The Impact of Chirped Pulse Millimeter-Wave Technology on the Spectroscopy, Dynamics, and Manipulation of Molecules in Rydberg States

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Professor Robert Field of MIT is supported by the Chemical Structure, Dynamics, and Mechanisms Program to develop experimental methods that exploit the interaction of Chirped Pulse millimeter wave (CPmmW) radiation with large Rydberg-Rydberg transition moments (kilo-Debye) in excited molecules. The CPmmW-based approach will enable the development of schemes for efficiently populating core-nonpenetrating Rydberg states, which are of special interest in part because of their enormous transition moments and relatively long lifetimes ( 1 microsecond). The crucial feature of CPmmW spectroscopy is that Rydberg-Rydberg transitions are detected directly via the Free Induction Decay (FID) signal that results when the CPmmW pulse polarizes all two-level systems that fall within the ca. 10 GHz wide spectral region of the chirp (10^5 resolution elements in a single 10 nanosecond duration CP). This NMR-like scheme is vastly superior to the single-resolution- element-at-a-time indirect detection schemes that are universally used in pulsed supersonic molecular beam spectroscopy. The interpretation of experimental spectra will be done in the context of Multichannel Quantum Defect Theory (MQDT), which is a beyond-Hydrogen, scattering-based framework for assembling, interpreting, and extrapolating all information about the electronic structure of a molecule. Its building blocks are channels, each comprised of an infinite number of electronic states, rather than Born-Oppenheimer potential energy curves. Although the quantum defect matrix elements provide a compact numerical description of structure and dynamics, the fundamental physical meanings encoded in these matrix elements remain obscure. The most ambitious objective of this project is to uncover the more compact physical representation that lies beyond the numerical MQDT matrix elements. Core-nonpenetrating Rydberg states are a neglected state of matter. Knowledge and exploitation of their unique properties will ignite research in areas ranging from fundamental science to practical applications. For example, MQDT can potentially provide a complete picture of the structure and dynamics of a molecule, which will be essential for the development of molecular electronic devices and quantum computing. Professor Field expects to continue providing assistance to spectroscopists, users of spectroscopic data, and creators of spectrum-based approaches in other areas of science. He has a passion for sharing his unique vision of how intramolecular dynamics is encoded in spectroscopic arcanae, and for devising elegantly simple experimental methods to interrogate and exploit molecules that are not amenable to simple, textbook conceptualization. Students and postdocs in the Field laboratory are challenged to design original experiments, build unconventional fit models for their unconventional spectra, and perform rigorous yet intuition-based quantum mechanical and quantum optics calculations. Members of Field's research group leave MIT with the confidence, instincts, and vision to formulate and solve both fundamental and applied problems.