How physicists simulated a 'baby' wormhole and what it means for the future

It was around 2 am when Alexander Zlokapa, a member of the team and a PhD student of MIT, was running quantum circuits in Google's mighty quantum computer.  "I was watching the data as it was coming out. There's a little bit of a noisy peak at first. I thought it was probably just a noise artefact but as the data kept coming and it kept getting clearer, I saw a peak and I sent it off to Maria and others, saying, 'Guys, I think we have a wormhole!'" he shared the experience.

On 30 November 2022, a team of physicists led by Maria Spiropulu of the California Institute of Technology (CalTech) created something that we had only read in the pages of science fiction. For those unaware, a wormhole is a hypothetical passage connecting two distant points in spacetime that can allow travelling extremely long distances in a very short period of time. 

The team simulated a wormhole using a quantum computer and sent information from one side to the other for the first time, potentially showing that quantum entanglement and wormholes may be two different explanations for the very same phenomena.

In 1935, Albert Einstein wrote a paper with Nathan Rosen, in which the Einstein-Rosen bridge made its first appearance. And this bridge theoretically connects two seemingly unconnected pieces of spacetime. ER (Einstein and Rosen) pointed out that solutions to general relativity allowed for two black holes which are connected, but with a kind of bridge – what we call a wormhole.

But the problem with wormholes is that they are unstable passages and therefore are non-traversable. A wormhole opens and closes and it gets chaotic and gets destroyed very fast. So Einstein, when he proposed the wormhole, was very frustrated because nothing could go through one. So, what good is a wormhole if you cannot put anything through it? He later realised that he was not considering quantum physics.

The very same year came another paper – the EPR paper by Einstein, Rosen and Podolsky. EPR is about quantum entanglement, what Einstein called "spooky action at a distance". Entanglement is the property that subatomic particles are partners. Even if you take them apart and take them to the other edge of the universe, they could be connected. If you measure the one you know what the other would be. So, entanglement is a strong correlation.

However, it has been a challenge over decades to understand better how quantum physics and general relativity fit together. In 2013, Juan Maldacena and Leonard Susskind said ER = EPR. Wormholes and entanglement are the same things – a totally unexpected finding. The basic idea was that when you have quantum entanglement between two black holes, there may be a wormhole connecting them.

In fact, one of the magical things about quantum mechanics is that you can actually have negative energy, and this allows you to do things that you would otherwise have thought were impossible. Daniel Jafferis of Harvard University showed that if you introduce a negative energy shockwave, you can support your wormhole and get something from one end to the other.

Now, you can tackle the same physics from these two different angles and that's the most concrete path forward the scientists have in building a full theory of quantum gravity. The physics of black holes is the physics of quantum gravity. 

But they cannot devise an experiment in the black hole and validate that. So, scientists decided to give it a try in the laboratory. What if there could be quantum systems whose dual description looks like wormholes? This leads Scientists to turn to the best quantum system that they know how to manipulate: a quantum computer. 

Breaking spacetime

They turned to Google's quantum AI team to gain access to Google's Sycamore device, one of the world's most powerful, but still comparatively small-scale and still error-prone, quantum computers.

The team's goal was to assemble the quantum states necessary to create a wormhole in the Sycamore device. An assembly of seven encoded quantum bits (Qubits) on the left-hand side of the Sycamore device was the entrance. Each qubit on the left-hand side was then entangled with one of seven other qubits on the right-hand side which would then act as the exit.

After two years of gradual improvements and noise reduction efforts, the team ran the process on Sycamore and saw a peak that confirmed their results. By measuring this process many times and looking at the input states that were injected into the wormhole versus those that emerged from it, the team claimed reliably that they could send a qubit through the wormhole.

What now?

This experiment is founded upon the idea that the quantum description and the spacetime description are alternating versions of the same physical properties. What this means and how we think about it still may be slightly confusing. 

But that does not mean that the results are made up. Unlike simple quantum entanglement where it's challenging to come up with any digestible interpretation of how or why a measurement on one particle affects its partner even thousands of light years away, the results of this experiment feel much more concrete.

However, this experiment will also probably trigger a lot of opinions about its practicality and its interpretation and whether it holds for our universe. 

Our universe is often referred to as a de Sitter space, an ever-expanding sphere driven outward by its positive energy. Whereas, the quantum phenomena mapped to something is called an anti-de Sitter space: a hyperbolic space geometry with a minus sign rather than a plus sign around some important gravitational constants. 

It is to be noted that the scientists themselves made clear that this is not an actual wormhole and they remain a long way from being able to send people or other living beings through such a portal.

"Experimentally, for me, I will tell you that it's very, very far away. People come to me and ask me, 'Can you put your dog in the wormhole?' So, no," Spiropulu told reporters during a video briefing. But scientists have to start from somewhere. In that case "...that's a huge leap,"  the physicist and study co-author Joseph Lykken told The Guardian.