Using time-resolved photoelectron imaging, a time-dependent electron orbital alignment is observed during the recurrences of a Rydberg rotational wave packet in krypton. The time-dependent alignment is created via excitation of two ac-Stark shifted states (5d′[5/2]3 and 8d[1/2]1) using a three-photon femtosecond pulse excitation. A straightforward analysis of the measured photoelectron distributions using angular momentum algebra shows that the observed periodic change in the electron orbital alignment is accompanied by a time-dependent change of the associated Bell states. These Bell states describe the entangled system of excited electron and ionic core. Hence, these experiments present a relatively simple excitation scheme for creating a decoherence-free entangled superposition.

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Sequences of pulses with different spectra are used to control rotational wave packet dynamics in Li(2) by exploiting quantum interference phenomena. Wave packet superpositions are excited in a two-step resonant Raman process by two different pulses. Interferences between individual states shared by both wave packets can be used to enhance or destroy specific components of a superposition by varying the time delay between the pulses and/or the relative phase within the pulses. Elimination of selected quantum beats is achieved by greater than 94% for each case. A simple, yet effective, method for generating different color phase-locked pairs of laser pulses in a liquid-crystal pulse shaper setup without the need for interferometric stabilization schemes is described. The ability to manipulate single states of a superposition is an important advancement for intuitive control schemes and provides a potential new approach for initialization schemes in the field of quantum information.

Using one color ultrafast pump-probe spectroscopy, the authors create N-level multiphoton rotational wave packets via resonant optical pumping between the A((1)Sigma(u) (+)) and E((1)Sigma(g) (+)) electronically bound states of Li(2) from a single optically state-selected rovibrational state |nu(A)=11, j(A)=28>. The authors find that excitation with a single amplitude shaped femtosecond pulse allows the direct observation of up to a six photon absorption, which generates a coherent superposition of 13 rotational states. The multilevel rotational wave packet is theoretically treated with the multipole moment formalism in order to characterize the experimentally observed time-dependent alignment. In particular, the authors find that the magnetic state distributions measured among coherently excited rotational states generated by the resonant multiphoton pumping reduces the measured coherence amplitudes by as much as 40%.