Tailoring Rydberg Wavepackets

Advances in experimental technique now allow study of the behavior of Rydberg atoms subject to one, or more, pulsed unidirectional electric fields, termed half-cycle pulses (HCPs), whose duration is much less than the classical electron orbital period. In this limit, each HCP simply delivers an impulsive momentum transfer or ``kick" to the excited electron. The application of a carefully-tailored sequence of HCPs provides a powerful means to control and manipulate atomic wavefunctions. This task is greatly simplified if the initial wavefunction is first localised in phase space. This can be achieved by exciting quasi-one-dimensional (quasi-1D) Rydberg Stark states and applying a periodic train of HCPs. The phase space for such kicked atoms contains a series of stable islands embedded in a chaotic sea. Only that portion of the initial wavefunction positioned within a stable island survives leading to creation of a non-dispersive wavepacket that undergoes transient phase space localization and that can be steered toward different regions of phase space by ``chirping'' the frequency and/or amplitude of the HCP train. Application of a single HCP to a quasi-1D atom can also lead to strong transient phase space localization that can be trapped for extended periods using a train of subsequent HCPs. Once localized, further HCPs can be used to engineer a desired final state. For example, a HCP might be used to launch the electron into a near circular orbit or into a highly-elliptical orbit. Although this leads to population of a distribution of higher-n states, this distribution can be narrowed using additional HCPs. These approaches to atomic engineering will be discussed with the aid of recent results.