Broadband electron spin resonance spectroscopy with a superconducting resonator, Part 2 : Experiments

Electron spin resonance (ESR) spectroscopy is a useful characterization tool for quantum materials that is traditionally limited in terms of sensitivity, probing frequency, and volume. Here, we present an alternative: a longitudinal spin-cavity coupling mechanism based on the effects of the spin polarization on high-kinetic-inductance superconducting resonators. This interaction allows for broadband measurements to probe spin transitions.

We report experimental evidence of this longitudinal spin-resonator interaction where the resonator is affected by the spins polarization for detunings between the spin and the resonator larger than 1 GHz, where the contribution of the dispersive interaction is vanishing. In the specific implementation, numerical simulations show that the main contributions come from near-surface spins. This novel coupling can lead to new characterization tools and methods of quantum defects, complex quantum materials and many other paramagnetic systems.