Analog simulation of the nonideal behavior of superconducting Josephson microbridges

Luis B. Gómez, Shinichi Kitamura, Takahiro Kubo +2 more

E. D. Vol, A. N. Omel’yanchuk

We study theoretically superconducting microstructures of a special configuration, viz., Josephson multi-terminals (JMT), which are systems of interconnected microbridges. The nonlinear interaction of individual bridge junctions in JMT is due to fact that they have a common center and, hence, that the superconducting order parameter in each weak link is a function of the currents through all other microbridges. JMT is a nonlinear parametric element controlled by the current and the magnetic field. Dynamic equations have been derived, which govern the behavior of JMT versus the control parameters, viz., transport control currents or fluxes of an external magnetic field. We consider various JMT working regimes: synchronization of Josephson oscillations, degeneration of metastable states, and broken symmetry of the ground state in magnetic field.

Yuki Yamanashi, Akira Sugiyama, Shunpei Imagawa +1 more

Ling Jiang, T. Shiino, Sukeyasu Steven Yamamoto +1 more

In this paper, we present the intrinsic mixing behavior of superconducting niobium titanium nitride hot electron bolometer mixer based on in-situ technique. We make detailed comparison between simulated and measured performance of the HEB mixers at 0.8 and 1.5 THz. A distributed hot spot model which is based on solving a heat balance equation is employed to characterize current-voltage curve, electron and phonon temperature distribution along superconducting microbridge, intermediate frequency gain bandwidth and intrinsic noise temperature of the mixers. The simulated intermediate frequency gain bandwidth decreases with the increase of microbridge length, which is in good agreement with measured results. For the microbridge with 0.15 µm in length, the IF gain bandwidth is simulated to be 2.6 GHz at 0.8 and 1.5 THz. When the microbridge length is increased to 0.3 µm, the calculated IF gain bandwidth is 1.8 GHz. The simulated results demonstrate the IF gain bandwidth is only related with microbridge length, independent of RF frequency. It's very useful to find the critical parameters which mainly affects the mixer noise temperature and IF gain bandwidth. In this paper we will give the critical factors as the reference for fabrication and measurement of HEB mixers. We have found that when the ratio of length to width of the microbridge is set to be around 0.15, the simulated and measured mixer noise temperature show the lowest value. More details will be presented in the paper.

N. F. Pedersen, O. H. Soerensen, J. Mygind +3 more

We report direct measurements of the Josephson radiation emitted in X band from a superconducting thin-film microbridge coupled to a resonance cavity. Power is emitted if one of the harmonics of the Josephson frequency is in the bandwidth of the receiver. The maximum power emitted during our experiment was 10−13 W. The Josephson radiation could easily be detected at frequencies off resonance.

Pascal Febvre, Torsten Reich, Hannes Toepfer +5 more