Engineering the optical-spin interface of molecular qubits by modulating spin-flip emission lifetimes

Optically addressable molecular qubits based on spin-flip (SF) emissive transitions are emerging as promising platforms for quantum technologies, combining optical addressability with chemical tunability. Yet, the mechanisms governing their SF radiative lifetimes, which are crucial for efficient optical readout, remain poorly understood. In this work, we employ a combination of computational approaches to explore how chemical and structural factors control the emissive behavior of Cr⁴⁺ and Mo⁴⁺ molecular qubits. By analyzing the optical and electronic structure of the qubits, we identify the interdependence between the metal-ligand bonding environment, molecular symmetry, and the radiative SF emission rate. Furthermore, our analysis reveals how structural rearrangements resulting from applied strain efficiently modulate the radiative lifetime of Cr⁴⁺ qubits, which is relevant for quantum sensing applications. This study outlines a quantitative framework for rationally designing molecular spin qubits and SF emitters with controllable optical properties for quantum information applications.