime (-n3), small energy interval(-n-3), big electric dipole moment(-n2), and strong long-range interaction between each other. Because of their big polarizability(-n7), Rydberg atoms are very sensitive to external field. Hence, we can use the external field to control the atomic energy levels and the interaction between them. Early studies of Rydberg atoms have focused on the room temperature sample which has limitation of thermal movement, Doppler broadening and so on. With the development of laser cooling and trapping, we can obtain the ultracold Rydberg atoms with temperature of μ-Kelvin regime in which the kinetic energy of Rydberg atoms is much smaller than their interaction potential. Therefore, it is possible to study the long-range interaction and the so-called "dipole blockade" of Rydberg atoms.Due to their large polarizability, the interaction of Rydberg atoms could be manipulated by adjusting the external electric field. Because of their long lifetime, the interaction could be studied in the scale of microsecond. The strong dipole-dipole interaction and the van der Waals interaction cause the energy level shift and result in the dipole blockade effect, which may be used to achieve the excitation of a single Rydberg atom and make Rydberg atoms as the potential candidate for realizing quantum logic gates and quantum memory.The main works of this paper include preparing nS ultracold Rydberg atoms by using two-photon excitation of ultracold Ryberg atoms in MOT; Measuring of free ions signal and Rydberg signal through pulsed field ionization method and micro channel plate detection technology, investigating long-range interaction and dipole-blockade effect of nS Rydberg atoms by changing the experimental parameters such as the time of interaction and the pulse width of excitation laser. The measured results agree well with the theoretical results. The innovation of this work is shown in the following parts:1Ionization behavior of ultracold Rydberg atoms is investigated by changing the interaction time and pulse width of excitation laser.The evolution process of ultracold cesium Rydberg atoms to ultracold plasma is studied in details and the initial ionization mechanism is obtained. Ionization rates of70S state of ultracold cesium Rydberg atoms are calculated theoretically, and the experimental results are consistent with the theory.2The excitation blockade effect of nS states of ultracold cesium Rydberg atoms is investigated by varying the intensity and pulse width of the excitation laser and the dependence of excitation blockade on Rabi frequency of excitation laser is obtained. The result demonstrated that excitation blockade effect can be enhanced by external electric field. The interaction model is introduced to explain the experimental results and shows agreement with each other.