Electron capture cross sections for coherent elliptic Rydberg states have been measured as a function of eccentricity. The ion impact velocity was parallel to the minor axis of the associated, classical elliptic orbit and both clockwise and anticlockwise orbital motion of the electron were studied. The incoming ions were 2.5 keV 23 Na + and the Rydberg target, with principal quantum number n=25, was formed by laser excitation of Li atoms with subsequent adiabatic switching of crossed, external electric and magnetic fields. A strong dependence on eccentricity and sense of orbital motion was found.
Doubly excited coherent elliptic states (DECESs) of an atom could be produced by exciting an atomic electron to a Rydberg state, applying the adiabatic field-switching technique to obtain a coherent elliptic state (CES) and by subsequent excitation of an atomic core electron into a low-lying excited state. The DECESs decay by autoionization and radiative transitions. As an example, the autoionization widths are calculated for DECESs in He. The dependence of the widths on the eccentricity of the CES, principal quantum number of the Rydberg electron, orientation of the inner electron orbital and electron exchange is studied and interpreted.
The authors propose to prepare oriented circular Rydberg states in atoms (i.e. states where one valence electron has spherical quantum numbers: m=l=n-1>>1) by combining the specific advantages of the adiabatic crossed-field method, recently tested in alkali and alkaline earth atoms, and of the adiabatic RF field method whose principle was described in 1986. The formal equivalence of the two methods is pointed out. Their association is made possible by considering the dynamical symmetry of the Coulomb potential. In order to illustrate the new process, calculations have been performed for the manifold n=5 of hydrogen.
Circular Rydberg states with
n=70 have been prepared in helium using a modified version of the crossed-fields method. This approach to the preparation of high-
n circular Rydberg states overcomes limitations of the standard crossed-fields method which arise at this, and higher, values of
n. The experiments were performed with atoms traveling in pulsed supersonic beams that were initially laser photoexcited from the metastable
1s2s3S1 level to the
1s73s3S1 level by resonance-enhanced two-color two-photon excitation in a magnetic field of 16.154 G. These excited atoms were then polarized using a perpendicular electric field of 0.844 V/cm, and transferred by a pulse of microwave radiation to the state that, when adiabatically depolarized, evolves into the
n=70 circular state in zero electric field. The excited atoms were detected by state-selective electric field ionization. Each step of the circular state preparation process was validated by comparison with the calculated atomic energy-level structure in the perpendicular electric and magnetic fields used. Of the atoms initially excited to the
1s73s3S1 level, $\ensuremath{\sim}80%$ were transferred to the
n=70 circular state. At these high values of $n, \mathrm{\ensuremath{\Delta}}n=1$ circular-to-circular Rydberg state transitions occur at frequencies below 20 GHz. Consequently, atoms in these states, and the circular state preparation process presented here, are well suited to hybrid cavity QED experiments with Rydberg atoms and superconducting microwave circuits.
Circular atoms, i.e., Rydberg atoms with maximum angular momentum, are semiclassical atoms of great interest for Rydberg constant metrology and QED tests. Following a suggestion by Delande and Gay, we have prepared circular atoms by a new method, involving the adiabatic switching of crossed electric and magnetic fields. The method, which is demonstrated for Rydberg states of lithium (principal quantum number
n=20to25, is applicable over a wide variety of experiment conditions.