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Physicists Create a Holographic Wormhole Using a Quantum Computer
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quantum gravity


PHYSICISTS CREATE A HOLOGRAPHIC WORMHOLE USING A QUANTUM COMPUTER

By Natalie Wolchover

November 30, 2022

The unprecedented experiment explores the possibility that space-time somehow
emerges from quantum information, even as the work’s interpretation remains
disputed.
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Researchers were able to send a signal through the open wormhole, though it’s
not clear in what sense the wormhole can be said to exist.

Kim Taylor for Quanta Magazine


INTRODUCTION

Editor’s note: In February 2023, a team of physicists led by Norman Yao of
Harvard University published a comment about the holographic wormhole experiment
described in this article. After analyzing the mathematical properties of the
model used to simulate the wormhole in a quantum computer, the group concluded
that the teleportation demonstration should not be thought of as a holographic
wormhole. They argue that the model underlying the experiment was too simple to
capture key properties of gravitational systems such as black holes and
wormholes. The comment has not yet been peer reviewed, but independent experts
contacted by Quanta find the arguments compelling. Our ongoing coverage is
available here:
https://www.quantamagazine.org/wormhole-experiment-called-into-question-20230323/


By Natalie Wolchover

Senior Editor

--------------------------------------------------------------------------------

November 30, 2022

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AdS/CFTblack hole information paradoxblack holesentanglementexperimental
physicsphysicsquantum computingquantum gravityquantum information theoryquantum
physicstheoretical physicswormholesAll topics



INTRODUCTION

Physicists have purportedly created the first-ever wormhole, a kind of tunnel
theorized in 1935 by Albert Einstein and Nathan Rosen that leads from one place
to another by passing into an extra dimension of space.

The wormhole emerged like a hologram out of quantum bits of information, or
“qubits,” stored in tiny superconducting circuits. By manipulating the qubits,
the physicists then sent information through the wormhole, they reported today
in the journal Nature.

The team, led by Maria Spiropulu of the California Institute of Technology,
implemented the novel “wormhole teleportation protocol” using Google’s quantum
computer, a device called Sycamore housed at Google Quantum AI in Santa Barbara,
California. With this first-of-its-kind “quantum gravity experiment on a chip,”
as Spiropulu described it, she and her team beat a competing group of physicists
who aim to do wormhole teleportation with IBM and Quantinuum’s quantum
computers.

When Spiropulu saw the key signature indicating that qubits were passing through
the wormhole, she said, “I was shaken.”

The experiment can be seen as evidence for the holographic principle, a sweeping
hypothesis about how the two pillars of fundamental physics, quantum mechanics
and general relativity, fit together. Physicists have strived since the 1930s to
reconcile these disjointed theories — one, a rulebook for atoms and subatomic
particles, the other, Einstein’s description of how matter and energy warp the
space-time fabric, generating gravity. The holographic principle, ascendant
since the 1990s, posits a mathematical equivalence or “duality” between the two
frameworks. It says the bendy space-time continuum described by general
relativity is really a quantum system of particles in disguise. Space-time and
gravity emerge from quantum effects much as a 3D hologram projects out of a 2D
pattern.

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Video: Wormholes were first envisioned almost a century ago, but it would take a
number of theoretical leaps and a “crazy” team of experimentalists to build one
on a quantum computer.

Emily Buder, Bongani Mlambo, Ibrahim Rayintakath, Rui Braz and Kim Taylor for
Quanta Magazine; Kristina Armitage/Quanta Magazine


INTRODUCTION

Indeed, the new experiment confirms that quantum effects, of the type that we
can control in a quantum computer, can give rise to a phenomenon that we expect
to see in relativity — a wormhole. The evolving system of qubits in the Sycamore
chip “has this really cool alternative description,” said John Preskill, a
theoretical physicist at Caltech who was not involved in the experiment. “You
can think of the system in a very different language as being gravitational.”

To be clear, unlike an ordinary hologram, the wormhole isn’t something we can
see. While it can be considered “a filament of real space-time,” according to
co-author Daniel Jafferis of Harvard University, lead developer of the wormhole
teleportation protocol, it’s not part of the same reality that we and the
Sycamore computer inhabit. The holographic principle says that the two realities
— the one with the wormhole and the one with the qubits — are alternate versions
of the same physics, but how to conceptualize this kind of duality remains
mysterious.

