Materials composed of conjugated organic molecules mediate energy conversion essential to life on earth, as in photosynthesis, and have great potential in quantum information science (QIS). For example, Josephson junctions based on superconductors, which are currently the primary material in quantum computing, only function at extremely cold temperatures owing, in part, to weak interaction strengths that result in superpositions with coherent oscillations in the microwave frequency range. Molecular aggregates are an alternative materials platform whose collective excitations, or Frenkel excitons, can exhibit much stronger interaction strengths, larger than thermal energy at room temperature; as such, they can potentially yield exciton-exciton superpositions with coherent oscillations in the infrared (~100 THz). In this talk, I will discuss our efforts examining the feasibility of DNA-assembled molecular aggregates as materials for QIS. We characterize the materials using a combination of ultrafast nonlinear and Stark optical spectroscopies, often in collaboration with a broader consortium of synthetic chemists, theoretical physicists, and computational materials scientists. First, I will describe the advantages of using DNA as a scaffold for molecular aggregation, including how it may be used to tailor the aggregate environment and overcome a generally problematic collective effect we call aggregation-induced quenching. Next, I will discuss our work characterizing the difference dipole moment of the constituent molecules, whose magnitude governs bi-exciton interactions, along with how substituents intended to increase its magnitude impact other important properties such as excited-state lifetime. Lastly, I will present our recent work indirectly characterizing single-exciton coherence, and our work toward directly characterize this important property of molecular aggregates. In addition to the new knowledge we have generated, we continue to make essential progress toward addressing the feasibility of DNA-assembled molecular aggregates in QIS.
Dr. Ryan D. Pensack is currently a Principal Research Scholar and Graduate Faculty in the Micron School of Materials Science and Engineering at Boise State University. He leads a research group with expertise in ultrafast nonlinear and Stark optical spectroscopies of nanoscale electronic materials. His group currently uses DNA as a scaffold to study the feasibility of aggregates of conjugated organic molecules as materials exhibiting quantum phenomena at temperatures higher than that of liquid helium (> 4 K). Ryan previously worked as a postdoctoral fellow at Princeton and the University of Toronto (2012-2017), received his PhD. in Chemistry at Penn State (2012), and B.A. in Chemistry at Rutgers-Newark (2006).