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Gain, directionality, and noise in microwave SQUID amplifiers: Input-output approach

Archana Kamal, John Clarke, and Michel H. Devoret
Phys. Rev. B 86, 144510 – Published 10 October 2012

Abstract

We present a new theoretical framework to analyze microwave amplifiers based on the dc SQUID. Our analysis applies input-output theory generalized for Josephson junction devices biased in the running state. Using this approach, we express the high-frequency dynamics of the SQUID as a scattering between the participating modes. This enables us to elucidate the inherently nonreciprocal nature of gain as a function of bias current and input frequency. This method can, in principle, accommodate an arbitrary number of Josephson harmonics generated in the running state of the junction. We report detailed calculations taking into account the first few harmonics that provide simple semiquantitative results showing a degradation of gain, directionality, and noise of the device as a function of increasing signal frequency. We also discuss the fundamental limits on device performance and applications of this formalism to real devices.

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  • Received 29 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.144510

©2012 American Physical Society

Authors & Affiliations

Archana Kamal1,*, John Clarke2, and Michel H. Devoret1

  • 1Departments of Applied Physics, Yale University, New Haven, Connecticut 06520, USA
  • 2Department of Physics, University of California, Berkeley, California 94720, USA

  • *archana.kamal@yale.edu

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Vol. 86, Iss. 14 — 1 October 2012

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