In 1969 Penrose predicted that matter falling into a rotating black hole could gain energy from the rotational motion of the spacetime geometry. A few years (1971) later a similar concept was proposed by Zel'dovich who realised that waves may be excited from the quantum vacuum state by a rotating black hole or, by analogy, from a rotating metallic object. The amplification of waves from a rapidly rotating object is now known as superradiance.
We are developing experiments based on light beams with orbital angular momentum that can recreate a spinning or vortex spacetime geometry. The light beam vorticity is impressed into the optical medium either through the medium nonlinearity and then we may search for signs of superradiance (i.e. amplification) from waves that are scattered from the medium.
In another set of experiments (photograph at top of the page) we are using the thermal nonlinearity of certain liquids (e.g. graphene dissolved in methanol) to create a photon fluid: waves and ripples move across the beam following exactly the same equations of waves and ripples moving across a water surface. The photon fluid is then made to flow in the same way as a draining bathtub and the vortex flow can be used to simulate a rotating black hole. These studies are interesting in their own right as they allow to create (in a room-temperature system) superfluids where various related phenomena such as superfluid instability and turbulence may be studied.
Amplification from a rotating cylinder featured in the "Big Bang Theory"