Resonant Hawking radiation in Bose-Einstein condensates

TL;DR

This paper investigates how double-barrier interfaces in Bose-Einstein condensates can produce resonant Hawking radiation with sharp, non-thermal spectral peaks due to coherent phonon scattering and tunneling effects.

Contribution

It demonstrates the occurrence of resonant tunneling and non-thermal spectra in analog Hawking radiation within Bose-Einstein condensates with double barriers.

Findings

Resonant tunneling causes sharp spectral peaks in Hawking radiation.

Peaks are mainly due to decaying resonances, not instabilities.

Spontaneous emission can dominate at nonzero temperatures.

Abstract

We study double-barrier interfaces separating regions of asymptotically subsonic and supersonic flow of Bose condensed atoms. These setups contain at least one black hole sonic horizon from which the analog of Hawking radiation should be generated and emitted against the flow in the subsonic region. Multiple coherent scattering by the double-barrier structure strongly modulates the transmission probability of phonons, rendering it very sensitive to their frequency. As a result, resonant tunneling occurs with high probability within a few narrow frequency intervals. This gives rise to highly non-thermal spectra with sharp peaks. We find that these peaks are mostly associated to decaying resonances and only occasionally to dynamical instabilities. Even at achievable nonzero temperatures, the radiation peaks can be dominated by the spontaneous emission, i.e. enhanced zero-point fluctuations, and not, as often in analog models, by stimulated emission.