A three-dimensional multimode lumped-element resonator for collective spin manipulation and dispersive readout

We report a three-dimensional lumped-element multimode microwave resonator that enables homogeneous collective manipulation and dispersive readout of a macroscopic spin ensemble. By exploiting geometric symmetry, two anti-symmetric modes with strongly suppressed crosstalk are engineered to spatially overlap and couple to the same ensemble at distinct frequencies. Using negatively charged nitrogen-vacancy (NV−) centers in diamond at 28 mK, we observe a collective coupling strength of 5.0 MHz, which is in the vicinity of strong-coupling regime, and demonstrate nondestructive dispersive readout via a detuned mode. The compact design, tunable coupling, and high field homogeneity make this resonator a versatile device for hybrid spin–photon systems and multimode solid-state quantum technologies.