*Recent headlines about physicists creating a wormhole using Google’s quantum computer are misleading. Not only did they not create a wormhole in spacetime, as Einstein’s equations suggest, they didn’t even create a hologram of a wormhole, as claimed. original article from Nature. Martin Bauer explains what the Sycamore experience really was. *

A “wormhole” is a structure connecting disparate points in space based on special solutions of Einstein’s field equations. It is a feature of space-time geometry often represented by folded paper, bringing distant points into direct contact. Dreams of sending information or even crossing huge distances in space by traveling through a space-time tunnel have fascinated scientists and science fiction writers ever since wormholes were described. for the first time by Einstein and Rosen in 1935. However, we have never observed such a wormhole, nor is it clear whether they even exist in our Universe.

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Recent reports of a new result seem to suggest otherwise: “*Physicists are creating the tiniest, tiniest wormhole you can imagine’* writes for example the New York Times. So did physicists create a wormhole by changing the geometry of spacetime? No, they didn’t. The Nature title on the same result reads: “*A holographic wormhole traversed in a quantum computer”*. Holograms are two-dimensional images that appear three-dimensional, or more generally, they capture all the information of a three-dimensional object. Does this mean that physicists have created a hologram of a wormhole, showing that information from a real space-time tunnel can be captured on a surface? No, they didn’t either.

In order to understand the origin of the confusion, we need to look at what was actually done in the experiment and how that relates to the wormhole concept. Physicists from Caltech, Harvard, MIT and Fermilab ran a program on Google’s Sycamore quantum computer and measured observables in a highly entangled system. Quantum computers are computers in which regular bits, which can take the values 1 or 0, are replaced by quantum bits (qubits) which can contain the values 0 or 1 but also superpositions of these. Because they are quantum mechanical systems, qubits can be entangled. Entanglement is a quantum mechanical effect in which two distinct objects must be described by the same wave function, even though they are spatially separated. Measurements on the parts of the system are then correlated with the other part in a way that is unique to quantum mechanics. It’s such an important prediction that experimental verification of quantum entanglement using photons was rewarded with the Nobel Prize in Physics this year. Qubits on quantum computers can be entangled in the same way, and although the number of stable qubits on quantum computers is currently very limited, they promise to outperform classical computers in the future.

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This experiment could have been performed without anyone involved even knowing Einstein’s equations.

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It all sounds like good old quantum mechanics. There’s no notion of a wormhole or even gravity here. In fact, this experiment could have been performed without anyone involved even knowing Einstein’s equations. So how do we get from here to a wormhole?

The interpretation of the wormhole goes back to one of the most intriguing results in fundamental physics of recent decades. In 1997, Juan Maldacena conjectured that the equations describing specific quantum systems describe the same physics as the equations for a theory of gravity in spacetime with large negative curvature. Although this could not be a theory of our own Universe because our Universe has positive curvature, it was a breakthrough.

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Until now, quantum mechanics and gravity were like oil and water; any attempt to merge the two into a single theoretical framework is fraught with problems. Suddenly there was a theoretical model where the two were like two sides of the same coin, dual descriptions of the same system: one in terms of gravity and the other in terms of quantum mechanics – like two languages very different describing the same object. Since this duality only works if the theory of gravity corresponds to a space-time of a dimension higher than that in which the theory of quantum mechanics is defined, the quantum system can be considered as a hologram of the theory of gravity. gravity.

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Suddenly there was a theoretical model where quantum mechanics and gravity looked like two sides of the same coin, dual descriptions of the same system.

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Two different languages require a dictionary to be translated, and many physicists working on Maldacena’s conjecture work attempt to establish what, for example, a black hole (an object in the language of gravity) would be in quantum language. In principle, one could then perform calculations in the theory of gravity, translate the results into quantum theory using the dictionary and check whether the result is consistent. In 2013, Maldacena and Susskind proposed that in this dictionary, quantum entanglement corresponds to a wormhole on the side of gravity.

Quantum entanglement in quantum mechanics as corresponding to a wormhole in the theory of relativity.

Since a program on quantum computers can be described in terms of one parameter: time, it can be considered a one-dimensional quantum mechanical system. They therefore assumed that a carefully prepared quantum system with entangled states on a quantum computer can be described by the equations of a 2-dimensional wormhole. Again, these cannot be dimensions of our own spacetime, but a set of equations that would describe such an object in an abstract 2-dimensional spacetime.

Physicists working on the Sycamore experiment have demonstrated that it is possible to perform manipulations on the entangled quantum system so that a message injected into one part of the system can be picked up in another part in a way that can be described as a message going through a 2-dimensional wormhole in the double description. It is in this sense that the dynamics of crossing a holographic wormhole has been reproduced on a quantum computer. In this case, the program only operated on 9 qubits, which makes the application of duality more difficult and even debatable since the conjecture arbitrarily assumes many qubits to operate. But there is no doubt that this experiment and others inspired by duality will be performed on more advanced quantum computers in the near future and the authors expect new quantitative insights into the theory of gravity if they can. repeat the experiment with about 100 qubits.

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Physicists working on the Sycamore experiment have demonstrated that it is possible to perform manipulations on the entangled quantum system so that a message injected into one part of the system can be picked up in another part.

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One can choose to simply ignore the duality aspect of the experiment and treat it as further confirmation of quantum mechanics, or one can interpret it as proof that duality works as expected. A useful analogy is that of water circuits which are often used to learn about electrical circuits. One can consider water circuits as a confirmation of hydraulic theory, but one can also gain a better understanding of electricity without ever getting electrocuted. Similarly, the quantum computer program never risked breaking up spacetime. Conjectured duality goes much deeper than the hydraulic analogy, and quantum computers can provide valuable insight into dual theory that could one day help us understand whether our own, much more complicated Universe also has holographic properties.

*Water circuit – Electrical circuit analogy*

There are many reasons for the confusion of messages around this experimental result. Wormholes are an extremely popular physical concept that immediately triggers the image of spacetime tunnels, as the word is used in a more abstract sense by physicists working on the subject. Science journalists need to make science sexy. Often, titles of articles as well as titles of books are not even set by authors but constructed by editors to grab the maximum attention of the audience.

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And there’s the fact that the authors chose not to share a preprint before publication. Sharing the results widely before they are published allows other physicists to comment on and correct overly dramatic and erroneous statements. A process that is good for science and has been the established standard accepted by many scientific journals in physics for many decades. It is the responsibility of scientists and journalists to ensure that results like this are reported in a way that does not mislead the reader, but it is also the responsibility of the reader to read on. beyond the title.

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