Title: Induced density correlations in a sonic black hole condensate,
Abstract: Analog black/white hole pairs, consisting of a region of supersonic flow,
have been achieved in a recent experiment by J. Steinhauer using an elongated
Bose-Einstein condensate. A growing standing density wave, and a checkerboard
feature in the density-density correlation function, were observed in the
supersonic region. We model the density-density correlation function, taking
into account both quantum fluctuations and the shot-to-shot variation of atom
number normally present in ultracold-atom experiments. We find that quantum
fluctuations alone produce some, but not all, of the features of the
correlation function, whereas atom-number fluctuation alone can produce all the
observed features, and agreement is best when both are included. In both cases,
the density-density correlation is not intrinsic to the fluctuations, but
rather is induced by modulation of the standing wave caused by the
fluctuations.