Coupling nitrogen-vacancy center spins in diamond to a grape dimer

Two grapes irradiated inside a microwave (MW) oven typically produce a series of sparks and can ignite a violent plasma. The underlying cause of the plasma has been attributed to the formation of morphological-dependent resonances (MDRs) in the aqueous dielectric dimers that lead to the generation of a strong evanescent MW hotspot between them. Previous experiments have focused on the electric field component of the field as the driving force behind the plasma ignition. Here we couple an ensemble of nitrogen-vacancy (N-<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mi>V</a:mi></a:math>) spins in nanodiamonds (NDs) to the magnetic field component of the dimer MW field. We demonstrate the efficient coupling of the N-<d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mi>V</d:mi></d:math> spins to the MW magnetic field hotspot formed between the grape dimers using optically detected magnetic resonance (ODMR). The ODMR measurements are performed by coupling N-<g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:mi>V</g:mi></g:math> spins in NDs to the evanescent MW fields of a copper wire. When placing a pair of grapes around the NDs and matching the ND position with the expected magnetic field hotspot, we see an enhancement in the ODMR contrast by more than a factor of 2 compared to the measurements without grapes. Using finite-element modeling, we attribute our experimental observation of the field enhancement to the MW hotspot formation between the grape dimers. The present study not only validates previous work on understanding grape-dimer resonator geometries, but it also opens up another avenue for exploring alternative MW resonator designs for quantum technologies. Published by the American Physical Society 2024