Creation of a black hole bomb instability in an electromagnetic system

The amplification and generation of electromagnetic radiation by a rotating metallic or lossy cylinder, first theorized by Zeldovich in the 1970s, is tightly connected to the concepts of quantum friction, energy extraction from rotating black holes and runaway mechanisms such as black hole bombs. Despite recent advances including acoustic analogues of the Zeldovich effect and the observation of a negative resistance in a low-frequency electromagnetic model, actual positive signal amplitude gain, the spontaneous generation of electromagnetic waves and runaway amplifi- cation effects have never been experimentally verified. Here, we demonstrate experimentally that a mechanically rotating metallic cylinder not only definitively acts as an amplifier of a rotating elec- tromagnetic field mode but also, when paired with a low-loss resonator, becomes unstable and acts as a generator, seeded only by noise. The system exhibits an exponential runaway amplification of spontaneously generated electromagnetic modes thus demonstrating the electromagnetic analogue of Press and Teukolskys black hole bomb. The exponential amplification from noise supports theoretical investigations into black hole instabilities and is promising for the development of future experiments to observe quantum friction in the form of the Zeldovich effect seeded by the quantum vacuum.