Dynamical Casimir effect in a Josephson metamaterial

TL;DR

This paper demonstrates the dynamical Casimir effect by generating correlated photon pairs in a microwave cavity with a flux-modulated Josephson metamaterial, confirming theoretical predictions in a quantum regime.

Contribution

It presents the first experimental observation of the dynamical Casimir effect using a Josephson metamaterial in a microwave cavity, with results matching quantum theoretical models.

Findings

Generation of energy-correlated photon pairs from the vacuum

Bimodal frequency distribution of the emitted photons

Excellent agreement with quantum theoretical predictions

Abstract

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 effects are known as the static and dynamical Casimir effect, respectively. Here we demonstrate the dynamical Casimir effect using a Josephson metamaterial embedded in a microwave cavity at 5.4 GHz. We achieve the non-adiabatic change in the effective 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 effects cannot be of consequence.