Dipole-Dipole Interactions in a Frozen Rydberg Gas

John R. Lowell

Published May 1, 1998• 1 citation

Abstract

Abstract : We investigate here the characteristics of energy resonant dipole-dipole interactions between Rydberg atoms in Magneto-Optical Trap. These resonant processes occur in a kinetic energy regime in which the atoms may be considered stationary over the time scale of the experiment. Coupled with the long range of the interactions considered, this leads to multi-atom interactions becoming non-negligible. A simple model is outlined to provide insight into the effects of these multi-atom interactions which lead to some interesting behaviors. Experiments which examine the broadening of the dipole-dipole resonances and observe the time dependence of the interaction signal are discussed. Examination of adiabatic character of population transfer caused by slewing across the resonance is discussed in another experiment, as is the scaling behavior of the resonance linewidths and on-resonant signal growth rates. We end by discussing an experiment which takes advantage of some of the characteristics of these interactions to measure the tensor polarizability of Rydberg states of Rb.

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Dipole-Dipole Interactions in a Frozen Rydberg Gas

John R. Lowell

Published May 1, 1998• 1 citation

OpenAlex

Abstract

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Rydberg-wave-packet evolution in a frozen gas of dipole-dipole-coupled atoms

Tao Zhou, Sha Li, R. R. Jones

We have studied the evolution of Rydberg wave packets in the presence of interatomic dipole-dipole interactions in a frozen Rb gas. Rb atoms in a magneto-optical trap (MOT) are first laser excited to $ns$ Rydberg eigenstates. A picosecond THz pulse further excites them into coherent superposition states involving the initial-level and neighboring $np$ states. A second, identical, time-delayed THz pulse probes the wave-packet dynamics. As the wave packets evolve they are influenced by dipole-dipole interactions, predominantly pairwise excitation-exchange processes of the form $|s\ensuremath{\rangle}|p\ensuremath{\rangle}\ensuremath{\leftrightarrow}|p\ensuremath{\rangle}|s\ensuremath{\rangle}$. The coherent electronic evolution of the ensemble dephases due to the variation in dipole-dipole coupling strength between atom pairs in the MOT. The experimental results are in good agreement with numerical calculations that simulate the interactions between nearest neighbors in a frozen gas.We have studied the evolution of Rydberg wave packets in the presence of interatomic dipole-dipole interactions in a frozen Rb gas. Rb atoms in a magneto-optical trap (MOT) are first laser excited to $ns$ Rydberg eigenstates. A picosecond THz pulse further excites them into coherent superposition states involving the initial-level and neighboring $np$ states. A second, identical, time-delayed THz pulse probes the wave-packet dynamics. As the wave packets evolve they are influenced by dipole-dipole interactions, predominantly pairwise excitation-exchange processes of the form $|s\ensuremath{\rangle}|p\ensuremath{\rangle}\ensuremath{\leftrightarrow}|p\ensuremath{\rangle}|s\ensuremath{\rangle}$. The coherent electronic evolution of the ensemble dephases due to the variation in dipole-dipole coupling strength between atom pairs in the MOT. The experimental results are in good agreement with numerical calculations that simulate the interactions between nearest neighbors in a frozen gas.

Physical Review AJun 16, 20147 citations

n=34

n=40

in a frozen gas of Rb Rydberg atoms. It is resonant when the microwave frequency is halfway between the $ns\phantom{\rule{0.16em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}n{p}_{1/2}$ and $ns\ensuremath{\rightarrow}n{p}_{3/2}$ frequencies, which range from 57 to 106 GHz. The process cannot occur in isolated atoms, nor can it occur if the magnetic quantum numbers are unchanged, an implicit assumption of one-dimensional models. A Floquet-Forster model shows that the coupling between the initial and final states involves the absorption of two microwave photons and the dipole-dipole interaction, which leads to a coupling proportional to the product of the density, the microwave field squared, and

{n}^{*14}

, where

{n}^{*}

is the effective quantum number of the

n{p}_{3/2}

state. We have experimentally verified these dependences. The observed resonances are asymmetric, with a low-frequency tail, which we attribute to the van der Waals shift of the final

n{p}_{1/2}n{p}_{3/2}

state due to its dipole-dipole interaction with the nearby

ns(n+1)s

state. While the van der Waals shift is negligible for most of the atoms in the Rydberg gas, it is not for the pairs of close atoms which undergo this transition.

We have studied the evolution of Rydberg wave packets in the presence of interatomic dipole-dipole interactions in a frozen Rb gas. Rb atoms in a magneto-optical trap (MOT) are first laser excited to

ns

Rydberg eigenstates. A picosecond THz pulse further excites them into coherent superposition states involving the initial-level and neighboring

np

states. A second, identical, time-delayed THz pulse probes the wave-packet dynamics. As the wave packets evolve they are influenced by dipole-dipole interactions, predominantly pairwise excitation-exchange processes of the form $|s\ensuremath{\rangle}|p\ensuremath{\rangle}\ensuremath{\leftrightarrow}|p\ensuremath{\rangle}|s\ensuremath{\rangle}$. The coherent electronic evolution of the ensemble dephases due to the variation in dipole-dipole coupling strength between atom pairs in the MOT. The experimental results are in good agreement with numerical calculations that simulate the interactions between nearest neighbors in a frozen gas.