Title :
Sub-gap leakage in Nb/AlOx/Nb and Al/AlOx/Al Josephson junctions
Author :
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.
Author_Institution :
Dept. of Phys., Maryland Univ., College Park, MD, USA
fDate :
3/1/2001 12:00:00 AM
Abstract :
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/AlOx/Nb and Al/AlOx/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 μA and critical current densities between 100 and 3000 A/cm2. We fabricated the Al-based samples using double-angle evaporation and obtained critical currents of a few μA with critical current densities of about 30 A/cm2. 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
Keywords :
Josephson effect; aluminium; aluminium compounds; critical current density (superconductivity); critical currents; leakage currents; niobium; 90 mK to 1 K; Al-AlO-Al; Al/AlOx/Al Josephson junction; BCS theory; DC current-voltage characteristics; Nb-AlO-Nb; Nb/AlOx/Nb Josephson junction; critical current; critical current density; decoherence time; double-angle evaporation; energy dissipation; quantum computing; sub-gap leakage current; temperature dependence; Computer applications; Critical current; Critical current density; Current measurement; Current-voltage characteristics; Density measurement; Josephson junctions; Niobium; Quantum computing; Temperature distribution;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
