  We exploit InSb's magnetic-induced optical properties to propose THz
sub-wavelength antenna designs that actively tune the radiative decay rates of
dipole emitters at their proximity. The proposed designs include a spherical
InSb antenna and a cylindrical Si-InSb hybrid antenna that demonstrate distinct
behaviors; the former dramatically enhances both radiative and non-radiative
decay rates in the epsilon-near-zero region due to the dominant contribution of
the Zeeman splitting electric octupole mode. The latter realizes significant
radiative decay rate enhancement via magnetic octupole mode, mitigating the
quenching process and accelerating the photon production rate. A deep
learning-based optimization of emitter positioning further enhances the quantum
efficiency of the proposed hybrid system. These novel mechanisms are
potentially promising for tunable THz single-photon sources in integrated
quantum networks.
