We demonstrate a protocol to create localized wave packets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wave packets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wave packets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in a circular classical orbit around the nucleus. The possible extension of the approach to create "planetary atoms" in highly correlated stable multiply excited states is discussed.

Nondispersive localized Trojan wave packets with n i $ 305 moving in near-circular Bohr-like orbits are created and transported to localized near-circular Trojan states of higher n, n f $ 600, by driving with a linearly polarized sinusoidal electric field whose period is slowly increased. The protocol is remarkably efficient with over 80% of the initial atoms being transferred to the higher n states, a result confirmed by classical trajectory Monte Carlo simulations.

We demonstrate that the quantum coherence of mesoscopic very-high-n, n∼305, Rydberg wave packets travelling along nearly circular orbits can be maintained on microsecond time scales corresponding to hundreds of classical orbital periods. The coherence is probed through collapses and revivals of periodic oscillations in the average electron position. The temporal interferences of spatially separated Schrödinger cat-like wave packets are also observed. A novel hybrid quantum–classical trajectory method is employed to simulate the wave packet dynamics.

We present an experimental and theoretical study of the chaotic ionization of quasi-onedimensional potassium Rydberg wavepackets via a phase-space turnstile mechanism. Turnstiles form a general transport mechanism for numerous chaotic systems, and this study explicitly illuminates their relevance to atomic ionization. We create time-dependent Rydberg wavepackets, subject them to alternating applied electric-field "kicks", and measure the electron survival probability. Ionization depends not only on the initial electron energy, but also on the phase-space position of the electron with respect to the turnstile -that part of the electron packet inside the turnstile ionizes after the applied ionization sequence, while that part outside the turnstile does not. The survival data thus encode information on the geometry and location of the turnstile, and are in good agreement with theoretical predictions.

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