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The dynamical Casimir effect [1–4] is a very general prediction
of quantum field theory: whenever the boundary
conditions of a quantum field are quickly varied in time,
pairs of quanta are generated off the vacuum state by parametric
amplification of zero-point noise. The simplest and
most celebrated example of dynamical Casimir effect has
been predicted for an optical cavity whose plane-parallel
metallic mirrors are made to rapidly oscillate in time along
the cavity axis [5–7]. So far, no experimental observation
of this effect has been reported, the main reason being
the extremely low intensity of the emission for the
experimentally accessible values of the mirror oscillation
speed [7,8]. Alternative schemes to modulate the effective
optical length of a cavity by acting on the refractive index
of the cavity material have been proposed and shown
to give a sizeable intensity of dynamical Casimir emission
for realistic parameters [9–22]. A related but somehow
controversial configuration was considered in [23–26].
Experiments in the direction of [18,19] are presently in
the course of development [27]. Promising preliminary results
using superconducting devices have been recently
presented.
Since the original proposal by Unruh [30], the advances
in the field of the so-called analog models [31] have
pointed out the possibility of simulating the physics of
a quantum field on a generic curved space-time in tabletop
condensed-matter experiments: the propagation of
elementary excitations in spatially and temporally inhomogeneous
systems can in fact be recast in terms of a
relativistic wave equation on an effective curved spacetime.
In the simplest case of acoustic waves in a fluid,
the space-time metric is fixed by the spatial and temporal
profiles of the sound speed and of the flow velocity.
Upon quantization of the resulting field theory, an analog
dynamical Casimir effect is then expected to appear
whenever the boundary conditions on the phonon modes
and/or the sound speed of a spatially homogeneous system
are rapidly varied in time [32,33]. On the other hand,
an analog Hawking radiation is expected to appear in the
presence of an acoustic horizon separating an upstream
region of sub-sonic flow from a downstream one of supersonic
flow [30,34–41].
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※ 編輯: smartcatcher (140.109.113.32), 06/21/2016 11:54:32
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