Artwork depicting a quantum experiment that observes the behavior of a traversable wormhole. Credit: inqnet/A. Muller (Caltech)
Physicists observe the dynamics of wormholes using a quantum computer in a step towards studying quantum gravity in the laboratory.
For the first time, scientists have developed a quantum experiment that allows them to study the dynamics, or behavior, of a particular type of theoretical wormhole. The experiment allows researchers to probe the connections between theoretical wormholes and quantum physics, a prediction of so-called quantum gravity. Quantum gravity refers to a set of theories that seek to relate gravity to quantum physics, two fundamental and well-studied descriptions of nature that seem inherently incompatible with each other. Note that the experiment did not create an actual wormhole (a break in space and time known as the Einstein-Rosen Bridge).
“We have found a quantum system that exhibits the key properties of a gravitational wormhole, but is small enough to be implemented on today’s quantum hardware,” says Maria Spiropulu, principal investigator of the program. research US Department of Energy Office of Science Quantum Communication Channels for Fundamental Physics (QCFP) and Professor of Physics Shang-Yi Ch’en at Caltech.
“This work is 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 planned experiments that may probe the effects of quantum gravity in the future using quantum sensing, but it does provide a powerful test bed for put into practice the ideas of quantum gravity.
The research was published in the journal Nature on December 1. Daniel Jafferis of Harvard University and Alexander Zlokapa (BS ’21), a former Caltech undergraduate who started this project for his undergraduate thesis with Spiropulu and has since continued his graduate studies at
” data-gt-translate-attributes=”[{” attribute=””>MIT are the study’s first authors.
This illustration of a wormhole (Einstein-Rosen bridge) depicts a tunnel with two ends at separate points in spacetime. A wormhole is a speculative structure connecting disparate points in spacetime, and is based on a special solution of the Einstein field equations.
Wormholes are bridges between two remote regions in spacetime. They have not been observed experimentally, but scientists have theorized about their existence and properties for close to 100 years. In 1935, Albert Einstein and Nathan Rosen described wormholes as tunnels through the fabric of spacetime in accordance with Einstein’s general theory of relativity, which describes gravity as a curvature of spacetime. Researchers call wormholes Einstein–Rosen bridges after the two physicists who invoked them, while the term “wormhole” itself was coined by physicist John Wheeler in the 1950s.
The notion that wormholes and quantum physics, specifically entanglement (a phenomenon in which two particles can remain connected across vast distances), may have a connection was first proposed in theoretical research by Juan Maldacena and Leonard Susskind in 2013. The physicists speculated that wormholes (or “ER”) were equivalent to entanglement (also known as “EPR” after Albert Einstein, Boris Podolsky [PhD ’28], and Nathan Rosen, who first proposed the concept). Essentially, this work established a new kind of theoretical connection between the worlds of gravity and quantum physics. “It was a very bold and poetic idea,” Spiropulu says of the ER=EPR work.
Later, in 2017, Jafferis, along with his colleagues Ping Gao and Aron Wall, extended the ER=EPR idea not just to wormholes, but to traversable wormholes. Scientists have concocted a scenario in which negative repulsive energy keeps a wormhole open long enough for something to pass through. The researchers showed that this gravitational description of a traversable wormhole is equivalent to a process known as quantum teleportation. In quantum teleportation, a protocol that has been experimentally demonstrated over long distances via fiber optics and by air, information is transported through space using the principles of quantum entanglement.
The present work explores the equivalence of wormholes with quantum teleportation. The Caltech-led team has performed the first experiments that probe the idea that information traveling from one point in space to another can be described either in the language of gravity (wormholes) or in the language of quantum physics (quantum entanglement).
A key discovery that inspired possible experiments occurred in 2015, when Caltech’s Alexei Kitaev, Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics, showed that a simple quantum system could exhibit the same duality described more later by Gao, Jafferis and Wall, as that the quantum dynamics of the model is equivalent to the effects of quantum gravity. This Sachdev-Ye-Kitaev, or SYK model (named after Kitaev, and Subir Sachdev and Jinwu Ye, two other researchers who worked on its development before) has led researchers to suggest that some theoretical wormhole ideas might be further investigated by experimenting with quantum processors.
