Molecular Diradical Spin Qubits in a Crystalline Host as a Platform for Quantum Sensing

Doping a luminescent tris-(2,4,6-trichlorophenyl)-methyl diradical m (TTM) ₂ into a host crystal of its diamagnetic precursor m (HTTM) ₂ creates a molecular color center with enhanced optical-spin interface properties important for quantum sensing. Optical polarization of the |T₀⟩ sublevel of the diradical triplet ground state is achieved by spin-selective intersystem crossing from the |T₊⟩ and |T_-⟩ sublevels of the triplet excited state at ambient and cryogenic temperatures. Coherent spin control of m (TTM) ₂ doped into m (HTTM) ₂ using pulsed optically detected magnetic resonance (ODMR) spectroscopy results in a 10-fold improvement in ODMR contrast over that observed for randomly oriented m (TTM) ₂ using continuous-wave ODMR. The diradical doped crystal powders achieve spin coherence times of 2.8, 3.4, and 7.4 μs at 294, 85, and 5 K, respectively. The diradical photoluminescence is sensitive to weak applied magnetic fields independent of temperature, excitation wavelength, and dopant concentration, providing a promising pathway toward robust quantum sensing of anisotropic magnetic fields under ambient conditions.