Flicker (1/f) noise in the critical current of Josephson junctions at 0.09-4.2 K

We have measured the low-frequency noise in the critical current I-c of six dc superconducting quantum interference devices (SQUIDs) with resistively shunted Nb-NbOx-PbIn Josephson junctions in the temperature range T=0.09-4.2 K. Each device is voltage biased, the applied flux is an integer number of flux quanta, and the current fluctuations are measured with a second dc SQUID. At low frequencies f, there is a component of the power spectrum of the critical current fluctuations given approximately by S-Ic(f)=(CIcT2)-T-2/Af, where A is the area of both junctions, and Capproximate to(3.9+/-0.4)x10(-23) m(2)/K-2. For quantum bits based on Josephson junctions, the scaling of S-Ic(f) with T-2 implies that the dephasing time limited by critical current l/f noise should scale as 1/T for temperatures down to at least 0.09 K. (C) 2004 American Institute of Physics.