In one minute

S. Finazzi and R. Parentani study elongated Bose-Einstein condensates whose flow crosses the speed of sound twice. In the gravitational analogy these flows form a pair of black hole and white hole horizons. Without periodic boundaries, the phonon spectrum has a finite set of complex-frequency modes that produce a laser effect, because the supersonic region acts as a resonant cavity. Numerical computation of the complex frequencies and the density-density correlations gives patterns with very specific signatures. The laser effect is self-amplified Hawking radiation, confirmed by comparing the early outgoing flux with standard black hole radiation. Because the analysis rests on the Bogoliubov-de Gennes equation, none of its results depend on the gravitational analogy itself.

Black hole lasers in Bose-Einstein condensates