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Research Article

Dynamical Casimir effect in a Josephson metamaterial

Pasi Lähteenmäki, G. S. Paraoanu, Juha Hassel, and Pertti J. Hakonen
  1. aO. V. Lounasmaa Laboratory, Aalto University, 00076, Espoo, Finland; and
  2. bVTT Technical Research Centre of Finland, 02044, Espoo, Finland

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PNAS first published February 12, 2013; https://doi.org/10.1073/pnas.1212705110
Pasi Lähteenmäki
aO. V. Lounasmaa Laboratory, Aalto University, 00076, Espoo, Finland; and
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  • For correspondence: pasi.lahteenmaki@aalto.fi
G. S. Paraoanu
aO. V. Lounasmaa Laboratory, Aalto University, 00076, Espoo, Finland; and
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Juha Hassel
bVTT Technical Research Centre of Finland, 02044, Espoo, Finland
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Pertti J. Hakonen
aO. V. Lounasmaa Laboratory, Aalto University, 00076, Espoo, Finland; and
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  1. Edited by Steven M. Girvin, Yale University, New Haven, CT, and approved January 8, 2013 (received for review August 13, 2012)

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Abstract

The zero-point energy stored in the modes of an electromagnetic cavity has experimentally detectable effects, giving rise to an attractive interaction between the opposite walls, the static Casimir effect. A dynamical version of this effect was predicted to occur when the vacuum energy is changed either by moving the walls of the cavity or by changing the index of refraction, resulting in the conversion of vacuum fluctuations into real photons. Here, we demonstrate the dynamical Casimir effect using a Josephson metamaterial embedded in a microwave cavity at 5.4 GHz. We modulate the effective length of the cavity by flux-biasing the metamaterial based on superconducting quantum interference devices (SQUIDs), which results in variation of a few percentage points in the speed of light. We extract the full 4 × 4 covariance matrix of the emitted microwave radiation, demonstrating that photons at frequencies symmetrical with respect to half of the modulation frequency are generated in pairs. At large detunings of the cavity from half of the modulation frequency, we find power spectra that clearly show the theoretically predicted hallmark of the Casimir effect: a bimodal, “sparrow-tail” structure. The observed substantial photon flux cannot be assigned to parametric amplification of thermal fluctuations; its creation is a direct consequence of the noncommutativity structure of quantum field theory.

  • Josephson junction
  • nanoelectronics
  • quantum mechanics

Footnotes

  • ↵1To whom correspondence should be addressed. E-mail: pasi.lahteenmaki{at}aalto.fi.
  • Author contributions: P.L. and J.H. designed research; P.L. performed research; P.L. and G.S.P. analyzed data; and P.L., G.S.P., and P.J.H. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1212705110/-/DCSupplemental.

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DCE in a Josephson metamaterial
Pasi Lähteenmäki, G. S. Paraoanu, Juha Hassel, Pertti J. Hakonen
Proceedings of the National Academy of Sciences Feb 2013, 201212705; DOI: 10.1073/pnas.1212705110

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DCE in a Josephson metamaterial
Pasi Lähteenmäki, G. S. Paraoanu, Juha Hassel, Pertti J. Hakonen
Proceedings of the National Academy of Sciences Feb 2013, 201212705; DOI: 10.1073/pnas.1212705110
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