Accessible electron spin resonance instrumentation within cryostat environments; a step towards sub-Kelvin ESR

ESR has been increasingly used within the field of quantum information for coherent manipulation and readout of qubit states. These advances have brought about the growing use of unconventional and homebuilt ESR instruments, allowing for a high degree of control and customization over experimental parameters. In addition, ESR has recently been used as a probe of exotic excitations in quantum magnets, mainly focusing on studying the existence and dynamics of spinons in quantum spin chain materials. Investigating these types of systems requires sub-Kelvin temperatures, only reachable inside dilution refrigerators. Apart from a few innovative laboratories, most low-temperature ESR is limited to above few Kelvin.

As a step towards full implementation at millikelvin temperatures, we utilize this modular approach to design and assemble a simple CW spectrometer to characterize the g-factors of materials of interest. Our probe is easily implemented into an existing measurement platform (Quantum Design PPMS), facilitating reproducibility in groups with similar equipment.