Pursuing these ideas, in 2019, Jafferis and Gao showed that by entangling two SYK models, researchers should be able to perform wormhole teleportation and thereby produce and measure the expected dynamical properties of traversable wormholes.
In the new study, the team of physicists performed this type of experiment for the first time. They used a SYK-like “baby” model prepared to preserve gravitational properties, and they observed wormhole dynamics on a Google quantum device, namely the Sycamore quantum processor. To do this, the team first had to reduce the SYK model to a simplified form, a feat they achieved using machine learning tools on conventional computers.
“We used learning techniques to find and prepare a simple SYK-like quantum system that could be encoded in current quantum architectures and would preserve gravitational properties,” says Spiropulu. “In other words, we simplified the microscopic description of the SYK quantum system and studied the resulting effective model that we found on the quantum processor. It is curious and surprising to see how the optimization on a characteristic of the model has preserved the other metrics! We are planning further tests to get better information about the model itself.
In the experiment, the researchers inserted a qubit – the quantum equivalent of a bit in conventional silicon-based computers – into one of their SYK-like systems and watched information emerge from the other. system. Information traveled from one quantum system to another by quantum teleportation or, speaking in the complementary language of gravity, quantum information traveled through the traversable wormhole.
“We performed a kind of quantum teleportation equivalent to a traversable wormhole in the gravity picture. To do this, we had to simplify the quantum system to the smallest example that preserves gravitational characteristics so that we could implement it on Google’s Sycamore quantum processor,” says Zlokapa.
Co-author Samantha Davis, a graduate student at Caltech, adds, “It took a long time to get to the results, and we surprised ourselves with the result.”
“The near-term importance of this kind of experiment is that the gravitational perspective provides a simple way to understand an otherwise mysterious multi-particle quantum phenomenon,” says John Preskill, Richard P. Feynman Professor of Theoretical Physics at Caltech and Director of the Institute for Quantum Information and Matter (IQIM). “What I found interesting about this new Google experiment is that, using machine learning, they were able to make the system simple enough to simulate on an existing quantum machine while still maintaining a reasonable caricature of what the image of gravity predicts.”
In the study, physicists report expected wormhole behavior from both a gravity and quantum physics perspective. For example, while quantum information can be transmitted through the device, or teleported, in a variety of ways, the experimental process was found to be equivalent, at least in some respects, to what might happen if the information passed through a hole. of worm. To do this, the team attempted to “hold the wormhole down” using pulses of negative repulsive energy or the opposing positive energy. They observed key signatures of a traversable wormhole only when the equivalent of negative energy was applied, which is consistent with expected wormhole behavior.
“The high fidelity of the quantum processor we used was key,” says Spiropulu. “If the error rates were 50% higher, the signal would have been entirely obscured. If they were half that, we would have 10 times the signal!
In the future, the researchers hope to extend this work to more complex quantum circuits. Although authentic quantum computers are still years away, the team plans to continue performing experiments of this nature on
” data-gt-translate-attributes=”[{” attribute=””>quantum computing platforms.
“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,” says Spiropulu. “We are excited to take this small step toward testing these ideas on quantum hardware and will keep going.”
Reference: “Traversable wormhole dynamics on a quantum processor” by Daniel Jafferis, Alexander Zlokapa, Joseph D. Lykken, David K. Kolchmeyer, Samantha I. Davis, Nikolai Lauk, Hartmut Neven and Maria Spiropulu, 30 November 2022, Nature.
DOI: 10.1038/s41586-022-05424-3
The study was funded by the U.S. Department of Energy Office of Science via the QCCFP research program. Other authors include: Joseph Lykken of Fermilab; David Kolchmeyer, formerly at Harvard and now a postdoc at MIT; Nikolai Lauk, formerly a postdoc at Caltech; and Hartmut Neven of Google.
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