Development of 0.5-V Josephson junction array devices for quantum voltage standards

The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/NbxSi1-x/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current(dc) quantum voltage of about 0.5 V with a ~1-mA current margin of the 1 st quantum voltage step is obtained.To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology(NIST) programmable Josephson voltage standard(PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.

Quadruple-stacked Nb/NbxSi1-x/Nb Josephson junctions for large-scale array application

Large-scale Josephson junction(JJ)arrays are essential in many applications,especially quantum voltage standards application for which hundreds of thousands of junctions are required to realize a high quantum voltage.For almost all applications,high-quality JJ arrays must be realized in a small chip area.This study proposes vertically quadruplestacked Nb/(NbxSi1-x/Nb)4 JJs to increase the integration density of junctions in an array.The current–voltage(I–V)characteristics of a single stack of Nb/(NbxSi1??x/Nb)4 JJs have been measured at 4.2 K.The uniformity of junctions in one stack and the uniformity of several stacks over the entire 2 inches wafer have been analyzed.By optimizing the fabrication parameters,a large-scale quadruple-stacked Nb/(NbxSi1??x/Nb)4 array consisting of 400000 junctions is realized.Good DC I–V characteristics are obtained,indicating the good uniformity of the large-scale array.

Adaptive suppression of passive intermodulation in digital satellite transceivers

For the performance issues of satellite transceivers suffering passive intermodulation interference,a novel and effective digital suppression algorithm is presented in this paper.In contrast to analog approaches,digital passive intermodulation（PIM） suppression approaches can be easily reconfigured and therefore are highly attractive for future satellite communication systems.A simplified model of nonlinear distortion from passive microwave devices is established in consideration of the memory effect.The multiple high-order PIM products falling into the receiving band can be described as a bilinear predictor function.A suppression algorithm based on a bilinear polynomial decorrelated adaptive filter is proposed for baseband digital signal processing.In consideration of the time-varying characteristics of passive intermodulation,this algorithm can achieve the rapidness of online interference estimation and low complexity with less consumption of resources.Numerical simulation results show that the algorithm can effectively compensate the passive intermodulation interference,and achieve a high signal-to-interference ratio gain.