Dynamical Casimir effect in a Josephson metamaterial

P. Lähteenmäki, G.S. Paraoanu, Juha Hassel, P.J. Hakonen

Research output: Contribution to journalArticleScientificpeer-review

159 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)4234-4238
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number11
DOIs
Publication statusPublished - 2013
MoE publication typeA1 Journal article-refereed

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cavities
frequency modulation
photons
microwaves
vacuum
zero point energy
power spectra
refraction
electromagnetism
interference
interactions
energy

Keywords

  • Josephson junctions
  • nanoelectronics
  • quantum mechanics

Cite this

Lähteenmäki, P. ; Paraoanu, G.S. ; Hassel, Juha ; Hakonen, P.J. / Dynamical Casimir effect in a Josephson metamaterial. In: Proceedings of the National Academy of Sciences of the United States of America. 2013 ; Vol. 110, No. 11. pp. 4234-4238.
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Dynamical Casimir effect in a Josephson metamaterial. / Lähteenmäki, P.; Paraoanu, G.S.; Hassel, Juha; Hakonen, P.J.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 110, No. 11, 2013, p. 4234-4238.

Research output: Contribution to journalArticleScientificpeer-review

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AU - Lähteenmäki, P.

AU - Paraoanu, G.S.

AU - Hassel, Juha

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N2 - 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.

AB - 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.

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