Observation of self-amplifying Hawking radiation in an analogue black-hole laser
Jeff Steinhauer
Abstract and summary · read the original at the source
In one page
Hawking predicted in 1974 that a black hole should glow. Unruh pointed out in 1981 that you do not need gravity to make a horizon — any flow that outruns its own wave speed will do, and sound cannot swim back upstream out of it. Jeff Steinhauer builds exactly that at the Technion, in a rubidium condensate so cold and so thin that its shallow trap holds less than a tenth of the atoms’ weight. A sharp step of laser light accelerates the fluid past the speed of sound, making an outer horizon; further along the flow slows below it again, making an inner horizon, the arrangement a charged black hole has. Now the trapped negative-energy partners bounce between the two and stimulate more emission each pass. Steinhauer measures the escaping Hawking flux in the correlations between pairs of points, watches the trapped mode grow exponentially, and counts about three Hawking particles created for every particle that strikes the horizon.
Why it matters hereThis is chapter five’s claim made into hardware: treat a quantum fluid as a spacetime and horizon physics becomes an experiment on a bench rather than an observation you can never make. It also does something the single-horizon experiments cannot — it amplifies the effect, which is what turns a faint prediction into a measurable signal.
What it claims
01A step-like ‘waterfall’ potential made by a knife-edged laser beam accelerates the condensate past its own speed of sound, creating an outer horizon; further downstream the flow climbs the trap and drops back below the speed of sound, creating an inner horizon. That two-horizon arrangement is the analogue of a charged black hole, and it is what makes lasing possible.Fig. 1c and the experimental description following it
Published and peer-reviewed02The escaping Hawking radiation is seen directly in the density–density correlation function as bands extending beyond the outer horizon into the subsonic region — the output of the black-hole laser — while the region between the horizons shows the checkerboard pattern predicted for a standing negative-energy mode.Fig. 4, panels a to g; the paragraph naming the escaping flux
Published and peer-reviewed03The amplitude of that mode grows exponentially in time, which is what separates a black-hole laser from the alternatives: a single horizon gives no growth, white-hole radiation gives linear or logarithmic growth, and white-hole undulations give no growth.Fig. 5; the paragraph beginning ‘The scale of Fig. 5 is logarithmic’
Published and peer-reviewed04From the ratio of the lasing growth time to the round-trip time between horizons, roughly three Hawking particles are produced for each negative-energy particle striking the outer horizon, and the lasing frequency comes out at about 0.3 of the Hawking temperature — consistent with the horizon mixing only modes below that temperature.Eqs. (1) and (3); Fig. 6b and 6c; Conclusion
Published and peer-reviewed05The starting state is quantum rather than thermal. The measured static structure factor falls as the wavenumber falls, the opposite of a thermally dominated gas, putting the initial temperature between zero and about a tenth of the chemical potential — a thermal fraction of about two parts in a hundred thousand.Fig. 3b and the paragraph on the static structure factor
Published and peer-reviewed06Steinhauer turns the result outward: strong laser-like Hawking radiation seen coming from a real astrophysical black hole would imply both an inner horizon and a dispersion relation that curves upward at short wavelength, and the same apparatus is proposed as a platform for simulating the expansion of the early universe.Conclusion, final paragraph
What to watch
Read it · abstract
Abstract
It has been proposed that a black hole horizon should generate Hawking radiation. In order to test this theory, we have created a narrow, low density, very low temperature atomic Bose-Einstein condensate, containing an analog black hole horizon and an inner horizon, as in a charged black hole. We observe Hawking radiation emitted by the black hole. This is the output of the black hole laser. We also observe the exponential growth of a standing wave between the horizons. The latter results from interference between the negative energy partners of the Hawking radiation and the negative energy particles reflected from the inner horizon. We thus observe self-amplifying Hawking radiation.
Jeff Steinhauer, Department of Physics, Technion — Israel Institute of Technology, Haifa. Nature Physics 10, 864–869 (2014); preprint arXiv:1409.6550.
(Abstract only. The complete article is at the publisher and the author version is free to read on arXiv — see the rights note for why the full text is not reproduced here, and for the three companion sheets in this library.)
The way in
https://doi.org/10.1038/nphys3104Licence checked directly. Published as Nature Physics 10, 864–869 (2014); the Crossref record for the DOI carries only Springer Nature’s text-and-data-mining terms. The author version is on arXiv as 1409.6550, submitted 23 September 2014 with a second version on 9 November 2014 correcting one equation, and the arXiv record states the arXiv.org perpetual non-exclusive distribution licence — not a Creative Commons licence, checked on the arXiv abstract page on 2026-09-08. So this sheet carries the summary, the claims and Steinhauer’s own abstract and sends the reader to the source. The claims below were written from the arXiv text, whose figure numbering the locators use; that version is titled ‘Observation of self-amplifying Hawking radiation in an analog black hole laser’. Steinhauer works in the Department of Physics at the Technion, Israel Institute of Technology, Haifa; the work was supported by the Russell Berrie Nanotechnology Institute and the Israel Science Foundation. Three companion sheets in this library carry the rest of this line of work: Finazzi and Parentani’s theory paper ‘Black hole lasers in Bose–Einstein condensates’, New Journal of Physics 12, 095015 (2010), at /library/stm-b057755b99; Steinhauer’s ‘Observation of quantum Hawking radiation and its entanglement in an analogue black hole’, Nature Physics 12, 959 (2016), at /library/stm-a3449e5f7e; and Muñoz de Nova, Golubkov, Kolobov and Steinhauer’s ‘Observation of thermal Hawking radiation and its temperature in an analogue black hole’, Nature 569, 688 (2019), at /library/stm-95010a1182.
How to cite it
Jeff Steinhauer (2014) Observation of self-amplifying Hawking radiation in an analogue black-hole laser. doi:10.1038/nphys3104
Where it sits in the curriculum
The vacuum as a quantum fluidWhat the vacuum isThe metric, warp drives and wormholes