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Perturbed Rydberg Atoms

(wikipedia link to Rydberg atoms)

For many years, we have had a strong effort in studying highly excited atoms and molecules. The interest in this area is that highly excited atoms can be understood using classical and quantum ideas. They also have been very common elements in quantum simulators and proposed quantum computers. We are particularly interested in the properties of these electronic states when they are strongly perturbed. The perturbations break the spherical symmetry of the atom and give rise to an interesting interplay between different types of motion. Also, specific and well controlled experiments can be performed on these systems.



For these calculations, we often solve both the classical equations of motion and the time dependent Schrodinger equation which governs the quantum behavior. Depending on the system being studied, the quantum calculations solve for the wavefunction can be converged for distances out to 10-6 m from the ion and include angular momentum up to 1000 hbar. Below is a brief description of results in two recent publications.

P. Giannakeas, M. T. Eiles, F. Robicheaux, and J. M. Rost, "Dressed ion-pair states of an ultralong-range Rydberg molecule," Phys. Rev. Lett. 125, 123401 (2020). PDF (2090 kB)

This paper predicts the existence of a new class of states when a cold atom perturbs a Rydberg state. The resulting energy versus distance from the ionic core of the Rydberg state to the cold atom leads to quantized motion that looks like that of a hydrogen atom with tiny charges for the proton and electron. The resulting energy levels are those of hydrogen with a surprisingly small Rydberg constant.


This image shows several aspects of these perturbed states. The image (a) shows the energy of different states vs the distance between the ionic core and the cold atom that perturbs the Rydberg state. The images (b) show the electron density for the different kinds of perturbed states (left panel shows the full wave function and right banel zooms in about 10X). The image (c) gives a sense of energy scale for the electron (-1/r) and the quantized motion (v-1, v, v+1...). The images show a typical Rydberg state perturbed by a cold atom (upper) and one leading to states like in images (b) (lower).


A.S. Stodolna, F. Lepine, T. Bergeman, F. Robicheaux, A. Gijsbertsen, J.H. Jungmann, C. Bordas, and M.J.J. Vrakking, "Visualizing the coupling between red and blue Stark states using photoionization microscopy," Phys. Rev. Lett. 113, 103002 (2014). PDF (1210 kB)

This paper is a collaboration between experiment and theory to study coupling between different types of states of atoms in electric fields. Electric fields can mix the angular momentum of a weakly bound electron giving states with qualitatively different character. Some have very large dipole moments aligned with the electric field and some are anti-aligned. For some states, small changes in electric field strength can cause states with qualitatively different character to have similar energy. Since states with nearly the same energy can be mixed by small perturbations, the small region occupied by the core electrons can lead to nearly complete mixing between the states.



This image is a schematic of how the experiment works. The electron is excited to the region near these states and can be pulled from the atom by the electric field. The transverse part of the electron wave can be imaged and gives a set of concentric rings. The intensity and radii of the rings reflect the state of the electron when it leaves the atom.



This image is a figure from the paper showing how the rings evolve over a very small range of energy. The different character of the rings reflect the different character of the states on the atom.

We used similar techniques to study H atoms: A.S. Stodolna, A. Rouzee, F. Lepine, S. Cohen, F. Robicheaux, A. Gijsbertsen, J.H. Jungman, C. Bordas, and M.J.J. Vrakking, "Hydrogen atoms under magnification: direct observation of the nodal structure of Stark states," Phys. Rev. Lett. 110, 213001 (2013). PDF (1,150 kB) Physics Focus (viewpoint)
and in
S. Cohen, M.M. Harb, A. Ollagnier, F. Robicheaux, M.J.J. Vrakking, T. Barillot, F. Lepine, and C. Bordas, "Wave function microscopy of quasibound atomic states," Phys. Rev. Lett. 110, 183001 (2013). PDF (481 kB)

Five Recent Publications

P. Giannakeas, M. T. Eiles, F. Robicheaux, and J. M. Rost, "Generalized local frame-transformation theory for ultralong-range Rydberg molecules," Phys. Rev. A 102, 033315 (2020). PDF (2000 kB)

E. Moufarej, M. Vielle-Grosjean, G. Khalili, A.J. McCulloch, F. Robicheaux, Y.J. Picard, and D. Comparat, "Forced field ionization of Rydberg states for the production of monochromatic beams," Phys. Rev. A 95, 043409 (2017). PDF (1080 kB)

X. Wang and F. Robicheaux, "Energy shift and state mixing of Rydberg atoms in ponderomotive optical traps," J. Phys. B 49, 164005 (2016). PDF (934 kB)

P. Giannakeas, Chris H. Greene, and F. Robicheaux, "Generalized local-frame-transformation theory for excited species in external fields," Phys. Rev. A 94, 013419 (2016). PDF (486 kB)

S. Cohen, M. M. Harb, A. Ollagnier, F. Robicheaux, M. J. J. Vrakking, T. Barillot, F. Lepine, and C. Bordas, "Photoionization microscopy of the lithium atom: Wave-function imaging of quasibound and continuum Stark states," Phys. Rev. A 94, 013414 (2016). PDF (1650 kB)

Francis Image

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