Understanding, improving, and designing the microwave delivery and detection circuits of an electron paramagnetic resonance setup are key challenges for high sensitivity spectrometers. One goal in this context is the investigation of small spin ensembles. In this regard, on-chip microwave resonator structures provide a promising pathway, although they come along with an inhomogeneous magnetic excitation field. Moreover, the use of superconducting circuits and low temperatures allows for a suppression of the ohmic losses in the resonator structure and offer high spin polarizations naturally improving the EPR signal.
This project follows two main approaches: (i) the improvement of the EPR detection sensitivity by employing ultra-sensitive microwave analysis techniques as well as optimized low-loss and downsized microwave detection circuits adapted from the field of circuit quantum electrodynamics, and (ii) an improved control over the spin ensembles by employing optimized pulse sequences. Harnessing these new developments is expected to yield increased detection sensitivity, as well as higher signal-to-noise ratio corresponding to shorter acquisition times. These improvements shall be applied to solid state EPR at millikelvin temperatures, and in particular to defects in silicon.