Using the adiabatic crossed-field method we have prepared for the first time doubly excited barium atoms with one valence electron in an oriented circular Rydberg state (n=21, l=m=20, denoted 21c) and the other electron in a
6pj state. In a fraction of these atoms the inner electron decays radiatively to a ${5\mathrm{d}}_{\mathrm{j}\ensuremath{'}}$ metastable level. The obtained circular-metastable doubly excited atoms are very stable. For the (${5\mathrm{d}}_{3/2>}$21c) state the autoionization lifetime \ensuremath{\tau} is longer than 400 \ensuremath{\mu}s; for the (${5\mathrm{d}}_{5/2}$21c) state, \ensuremath{\tau}=1\ifmmode\pm\else\textpm\fi{}0.2 \ensuremath{\mu}s. the specific role of the 5d electron is demonstrated. \textcopyright{} 1990 The American Physical Society
We report the observation of unusual doubly excited states of barium: Ba (5dj, 21c). One of the valence electrons of Ba is prepared in an oriented circular Rydberg state (n = 21, l = m = 20, denoted 21c) by the adiabatic crossed-fields method. The other electron is excited to a 6pj state which decays radiatively to a 5dj metastable level. The measured autoionization lifetime of Ba (5d5/2, 21c) is T ~ 1 μ s , whereas for Ba (5d3/2, 21c), τ is estimated to be longer than 400 μs. This very large difference of lifetimes between the fine-structure states of the inner electron has been analysed.
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.
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.
This paper is devoted to the autoionization process of large-angular-momentum Rydberg states. After a brief account of autoionization formalism in nonrelativistic theory and single-configuration approximation, we apply it to atomic states with one electron of large angular momentum. The dominant contribution is the direct one and the exchange contribution is ignored. In this framework, the autoionization width varies with the principal quantum number as ${n}^{\mathrm{\ensuremath{-}}3}$ and exponentially with the angular momentum. When two excited electrons interact with a spherically symmetric core, it is demonstrated that the interaction between the Rydberg electron and the core polarized by the valence electron is proportional to the interaction between the two active electrons. Using newly derived radial matrix elements, we obtain a generally good agreement between our results and experiments on barium and strontium. Large-l Rydberg states are shown to be stable versus autoionization as soon as l is about 7. Possible refinements of our method are reviewed.
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.