Backreaction of stimulated Hawking radiation in an optical analogue

Hawking radiation 1 —the emission of quantum particles at the event horizon of a black hole 2 —connects gravity with quantum mechanics and thermodynamics 3 , 4 , 5 . But Hawking radiation has never been observed in astronomy, only in laboratory analogues 6 , 7 , 8 , 9 , and the chances of ever observing it in space are astronomically small 9 .

Hawking radiation 1 —the emission of quantum particles at the event horizon of a black hole 2 —connects gravity with quantum mechanics and thermodynamics 3 , 4 , 5 . But Hawking radiation has never been observed in astronomy, only in laboratory analogues 6 , 7 , 8 , 9 , and the chances of ever observing it in space are astronomically small 9 . The energy of Hawking radiation must come from the gravitational field around the black hole 2 , but how field quanta generate Hawking quanta has been unknown. Here we report on experimental and theoretical evidence for the process that generates Hawking radiation in a fibre-optical analogue of the event horizon 10 , 11 . There, as in gravity 2 , it has been believed that Hawking radiation comes from a complicated, cascaded process 12 ; here we have identified theoretically a simple, direct process and observed experimentally how this process reacts back onto the field. Our findings suggest an equally direct process for other laboratory analogues 6 , 7 , 8 , 13 , 14 , 15 , 16 , 17 and perhaps also for gravitational fields, shedding light on how black holes might radiate.

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