Acoustic white holes in flowing atomic Bose-Einstein condensates

TL;DR

This paper investigates acoustic white holes in flowing Bose-Einstein condensates, demonstrating their stability, phonon scattering, quantum fluctuation effects, and radiation signatures, with both numerical simulations and analytical theory.

Contribution

It provides the first detailed numerical and analytical study of acoustic white holes, including their stability, phonon scattering, and quantum radiation features.

Findings

White holes are dynamically stable in BECs.

Phonon wavepackets exhibit nonlinear back-action on the horizon.

Density correlations reveal signatures of white hole radiation.

Abstract

We study acoustic white holes in a steadily flowing atomic Bose-Einstein condensate. A white hole configuration is obtained when the flow velocity goes from a super-sonic value in the upstream region to a sub-sonic one in the downstream region. The scattering of phonon wavepackets on a white hole horizon is numerically studied in terms of the Gross-Pitaevskii equation of mean-field theory: dynamical stability of the acoustic white hole is found, as well as a signature of a nonlinear back-action of the incident phonon wavepacket onto the horizon. The correlation pattern of density fluctuations is numerically studied by means of the truncated-Wigner method which includes quantum fluctuations. Signatures of the white hole radiation of correlated phonon pairs by the horizon are characterized; analogies and differences with Hawking radiation from acoustic black holes are discussed. In particular, a short wavelength feature is identified in the density correlation function, whose amplitude steadily grows in time since the formation of the horizon. The numerical observations are quantitatively interpreted by means of an analytical Bogoliubov theory of quantum fluctuations for a white hole configuration within the step-like horizon approximation.