The ability to confine light at very small volumes is of paramount importance in order to enhance light-matter interaction both for devices and fundamental studies. The Terahertz and sub-THz spectral domains are particularly prominent for building metallic resonators with ultra-sub-wavelength mode volumes. Indeed, the corresponding wavelengths are large (wavelength= 1mm – 100µm), one can leverage from nanofabrication techniques with nanometer resolution, and metals feature low losses, and even superconducting materials such as NbN are available. In the present project, we will exploit such resonators made of NbN in order to realize and study an elementary system for both electronic transport and light-matter interaction: a semiconductor tunnel junction coupled with an ultra-subwavelength metamaterial resonator. This structure can operate in the Dynamical Coulomb Blockade, where the tunneling of electrons is coupled to the electromagnetic fluctuations of the resonator, providing thus a probe for the its quantum state. Amongs other applications, such device can be used to perform quantum measurements of NBN qubits operating in the 100 GHz range.