Spin bath-mediated decoherence in superconductors
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We consider a SQUID tunneling between 2 nearly degenerate flux states. Decoherence caused by paramagnetic and nuclear spins in the low-$T$ limit is shown to be much stronger than that from electronic excitations. The decoherence time $τ_ϕ$ is determined by the linewidth $E_o$ of spin bath states, which can be reduced by a correct choice of ring geometry and isotopic purification. $E_o$ can be measured in either field sweep or microwave absorption experiments, allowing both a test of the theory and design control.
5 pages, LaTex, 3 figures, submitted to PRL in May, 2000
5 pages, LaTex, 3 figures, submitted to PRL in May, 2000