Measuring Superconductor Magnetic Noise

Wenlei Shan, Sheng‐Cai Shi, Yutaro Sekímoto +1 more

We have investigated the effect of a moderately strong magnetic field (up to 1200 Gauss, 13 quantum fluxes within a single junction) on the heterodyne mixing performance of a 385-500GHz superconductor-insulator-superconductor mixer. Both experimental and numerical results indicate that the mixer conversion gain can be significantly reduced by a magnetic field. Surprisingly, the mixer noise shows very weak dependence. The overall receiver noise increase is merely caused by the intermediate frequency noise contribution amplified by a factor of gain reduction. At the expense of little system noise degradation, a relatively strong magnet field can make the mixer more stable at the bias point corresponding to its noise minimum

Jørn Bindslev Hansen

Brigitte Léridon, Pascal Febvre, Sylvie George +2 more

Josephson currents have been observed to drain instabilities and decrease the sensitivity of a heterodyne superconductor-insulator-superconductor (SIS) receiver operated at submillimeter wavelengths. A static magnetic field is usually applied on the SIS junction to reduce the magnitude of its critical Josephson currents and enable quasiparticle mixing. We measured the SIS mixer output power at the intermediate frequency (IF) versus the dc bias voltage of an array of two 1 μm2 Nb/Al–Al2O3/Nb junctions. We show evidence of additional, magnetic-field-sensitive noise, peaked at the Shapiro steps voltages, which is due to high-frequency Josephson currents converted to the IF by quasiparticle mixing.

S. Sendelbach, Antonio Puglielli, Chang‐Beom Eom +3 more

R. McDermott

Masayoshi Kobayashi, Shinji Ohara, Akira Katsuno +2 more

The effects of a magnetic field on the noise due to the Josephson current in a superconductor-insulator-superconductor (SIS) mixer were investigated. The noise was found to be suppressed by an applied magnetic field small enough not to affect the DC characteristics of the mixer adversely. The quantum mixing effect between 70 GHz and 10 GHz radiations was clearly observed at bias voltages of 1∼3 mV, as a result of the noise suppression.