Control of Molecular Quantum State Character by Coherence Effects

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Marjatta Lyyra's research group at Temple University is supported by the Atomic, Molecular and Optical Physics Program to carry out a series of fundamental studies of the interaction of light with small molecules in the frequency domain. Her group has developed applications of quantum optics for molecular systems including electromagnetically induced transparency and the Autler-Townes (AT) effect. These studies have facilitated a shift of quantum optics studies to molecular systems with practical applications as the goal. The complex molecular energy level structure, molecular interactions, and relaxation pathways provide a rich testing ground of coherence effects for controlling molecular dynamics and quantum state character. Through combined experimental and theoretical studies her research group has demonstrated control of molecular angular momentum alignment, for example. Another important application of the Autler-Townes effect is its use as a precision probe of the internuclear distance-dependent transition dipole moment functions, which are at the heart of the interaction of light with molecules. These measurements rely on the measurement of the Autler-Townes splitting from the lineshape of the control laser transition combined with an accurate measurement of the electric field amplitude of this laser. Another application of the AT effect involves external optical control over the mixing between a pair of closely-spaced molecular singlet and triplet eigenstates that are weakly perturbed by the spin-orbit interaction. The AT effect causes the nominal singlet level to split into a pair of field modified levels, one of which tunes closer to the triplet, resulting in increased singlet-triplet mixing, and the other farther from the triplet, resulting in decreased singlet-triplet mixing. Thus this optical control mechanism can be used to "tune" the spin-orbit mixing coefficients and as a result control quantum state singlet and triplet character.In addition to developing new applications of quantum interference and coherence effects, this research bridges traditionally separate research communities: molecular spectroscopy and dynamics on one hand, and quantum optics and control on the other hand. Due to the fundamental nature of this research the results are broadly applicable. Examples include finding optimal excitation pathways for ultracold molecule formation and role of valence electron spin polarization in photochemistry.In this project, young scientists, many of whom are women, participate in forefront scientific research at the undergraduate, graduate and postdoctoral levels and as a result develop critical experience and confidence for their future participation in the scientific and technical workforce.