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 ten-fold improvement in ODMR contrast over that observed for randomly ordered m(TTM)2 using continuous-wave ODMR The diradical doped crystals achieve spin coherence times of 2.8, 3.4, and 7.4 s at 294 K, 85 K, 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 towards robust quantum sensing of anisotropic magnetic fields under ambient conditions.