Particle physics research

Physicists’ findings open a promising way to confirm the quantum origin of Hawking radiation

LSU physicists have taken advantage of quantum information theory techniques to reveal a mechanism to amplify or “boost” entanglement production in the Hawking effect in a controlled way. Additionally, these scientists propose a protocol to test this idea in the laboratory using artificially produced event horizons. These results were recently published in Physical examination letters“Quantum Aspects of Stimulated Hawking Radiation in an Analog White-Black Hole Pair”, where Ivan Agullo, Anthony J. Brady, and Dimitrios Kranas present these ideas and apply them to optical systems containing the analog of a white hole pair -black.

Black holes are among the most mystifying objects in our universe, largely due to the fact that their inner workings are hidden behind a completely obscuring veil – the black hole event horizon.

In 1974, Stephen Hawking added more mystique to the character of black holes by showing that, once quantum effects are taken into account, a black hole is not really black at all but, instead, emits radiation, like if it was a hot body, gradually losing mass in the so-called “Hawking evaporation process”. Moreover, Hawking’s calculations showed that the emitted radiation is quantum mechanically entangled with the innards of the black hole itself. This entanglement is the quantum signature of the Hawking effect. This stunning result is difficult, if not impossible, to test on astrophysical black holes, because Hawking’s faint radiation is dwarfed by other sources of radiation in the cosmos.

On the other hand, in the 1980s, a seminal paper by William Unruh established that the spontaneous production of entangled Hawking particles occurs in any system that can support an efficient event horizon. Such systems generally fall under “analog gravity systems” and opened a window for testing Hawking’s ideas in the laboratory.

Serious experimental investigations of analog gravity systems—made of Bose-Einstein condensates, nonlinear fiber optics, or even running water—have been underway for more than a decade. Stimulated and spontaneously generated Hawking radiation has recently been observed on several platforms, but the measurement of entanglement has proven elusive due to its weak and fragile character.

“We show that by illuminating the horizon, or horizons, with appropriately chosen quantum states, one can tunably amplify the production of entanglement in the Hawking process,” said Associate Professor Ivan Agullo. “As an example, we apply these ideas to the concrete case of a pair of white-black analog holes that share an interior and are produced in a nonlinear optical material.”

“Many of the quantum information tools used in this research came from my graduate research with Professor Jonathan P. Dowling,” said Anthony Brady, a 2021 former PhD student, postdoctoral researcher at the University of Arizona. “Jon was a charismatic character, and he brought his charisma and nonconformity to his science, as well as his advice. He encouraged me to work on quirky ideas, like analog black holes, and see if I I could merge techniques from various areas of physics — like quantum information and analog gravity — to produce something new, or “cute,” as he liked to call it.”

“The Hawking process is one of the richest physical phenomena connecting seemingly unrelated areas of physics, from quantum theory to thermodynamics and relativity,” said LSU graduate student Dimitrios Kranas. “Analog black holes have added an extra flavor to the effect, at the same time giving us the exciting opportunity to test it in the lab. Our detailed numerical analysis allows us to probe new features of Hawking’s process, helping us to understand better the similarities and differences between astrophysical and analog black holes.”

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