Opinions will differ about the fundamental implications of the result.
Crucially, the holographic wormhole in the experiment consists of a different
kind of space-time than the space-time of our own universe. It’s debatable
whether the experiment furthers the hypothesis that the space-time we inhabit is
also holographic, patterned by quantum bits.

“I think it is true that gravity in our universe is emergent from some quantum
[bits] in the same way that this little baby one-dimensional wormhole is
emergent” from the Sycamore chip, Jafferis said. “Of course we don’t know that
for sure. We’re trying to understand it.”


INTO THE WORMHOLE

The story of the holographic wormhole traces back to two seemingly unrelated
papers published in 1935: one by Einstein and Rosen, known as ER, the other by
the two of them and Boris Podolsky, known as EPR. Both the ER and EPR papers
were initially judged as marginal works of the great E. That has changed.

In the ER paper, Einstein and his young assistant, Rosen, stumbled upon the
possibility of wormholes while attempting to extend general relativity into a
unified theory of everything — a description not only of space-time, but of the
subatomic particles suspended in it. They had homed in on snags in the
space-time fabric that the German physicist-soldier Karl Schwarzschild had found
among the folds of general relativity in 1916, mere months after Einstein
published the theory. Schwarzschild showed that mass can gravitationally attract
itself so much that it becomes infinitely concentrated at a point, curving
space-time so sharply there that variables turn infinite and Einstein’s
equations malfunction. We now know that these “singularities” exist throughout
the universe. They are points we can neither describe nor see, each one hidden
at the center of a black hole that gravitationally traps all nearby light.
Singularities are where a quantum theory of gravity is most needed.

Albert Einstein, pictured on the top in 1920, and Nathan Rosen, pictured around
1955, stumbled across the possibility of wormholes in a 1935 paper.

The Scientific Monthly (top); AIP Emilio Segrè Visual Archives, Physics Today
Collection

Albert Einstein, pictured on the left in 1920, and Nathan Rosen, pictured around
1955, stumbled across the possibility of wormholes in a 1935 paper.

The Scientific Monthly (left); AIP Emilio Segrè Visual Archives, Physics Today
Collection


INTRODUCTION

Einstein and Rosen speculated that Schwarzschild’s math might be a way to plug
elementary particles into general relativity. To make the picture work, they
snipped the singularity out of his equations, swapping in new variables that
replaced the sharp point with an extra-dimensional tube sliding to another part
of space-time. Einstein and Rosen argued, wrongly but presciently, that these
“bridges” (or wormholes) might represent particles.

Ironically, in striving to link wormholes and particles, the duo did not
consider the strange particle phenomenon they had identified two months earlier
with Podolsky, in the EPR paper: quantum entanglement.

Entanglement arises when two particles interact. According to quantum rules,
particles can have multiple possible states at once. This means an interaction
between particles has multiple possible outcomes, depending on which state each
particle is in to begin with. Always, though, their resulting states will be
linked — 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
combined states they might be in.

The shocking consequence, which caused the EPR authors to doubt quantum theory,
is “spooky action at a distance,” as Einstein put it: Measuring particle A
(which picks out one reality from among its possibilities) instantly decides the
corresponding state of B, no matter how far away B is.

Entanglement has shot up in perceived importance since physicists discovered in
the 1990s that it allows new kinds of computations. Entangling two qubits —
quantum objects like particles that exist in two possible states, 0 and 1 —
yields four possible states with different likelihoods (0 and 0, 0 and 1, 1 and
0, and 1 and 1). Three qubits make eight simultaneous possibilities, and so on;
the power of a “quantum computer” grows exponentially with each additional
entangled qubit. Cleverly orchestrate the entanglement, and you can cancel out
all combinations of 0s and 1s except the sequence that gives the answer to a
calculation. Prototype quantum computers made of a few dozen qubits have
materialized in the last couple of years, led by Google’s 54-qubit Sycamore
machine.

