A zero breakthrough! Quantum computers create wormholes for the first time
Wormholes, a type of tunneling proposed by Albert Einstein and Nathan Rosen in 1935, lead from one place to another by entering an extra dimension of space. Now, wormholes have been successfully created in a quantum computer, a wormhole that acts like a hologram and consists of quantum bits of information or quantum bits stored in a miniature superconducting circuit. By manipulating these quantum bits, physicists can send information through a wormhole.
A team led by Maria Spiropulu of the California Institute of Technology has implemented this novel "wormhole stealth transfer protocol" using Google's quantum computer "Hoverwood. With this first-of-its-kind "quantum gravity on a chip experiment," as Spiropulu describes it, the team beat out a competing group of physicists whose goal was to use quantum computers from IBM and Quantinuum for wormhole teleportation.
"I was blown away," Spiropulu said when she saw the quantum bits shown to pass through the wormhole.
This experiment can be seen as evidence for the holographic principle, a comprehensive hypothesis about how the two pillars of fundamental physics (quantum mechanics and general relativity) fit together. Since the 1930s, physicists have struggled to reconcile these disparate theories: one is a rulebook for atoms and subatomic particles, and the other is Einstein's description of how matter and energy distort the structure of spacetime and create gravity. The holographic principle, which has been at the forefront since the 1990s, proposes a mathematical equivalence or "duality" between these two frameworks. It says that the curved space-time continuum described by general relativity is actually a quantum system disguised as a particle; space-time and gravity arise from quantum effects, just as a three-dimensional hologram is projected from a two-dimensional pattern.
In fact, new experiments confirm that quantum effects that we can control in a quantum computer can produce a phenomenon we expect to see in relativity: wormholes.
To be clear, unlike a normal hologram, a wormhole is not something we can see. Although it can be thought of as a "filament of real space-time," according to co-author Daniel Jafferis of Harvard University, lead developer of the Wormhole Invisible Transfer Protocol, it is a different reality than the one we live in with the Humboldt computer. It's different. The holographic principle suggests that the two realities (the one with wormholes and the one with quantum bits) are different versions of the same physics, but how this duality is conceptualized remains mysterious.
People will have different views on the underlying meaning of this result. Crucially, the holographic wormhole in the experiment consists of a spacetime that is different from our own cosmic spacetime. Whether the experiment further confirms that the spacetime we are in is also holographic remains open to debate.
I think that the gravity in our universe is indeed generated by some quanta (bits), just like this little baby's one-dimensional wormhole is generated by a "hovering wood" chip," Jafferis said. Of course, we don't know that for sure. We're trying to understand it, too."
The story of holographic wormholes goes back to two seemingly unrelated papers published in 1935: one by Einstein and Rosen, known as ER, and the other by both of them and Boris Podolsky, known as EPR. both the ER and EPR papers were initially judged to be fringe works of the great Einstein, and now that has changed.
Einstein in 1920 on the left and Rosen around 1955 on the right, who stumbled upon the possibility of wormholes in a 1935 paper.
In the ER paper, Einstein and his young assistant Rosen stumbled upon the possibility of wormholes while trying to extend general relativity into a unified theory of everything: not only a description of spacetime, but also of the subatomic particles suspended in it. in 1916, only a few months after Einstein published his theory of general relativity, German physicist Karl Swasey discovered in the folds of general relativity the possibility of spacetime flaw in the structure.
Swasey showed that mass can attract itself gravitationally to the point where it is infinitely concentrated at one point, bending space-time so sharply that the variables become infinite and Einstein's equations go awry. We now know that these "singularities" exist throughout the universe. They are points that we can neither describe nor see, each hidden in the center of a black hole, capturing all nearby light by gravity.
Singularities are where quantum gravity theory is most needed.
Einstein and Rosen speculated that Swasey's mathematics might be a way to incorporate elementary particles into general relativity. To make the picture work, they removed the singularity from his equation and replaced it with a new variable, replacing the sharp point with a hyperdimensional pipe that slides to the other side of spacetime. Einstein and Rosen were wrong but prescient in thinking that these wormholes might represent particles.
Ironically, in their efforts to link wormholes and particles, the two did not consider the strange particle phenomenon they had discovered with Podolsky two months earlier in their EPR paper: quantum entanglement.
Entanglement arises when two particles interact with each other. According to quantum rules, particles can have multiple possible states at the same time. This means that the interaction between the particles has multiple possible outcomes, depending on which state each particle starts out in. However, the states they produce are always connected: how particle A ends up depends on how particle B turns out. After such an interaction, the particles have a shared formula that specifies the various combinations of states they may be in.
