Optically Addressable Molecular Spin Systems for Quantum Technologies

Quantum sensors have been demonstrated across a range of platforms, including solid-state defect centers such as those in diamond or hexagonal boron nitride. While these systems have made remarkable progress, they often face limitations in tunability, scalability, deterministic qubit placement, or targeting specific sensing tasks.
Molecular and low-dimensional systems provide a highly adaptable platform for quantum sensing. Their spin and optical properties can be tailored to the sensing task, whether adjusting excitation and readout wavelengths or optimizing sensitivity to particular analytes, while maintaining molecular reproducibility and operation at room temperature.
I will begin by briefly highlighting my broader experimental work on spin phenomena across various systems, including intrinsic edge-state magnetism in phosphorene nanoribbons [1], structure–property relationships in singlet fission chromophores enabling control of correlated triplet-pair spin states [2], and the chiral-induced spin selectivity (CISS) effect which can allow access to highly spin-polarized states at room temperature [3].
I will then focus on spin-radical organic semiconductors, a central direction of my current research. These systems combine open-shell electronic structure with high luminescence [4,5] and access to high-spin excited states [6], providing a direct route to spin initialization and read-out.
I will present a fully organic diradical system comprising two chlorinated trityl (TTM) units connected via a meta-linked fluorene bridge, which exhibits spin-dependent luminescence with near-unity photoluminescence quantum yield [7]. Electron paramagnetic resonance (EPR) spectroscopy reveals a triplet dark ground state, and transient EPR measurements indicate spin-sublevel selective intersystem crossing, with ground-state polarization persisting up to 200 μs at 200 K. Coherent spin control is demonstrated using pulsed EPR, while optical initialization and read-out are achieved via optically detected magnetic resonance (ODMR) [7]. The exceptional combination of high luminescence, localized spin character, and coherent addressability positions this diradical system as a compelling new platform for optically controllable molecular spin semiconductors with potential applications in quantum information processing and sensing.
Lastly, I will discuss future opportunities for optically addressable molecular spin systems in quantum sensing and photonic quantum technologies. The chemical tunability of molecular platforms offers unique opportunities to develop targeted quantum sensors for healthcare, environmental monitoring, and other real-world applications. I will also discuss how molecular spin qubits can be integrated with photonic architectures to create hybrid quantum systems, combining the chemical programmability of molecular platforms with the scalability and connectivity offered by photonics. [1] Ashoka, A., Clancy, A.J., Panjwani, N.A. et al., Nature, 639, 348-353, 2025 [2] Kim, W., Panjwani, N.A., et al., Cell Reports Physical Science, 5, 102045, 2024 [3] Chiesa, A. et al., J. Phys. Chem. Lett.,16, 21, 5358–5372, 2025
[4] Ai X., et al., Nature, 563, 536, 2018
[5] Cho H. et al., Advanced Materials, 35, 2303666, 2023
[6] Gorgon S. et al., Nature, 620, 538, 2023
[7] Chowdhury R., Murto P., Panjwani N. A., et al., Nature Chemistry, 17, 1410–1417, 2025