Strong coupling of electromagnetic and magnetic modes in a tunable waveguide cavity

Strong coupling is obtained for a system consisting of two yttrium iron garnet spheres of 1.99 mm and 1.27 mm in diameter respectively placed in a tunable waveguide cavity resonating at 9.31 GHz. The total experimental coupling strength constant, obtained using a model consisting of three coupled oscillators, is 96 MHz which agrees well with the theoretical prediction. We show that the tunability aspect of the cavity allows for the observation of the spheres' resonances in both the strongly coupled and the non-coupled regimes.