The first simulation of a wormhole on a quantum computer may not have been an accurate representation of a wormhole after all. Since the original simulation was announced last year, another group of researchers has examined the physics behind the work and found several problems that could scupper the results.
At the centre of the original work is a concept called a 鈥渉olographic wormhole鈥�, which is a depiction of a wormhole that has been simplified using techniques from quantum mechanics to make it easier to simulate. Importantly, the holographic version is still complex enough to reveal details about the original, similar to how a two-dimensional hologram can show three-dimensional details of an object.
In November 2022, at the California Institute of Technology and her colleagues announced that they had used Google鈥檚 Sycamore quantum computer to simulate a holographic wormhole. They also said that they had sent signals through the simulated holographic wormhole using a phenomenon called quantum teleportation, in which information about a quantum state is sent in one side of the system and emerges from the other.
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The researchers said results from the simulation were as expected, but when at the University of California, Berkeley, and his colleagues looked at the details themselves, they found three major problems that they say indicate the simulation had little, if any, relevance to how wormholes behave.
The first problem has to do with how the simulated wormhole reacted to the signals being sent through it. Theory suggests that this should cause some oscillation in the system, which could be interpreted as the wormhole jiggling, but eventually it would settle back into a steady state. While this appeared to happen in the original work when many tests were averaged together, Yao and his colleagues found that for each individual test, the system continued to oscillate indefinitely, which doesn鈥檛 match the expected behaviour of a wormhole.
The second issue was related to the signals themselves. One of the signatures of a real wormhole 鈥� and therefore of a good holographic representation of a wormhole 鈥� is that the signal comes out looking the same as it went in. Yao and his team found that while this worked for some signals 鈥� those similar to the ones the researchers used to train a machine learning algorithm used to simplify the system 鈥� it didn鈥檛 work for others.
Finally, and perhaps most significantly, the team found a problem relating to a quantum phenomenon called size winding. Size winding is important because its presence seems to be a strong indicator of whether a quantum system is an accurate holographic representation of a gravitational system like a wormhole. However, it seems that for this particular quantum system, the size winding would disappear if the model was made larger or more detailed. Therefore, the perfect size winding observed by the original authors may just be a relic of the model鈥檚 small size and simplicity.
Spiropulu says that these issues don鈥檛 apply to the simulation as a whole, only to individual parts of it. 鈥淭he authors of the comment argue about the many-body properties of the individual decoupled quantum systems of our model,鈥� she says. 鈥淲e observed features of the coupled systems consistent with traversable wormhole teleportation.鈥�
Nevertheless, other researchers in the field who are part of neither team have also expressed doubt about the simulation. at Stanford University in California says that he believes the experiment did simulate a wormhole, but only in the broadest sense. 鈥淲hat is not so clear is whether the experiment is any better than garden-variety quantum teleportation and does it really capture the features of macroscopic general relativity that the authors might like to claim鈥� only in the most fuzzy of ways (at best),鈥� he says.
at CalTech says that he has become 鈥渓ess confident that the evidence supports a useful gravitational interpretation of the previously reported results鈥�.
Similar experiments in the future have great promise to teach us about the properties of wormholes, Susskind says, but they will have to be more complex than this one before we can extract any new information from them.
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