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.

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.

The evolution of Rydberg states of hydrogen and alkali-metal atoms subject to short half-cycle pulses is studied. The convergence of the numerical solutions of the time-dependent Schrodinger equation based on an expansion of the electronic wave function in a finite basis set of Sturmian functions is analyzed in detail. It is shown that the accuracy of such calculations can be established by investigating the stabilization of the transition probabilities with respect to the parameters that define the basis set. The dependence of the quantum and classical ionization thresholds on the pulse shape is investigated. The calculations are compared with experimental data for various pulse profiles, which feature slow or fast rise times. The results show that the ionization thresholds for long pulses are very sensitive to the rise time of the electric field. @S1050-2947~98!00309-6# PACS number~s!: 32.80.Rm, 02.60.2x During the last few years, the ionization and excitation of Rydberg atoms by pulsed unidirectional electric fields, termed half-cycle pulses ~HCPs!, have been investigated ex- tensively. Experiments have reached the regime in which the effective duration of the pulses T p and the peak fieldsFp are of the order of the classical electron orbital period Tni 52pn i and the Coulomb electric field Fn i 5n i4 in the

The ionization of potassium Rydberg atoms with by pulsed unidirectional electric fields, termed half-cycle pulses (HCPs), with various well characterized shapes (rectangular, triangular and sawtooth) and durations comparable to the classical electron orbital period is investigated. The experimental results are compared with classical trajectory Monte Carlo (CTMC) simulations and the classically scaled results of quantum calculations undertaken at n = 5. The data show that in the intermediate regime, , the threshold field for ionization becomes sensitive to the shape and rise time of the HCP, increasing with increasing rise time. For each pulse shape, the agreement between the experimental measurements and both the CTMC and quantum calculations is very good.