Dynamical Casimir effect in a Josephson metamaterial

Researchers showed the dynamical Casimir effect using a Josephson metamaterial embedded in a microwave cavity. They showed that under certain conditions, real photons are generated in pairs, a The researchers also showed that photons at frequencies symmetric with respect to half the modulation frequency of the cavity are generated in pairs.

Lähteenmäki describes next steps in their research. “Instead of a continuous wave pump, we could have a straight flux line and feed it with a step-like flux pulse,” Lähteenmäki says. “This would allow the creation of an analogue to a black hole event horizon. In fact,” he adds, “we’re hoping to create an artificial event horizon in a metamaterial similar to the one used in our current research and study Hawking radiation originating from it. Also, it would be nice to be able to run experiments on Bell’s inequalities.”

His personal interests, Lähteenmäki says, are fundamental quantum mechanics, quantum information and properties of the vacuum itself. “The obvious applications for these devices,” he notes, “come from quantum computation, and in general they may serve as components for multitude of sensitive measurements. I believe the interest towards low loss metamaterials is high and the field is just getting started. Our results show that these devices have potential and can offer a fruitful platform for many experiments and perhaps practical devices as well. Improving such devices – especially eliminating the losses and making them function more robustly – would allow them to create a general purpose component suitable for creating entangled microwave photon pairs, low noise amplification, squeezed vacuum, and other functions that can be very useful for quantum computation and general experiments in the quantum mechanics and in studying the vacuum.”

Another possibility, Lähteenmäki adds, is to create a metamaterial which would allow them to stop signal propagation in the material entirely and allow them to resume it later. “This would act as a kind of slow light memory that would store the photon for later use.” Other areas of research might benefit from their study as well, Lähteenmäki says. “There are some connections to cosmology, the big bang, cosmic inflation, and other areas.

These metamaterials could possibly offer an analogy to such events and serve as a platform to simulate the evolution of such conditions. Who knows,” he ponders, concluding that “perhaps we’d find clues to the mysteries of dark matter and dark energy or other fundamental questions from such systems.”

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.

Arxiv – Dynamical Casimir e ect in a Josephson metamaterial

Vacuum modes confined into an electromagnetic cavity give rise to an attractive interaction between the opposite walls. When the distance between the walls is changed non-adiabatically, virtual vacuum modes are turned into real particles, i.e. photons are generated out of the vacuum. These e ffects are known as the static and dynamical Casimir effect, respectively. Here we demonstrate the dynamical Casimir eff ect using a Josephson metamaterial embedded in a microwave cavity at 5.4 GHz. We achieve the non-adiabatic change in the e ffective length of the cavity by flux-modulation of the SQUID-based metamaterial, which results in a few percent variation in the velocity of light. We show that energy-correlated photons are generated from the ground state of the cavity and that their power spectra display a bimodal frequency distribution. These results are in excellent agreement with theoretical predictions, all the way to the regime where classical parametric eff ects cannot be of consequence.

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