Magnetic wideband VHF localized field probe using magnon polaritons

Abstract: We present here an optimisation and demonstration of a wide band instrument capable of measuring localised and directionally alternated magnetic fields below pT in the very high frequency (VHF) range. We take advantage of the magnon-photon hybridization between a yttrium iron garnet (YIG) sphere and a copper resonant cavity to employ a resonant heterodyne detection scheme. The measurement is near instantaneous due to the strong coupling attained between magnons and photons.In this work measurements are reported showing a significant widening of the measurement bandwidth, obtained by tuning the YIG Larmor frequency with a bias magnetic field and adjusting the magnon-photon coupling strength. Minimum sensitivity in the sub pT regime is demonstrated in the range 150 -- 225 MHz at room temperature and expected to go to fT in cryogenic temperatures. Dynamic range is estimated to be above 100 dB. The sensitivity is found to be independent on size, being ready to in-chip miniaturization. Such device can be an important building block to quantum circuits, such as baluns, transducers or signal processing units.