Trigonal Bipyramidal V³⁺ Complex as an Optically Addressable Molecular Qubit Candidate

Abstract

Synthetic chemistry enables a bottom-up approach to quantum information science, where atoms can be deterministically positioned in a quantum bit or qubit. Two key requirements to realize quantum technologies are qubit initialization and read-out. By imbuing molecular spins with optical initialization and readout mechanisms, analogous to solid-state defects, molecules could be integrated into existing quantum infrastructure. To mimic the electronic structure of optically addressable defect sites, we designed the spin-triplet, V³⁺ complex, (C₆F₅)₃trenVCN^<i>t</i>Bu (<b>1</b>). We measured the static spin properties as well as the spin coherence time of <b>1</b> demonstrating coherent control of this spin qubit with a 240 GHz electron paramagnetic resonance spectrometer powered by a free electron laser. We found that <b>1</b> exhibited narrow, near-infrared photoluminescence (PL) from a spin-singlet excited state. Using variable magnetic field PL spectroscopy, we resolved emission into each of the ground-state spin sublevels, a crucial component for spin-selective optical initialization and readout. This work demonstrates that trigonally symmetric, heteroleptic V³⁺ complexes are candidates for optical spin addressability.