Prof. Francis Robicheaux Dr. Robicheaux is a
professor at Auburn University since 1993 and a Fellow of the American
Physical Society since 2002. His research area is Theoretical Atomic
Physics, mainly focusing on time dependent atomic phenomena, highly
excited (Rydberg) atoms, electron scattering, strong fields and
ultracold plasmas. He is a member of the ALPHA collaboration which was the first group
to trap the antimatter version of the Hydrogen atom and the first group to quantitatively measure some of its properties.


Rydberg Atoms in Strong Fields(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. We are particularly interested in the behavior of these atoms in strong fields. The fields 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. T. Topcu and F. Robicheaux, “Multiphoton adiabatic rapid passage: classical transition induced by separatrix crossing,” J. Phys. B 42, 044014 (2009). PDF (515 kB) In this paper, we reinterpreted the recent experimental results from Tom Gallagher's group (H. Maeda, J.H. Gurian, D.V.L. Norum, and T.F. Gallagher, Phys. Rev. Lett. 96, 073002 (2006).) where they measured a 10 photon transition in Rb by chirping a microwave field. This appears to be a quintessential quantum process but we found that it was possible to obtain a classical explanation of the results. We also found that the final state contained many more angular momenta than could be explained by a 10 photon transtions. There is a classical version of this process that, remarkably, gives a high localization of the final energy. The explanation is that the microwave field puts an island in the Poincare surface of section plot. By chirping the frequency of the microwaves, the island moves to lower action and the population swings through the separatrix and the chaotic sea to the upper side of the island. They finish with a small range of final action. Y. Ni, S. Zamith, F. Lepine, T. Martchenko, M. Kling, O. Ghafur, H.G. Muller, G. Berden, F. Robicheaux, and M.J.J. Vrakking, “Abovethreshold ionization in a strong dc electric field,” Phys. Rev. A 78, 013413 (2008). PDF (730 kB) This paper was a collaboration with Marc Vrakking's experimental group to look at the strong field ionization of a highly excited state in a static electric field. Five Recent Publications
T. Topcu and F. Robicheaux, “Chaotic ionization of a highly excited hydrogen atom in parallel electric and magnetic fields,” J. Phys. B 40, 1925 (2007). PDF (2150 kB) M. Strom, C. Sathe, M. Agaker, J. Soderstrom, J.E. Rubensson, S. Stranges, R. Richter, M. Alagia, T.W. Gorczyca, and F. Robicheaux, "Magneticfield induced enhancement in the fluorescence yield spectrum of doubly excited states in helium," Phys. Rev. Lett. 97, 253002 (2006). PDF (548 kB) T. Topcu, M. S. Pindzola, C. P. Balance, D. C. Griffin, and F. Robicheaux, “Electronimpact ionization of highly excited hydrogenlike ions in a collinear swave model,” Phys. Rev. A 74, 062708 (2006). PDF (694 kB) A. Wetzels, A. Gurtler, L.D. Noordam, and F. Robicheaux, "Farinfrared RydbergRydberg transitions in a magnetic field: Deexcitation of antihydrogen atoms", Phys. Rev. A 73, 062507 (2006). PDF (269 kB) C. Sathe, M. Strom, M. Agaker, J. Soderstrom, J.E. Rubensson, R. Richter, M. Alagia, S. Stranges, T.W. Gorczyca, and F. Robicheaux, "Double excitations of helium in weak static electric fields," Phys. Rev. Lett. 96, 043002 (2006). PDF (897 kB) 
robicfj[at]auburn.edu Links: 