Mixing in Josephson tunnel junctions

M. C. Wicks

Thin film niobium nitride Josephson tunnel junctions have been used as harmonic mixers in experiments to measure the frequency of various submillimetre wavelength laser lines. The Josephson junctions were used as harmonic mixers with an 18-40 GHz microwave synthesiser providing the local oscillator signal. Harmonics up to the 140th of ∼18 GHz, generated within the junction, mixed with optically pumped laser lines up to 2.5 THz to produce output signals around 20 MHz. Results of frequency measurements and data on the performance of the mixing system, including signal to noise ratios and frequency response, will be presented.

B. T. Ulrich, T. Lee

D. N. Langenberg, William H. Parker, Barry N. Taylor

P. Russer

V. Gubankov, K. Y. Constantinian, V. P. Koshelets +2 more

The electrophysics and microwave properties of Niobium oxide-barrier tunnel junctions with critical current densities up to 105A/cm2were studied. Millimeter wave mixing using strong nonlinearity of quasi-particle tunnelling curve is described. Nonhysteretic Josephson junctions obtained by the low inductance resistive shunting of the tunnel structures were investigated in the large frequency band. The frequency range where these junctions obey the resistively shunted junction model was determined. The shunted tunnel junctions have been shown to be suitable for various applications which require stable enough Josephson junctions with nonhysteretic I-V curve (IVC).

M. C. Wicks

Beats between the harmonics of a microwave signal and various submillimetre laser lines above 890 GHz have been observed in the output from NbN Josephson junctions. Results of these mixing experiments will be described and discussed.