Meanwhile, quantum gravity researchers have fixated on quantum entanglement for
another reason: as the possible source code of the space-time hologram.


ER = EPR

Talk of emergent space-time and holography started in the late 1980s, after the
black hole theorist John Wheeler promulgated the view that space-time and
everything in it might spring from information. Soon, other researchers,
including the Dutch physicist Gerard ’t Hooft, wondered whether this emergence
might resemble the projection of a hologram. Examples had cropped up in black
hole studies and in string theory, where one description of a physical scenario
could be translated into an equally valid view of it with one extra spatial
dimension. In a 1994 paper titled “The World as a Hologram,” Leonard Susskind, a
quantum gravity theorist at Stanford University, fleshed out ’t Hooft’s
holographic principle, arguing that a volume of bendy space-time described by
general relativity is equivalent, or “dual,” to a system of quantum particles on
the region’s lower-dimensional boundary.

A momentous example of holography arrived three years later. Juan Maldacena, a
quantum gravity theorist now at the Institute for Advanced Study in Princeton,
New Jersey, discovered that a kind of space called anti-de Sitter (AdS) space
is, indeed, a hologram.

Juan Maldacena (top) and Leonard Susskind are leaders of the approach to quantum
gravity known as holography. In 2013, they proposed that wormholes in space-time
are equivalent to quantum entanglement, a conjecture known as ER = EPR.

Sasha Maslov for Quanta Magazine (top); Linda A. Cicero/Stanford News Service

Juan Maldacena (left) and Leonard Susskind are leaders of the approach to
quantum gravity known as holography. In 2013, they proposed that wormholes in
space-time are equivalent to quantum entanglement, a conjecture known as ER =
EPR.

Sasha Maslov for Quanta Magazine (left); Linda A. Cicero/Stanford News Service


INTRODUCTION

The actual universe is de Sitter space, an ever-growing sphere driven outward by
its own positive energy. By contrast, AdS space is infused with negative energy
— resulting from a difference in the sign of one constant in the equations of
general relativity — giving the space a “hyperbolic” geometry: Objects shrink as
they move outward from the center of the space, becoming infinitesimal at an
outer boundary. Maldacena showed that space-time and gravity inside an AdS
universe exactly correspond to properties of a quantum system on the boundary
(specifically a system called a conformal field theory, or CFT).

Maldacena’s bombshell 1997 paper describing this “AdS/CFT correspondence” has
been cited by subsequent studies 22,000 times — more than twice a day on
average. “Trying to exploit ideas based on AdS/CFT has been the main goal of
thousands of the best theorists for decades,” said Peter Woit, a mathematical
physicist at Columbia University.

As Maldacena himself explored his AdS/CFT map between dynamical space-times and
quantum systems, he made a new discovery about wormholes. He was studying a
particular entanglement pattern involving two sets of particles, where each
particle in one set is entangled with a particle in the other. Maldacena showed
that this state is mathematically dual to a rather dramatic hologram: a pair of
black holes in AdS space whose interiors connect via a wormhole.

A decade had to pass before Maldacena, in 2013 (under circumstances that “to be
frank, I do not remember,” he says),  realized that his discovery might signify
a more general correspondence between quantum entanglement and connection via
wormhole. He coined a cryptic little equation — ER = EPR — in an email to
Susskind, who understood immediately. The two quickly developed the conjecture
together, writing, “We argue that the Einstein Rosen bridge between two black
holes is created by EPR-like correlations between the microstates of the two
black holes,” and that the duality might be more general than that: “It is very
tempting to think that any EPR correlated system is connected by some sort of ER
bridge.”

Maybe a wormhole links every entangled pair of particles in the universe,
forging a spatial connection that records their shared histories. Maybe
Einstein’s hunch that wormholes have to do with particles was right.


A STURDY BRIDGE

When Jafferis heard Maldacena lecture about ER = EPR at a conference in 2013, he
realized that the conjectured duality should allow you to design bespoke
wormholes by tailoring the entanglement pattern.

