"If the predictions are borne out, the work may offer clues about where to look for the most elusive theory in physics: one that unites quantum mechanics with the theory of general relativity that describes gravity. And, for good measure, it would support the idea that space-time is not the fundamental backdrop against which the universe plays out but is itself woven from the interconnections between particles described by quantum entanglement."
"Hawking initially believed that even if a black hole fully evaporated, the information it had consumed would remain lost forever. But an idea known as the AdS/CFT correspondence shows how the photons of Hawking radiation might be able to encode information about the interior of the black hole, thereby carrying that information back out into the universe at large."
"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, said Maldacena, “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."
"The AdS/CFT correspondence is a key component of one proposed solution, since it supplies the means by which quantum entanglement could imprint the information on Hawking radiation and prevent it from being irrevocably lost.
In 2004, Hawking himself explained how, assuming 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 the University of California, Berkeley described 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.”"
"Hayden and Preskill had hit on a connection between black hole thermodynamics and quantum information theory that invokes a phenomenon called quantum scrambling."
"You can’t distinguish two scrambled systems even if you look not just locally but at correlations across both systems. “Scrambling is a very strong form of thermalization,” said Yao. “It is the delocalization of quantum information.”"
"black holes are special. Just as the rate at which a pack of cards gets shuffled depends on the technique you use, the scrambling rate of a system depends on the details of how the particles in that system interact. These details are described mathematically by a function called a Hamiltonian. And it turns out that the Hamiltonian governing black holes means they scramble quantum information at the fastest rate possible."
"Gao and colleagues showed how, by adding a further coupling between the black holes, you could make the transfer of quantum information between them formally identical to the process called quantum teleportation. Here the entanglement between two particles is used to transfer the quantum state of one of them to the other. The target particle ends up looking identical to the initial one — in fact, there is no meaningful way to say it is not the same particle, vanished from one part of space and reconstituted in another. “Their entanglement acts like a bridge” for the information, said Yao."
"But according to the AdS/CFT correspondence, the channel between the black holes created by entanglement is equivalent, in a description based on general relativity, to a wormhole in space-time that connects them. In this view, qubits enter one black hole and travel down the wormhole to the other."
"Jafferis and Wall showed how quantum information theory and teleportation could be used (within the AdS/CFT picture) to make a wormhole that is traversable. "
"If the AdS/CFT correspondence is real, it allows a radical change in perspective. In principle, researchers could construct systems entirely equivalent to wormhole-connected black holes by entangling quantum circuits in the right way and teleporting qubits between them."
"Brown and colleagues now suggest that quantum circuits very much like these could be used to construct a simple analogue of the situation envisioned by Gao, Jafferis and Wall for a traversable wormhole that could teleport a qubit. In the version they imagine, each of the two black holes is made up of just a few qubits, all of which are maximally entangled with one another. Their protocol introduces a further interaction between these two groups of qubits, which acts as the additional channel needed by Gao and colleagues to complete the teleportation process."
"here’s the mind-bending thing: If the AdS/CFT correspondence is right, then these experiments would be more than a laboratory analogue of a black hole. The two types of systems would be entirely equivalent. The coupled ions are precisely what, in an AdS space, a (very tiny) black hole would look like. It’s an illustration of how, if Maldacena’s conjecture tells us something real about the way the universe is constituted, our intuitions about what things are would be shattered."
"Can that be done? “Absolutely,” said Monroe. What one would expect to see is that, first, a quantum bit of information fed into one of the two black-hole-type qubit systems would be scrambled and appear to vanish. But after a predictable amount of time, it would pop out again, unscrambled, in the other group of qubits, having jumped down the wormhole. The surprise is not so much that the information is transferred — the two systems are coupled, after all. It’s that the information reappears in a readable form, needing no decoding, even though the first “black hole” fully scrambled it."
"There is nothing in the theoretical analysis of these quantum circuits that isn’t fully consistent with standard quantum theory. But it is simpler and more economical to describe what is going on in the language of gravity: as a passage along a wormhole. “While you could explain it all by using the Schrödinger equation, there’s a much simpler explanation that invokes black holes,” said Brown."
"You could, for example, describe superconductivity — another quantum phenomenon — purely in terms of electron wave functions. But it’s much simpler to use a “quasiparticle” picture: to consider the so-called Cooper pairs of entangled electrons. We don’t question the reality of these quasiparticles — and so why should we deny the reality of qubit wormholes?"
"more ambitious versions of the experiment using many-qubit systems could reveal interesting properties of space-time itself. “If these experiments can be done, it might become possible to create more and more complex entangled systems that could test more aspects of the emergence of space-time from quantum systems,” said Maldacena. Added Nezami: “A sophisticated experiment of this type could even provide an experimental probe of the mathematics of string theory.”"
https://www.quantamagazine.org/wormho...-hole-information-in-the-lab-20200227
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