How Space and Time Could Be a Quantum Error-Correcting Code | Quanta Magazine

The key to the error correction is to store information not just in individual qubits, but in groups of entangled qubits. Sounds to me like that means the introduction of redundancy, similar to the codes for amino acids in DNA.That year — 2014 — three young quantum gravity researchers came to an astonishing realization. They were working in physicists’ theoretical playground of choice: a toy universe called “anti-de Sitter space” that works like a hologram. The bendy fabric of space-time in the interior of the universe is a projection that emerges from entangled quantum particles living on its outer boundary. Ahmed Almheiri, Xi Dong and Daniel Harlow did calculations suggesting thatthis holographic “emergence” of space-time works just like a quantum error-correcting code. They conjectured in theJournal of High Energy Physicsthatspace-time itself is a code— in anti-de Sitter (AdS) universes, at least. The paper has triggered a wave of activity in the quantum gravity community, and new quantum error-correcting codes have been discovered that capture more properties of space-time.

John Preskill, a theoretical physicist at the California Institute of Technology, saysquantum error correction explains how space-time achieves its “intrinsic robustness,” despite being woven out of fragile quantum stuff.“We’re not walking on eggshells to make sure we don’t make the geometry fall apart,” Preskill said. “I think this connection with quantum error correction is the deepest explanation we have for why that’s the case.”

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“Space-time is a lot smarter than us,” Almheiri said. “The kind of quantum error-correcting code which is implemented in these constructions is a very efficient code.”

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“Quantum error correction, to me, it’s like magic,” Almheiri said.

So is spacetime, like DNA, a code? And if so, what does that imply about the code's source?On the physics side,it remains to be seen whether de Sitter universes like ours can be described holographically, in terms of qubits and codes. “The whole connection is known for a world that is manifestly not our world,” Aaronson said. In a paper last summer, Dong, who is now at the University of California, Santa Barbara, and his co-authors Eva Silverstein and Gonzalo Torroba took a step in the de Sitter direction, with an attempt at a primitive holographic description. Researchers are still studying that particular proposal,but Preskill thinks the language of quantum error correction will ultimately carry over to actual space-time.

“It’s really entanglement which is holding the space together,” he said. “If you want to weave space-time together out of little pieces, you have to entangle them in the right way. And the right way is to build a quantum error-correcting code.”