Optically Detected Magnetic Resonance on Carbene Molecular Qubits

Solid-state quantum systems with optical and spin degrees of freedom have found widespread application in emerging quantum technologies. Recently, molecular qubits came forward as precisely tunable entities that present a compelling alternative to well-established yet hard-to-tune point defects in solid-state systems. In this work, we disclose ground-state triplet carbenes as purely organic qubits comprising two unpaired electrons in close proximity that can be generated in a crystalline matrix with high spatial accuracy via in situ photoactivation. We further demonstrate how state-of-the-art multireference quantum chemical calculations provide insight into their fundamental spin characteristics. As a result, several key assets were realized in a single solid-state qubit material under cryogenic conditions: The exclusive use of light elements (C, H, N, O), photolithographic patterning, optical spin-selective transitions, and a large zero-field splitting in the GHz regime, which, taken together, lays the ground for optically detected magnetic resonance with remarkable fluorescence contrast of >40% and record-high spin coherence times of T2 = 157(4) μs at 5 K.