Laser-Induced Quantum Field Research Project

​Outline of Research

Is the interior of a black hole truly pitch-black and impossible to look into?

In our Laser-Induced Quantum Field Research Project, we aim to illuminate the quantum vacuum, which is deeply related to the properties of black holes, using high-intensity lasers, and explore its contents.Recently, with the advancement of quantum information technology, a new perspective on ‘information’ has emerged in physics, leading to a new phase in our understanding of black holes, which were previously thought to be pitch-black and impenetrable. By bringing ideas from a wide range of fields, including particle physics, quantum information, quantum optics, nonlinear optics, and plasma physics, we will experimentally approach and verify unresolved and incomplete problems such as the information paradox and quantum gravity, as well as new areas of quantum information technology.

This project is supported by MEXT KAKENHI Grant-in-Aid for Transformative Research Areas A “Extreme Universe” and the JST FOREST.

Members

Research Background and Content

・Black Holes and the Information Paradox

More than 100 years have passed since Einstein's general theory of relativity predicted the existence of black holes, high-density compact object with event horizons from which even light cannot escape. Recently, astronomical observations have even succeeded in capturing the outline of an event horizon.

Black holes are thought to absorb not only matter but also light, appearing as completely dark objects that cannot be seen or emit any light. In other words, information absorbed into them seems to be lost forever.

On the other hand, Hawking incorporated quantum mechanical fluctuations into his theory and predicted that black holes emit light through thermal radiation (Hawking radiation) near the event horizon, as shown in Figure 1. This prediction differs from the currently observed phenomenon where gas around a black hole is heated by its gravity and emits light as a high-temperature plasma. Instead, Hawking radiation suggests that the black hole itself, including the region near the event horizon, emits light—a remarkable prediction. However, these two predictions seem to contradict each other, as one claims that black holes are completely dark, while the other claims that they emit light.

This led to the emergence of the unsolved paradox known as the ‘information paradox,’ which posits that although information appears to be lost when absorbed by a black hole, it should be preserved from a quantum mechanical perspective. This paradox is believed to be deeply connected to the development of the theory of quantum gravity, which is still incomplete, and to the further advancement of quantum information technology, which is currently attracting significant attention.

Figure 1. Simplified image of Hawking radiation

Particles within the event horizon are drawn in as negative energy (blue), and particles with positive energy (red) are emitted outside the event horizon, ultimately causing the black hole to evaporate through Hawking radiation.

・The Unruh effect linked to Hawking radiation and the equivalence principle

Hawking radiation, which is predicted to originate near the event horizon of a black hole, provides an important clue to the information loss paradox. However, its radiation temperature is inversely proportional to the mass of the black hole, making it generally much smaller than the temperature of the cosmic microwave background radiation and thus difficult to observe.

Among these, the Unruh effect, which is linked to Hawking radiation through the equivalence principle (the existence of a coordinate system that locally cancels out the gravitational field), one of the pillars of general relativity, is of particular interest. The Unruh effect is a phenomenon where the vacuum, which appears to be empty, appears to be emitting thermal radiation from the perspective of an observer in uniform acceleration. Experimental verification of this effect is considered crucial for resolving the information paradox.

However, like Hawking radiation, the Unruh effect is difficult to verify because it generally requires large accelerations.

・Experimental verification of the Unruh effect using high-intensity lasers

Lasers composed of photons, which are Bosons, excel in energy concentration and can impart extremely high acceleration to charged particles. Among these lasers, J-KAREN-P at Kansai Institute for Photon Science (KPSI) is the highest intensity laser in Japan and one of the top-class high-intensity lasers in the world. However, in recent years, laser intensity has continued to increase, due to lasers capable of outputting powers of 10 petawatts now operational in Europe and China. To compete with these, we are advancing the further intensification of J-KAREN-P at KPSI while utilizing these high-intensity lasers, including J-KAREN-P, to achieve high-acceleration fields previously unattainable. This will enable us to verify the Unruh effect and ultimately address the ‘information paradox.’