Black holes are one of those physical objects whose complete description escapes our theories. Quantum mechanics and general relativity don’t work particularly well together and this leads to paradoxes. According to relativity, nothing can escape a black hole, but in quantum mechanics, no information is ever lost.
This is the information paradox that physicists, including the late Stephen Hawking, have tried to find a solution to. In a paper published in Nature, researchers used a seven-qubit quantum computer to simulate whether or not information can be retrieved when something falls into a black hole. Now, researchers think that it is indeed possible.
Black holes emit a small amount of radiation from the region just outside the event horizon, the point of no return. This is known as Hawking radiation, and it leads over an incredible amount of time to black holes evaporating. Physicists believe that if they were able to study the black holes for this amount of time, the information would all be there.
But there might be another way. These Hawking photons are entangled with particles that fell in the black hole, which is very useful. Entangled particles are in a single quantum state even if they are separated by huge distances, so the properties of one affects the properties of the other.
Since quantum information is the same everywhere, the team was able to construct an analogous black hole. Researchers supposed that it would be possible to drop an entangled qubit inside a black hole to get some useful information from the escaping Hawking radiation.
“One can recover the information dropped into the black hole by doing a massive quantum calculation on these outgoing Hawking photons,” co-author Norman Yao, a UC Berkeley assistant professor of physics, said in a statement. “This is expected to be really, really hard, but if quantum mechanics is to be believed, it should, in principle, be possible. That’s exactly what we are doing here, but for a tiny three-qubit ‘black hole’ inside a seven-qubit quantum computer.”
The experimental set up has demonstrated the phenomenon of quantum information scrambling for the first time. Quantum scrambling is a chaotic shuffling of the information stored among a system made of many quantum particles. By measuring scrambling, the team can directly probe the dynamics of this process as well as create a good analogous for black holes.
This approach could be used to potentially diagnose complex noise in quantum computers and improve them.