Optically Detected Coherent Spin Control of Organic Molecular Color Center Qubits
Sebastian M. Kopp, Shunta Nakamura, Yong Rui Poh, Kathryn R. Peinkofer, Brian T. Phelan, Joel Yuen-Zhou, Matthew D. Krzyaniak, Michael R. Wasielewski
Abstract
Molecular optical-spin interfaces are emerging as promising alternatives to solid-state defects, such as diamond nitrogen vacancy centers for quantum information science applications. In this work, we report a new organic molecular color center consisting of two luminescent tris(2,4,6-trichlorophenyl)methyl ( TTM ) radicals connected at the 2,6-positions of a toluene bridge. Optical polarization of the |T 0 ⟩ sublevel of the triplet ground state is achieved by spin-selective excited-state intersystem crossing from the |T + ⟩ and |T – ⟩ sublevels of the triplet excited state. Steric hindrance between the toluene methyl group and the phenyls of the TTM radicals results in a structure that increases the excited-state intersystem crossing spin selectivity while reducing the electronic coupling between the TTM subunits. This results in an order of magnitude increase in the optically detected magnetic resonance contrast and longer excited-state lifetimes relative to the sterically unencumbered analogue. We demonstrate coherent microwave manipulation of the spin-polarized ground-state populations and coherences using optical detection of Rabi nutations, Hahn echo formation, and echo decay measurements at 85 K in a nuclear-spin-rich solvent matrix. This marks a crucial step toward leveraging the favorable spin relaxation times of organic molecules for applications as quantum sensors at temperatures that heretofore have been difficult to achieve by molecular color centers.