Wormholes are pathways through spacetime that connect two far-off places. Although they have not been experimentally observed, scientists have been theorizing about their existence and characteristics for almost a century. The notion that wormholes and quantum physics, precisely entanglement, may have a connection was first proposed in theoretical research in 2013. The physicists speculated that wormholes were equivalent to entanglement.

Later in 2017, the wormholes-entanglement idea was extended to not just wormholes but traversable wormholes. The scientists envisioned a scenario in which a wormhole is kept open long enough for something to pass from one end to the other by negative repulsive energy. The scientists demonstrated that the quantum teleportation method is identical to the gravitational description of a traversable wormhole. Information is sent over space using the principles of quantum entanglement in quantum teleportation. This protocol has been experimentally demonstrated over significant distances by optical fiber and over the air.

A new work by the California Institute of Technology explores the equivalence of wormholes with quantum teleportation. For the first time, scientists have developed a quantum experiment that allows them to study the dynamics, or behavior, of a special theoretical wormhole.

Instead of producing a real wormhole, a rift in space and time, the experiment allows scientists to explore the relationships between theoretical wormholes and quantum physics, which is a prediction of what is known as quantum gravity.

Scientists performed the first experiments that probed the idea that information traveling from one point in space to another can be described in either the language of gravity (the wormholes) or the language of quantum physics (quantum entanglement).

Maria Spiropulu, the principal investigator of the U.S. Department of Energy Office of Science research program Quantum Communication Channels for Fundamental Physics (QCCFP) and the Shang-Yi Ch’en Professor of Physics at Caltech said, “We found a quantum system that exhibits key properties of a gravitational wormhole yet is sufficiently small to implement on today’s quantum hardware. This work constitutes a step toward a larger program of testing quantum gravity physics using a quantum computer. It does not substitute for direct probes of quantum gravity in the same way as other planned experiments that might use quantum sensing to probe quantum gravity effects in the future. Still, it offers a powerful testbed to exercise quantum gravity ideas.”

In this study, physicists used a baby SYK-like model prepared to preserve gravitational properties. They observed the wormhole dynamics on a quantum device at Google, namely the Sycamore quantum processor. The team used machine learning technologies on conventional computers to convert the SYK model to a reduced form.

Spiropulu said, “We employed learning techniques to find and prepare a simple SYK-like quantum system that could be encoded in the current quantum architectures, and that would preserve the gravitational properties. 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 how optimizing one characteristic of the model preserved the other metrics! We have plans for more tests to get better insights on the model itself.”

Scientists inserted a qubit into one of their SYK-like systems and observed the information emerge from the other system. Quantum teleportation allowed the information to go from one quantum system to another; alternatively, in the language of gravity, the quantum information flowed via the traversable wormhole.

Alexander Zlokapa (BS ’21), a former undergraduate student at Caltech, said, “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 to implement it on the Sycamore quantum processor at Google.”

Co-author Samantha Davis, a graduate student at Caltech, adds, “It took a long time to arrive at the results, and we surprised ourselves with the outcome.”

John Preskill, the Richard P. Feynman Professor of Theoretical Physics at Caltech and director of the Institute for Quantum Information and Matter (IQIM), said, “The near-term significance of this type of experiment is that the gravitational perspective provides a simple way to understand an otherwise mysterious many-particle quantum phenomenon. What I found interesting about this new Google experiment is that, via machine learning, they could make the system simple enough to simulate on an existing quantum machine while retaining a good caricature of what the gravitation picture predicts.”

In work, physicists describe wormhole behavior predicted by quantum theory and gravity. In spite of the fact that quantum information can be transported or sent across the device in several different ways, it was demonstrated that the experimental procedure is at least somewhat similar to what would occur if the information were to pass through a wormhole.

The scientists tried to accomplish this by utilizing either pulses of the opposing, positive energy or negative, repulsive energy pulses to “prop open the wormhole.” Only when the equivalent of negative energy was used did they notice the distinctive signs of a traversable wormhole, which is consistent with how wormholes are predicted to function.

Spiropulu said, “The high fidelity of the quantum processor we used was essential. If the error rates were higher by 50 percent, the signal would have been entirely obscured. If they were half, we would have ten times the signal!”

“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. We are excited to take this small step toward testing these ideas on quantum hardware and will keep going.”

Journal Reference:

Daniel Jafferis, Alexander Zlokapa, Joseph D. Lykken, David K. Kolchmeyer, Samantha I. Davis, Nikolai Lauk, Hartmut Neven, Maria Spiropulu. Traversable wormhole dynamics on a quantum processor. Nature, 2022; 612 (7938): 51 DOI: 10.1038/s41586-022-05424-3