Confirmation of stimulated Hawking radiation, but not of black hole lasing

Abstract

Stimulated Hawking radiation in an analog black hole in a Bose-Einstein condensate was reported in 2014, and it was claimed that the stimulation was of the black hole lasing variety. The study was based on the observation of rapidly growing negative-energy waves. We find that the correlations between the Hawking and partner particles are directly observable in the experimental plots, which confirms the stimulated Hawking radiation. We further verify this result with new measurements. Also, the observed Hawking/partner correlations provide a sensitive, background-free probe of the underlying mechanism of the stimulation. The experiment inspired the prediction of the Bogoliubov-Cherenkov-Landau (BCL) mechanism of stimulated Hawking radiation. Through a numerical simulation in which the BCL mechanism is suppressed, we find that the partner particles have an infrared cutoff due to the finite distance between the outer and inner horizons, which limits the rate of black hole lasing. We compute this cutoff for the experiment, and the resulting Bogoliubov coefficient, and black hole lasing rate. This analysis shows that the growth rate of black hole lasing is too slow to explain the observations. It is likely that the observed stimulation was due to the BCL mechanism. Furthermore, zero frequency lasing modes play no role in our numerical simulation.