Lessons in molecular spin qubit engineering design with transition metal ions

Emerging quantum technologies promise powerful applications from nanometer-scale characterization of magnetic fields in new materials to inherently secure communication. For such technologies, angstrom-level synthetic control over quantum bits (qubits) imparts a valuable, yet currently quite challenging, opportunity to create tailor-made qubits for quantum sensing and communication tasks. While spin-bearing molecules provide a suitable platform for bespoke qubit design, these molecules generally lack mechanisms to optically initialize and read out the ground state spin, hindering their integration into the existing quantum measurement and control infrastructure. In this work, we illustrate how an interdisciplinary methodology allowed us to realize and then tune the targeted optical-spin control in molecules deemed 'molecular color centers' [1,2]. Additionally, we used readily modifiable synthetic handles, such as ligand field strength and molecular symmetry, to optimize the optical-spin interface and qubit performance [3]. With our general approach to color center design, we illustrated how to expand the library of molecular color centers, demonstrating how synthetic chemistry can bolster the burgeoning field of quantum information science [4,5]. With the lessons gleaned from these initial studies, we aim to construct the second generation of molecular color centers designed to address specific challenges in quantum sensing and communication.