Standard Einstein-Rosen bridges are a disappointment to sci-fi fans everywhere:
Were one to form, it would quickly collapse under its own gravity and pinch off
long before a spaceship or anything else could get through. But Jafferis
imagined stringing a wire or any other physical connection between the two sets
of entangled particles that encode a wormhole’s two mouths. With this kind of
coupling, operating on the particles on one side would induce changes to the
particles on the other, perhaps propping open the wormhole between them. “Could
it be that that makes the wormhole traversable?” Jafferis recalls wondering.
Having been fascinated by wormholes since childhood — a physics prodigy, he
started at Yale University at 14 — Jafferis pursued the question “almost for
fun.”


INTRODUCTION

Back at Harvard, he and Ping Gao, his graduate student at the time, and Aron
Wall, then a visiting researcher, eventually calculated that, indeed, by
coupling two sets of entangled particles, you can perform an operation on the
left-hand set that, in the dual, higher-dimensional space-time picture, holds
open the wormhole leading to the right-hand mouth and pushes a qubit through.

Jafferis, Gao and Wall’s 2016 discovery of this holographic, traversable
wormhole gave researchers a new window into the mechanics of holography. “The
fact that if you do the right things from the outside you can end up getting
through, it also means you can see inside” the wormhole, Jafferis said. “It
means that it’s possible to probe this fact that two entangled systems get
described by some connected geometry.”

Within months, Maldacena and two colleagues had built on the scheme by showing
that the traversable wormhole could be realized in a simple setting — “a quantum
system that’s simple enough that we can imagine making it,” Jafferis said.

The SYK model, as it’s called, 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, the model suddenly mattered much more starting in 2015 when the
theoretical physicist Alexei Kitaev discovered that it is holographic. At a
lecture that year in Santa Barbara, California, Kitaev (who became the K in SYK)
filled several chalkboards with evidence that the 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 identical symmetries
and other properties. “Some answers are the same in the two cases,” he told a
rapt audience. Maldacena was sitting in the front row.

Merrill Sherman/Quanta Magazine

Connecting the dots, Maldacena and co-authors proposed that two SYK models
linked together could encode the two mouths of Jafferis, Gao and Wall’s
traversable wormhole. Jafferis and Gao ran with the approach. By 2019, they
found their way to a concrete prescription for teleporting a qubit of
information from one system of four-way-interacting particles to another.
Rotating all the particles’ spin directions translates, in the dual space-time
picture, into a negative-energy shock wave that sweeps through the wormhole,
kicking the qubit forward and, at a predictable time, out of the mouth.

“Jafferis’ wormhole is the first concrete realization of ER = EPR, where he
shows the relation holds exactly for a particular system,” said Alex Zlokapa, a
graduate student at the Massachusetts Institute of Technology and a co-author on
the new experiment.


WORMHOLE IN THE LAB

As the theoretical work was developing, Maria Spiropulu, an accomplished
experimental particle physicist who was involved in the 2012 discovery of the
Higgs boson, was thinking about how to use nascent quantum computers to do
holographic quantum gravity experiments. In 2018 she persuaded Jafferis to join
her growing team, along with researchers at Google Quantum AI — keepers of the
Sycamore device.

To run Jafferis and Gao’s wormhole teleportation protocol on the
state-of-the-art but still small and error-prone quantum computer, Spiropulu’s
team had to greatly simplify the protocol. A full SYK model consists of
practically infinitely many particles coupled to one another with random
strengths as four-way interactions occur throughout. This is not feasible to
calculate; even using all 50-odd available qubits would have required hundreds
of thousands of circuit operations. The researchers set out to create a
holographic wormhole with just seven qubits and hundreds of operations. To do
this, they had to “sparsify” the seven-particle SYK model, encoding only the
strongest four-way interactions and eliding the rest, while retaining the
model’s holographic properties. “That took a couple of years to figure out a
clever way to do it,” Spiropulu said.



Maria Spiropulu, a physicist at the California Institute of Technology, led the
team behind the new wormhole experiment.

Bongani Mlambo for Quanta Magazine


INTRODUCTION

One secret to success was Zlokapa, a waifish orchestra kid who joined
Spiropulu’s research group as a Caltech undergrad. A gifted programmer, Zlokapa
mapped the particle interactions of the SYK model onto the connections between
neurons of a neural network, and trained the system to delete as many network
connections as possible while preserving a key wormhole signature. The procedure
reduced the number of four-way interactions from hundreds down to five.

