Quantum noise theory for the dc SQUID

Roger H. Koch, D. J. Van Harlingen, John Clarke

Research output: Contribution to journalArticlepeer-review


The noise temperature of a dc superconducting quantum interference device (SQUID) coupled to a tuned input circuit is computed using the complete quantum expression for the equilibrium noise in the shunt resistance of each junction. At T = 0, where the noise reduces to zero-point fluctuations, the noise temperature for an optimized system is hn/kB ln2, where n is the signal frequency. The computation is extended to nonzero temperatures, and it is shown that a SQUID operated at 1K can approach the quantum limit.

Original languageEnglish (US)
Pages (from-to)380-382
Number of pages3
JournalApplied Physics Letters
Issue number5
StatePublished - 1981
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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