Maria_Chiara Braidotti
University of Glagow - mariachiara.braidotti@glasgow.ac.ukSuperradiance is the amplification of waves scattered by a rapidly rotating object, first proposed by Roger Penrose as a way to extract energy from rotating black holes. Despite being a fundamental process in wave physics, astrophysical superradiance has not been observed yet due to the large distances involved. However, proposal based on analogue gravity studies have demonstrated their versatility providing the first measurement of superradiance in a hydrodynamic experiment. Here we report the first measurement of Penrose superradiance in nonlinear optical systems in the superfluid regime. A weak signal beam with orbital angular momentum is focused onto the core of a pump vortex. In the scattering, a negative norm idler wave is generated and trapped inside the pump core, while the signal gets amplified. Our results demonstrate the presence of Pensore superradiance in superfluids, unveiling the key role of the negative norm mode in the process, not possible in previous experiments.