Dynamical Casimir effect in a Josephson metamaterial

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 A fundamental theoretical result of modern quantum field theory is that the quantum vacuum is unstable (1-6) under certain external perturbations that otherwise produce no consequences in a classical treatment (7). As a result of this instability, virtual fluctuations populating the quantum vacuum are converted into real particles by the energy provided by the perturbation. For example, the application of intense electrical fields extracts electron-positron pairs from a vacuum (Schwinger effect), the bending of space-time in the intense gravitational field at event horizons is responsible for the evaporation of black holes (Hawking radiation), the acceleration of an observer in the Minkowski vacuum results in the detection of particles (Unruh effect), and sudden changes in the boundary conditions of electromagnetic field modes or in the speed of light (index of refraction) create photons [dynamical Casimir effect (DCE)] (8). The DCE is a particular case of parametric amplification of vacuum fluctuations (3, 4, 6). To date, preliminary evidence for the analog of Hawking radiation has been obtained (9), whereas in the case of the DCE, a very recent experiment has reported production of photons by the nonadiabatic change of a boundary condition (10). Many other theoretical estimations and proposals for observing this effect in a variety of physical systems exist in the literature (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).In this paper, we demonstrate the DCE by modulating the background in which the field propagates (3). We periodically change the index of refraction (which...

Dynamical Casimir effect in stochastic systems: Photon harvesting through noise

“…To date, several experimental schemes to observe the DCE have been proposed [12][13][14][15][16][17][18], but only a few have succeeded [19,20]. The main limitation is because a non-negligible photon production can only be attained when the mirror's speed becomes comparable to the speed of light.…”

“…For instance, in Refs. [19,20], the equivalent action of a fast moving mirror is mimicked by an inductance variation of a superconducting quantum interference device (SQUID) controlled by a fast oscillating magnetic flux. Unlike actual mirrors, the inductance of a SQUID can be driven at high frequencies (> 10 GHZ), which enables an experimentally detectable photon production.…”

Dynamical Lamb Effect: Prediction and Possibility of Experimental Detection

“…One of the examples of such nonstationary QED phenomena is the dynamical Casimir effect. It is remarkable that it was a superconducting system, which led to the first observation of the dynamical Casimir effect [1,2].A presence of an additional atom in a cavity with time-dependent parameters leads to other nonstationary QED phenomena. For instance, an atom can be parametrically excited, even if the cavity was initially empty.…”

“…One of the examples of such nonstationary QED phenomena is the dynamical Casimir effect. It is remarkable that it was a superconducting system, which led to the first observation of the dynamical Casimir effect [1,2].…”

“…Oscillations of the same type appear also for various photon characteristics of the system. Regardless of the relation between amplitude of the switching g and ω, the maximum probability reaches the finite value 2 4 S on a characteristic time scale ~ 1/g, which depends on the amplitude of the inverse coupling strength only. In contrast to the probability in the regime of a single switching (6), the time dependence of w↑(t) in parametric resonance regime (7) does not contain high-frequency oscillations at ω.…”