Fifty Years of the Dynamical Casimir Effect
Viktor Dodonov
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In one page
Shake a mirror hard enough and light comes out of nothing. That is the dynamical Casimir effect, and Viktor Dodonov — one of the people who named it — wrote this review for its fiftieth anniversary. The story starts in June 1969 with a doctoral thesis: G. T. Moore showed that moving the ideal walls of a one-dimensional cavity turns the vacuum's own fluctuations into real photons. DeWitt did it for a single mirror, Fulling and Davies filled in the detail, and by 2020 more than three hundred papers carried the phrase. Dodonov's definition is the one worth keeping: macroscopic phenomena caused by changing the vacuum quantum state of a field through fast changes in the boundaries that confine it. The breakthrough, when it came, was not a mirror at all. Superconducting circuits, where a Josephson junction moves an effective boundary at up to a quarter of light speed, made the photons in the gigahertz band.
Why it matters hereChapter 6 needs one result that turns the vacuum from a calculation into a source, and this is the review that maps it — light made from nothing, published, and realised on more than one platform. It also names the measurement still outstanding, the effect with real moving boundaries, which is exactly the shape an honest open question should have.
What it claims
01The dynamical Casimir effect is defined as macroscopic phenomena caused by changes of the vacuum quantum states of fields due to fast time variations of the positions, or properties, of the boundaries confining those fields; its most important manifestation is the creation of real field quanta — photons — by the motion of neutral boundaries.Section 1, Introduction
Settled physics02The line begins with G. T. Moore, whose 1969 thesis work — published in 1970 — showed in a simplified one-dimensional model that motions of the ideal boundaries of a cavity generate quanta of the electromagnetic field from the initial vacuum state; DeWitt then showed particle creation from vacuum in a single-mirror set-up, and Fulling and Davies studied it in more detail.Section 1, Introduction
Settled physics03The field is now substantial: more than 300 papers containing the words dynamical Casimir have been published, over 100 of them in the decade to 2020, and Moore's paper has been cited more than 400 times.Section 1, Introduction
Settled physics04The experimental success came from superconducting circuits rather than moving mirrors: a coplanar waveguide combined with a Josephson junction reaches an effective boundary velocity of up to 25 percent of the speed of light in vacuum, and the experiments were performed in the few-gigahertz range — one by periodic fast changes of the boundary conditions at one side of an open strip-line waveguide, another by parametric resonance from changing the effective speed of light.Section 4.1, Circuit DCE
Settled physics05Analogues of the effect have been studied right across condensed matter — Bose–Einstein condensates and ultracold gases, plasmon resonances in metallic nanoparticles, polaritons, magnons and phonons — where replacing electromagnetic waves with sound analogues allows much higher ratios of effective boundary velocity to wave speed, including supersonic regimes.Section 4.2, Analogs of DCE in Condensed Matter
Settled physics06Observation of the real dynamical Casimir effect in a cavity with genuinely moving boundaries remains a challenge — in the review's own closing word, a dream — and that is the outstanding measurement in this field.Section 7, Conclusions
What to watch
The way in
https://doi.org/10.3390/physics2010007Physics 2(1), 67–104; received 31 December 2019, accepted 10 February 2020, published 14 February 2020 by MDPI. Open access under a Creative Commons Attribution 4.0 International licence (CC BY 4.0), free to read at the journal. The author is at the Institute of Physics and International Center for Physics, University of Brasília.
How to cite it
Viktor Dodonov (2020) Fifty Years of the Dynamical Casimir Effect. doi:10.3390/physics2010007
Where it sits in the curriculum