Dual-frequency dielectric resonator for combined magnetic resonance of g∼2 paramagnetic species and diamond NV centers

Nitrogen-vacancy (NV) centers in diamond are leading platforms for quantum sensing, yet efficient control of macroscopic ensembles remains challenging. While resonant structures offer high microwave-to-magnetic-field conversion factor (C_p), their narrow bandwidths typically preclude simultaneous addressing of NV transitions and co-located g∼2 paramagnetic species, which are separated by ∼2.87 GHz at X-band. By enabling concurrent pulsed control of NVs and bath electron spins, one can facilitate advanced applications such as spin-bath driving and NV-assisted dynamic nuclear polarization in ensemble samples. We present a compact dual-frequency dielectric resonator designed to resolve this limitation by co-exciting the TE_01δ mode (∼9 GHz) and the HEM_12δ mode (∼11.8 GHz) within a high-permittivity (ε' ∼ 80) ceramic ring. This architecture concentrates magnetic fields in a shared sample volume just above the resonator surface while maintaining essential optical access and minimizing electric-field-induced heating. Experimental characterization demonstrates resonance frequencies of 8.78 GHz (Q ∼ 237) and 11.41 GHz (Q ∼ 64), with fine-tuning capabilities. Electron spin resonance (ESR) measurements on P1-rich diamond yielded microwave magnetic field, B₁, conversion factors of C_p ∼3.6 and ∼1.2 G/√W, for the respective modes. Additional validation via optically detected magnetic resonance (ODMR) confirmed high-fidelity Rabi oscillations for the low frequency mode (the NV transition |0>↔|-1>) π-pulse durations of ∼ 24 ns, using a peak microwave power of 63 W.