The subgap current in Nb/AlOx/Nb tunnel junctions

Milliken, F. P.; Koch, R. H.; Kirtley, J. R.; Rozen, J. R.
December 2004
Applied Physics Letters;12/13/2004, Vol. 85 Issue 24, p5941
Academic Journal
We have measured the subgap current at 0.8 K in several hysteretic 1.5×1.6 and 2.6×2.6 μm2 Nb/AlOx/Nb tunnel junctions. In zero magnetic field, the critical current Ic∼8 μA and the subgap resistance R∼0.3 MΩ. When we apply a magnetic field, Ic can be as low as 1 nA, and R is larger than 1 GΩ. This means that in a superconducting qubit made using Nb tunnel junctions, the decoherence rate from the quasiparticle conductance may be as low as 1/(100 μs).


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