“It’s quite beautiful. It started the whole thinking in this direction,” said Hrant Gharibyan, a quantum physicist at Caltech. “There’s a narrow window that you can throw stuff from the left universe to the right.”

The foundation of the work was one of the hotter trends in modern physics, holography.

Holography involves the study of profound relationships known as dualities. On their face, dual systems look completely different. They have different parts and play by different rules. But if two systems are dual, every aspect of one system can be precisely related to an element of the other system. Electric fields are dual to magnetic fields, for instance. A major finding in modern physics is that dualities also seem to link certain gravitational systems to quantum systems.

We might consider a collection of interacting particles, for instance, entirely within the framework of quantum theory. Or, as if by popping on a pair of 3D glasses, we might see the collection of particles as a black hole governed by the rules of gravity. Physicists have spent decades developing mathematical “dictionaries” that let them translate quantum elements into gravitational elements and vice versa, effectively putting on and taking off the glasses. They watch how particles, black holes and wormholes transform as one switches between the two perspectives. Calculations that are hard to do from one perspective are often easier from the other. A major hope of the field is to develop the ability to access the still mysterious rules of quantum gravity by studying better-understood quantum theories.

But questions abound as to how far the glasses trick will hold. Does every conceivable quantum theory pop into a gravity theory when viewed holographically? Can physicists understand gravity in our universe by finding its better-behaved quantum twin? No one knows. But many theorists have dedicated their careers to exploring a few well-understood holographic pairs of theories and are constantly searching for new examples.

Gao, Jafferis and Wall had already suggested in 2016 that passing through a wormhole (a gravitational enterprise) might have a quantum interpretation without the 3D glasses: the teleportation of quantum information. A couple of years later, another team made their speculation concrete.

In 2019, Gharibyan and his collaborators translated traversable wormholes into quantum language, publishing a step-by-step recipe for a peculiar quantum experiment that showcases the essence of holography. With the 3D glasses on, you see a wormhole. An object enters one black hole, traverses a sort of space-time bridge, and exits the other black hole. Take the glasses off, however, and you see the dual quantum system. Two black holes become two gigantic clouds of particles. The space-time bridge becomes a quantum mechanical link known as entanglement. And the act of traveling through the wormhole becomes an event that appears quite surprising from the quantum perspective: A particle carrying a qubit, a unit of quantum information, enters one cloud and becomes scrambled beyond all recognition. The qubit unscrambles and exits the entangled cloud as another particle — a development as unexpected as watching a butterfly being torn apart by a hurricane in Houston, only to see an identical butterfly pop out of a typhoon in Tokyo.

“Naïvely you’d never guess,” Gharibyan said, “that you could scramble and unscramble very chaotically, and the information comes out.”

But viewed through a holographic lens, the proceedings make perfect sense. The entangled clouds of particles are not a literal wormhole in our universe. But they are dual to a wormhole, meaning that they have a matching behavior for anything a traversable wormhole can do — including transporting a qubit.

This is what the team announced in the November Nature paper. They simulated the behavior of two clouds of entangled particles in a quantum computer and performed a teleportation that captured the essential aspects of traversing a wormhole from the holographic perspective.

But that wasn’t the only way to interpret their experiment.

Not All That Teleports Is Gravity

Over the past few years, researchers made another surprising discovery. Although they had spotted the scrambling teleportation recipe while using the gravitational lens, gravity wasn’t always essential.

Gravity scrambles information in a very particular way. In fact, theorists have argued that black holes must be the most efficient scramblers in nature. But when Gharibyan and his colleagues used clouds of particles that scrambled by different quantum rules than gravity, they realized that the clouds could still teleport by scrambling, albeit less efficiently. And when they looked at the alternative clouds through a holographic lens, they saw nothing — no wormholes.

Gharibyan’s group and another team led by Norman Yao at Berkeley put everything together in a pair of simultaneous papers in 2021. (Yao has since moved to Harvard.)