Sub-gap leakage in Nb/AlO sub(x)/Nb and Al/AlO sub(x)/Al Josephson junctions

• Published in: IEEE transactions on applied superconductivity Vol. 11; no. 1 I; pp. 1002 - 1005
• Main Authors: Gubrud, M A, Ejrnaes, M, Berkley, A J, Ramos R.C., Jr, Jin, I, Anderson, J R, Dragt, A J, Lobb, C J, Wellstood, F C
• Format: Journal Article
• Language: English
• Published: 01-03-2001
• ISSN: 1051-8223

In an effort to determine the suitability of Josephson junctions for applications in quantum computation, we measured low-noise dc current-voltage characteristics of Nb/AlO sub(x)/Nb and Al/AlO sub(x)/Al junctions in the temperature range from 90 mK to 1 K. Nb-based samples were obtained from several different facilities with critical currents of a few mu A and critical current densities between 100 and 3000 A/cm super(2). We fabricated the Al-based samples using double-angle evaporation and obtained critical currents of a few mu A with critical current densities of about 30 A/cm super(2 ). We found that the sub-gap leakage current in the Nb-based samples does not depend on temperature in the range 90 mK to 1 K, whereas that for the Al-based samples follows the expected BCS behavior to about 150 mK. Our Al-based samples have a lower level of dissipation than Nb-based devices; however, both Al- and Nb-based samples achieved dissipation levels sufficiently low for some quantum computing applications.