Tracking Energy Flow and Quantum Coherence through Nonadiabatic Transitions with Hyperspectral Ultrafast Optics

A group of researchers from Cornell University are funded to use ultrashort pulses of light to watch molecules as they relax to their initial state following the absorption of a photon. During this relaxation, the molecule switches from an excited state potential surface to its ground state potential in a process that involves changes in both electron orbitals and the molecular structure. For many molecules, the switching from one potential to another takes place at a single point on the potential energy landscape known as a conical intersection. As the molecule moves near this intersection, the motion of its electrons and nuclei become highly coupled, resulting in quantum interference. The time it takes a molecule to move through this intersection is exceedingly short, perhaps just a millionth of a billionth of a second, which makes detecting the quantum coherence extremely challenging. The research team will employ a novel, multi-color laser architecture to track the molecule's rapidly changing absorption spectrum after excitation with light on time scales as short as just a few femtoseconds. The team's discoveries could extend beyond just providing insight into fundamental behavior of molecules. Quantum coherence is a foundational principle of quantum information science (QIS), and the experimental methods developed by the Cornell team could one day provide insight into the factors that affect the persistence and collapse of quantum coherent states in chemical systems as they traverse complex energy landscapes. The project will also provide research opportunities for students, contributing to the development of a STEM workforce that is well-versed in the construction of sophisticated research instrumentation. The project focuses on learning how sub-eV electronic upper-state topographical features and electronic coherences mediate electronic relaxation from light-activated non-equilibrium states through conical intersections. The methods to be investigated include hyperspectral transient absorption electronic spectroscopy, covering UV through mid-IR wavelengths, with 10-fs and shorter instrument response function, and optical transient electronic Raman scattering using few-femtosecond light pulses. The molecular targets, which have been of perennial interest for their ability to illuminate fundamental mechanisms of photochemical conversion, will include neutral conjugated hydrocarbons (cyclic and linear) of different size and length, retinal systems including rhodopsins, and DNA nucleobases. Data will be shared with a theory team to pursue a primary project goal of achieving progress in the benchmarking of hybrid quantum mechanical/molecular mechanical (QM/MM) ab initio models of complex photosystems. The laser architecture to be used incorporates novel laser frequency conversion technology that can greatly simplify the optical hyperspectral few-cycle platform used for spectroscopy, eliminating the need for parallel ultrashort pulse amplifiers and dispersion management systems in each beamline, and replacing these with single-stage, dispersion-free frequency extension devices that can be integrated with commercial lasers. Once verified, these accessible benchtop spectroscopy techniques could be applied widely by the greater community. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2604276 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Jeffrey Moses | Institution: Cornell University, ITHACA, NY | Award Amount: $524,016 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2604276 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2604276.html