SPAIN – Now researchers at the Complutense University of Madrid have proposed a theoretical approach to detect this effect in the laboratory, a finding that an Israeli physicist claims to have succeeded.

In the 70s, astrophysicist Stephen Hawking predicted that a black hole could spontaneously emit pairs of particles. According to his theory, one would be swallowed by the hole but the other escape out what an outside observer would look like a spontaneous emission of radiation by the hole.

“The problem is that this issue is very weak. If we associate a temperature of this spectrum would be very small, so detecting it is an almost impossible task ,” admits Juan Ramón Muñoz de Nova, researcher at the Department of Materials Physics at the Complutense University of Madrid (UCM) and the Technological Institute Israel (Technion).

Scientists around the world have spent decades trying to mimic this phenomenon in the lab with optical fiber rings ion-particles of light and polariton hybrid materials or Bose-Einstein condensates (BEC), which are gases of cold atoms with the same quantum state.

“The advantage of the condensates is that its temperature is very low, so you can better study the issue of analogue Hawking radiation” says Muñoz.  “In addition, they know how to manipulate quite well and understood very well how the system excitations (phonons), which are analog sound waves work,” he adds.

With this simulation, the sound is trapped in a supersonic region in the same way that the particles do in a black hole.

In a study published in New Journal of Physics, with Fernando Sols and Ivar Zapata, also researchers from the UCM, tested two theoretical criteria that try to detect the presence of this radiation.

The first, developed by the authors themselves, reveals measurable violations of certain mathematical inequalities produced by the spontaneous emission of radiation from the acoustic black hole.

“We show that such violations are solely attributable to the spontaneous emission of radiation and cannot be due or thermal radiation or the undulations of the condensate wave function itself,” said the physicist.

 ‘A world first’

The second criterion, designed by Italian scientists, is based on detecting the quantum entanglement of phonons, which exist after the spontaneous emission of radiation. “In typical situations, both criteria are equivalent from the theoretical point of view. However, in the laboratory, can only be detected violations of certain types of inequalities,” said the researcher.

The next step now is to test these theoretical techniques in the laboratory, something the Spanish scientist is conducting in Israel next to an experimental group of Technion Institute.

 “If confirmed, would be a milestone in the world as it would be the first observation to date of the spontaneous emission of Hawking radiation,” Muñoz claimed.