https://www.theatlantic.com/science/archive/2020/02/key-quantum-teleportation/607201/
Excerpts
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The AdS/CFT correspondence was postulated by the theoretical physicist Juan Maldacena in 1997, and it’s widely regarded as one of the most promising directions in which to pursue theories of quantum gravity. It suggests that the physical structure of space-time in, say, four dimensions is equivalent to the operation of a quantum theory at a three-dimensional boundary.
This connection is strange, deep, and surprising. It says that if you construct a space-time with a particular kind of curvature (and thus gravity) known as an anti–de Sitter space—that’s the AdS part—the mathematical description turns out to be equivalent to the description of a kind of quantum field theory called a conformal field theory—that’s the CFT part—in one fewer dimension. In other words, the correspondence works like a hologram—all the information in the higher-dimensional space-time projection is encoded within the lower-dimensional quantum interactions. This “holographic principle” was first proposed by the physics Nobel laureate Gerard ’t Hooft, and Maldacena’s AdS/CFT correspondence provided the first concrete picture of how it might work for a particular form of space-time.
In this view, what looks like continuous space in the AdS universe manifests in the CFT quantum view as entanglement—the interdependence of quantum bits. Here, Maldacena says, “the emergence of space-time is supposed to happen in systems with a large number of qubits that are highly entangled and highly interacting.” In other words, quantum entanglement can produce a space-time that seems to have gravity in it. Gravity, you might say, is spun from quantum effects.
In 2004, Hawking himself explained how, assuming that the AdS/CFT conjecture is true, we could recover this information by capturing every single Hawking photon a black hole radiates over its entire lifetime before fully evaporating. As Norman Yao of UC Berkeley describes it, “If you were God and you collected all these Hawking photons, there is in principle some ungodly calculation you can do to re-extract the information in [each swallowed] qubit.”
But in 2007, Patrick Hayden and John Preskill revised this picture by showing that, in fact, after the halfway point the information emerges more rapidly than that. Weirdly enough, once the black hole is half-evaporated, any further quantum bit of information tossed into it “literally bounces right back,” Yao says. This is because the black hole has by that stage become so quantum-entangled with the Hawking radiation it has already emitted that any more information it swallows is effectively registered at once in any further radiation it emits. The black hole, Hayden and Preskill said, then acts like an “INFORMATION MIRROR.”