This shocking result led the authors of EPR to doubt the quantum theory, which, as Einstein said, is "a ghostly overdistance action". Measuring particle A (picking a reality from its possibilities) immediately determines the corresponding state of B, no matter how far away B is.
The importance of entanglement has skyrocketed since physicists discovered in the 1990s that entanglement allows for new kinds of computation. Entangling two quantum bits may produce four states with different possibilities (0 and 0, 0 and 1, 1 and 0, 1 and 1); three quantum bits produce eight simultaneous possibilities, and so on, with each additional entangled quantum bit increasing the power of the "quantum computer" exponentially. By cleverly arranging the entanglement, scientists can cancel all combinations of zeros and ones, except for the sequence that gives the answer to the calculation. Prototype quantum computers consisting of a few dozen quantum bits have been realized in the past few years, led by Google's 54-quantum-bit computer "Hoverwood.
Meanwhile, quantum gravity researchers are focusing on quantum entanglement for another reason: as a possible source code for spacetime holograms.
02ER=EPR
Talk of emergent spacetime and holography began in the late 1980s, after black hole theorist John Wheeler promulgated the idea that spacetime and everything in it could come from information. Soon other researchers, including the Dutch physicist Gerard 't Hooft, wondered if this emergence was analogous to the projection of a hologram. Examples had already emerged in black hole research and string theory, where a description of a physical scene could be translated into an equally valid view with an additional spatial dimension. in 1994, quantum gravity theorist Leonard Susskind of Stanford University fleshed out Hooft's holographic principle in a paper titled "The World as a Hologram," arguing that general relativity A volume of curved spacetime described by general relativity is equivalent, or "dual", to a system of quantum particles on the low-dimensional boundary of the region.
Three years later, an important example of holographic theory emerged. Juan Maldacena, a quantum gravity theorist now working at the Institute for Advanced Study in Princeton, New Jersey, discovered that a space called anti-de Sitter (AdS) is indeed a hologram.
Juan Maldacena (left) and Leonard Susskind, leaders of the quantum approach to gravity known as holography, proposed in 2013 that wormholes in space-time are equivalent to quantum entanglement, a conjecture known as ER=EPR.
The actual universe is de Sitter space, an ever-growing sphere driven outward by its own positive energy. In contrast, AdS space is infused with negative energy: a different sign of a constant in the equations of general relativity, which gives space its "hyperbolic" geometry. Maldacena showed that spacetime and gravity within the AdS universe correspond exactly to the properties of quantum systems on the boundary (in particular, a system known as Conformal Field Theory, or CFT).
Maldacena's explosive 1997 paper describing this "AdS/CFT correspondence" was cited 22,000 times in subsequent studies: an average of more than twice a day.
When Maldacena himself explored his AdS/CFT map between dynamical spacetime and quantum systems, he made a new discovery about wormholes. He was working on a special mode of entanglement involving two sets of particles, each of which is entangled with the other. maldacena showed that this state corresponds mathematically to a rather dramatic hologram: a pair of black holes in AdS space whose interiors are connected by a wormhole.
It was a decade later, in 2013, that Maldacena realized that his discovery might mark a more general correspondence between quantum entanglement and connection through wormholes: ER = EPR.
Perhaps a wormhole connects every pair of entangled particles in the universe, forming a spatial link that records their common history; perhaps Einstein's hunch that wormholes are related to particles was correct.
03Wormholes: a solid bridge
When Jafferis heard Maldacena's talk on ER=EPR at a conference in 2013, he realized that the conjectural duality should allow the design of custom wormholes by tailoring the entanglement pattern.
The standard Einstein-Rosen bridge (bridge) has frustrated science fiction fans everywhere. If one were to form, it would quickly collapse under its own gravity and be choked off before a spaceship or anything else could pass through. But Jafferis imagines a wire or any other physical connection strung between the two sets of entangled particles encoding the two mouths of the wormhole. With that coupling, manipulation of the particles on one side would induce changes in the particles on the other side, perhaps holding open the wormhole between them. "Could that be the case, making the wormhole traversable?" Jafferis recalls that he kept pursuing this question "just for fun."
Back at Harvard, he and Ping Gao, then a graduate student, and Aron Wall, then a visiting scholar, eventually calculated that by coupling two sets of entangled particles, they could manipulate the set of particles on the left side to hold open the wormhole to the right side of the mouth and push a quantum bit through in a dyadic, high-dimensional spacetime map.
