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 densitydensity 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.

Questioning the Recent Observation of Quantum Hawking Radiation

“…The observation of stimulated Hawking radiation of water waves was replicated and found to be anomalous scattering with and without a horizon . The demonstration of black–hole lasing in Bose–Einstein condensates has been regarded as a fluid–mechanical instability different from lasing, although the author disagrees . Nevertheless, these attempts of observing Hawking radiation in the laboratory have been tremendously fruitful, because their scientific debate has significantly advanced the subject.…”

Correlations on weakly time-dependent transcritical white-hole flows

“…That being said, there can be subtleties in how the background (or, in the context of Analogue Gravity, the effective metric) is to be defined, which in turn affects the identification of the fluctuations themselves. For example, in a quantum system where averages are taken over an ensemble of experimental realizations, one might like to be able to isolate quantum fluctuations but will necessarily have to include classical ones as well, and the latter might be dominant (see [10][11][12] for such an example involving density fluctuations in a Bose-Einstein condensate). In a classical context, for a steady water flow which is expected to be statistically stationary, the background can be identified as the constant component of the field (i.e., its time-average) while the fluctuations capture the entirety of the time-dependence of the field.…”

The influence of spacetime curvature on quantum emission in optical analogues to gravity

“…For those systems featuring a static horizon, the classical frequency shifting of waves at the horizon has been the traditional benchmark to demonstrate analogue gravity physics, although scattering of waves that could not be associated with a horizon has also been observed [6,11,13,23,24]. Correlated pairs of particles from horizons are considered an unmistakable signature of the quantum Hawking effect [26,27], and have therefore been extensively studied for fluid systems, in which their entanglement in various dispersive regimes has been investigated [28][29][30][31][32][33][34][35][36][37]. However, these studies have not contrasted horizon and horizonless spontaneous emission, and neither has this been done in other analogue systems and with many modes.…”