Quantum limited balanced superconducting 380-520 GHz mixer on a silicon membrane and mesoscopic tunnel devices for terahertz frequencies - Westig, Marc Peter

Heterodyne detection techniques using superconducting mixers are of great importance in radio-astronomical receivers due to their high sensitivity and their potential to achieve a high spectral-resolution in the order of one million. Present superconducting niobium mixer technologies potentially can reach the fundamental quantum noise limit up to frequencies of 700 GHz, provided that there is no additional noise contributed by the reference frequency source (LO). This work presents for the first time the experimental realization of an integrated balanced superconducting mixer reaching the fundamental quantum noise limit in the frequency range 380-520 GHz, having an instantaneous intermediate frequency bandwidth of 4-8 GHz. The balanced mixer sensitivity is hardly degraded by noise coming from the LO source. We present for the first time a quantitative measurement of the noise contribution of various LO sources using the balanced mixer device. In order to realize a balanced mixer at 1 THz, in the last part of this work we study the nonequilibrium superconductor physics of superconductor-insulator-superconductor junctions using the materials niobium, niobium-titanium-nitride and gold.