Dissertation Defense: Nick Wright

Title: Photophysical Characterization of Molecules and Molecular Aggregates for Applications in Quantum Computing Program: Materials Science and Engineering PhD Committee Chair: Jeunghoon Lee Committee: Jeunghoon Lee, Ryan Pensack, Daniel Turner, Bill Knowlton, Joseph Melinger Abstract: Modern computing has transformed our capacity for scientific and technological advancement.

However, modern computers are poorly suited for solving large problems with computational requirements that scale exponentially with input size. Quantum computing offers an alternative computational paradigm that exploits fundamental principles of quantum mechanics to directly solve these classes of problems that are intractable using classical hardware. Current quantum computing architectures rely on superconducting Josephson junctions.

These devices have taken quantum computing from theory into practical applications; however they require operation at millikelvin temperatures due to their GHz-scale superposition frequencies. This temperature requirement – which is orders of magnitude colder than the vacuum of space – makes supporting quantum computing infrastructure large, expensive, and difficult to scale.

Alternative materials that operate at more reasonable temperatures could aid in the widespread adoption of quantum computing. This dissertation investigates molecular materials based on conjugated organic molecules as an alternative platform for quantum computing hardware. Electronic interactions between molecules can produce delocalized excitons with THz-scale energy differences between exciton states.

Coherent superpositions of these exciton states with THz frequencies hold potential for use in quantum computing at temperatures far above the millikelvin range. This work explores the feasibility of using molecular materials for this application by characterizing their optical properties and dynamics with advanced ultrafast spectroscopy techniques.

Constructing quantum computing architecture from molecular materials requires understanding how the molecular structure of individual chromophores and the organization of chromophores within molecular materials impacts their electronic structure, optical properties, and dynamics. This dissertation establishes several design considerations for molecular materials intended to host high frequency superpositions.

Beyond applications in quantum computing, this work also contributes novel insight into vibrational relaxation and decoherence in photoexcited molecules. This work also contributes advancements in experimental methods for dispersion compensation in ultrafast laser pulses, enabling more accurate characterization of femtosecond-timescale dynamics of materials.