A quantum computer has successfully simulated a simplified wormhole, a kind of tunnel through space-time. In the simulation, researchers were able to send a piece of information through the wormhole.
For the first time has succeeded in simulating a holographic wormhole with the help of a quantum computer. The word ‘holographic’ here does not refer to a hologram as we know it, a three-dimensional image, but to a way of simplifying physics problems in which both tricky quantum effects and gravitational effects play a role.
Simulations like this wormhole may help physicists figure out how to unify quantum theory and gravity theory into one theory of quantum gravity. That’s one of the biggest questions in physics.
READ ALSO
A new extraction method for deep geothermal energy
Quantum mechanics determines the rules on the scale of tiny particles. The theory for gravity, the general theory of relativity, is precisely about giant objects. The problem is that these two theories are not compatible. This becomes painfully clear in situations where both play a role, as is the case in and around black holes.
Simplified view
The area around a black hole is very complex, but holography offers a way out. Holography is a technique to create a description of the system that is less complicated, but still equivalent to the original. Just as a two-dimensional hologram can reveal details in three dimensions.
Physicist Mary Spiropulu used Google’s Sycamore quantum computer, along with her colleagues at the California Institute of Technology, to simulate a holographic wormhole. They made one wormhole, a tunnel through spacetime, with a black hole at either end. In theory, you could send a message through this tunnel. Their simulation allowed the physicists to study and describe the journey of such a message through the wormhole.
If it were a real wormhole, the journey would be subject to gravitational effects. But to simplify the system, Spiropulu’s team replaced the effects of gravity with quantum effects. As a result, the consequences of relativity no longer need to be taken into account.
Send message
When the message travels through the wormhole, it undergoes quantum teleportation. Information about the state of two entangled particles is exchanged at a distance. In this simulation, the message used was a signal containing such a quantum state—a quantum bit, or qubit, that was in a superposition of both 1 and 0.
“The signal is scrambled. It’s going to be a kind of mush, it’s going to be chaos. And then it will be again disassembled, and emerges unscathed on the other side of the wormhole,” says Spiropulu. “Even on such a small scale, we were able to sustain the wormhole, and the observations matched our expectations.”
This is due to the quantum entanglement between the two black holes, which ensures that information that falls into one black hole comes out of the other unscathed. Quantum computers are based on entanglement, a property useful in this type of simulation experiment.
Low resolution
The simulation had a low resolution, because only nine qubits were used. That is, the simulation, like a photograph of a bird taken from afar, showed roughly the shape of the object depicted, but still needs to be fine-tuned. Only then did the properties of the wormhole come to light.
‘If you want to compare this model to a wormhole, you can, because there are a lot of similarities. But the model certainly leaves something to interpretation,’ says the physicist Adam Brown from Stanford University in California. He was not involved in this investigation.
More powerful quantum computer
Using a more powerful quantum computer can help clarify the picture further. ‘This is just a baby wormhole, a first step towards testing quantum gravity theories. As the quantum computers gain more capacity, we will start using larger quantum systems. Then we can also test bigger ideas about quantum gravity’, says Spiropulu.
This is important, because some quantum gravity theories are difficult or even impossible to fathom with classical computers. Quantum gravity is confusing. It’s difficult to derive predictions from theory, and it would be ideal to use quantum computers to answer questions about quantum gravity,” says Brown. “But that’s not what’s happening here. This is a very small quantum computer, so you can also do this simulation on a laptop. The cooling doesn’t even have to be switched on for that.’
Still, the similarity between this simulation and a ‘real’ wormhole suggests that it is possible to test ideas about quantum gravity using quantum computers. Maybe one day we will even understand the theory.