Jafferis, Gao and Wall discovered such holographic, traversable wormholes in 2016, giving researchers a new window into the mechanics of holography. "The fact that you can eventually get through if you do the right thing from the outside also means you can see inside the wormhole," Jafferis said. That means it's possible to probe the fact that two entangled systems would be described by some connected geometry."
Within months, Maldacena and two colleagues built on the program to show that traversable wormholes can be realized in a simple setting: "a quantum system as simple as we can imagine." The SYK model is a system of matter particles that interact in groups, rather than the usual pairs, first described by Subir Sachdev and Jinwu Ye in 1993; it suddenly became much more important starting in 2015, when theoretical physicist Alexei Kitaev discovered it was holographic. At a lecture in Santa Barbara, California, that year, Kitaev (the K in SYK) filled several blackboards with evidence that a particular version of the model, in which matter particles interact in groups of four, is mathematically mappable to a one-dimensional black hole in AdS space, with the same symmetries and other properties. "In both cases, some of the answers are the same."
Connecting the dots, Maldacena and co-authors proposed that two SYK models connected together could encode the two mouths of Jafferis, Gao and Wall's traversable wormhole.Jafferis and Gao used this approach to conduct their research. By 2019, they had found a concrete way to transfer quantum bits of information from one four-way interacting particle system to another. Rotating the spin direction of all particles, in a dual space-time diagram, translates into a negative energy shock wave that sweeps through the wormhole, kicking the quantum bits forward and, at a predictable time, out of the mouth.
Alex Zlokapa, a graduate student at MIT and co-author of the new experiment, said, "Jaffrith's wormhole is the first concrete implementation of ER=EPR, and he shows that the relationship holds exactly for a given system."
04Wormholes in the lab
As theoretical work develops, Maria Spiropulu, an accomplished experimental particle physicist who was involved in the 2012 discovery of the Higgs boson, is thinking about how to use nascent quantum computers to do holographic quantum gravity experiments. in 2018, she convinced Jafferis to join her growing team, along with researchers from Google's Quantum Artificial Intelligence --The guardians of the "Hoverwood" device.
To run Jafferis and Gao's wormhole stealth transfer protocol on a state-of-the-art but still small and error-prone quantum computer, Spiropulu's team had to greatly simplify the protocol. A complete SYK model consists of a practically infinite number of particles coupled to each other, whose strength is random because of the four-way interactions throughout. This is computationally infeasible: even using all 50+ available quantum bits would require hundreds of thousands of circuit operations. The researchers set out to create a holographic wormhole with just seven quantum bits and hundreds of operations. To do this, they had to "sparse" the seven-particle SYK model, encoding only the strongest four-way interactions and ignoring the rest, while preserving the model's holographic properties," Spiropulu says. "This took several years. "
Maria Spiropulu, a physicist at Caltech
One of the secrets to success was Zlokapa, who joined Spiropulu's research group as an undergraduate at Caltech. a gifted programmer, Zlokapa mapped the particle interactions of the SYK model onto the connections between the neurons of a neural network and trained the system to remove as many network connections as possible while retaining a key wormhole feature. The program reduced the number of four-way interactions from hundreds to five.
With this, the team began to program the quantum bits of the "hoverwood". Seven quantum bits encode 14 matter particles: seven on the left and seven on the right of the SYK system, where each particle on the left is entangled with a particle on the right. An eighth quantum bit, in some probabilistic combination of 0 and 1 states, is then exchanged with a particle from the left SYK model. The possible states of this quantum bit soon become entangled with the states of the other particles on the left, spreading its information evenly between them like a drop of ink in water. This is holographically equivalent to the left entrance of the quantum bit into a one-dimensional wormhole in AdS space.
Then comes the rotation of all the quantum bits corresponding to the negative energy pulse through the wormhole. The rotation causes the injected quantum bits to shift to the particle on the right SYK model, and then the information stops spreading, Preskill says, "as if chaos were running backward" and refocuses on the position of one of the particles on the right - the swapped left particle's entanglement partner. The states of the quantum bits are then measured in their entirety. Counting the zeros and ones in multiple experiments and comparing these statistics with the prepared state of the injected quantum bit reveals whether the quantum bit was transmitted or not.
Alex Zlokapa
The researchers looked for a peak in the data that represented the difference between the two cases. If they see this peak, it means that rotations of quantum bits corresponding to negative energy pulses allow quantum bits to be transmitted, while rotations in the opposite direction corresponding to normal positive energy pulses do not allow quantum bits to pass through (instead, they cause wormholes to close).