With that, the team started programming Sycamore’s qubits. Seven qubits encode
14 matter particles — seven each in the left and right SYK systems, where every
particle on the left is entangled with one on the right. An eighth qubit, in
some probabilistic combination of states 0 and 1, is then swapped with one of
the particles from the left SYK model. That qubit’s possible states quickly get
tangled up with the states of the other particles on the left, spreading its
information evenly among them like a drop of ink in water. This is
holographically dual to the qubit entering the left mouth of a one-dimensional
wormhole in AdS space.

Then comes the big rotation of all the qubits, dual to a pulse of negative
energy coursing through the wormhole. The rotation causes the injected qubit to
transfer to the particles of the right-hand SYK model. Then the information
un-spreads, Preskill said, “like chaos run backward,” and refocuses at the site
of a single particle on the right — the entangled partner of the left-hand
particle that was swapped out. Then the qubits’ states are all measured.
Tallying 0s and 1s over many experimental runs and comparing these statistics to
the prepared state of the injected qubits reveals whether qubits are teleporting
over.



Alex Zlokapa, a graduate student at the Massachusetts Institute of Technology
who joined the wormhole project as an undergrad, found a way to simplify the
wormhole protocol enough to run it on Google’s quantum computer.

Bongani Mlambo for Quanta Magazine


INTRODUCTION

The researchers look for a peak in the data that represents a difference between
two cases: If they see the peak, it means qubit rotations that are dual to
negative-energy pulses are allowing qubits to teleport, whereas rotations in the
opposite direction, which are dual to pulses of normal, positive energy, don’t
let qubits through. (Instead, they cause the wormhole to close.)

Late one night in January, after two years of gradual improvements and
noise-reduction efforts, Zlokapa ran the finished protocol on Sycamore remotely
from his childhood bedroom in the San Francisco Bay Area, where he was spending
winter break after his first semester of grad school.

The peak appeared on his computer screen.

The housing of one of several copies of the Sycamore chip, which consists of
50-odd qubits made of superconducting aluminum circuits.

Bongani Mlambo for Quanta Magazine

“It kept getting sharper and sharper,” he said. “I was sending screenshots of
the peak to Maria and getting very excited, writing, ‘I think we see a wormhole
now.’” The peak was “the first sign that you could see gravity on a quantum
computer.”

Spiropulu says she could hardly believe the clean, pronounced peak she was
seeing. “It was very similar to when I saw the first data for the Higgs
discovery,” she said. “Not because I didn’t expect it, but it came too much in
my face.”

Surprisingly, despite the skeletal simplicity of their wormhole, the researchers
detected a second signature of wormhole dynamics, a delicate pattern in the way
information spread and un-spread among the qubits known as “size-winding.” They
hadn’t trained their neural network to preserve this signal as it sparsified the
SYK model, so the fact that size-winding shows up anyway is an experimental
discovery about holography.

“We didn’t demand anything about this size-winding property, but we found that
it just popped out,” Jafferis said. This “confirmed the robustness” of the
holographic duality, he said. “Make one [property] appear, then you get all the
rest, which is a kind of evidence that this gravitational picture is the correct
one.”


THE MEANING OF THE WORMHOLE

Jafferis, who never expected to be part of a wormhole experiment (or any other),
thinks one of the most important takeaways is what the experiment says about
quantum mechanics. Quantum phenomena like entanglement are normally opaque and
abstract; we don’t know, for instance, how a measurement of particle A
determines B’s state from afar. But in the new experiment, an ineffable quantum
phenomenon — information teleporting between particles — has a tangible
interpretation as a particle receiving a kick of energy and moving at a
calculable speed from A to B. “There seems to be this nice story from the point
of view of the qubit; it moves causally,” said Jafferis. Maybe a quantum process
like teleportation “always feels gravitational to that qubit. If something like
that could come out of this experiment and other related experiments, that will
definitely tell us something deep about our universe.”



Maria Spiropulu on the campus of the California Institute of Technology.

