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Editorial of the Technological Innovation Website – 12/01/2022

Art representing the quantum experiment that studies traversable wormholes.

[Imagem: inqnet/A. Mueller/Caltech]

**Gravity and quantum entanglement**

An experiment made it possible for the first time to study the dynamics – the behavior – of a very special type of wormhole: A type that, at least theoretically, can be crossed, joining two distant points of the Universe.

The experiment did not create a real wormhole, which would tunnel through space and time, but it did allow researchers to investigate the connections between theoretical wormholes, studied in the field of relativity, and quantum gravity, a prediction of mechanics. quantum.

While Newtonian gravitation and Einstein’s space-time gravity are all “classical” descriptions of the force of gravity, quantum gravity refers to a set of theories that seek to connect gravity with quantum physics, two fundamental and well-studied descriptions of nature. who seem inherently incompatible with each other and therefore don’t usually talk to each other.

The experiment, running on a quantum computer, made it possible for the first time to study the same system – the wormhole – using both theoretical frameworks. And, somewhat surprisingly, the result proved to be fully compatible with the expectation of both theories.

“We found a quantum system that has the main properties of a gravitational wormhole, but small enough to be implemented on current quantum hardware,” said Professor Maria Spiropulu, from the California Institute of Technology (Caltech). “This work constitutes a step towards a larger program of testing the physics of quantum gravity using a quantum computer. It does not replace direct quantum gravity probes, in the same way as other experiments planned to investigate the effects of quantum gravity in the future using quantum sensing, but it offers a powerful testing ground for exercising ideas about quantum gravity.”

**Wormholes and teleportation**

Wormholes are bridges between two remote regions in spacetime. They have never been experimentally observed, but scientists have theorized about their existence and properties for nearly 100 years.

In 1935, Albert Einstein and Nathan Rosen described wormholes as tunnels through the fabric of space-time based on the General Theory of Relativity, which describes gravity as a curvature of space-time. This is why physicists today call wormholes Einstein-Rosen bridges, while the term “wormhole” was coined by physicist John Wheeler in the 1950s, the same person who coined the term “black hole”.

The notion that wormholes and quantum physics—specifically entanglement, a phenomenon in which two particles can remain connected across vast distances—might have a connection was first proposed by Juan Maldacena and Leonard Susskind in 2013. They speculated that wormholes were equivalent to entanglement, establishing a new kind of theoretical link between the worlds of gravity and quantum physics. “It was a very bold undertaking and a poetic idea,” commented Spiropulu of the proposal, which physicists now call ER = EPR, where ER is wormholes (Einstein-Rosen) and EPR is quantum entanglement (Einstein-Podolsky- Rosen).

Later, in 2017, Daniel Jafferis and his colleagues Ping Gao and Aron Wall extended the ER = EPR idea not only to wormholes, but traversable wormholes as well. They devised a scenario in which repulsive negative energy keeps a wormhole open long enough for something to pass from one end to the other.

They demonstrated that this gravitational description of a traversable wormhole is equivalent to a process known as quantum teleportation. In quantum teleportation, which has already been demonstrated experimentally over long distances via fiber optics and even through the air, information is transported through space using the principles of quantum entanglement.

[Imagem: Alan Stonebraker/American Physical Society]

**Quantum entanglement = going through a wormhole**

Now, Jafferis and his colleagues have taken the study of the equivalence of wormholes to quantum teleportation further. To do this, they carried out the first experiments that investigated the idea that information traveling from one point to another in space can be described in the language of gravity (wormholes) or in the language of quantum physics (quantum entanglement).

The team performed the unprecedented experiment using Google’s Sycamore quantum processor. They used a very abbreviated model, known as SYK (Sachdev-Ye-Kitaev), to preserve gravitational properties, and then observed the wormhole dynamics. To achieve this, the team first had to reduce the SYK model, in which quantum dynamics are equivalent to the effects of quantum gravity, to a simplified form, a feat they achieved using machine learning tools on conventional computers.

In the experiment, the researchers inserted a qubit into one of their SYK-like systems and watched information emerge from the other system. Information traveled from one qubit to another via quantum teleportation. And since ER = EPR, this can be interpreted as: Quantum teleportation has opened a wormhole in space-time. Or, speaking in the complementary language of gravity, the quantum information passed through the traversable wormhole.

**Bridge between relativity and quantum mechanics**

The results show the expected behavior of the wormhole from both the perspective of gravity and quantum physics. For example, although quantum information can be transmitted through the device, or teleported, in a number of ways, the experimental process has been shown to be equivalent, at least in some respects, to what might happen if the information traveled through a wormhole.

To achieve this, the team tried to “open the wormhole” using pulses of repulsive negative energy, or the opposite, positive energy. They observed key signatures of a wormhole traversable only when the equivalent negative energy was applied, which is consistent with the expected behavior of wormholes.

“The relationship between quantum entanglement, spacetime and quantum gravity is one of the most important questions in fundamental physics and an active area of theoretical research,” commented Spiropulu. “We’re excited to take this small step to test these ideas on quantum hardware, and we’ll keep moving forward.”

**Bibliography:**

Article: *Traversable wormhole dynamics on a quantum processor*

Authors: Daniel Jafferis, Alexander Zlokapa, Joseph D. Lykken, David K. Kolchmeyer, Samantha I. Davis, Nikolai Lauk, Hartmut Neven, Maria Spiropulu

Magazine: Nature

Vol.: 612, pages 51-55

DOI: 10.1038/s41586-022-05424-3

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