Late one night this January, after two years of incremental improvements and noise reduction efforts, Zlokapa ran the protocol on "Hoverwood" remotely from his childhood bedroom in the San Francisco Bay Area, where he was spending winter break after his first semester of graduate school.
The spike appeared on his computer screen. It kept getting clearer and clearer," he says. I sent a screenshot of the peak to Maria and was so excited that I thought we were now seeing a wormhole: the peak was the first indication that gravity could be seen on a quantum computer."
Surprisingly, despite the simple structure of their wormhole, the researchers detected a second feature of wormhole dynamics, a subtle pattern in the way information does and does not propagate between quantum bits, known as "size-winding". They did not train their neural network to retain this signal when sparing the SYK model, so the fact that "size-winding" shows up is an experimental discovery about holography anyway.
We didn't make any claims about this size-winding property, but we found that it just jumped out at us," Jafferis says. This confirms the 'robustness of holographic duality.' Letting one (property) appear and then getting all the others is a kind of evidence that this gravitational picture is correct."
A shell of one of several copies of the "Humboldt" chip, which consists of more than 50 quantum bits made up of superconducting aluminum circuits.
05The significance of wormholes
Jafferis, who never expected to be part of the wormhole experiment (or any other experiment), believes that one of the most important takeaways is what the experiment says about quantum mechanics. Quantum phenomena like entanglement are usually opaque and abstract; for example, we don't know how measurements of particle A determine the state of B from a distance. But in the new experiment, an ineffable quantum phenomenon: the transfer of information between particles, has a concrete explanation: that is, a particle receives some energy and moves from A to B with a calculable speed.
Susskind, who saw today's results in advance, said he hopes that future wormhole experiments involving more quantum bits can be used to explore the inside of wormholes as a way to study the quantum properties of gravity. "By making measurements of what's going through, you can interrogate it and see what's inside, and that seems to me to be an interesting way to do that," he said.
Some physicists would say that this experiment tells us nothing about our universe because it achieves parity between quantum mechanics and inverse de Sitter space, which is not the case with our universe.
In the 25 years since Maldacena discovered the AdS/CFT correspondence, physicists have been searching for a similar holographic duality for de Sitter space: a map from quantum systems to the positive-energy, expanding de Sitter universe in which we live. But progress has been much slower than with AdS, leading some to wonder if de Sitter space is holographic.
Woit, a critic of the AdS/CFT study, said, "What's needed is some completely different ideas."
Critics argue that the two spaces are fundamentally different. adS has an outer boundary, while DS space does not, so there is no smooth mathematical transition that can turn one into the other. And the hard boundary of AdS space is the very thing that makes holography easy in that environment; it provides the quantum surface on which space is projected. In contrast, in our Descent universe, the only boundaries are the farthest we can see and the infinite future. These are hazy surfaces that can try to project a spacetime hologram.
Renate Loll, a renowned quantum gravity theorist at Radboud University in the Netherlands, also emphasizes that the wormhole experiment involves two-dimensional space-time: a wormhole is a filament with a spatial dimension plus a temporal dimension. And in the four-dimensional spacetime where we actually live, gravity is more complex. "It is quite tempting to dwell on the complexity of the two-dimensional toy model, while ignoring the different and greater challenges that await us in four-dimensional quantum gravity. For that theory, I don't see how quantum computers can help much with the current capabilities ...... but I'm happy to be corrected."
Most quantum gravity researchers consider these to be difficult but solvable problems. Weaving entanglement patterns in 4D de Sitter space is more complicated than 2D AdS, but we can still extract general lessons by studying holography in a simpler setting. This camp tends to view the two types of spaces (dS and AdS), as more similar than different. Both are solutions to Einstein's theory of relativity, distinguished only by a minus sign: both the dS and AdS universes contain black holes, and they are both plagued by the same paradox; when you go deep into AdS space, away from its outer walls, it is difficult to distinguish the surroundings from dS.
Nonetheless, Susskind agrees that it's time to get real. "I think it's time to come out from under the protective layer of AdS space and open up to a world that might have more to do with cosmology."
"Whether the limits of such a quantum system, which is more complex than the systems programmed so far," will be realized in the laboratory, I don't know. What seems certain is that now that there is a holographic wormhole, more will open up."
Reference link：
https://www.quantamagazine.org/physicists-create-a-wormhole-using-a-quantum-computer-20221130/
