Optical analog of particle production in gravitational fields

Strong enough electric field is predicted to spontaneously create electron-positron pairs in vacuum via Schwinger effect. A somewhat similar effect is predicted to occur in sufficiently strong inhomogeneous gravitational fields. However, due to necessity of very large field strength, these effects were never observed in the experiment. Here we demonstrate that optical analogs of very strong gravitational fields (up to ~10^24 g) and very strong gravitational field gradients (up to ~10^31 s-2) may be created in electromagnetic metamaterial waveguides, leading to an optical analog of particle production in gravitational fields. Such waveguide geometries may also potentially be used to search for axion-like particles weakly interacting with electromagnetic field.