Dual-Frequency Dielectric Resonator for Combined Magnetic Resonance of g∼2 Paramagnetic Species and Diamond NV Centers

• First ESR resonator with two distinct, high-Q modes separated by ∼2.87 GHz. • Optimal for measuring flay sample situated just above the resonator surface • Enables efficient spin-bath driving in the vicinity of NV centers. • Suitable for DNP enhancement of nuclear-spin for NV-based quantum sensing. • Resonator performance validated via ESR and ODMR measurements in both modes. 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, B 1 , conversion factors of C p ∼3.6 a n d ∼ 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.