Noise-mediated cooperative behavior and signal detection in dc SQUIDs

Inchiosa, Mario E.; Bulsara, Adi R.
February 2000
AIP Conference Proceedings;2000, Vol. 502 Issue 1, p583
Academic Journal
We study the detection of very weak time-periodic magnetic signals via a double-junction (dc) Superconducting Quantum Interference Device (SQUID). The device, represented by two coupled nonlinear differential equations for the quantum mechanical junction phases, admits of long-time static or oscillatory solutions, the transition being controllable by experimental parameters. Signal detection is optimal when the device is “tuned” to the onset of the oscillatory solutions; i.e., when the minima in the 2D potential function disappear. Modeling the device via a derived input-output transfer characteristic yields a response (quantified via the signal-to-noise ratio at the signal frequency) in good agreement with recent experiments. We also present some preliminary results pertaining to coupled dc SQUIDs, taking into account the (incoherent) thermal noise sources in each of the Josephson junctions. As might be expected from previous work, coupling the SQUIDs and/or summing their outputs enhances the response to the external signal. © 2000 American Institute of Physics.


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