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I.
Invited Paper
IC SQUID Conference LBL 11055
Berlin, May 5-9, 1980
FLUCTUATIONS ANALYSIS
John Clarke
Department of Physics, University of California, Berkeley, and
Materials and Molecular Research Division, Lawrence Berkeley
Laboratory, Berkeley, California 94720
This paper briefly reviews sources of noise in Josephson junc-
tions, and the limits they impose on the sensitivity of dc and
rf SQUIDS. The results are strictly valid only for a resis-
tively shunted junction (RSJ) with zero capacitance, but should
be applicable to point contact junctions and microbridges in so
far as these devices can be approximated by the RSJ model. We
first discuss fluctuations arising from Nyquist noise in the
resistive shunt of a single junction in the limit eoR/k"'<<1
in which a classical treatment is appropriate, and then extend
the treatment to the limit el oRikBTl in which quantum effects
become important.
The Nyquist limit theory is used to calculate the noise in a
dc SQUID, and the results are compared with a number of practi-
cal devices. The quantum limit is briefly considered. Results
for the predicted sensitivity of rf SQUIDS are presented, and
also compared with a number of practical devices. Finally, the
importance of 1/f noise (f is the frequency) in limiting the
low frequency performance of SQUIDS is discussed.
II. Noise in the Resistively Shunted Junction
We consider a current-biased RSJk in which current fluctuations
are produced by the equilibrium noise in the shunt resistor.
I,
dh er pe p ra ti
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Clarke, J. Fluctuation analysis, article, January 1, 1980; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1052905/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.