Bongani Mlambo for Quanta Magazine


INTRODUCTION

Susskind, who got an early look at today’s results, said he hopes that future
wormhole experiments involving many more qubits can be used to explore the
wormhole’s interior as a way of investigating the quantum properties of gravity.
“By doing measurements on what went through, you interrogate it and see what was
in the inside,” he said. “That seems to me like an interesting way to go.”

Some physicists will say the experiment tells us nothing about our universe,
since it realizes a duality between quantum mechanics and anti-de Sitter space,
which our universe is not.

In the 25 years since Maldacena’s discovery of the AdS/CFT correspondence,
physicists have sought a similar holographic duality for de Sitter space — a map
going from a quantum system to the positively energized, expanding de Sitter
universe we live in. But progress has been far slower than for AdS, leading some
to doubt whether de Sitter space is holographic at all. “Questions like ‘What
about getting this to work in the more physical case of dS?’ are not new but
very old and have been the subject of tens of thousands of person-years of
unsuccessful effort,” said Woit, a critic of AdS/CFT research. “What’s needed
are some quite different ideas.”

Critics argue that the two kinds of space differ categorically: AdS has an outer
boundary and dS space does not, so there’s no smooth mathematical transition
that can morph one into the other. And AdS space’s hard boundary is the very
thing that makes holography easy in that setting, providing the quantum surface
from which to project the space. By comparison, in our de Sitter universe, the
only boundaries are the farthest we can see and the infinite future. These are
hazy surfaces from which to try projecting a space-time hologram.

Renate Loll, a noted quantum gravity theorist at Radboud University in the
Netherlands, also emphasized that the wormhole experiment concerns 2D space-time
— the wormhole is a filament, with one spatial dimension plus the time dimension
— whereas gravity is more complicated in the 4D space-time that we actually live
in. “It is rather tempting to get entangled in the intricacies of the 2D toy
models,” she said by email, “while losing sight of the different and bigger
challenges that await us in 4D quantum gravity. For that theory, I cannot see
how quantum computers with their current capabilities can be of much help … but
I will happily stand corrected.”


RELATED:

--------------------------------------------------------------------------------


 1. THE MOST FAMOUS PARADOX IN PHYSICS NEARS ITS END


 2. WORMHOLES REVEAL A WAY TO MANIPULATE BLACK HOLE INFORMATION IN THE LAB


 3. A DEEPENING CRISIS FORCES PHYSICISTS TO RETHINK STRUCTURE OF NATURE’S LAWS

Most quantum gravity researchers believe these are all difficult but solvable
problems — that the entanglement pattern that weaves 4D de Sitter space is more
complicated than for 2D AdS, but we can nevertheless extract general lessons by
studying holography in simpler settings. This camp tends to see the two types of
space, dS and AdS, as more similar than different. Both are solutions to
Einstein’s relativity theory, differing only by a minus sign. Both dS and AdS
universes contain black holes that are stricken with the same paradoxes. And
when you’re deep in AdS space, far from its outer wall, you can hardly
distinguish your surroundings from de Sitter.

Still, Susskind agrees that it’s time to get real. “I think it’s about time we
got out from under the protective layer of AdS space and open up into the world
that might have more to do with cosmology,” he said. “De Sitter space is another
beast.”

To that end, Susskind has a new idea. In a preprint posted online in September,
he proposed that de Sitter space might be a hologram of a different version of
the SYK model — not the one with four-way particle interactions, but one in
which the number of particles involved in each interaction grows as the square
root of the total number of particles. This “double-scaled limit” of the SYK
model is “behaving more like de Sitter than AdS,” he said. “There’s far from a
proof, but there is circumstantial evidence.”

Such a quantum system is more complex than the one programmed so far, and
“whether that limit is something that will be realized in the lab I don’t know,”
Susskind said. What seems certain is that, now that there’s one holographic
wormhole, more will open up.


By Natalie Wolchover

Senior Editor

--------------------------------------------------------------------------------

November 30, 2022

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AdS/CFTblack hole information paradoxblack holesentanglementexperimental
physicsphysicsquantum computingquantum gravityquantum information theoryquantum
physicstheoretical physicswormholesAll topics

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