Localization and manipulation of Rydberg wave packets using half cycle pulses are discussed. Rydberg wave packets can be localized by applying a train of half-cycle pulses equispaced in time. The localization in this “kicked” Rydberg atom can be due to trapping the wave packet inside the stable islands seen in the classical mixed phase space structure, or the scarred wave function representing quantum mechanical localization while the classical atoms show fast ionization. Chirping the frequency of a train of pulses and modulating the kick strength modify the phase space structure in time and the localized wave packet can be driven to the preferred location in phase space by properly adjusting the time evolution of the phase space structure.

We demonstrate that strong transient phase-space localization can be achieved by the application of a single impulsive ``kick'' in the form of a short (600 ps) unidirectional electric-field pulse to a strongly polarized, quasi-one-dimensional Rydberg atom. The underlying classical dynamics is analyzed and it is shown that phase-space localization results from a focusing effect analogous to rainbow scattering. Moreover, it is shown that the essential features of the classical analysis remain valid in a quantum-mechanical treatment of the system in terms of its phase-space Husimi distribution. The degree of phase-space localization is characterized by the coarse-grained Renyi entropy. Transient phase-space localization is demonstrated experimentally using extreme redshifted $m=0$ potassium Stark states in the $n=351$ manifold and a short probe pulse. The experimental data are in good agreement with theoretical predictions. The localized state provides an excellent starting point for further control and manipulation of the electron wave packet.

We demonstrate that strongly polarized quasi-one-dimensional very-high-n (potassium) Rydberg atoms can be produced by photoexcitation of selected Stark states in the presence of a weak dc field. Calculations show that, for m=0 states, significant photoexcitation occurs only in the vicinity of the Stark-shifted s, p, and d levels, and that those states located near the Stark-shifted d level have sizable polarizations. These predictions are confirmed by experiment. The degree of polarization of the product states is analyzed by studying differences in their ionization characteristics when subject to short pulsed electric fields applied parallel and antiparallel to the dc field.

We show that dynamics can, in general, be used to enhance the coherence of a Hamiltonian ensemble and we analyze the transient coherence using the coarse-grained entropy. We illustrate this concept using a Rydberg atom subject to an impulsive momentum transfer or "kick." Classical simulations predict that the wave packet generated by the kick undergoes strong transient phase-space localization, which forms an excellent starting point for its further control and manipulation. Moreover, we show that such localized states can be "trapped" for extended periods using a train of subsequent kicks.

A technique for generating Rydberg wavepackets in preferred target states is demonstrated that exploits the mixed phase space structure of the periodically `kicked' Rydberg atom. Experimental data and classical simulations for very-high-n Rydberg atoms are presented that show that application of a train of equispaced, unidirectional half-cycle pulses can lead to localization of the final wavepacket in classical stable islands. The product wavepackets are examined using a delayed half-cycle probe pulse. It is demonstrated that the motion of the wavepackets is either quasiperiodic or random depending on whether or not the initial state of the atom overlaps a stable island.

We propose a method for determining the time development of the position coordinates of a Rydberg wave packet using the sudden turn-on of a strong field (a ``field step''). The feasibility of the technique is investigated using wave packets created by a half cycle pulse (HCP) that comprise a superposition of very-high-lying Rydberg states. The time evolution of the wave packet is measured using probe pulses that are applied following a variable time delay. The probe pulse ionizes a fraction of the atoms and the survival probability exhibits pronounced oscillations that are associated with the quasiperiodic evolution of the wave packet. Good agreement is found between the experimental data and the results of classical trajectory Monte Carlo simulations. Extraction of classical phase space coordinates from the data is discussed.

The behavior of Rb(390p) atoms subject to a train of up to 50 half-cycle pulses (HCPs) with duration T-p << T-n, where T-n is the classical electron orbital period, is investigated. In this limit, each HCP simply delivers an impulsive momentum transfer or "kick'' to the electron. The response of atoms to a series of unidirectional kicks and to a series of kicks that alternate in direction is compared. For unidirectional kicks, the Rydberg atom survival probability has a pronounced maximum when the pulse repetition frequency v(p) is similar to 1.3 times the classical orbital frequency v(n). Classical simulations show this behavior provides a signature of dynamical stabilization. Evidence of dynamical stabilization and chaotic diffusion is also found in the distribution of final bound states. Very different behavior is observed for alternating kicks. The survival probability generally increases with v(p), although a small local maximum is evident when v(p)similar to v(n) Little evidence of dynamical stabilization is observed in either the calculated dependence of the survival probability on the number of applied kicks, in the measured final bound-state distribution, or in the classical phase space of the kicked atom. Model calculations for a one-dimensional "atom" reveal islands of stability, but their three-dimensional counterparts are found to be unstable.

A technique to manipulate the -state distribution of high-n Rydberg atoms is described that is based on the application of a large-amplitude rectangular electric field pulse whose rise and fall times are short compared to the classical electron orbital period and whose duration is comparable to the Stark period in the field. It is shown that by varying the duration (and/or amplitude) of this pulse, the final -state distribution can be controlled and that this distribution can be calculated reliably using classical trajectory Monte Carlo techniques.