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In an atomic Bose–Einstein condensate, Jeff Steinhauer formed a sonic horizon: phonons could escape on one side but were carried inward on the other. The study measured density correlations across that horizon, identifying outgoing Hawking phonons paired with partners inside the analogue black hole. A separate population measurement was consistent with an approximately thermal spectrum; the paper does not report radiation from an astrophysical black hole. Under the stated assumption that modes at different frequencies are uncorrelated, the author inferred entanglement over a range of higher energies from the correlation spectrum and measured populations. At lower energies, the inferred entanglement weakened or vanished. An oscillating-horizon experiment produced classical correlations, and a numerical simulation supplied a further comparison.

Observation of quantum Hawking radiation and its entanglement in an analogue black hole