Scientists have, for the first time, developed a quantum experiment that allows them to study
the dynamics, or behavior, of a special kind of theoretical wormhole.
The experiment has not created an actual wormhole (a rupture in space and time), rather it allows
researchers to probe connections between theoretical wormholes and quantum physics, a prediction
of so-called quantum gravity.
Quantum gravity refers to a set of theories that seek to connect gravity with quantum
physics, two fundamental and well-studied descriptions of nature that appear inherently
incompatible with each other.
Wormholes are bridges between two remote regions in spacetime.
They have not been observed experimentally, but scientists have theorized about their
existence and properties for close to 100 years.
In 1935, Albert Einstein and Nathan Rosen described wormholes as tunnels through the
fabric of spacetime in accordance with Einstein's general theory of relativity, which describes
gravity as a curvature of spacetime.
Researchers call wormholes Einstein–Rosen bridges after the two physicists who invoked
them, while the term "wormhole" itself was coined by physicist John Wheeler in the 1950s.
The notion that wormholes and quantum physics, specifically entanglement (a phenomenon in
which two particles can remain connected across vast distances), may have a connection was
first proposed in theoretical research by Juan Maldacena and Leonard Susskind in 2013.
The physicists speculated that wormholes (or "ER") were equivalent to entanglement (also
known as "EPR" after Albert Einstein, Boris Podolsky , and Nathan Rosen, who first proposed
the concept).
In essence, this work established a new kind of theoretical link between the worlds of
gravity and quantum physics.
Later, in 2017, Jafferis, along with his colleagues Ping Gao and Aron Wall, extended the ER = EPR
idea to not just wormholes but traversable wormholes.
The scientists concocted a scenario in which negative repulsive energy holds a wormhole
open long enough for something to pass through from one end to the other.
The researchers showed that this gravitational description of a traversable wormhole is equivalent
to a process known as quantum teleportation.
In quantum teleportation, a protocol that has been experimentally demonstrated over
long distances via optical fiber and over the air, information is transported across
space using the principles of quantum entanglement.
The present work explores the equivalence of wormholes with quantum teleportation.
The research team performed the first experiments that probe 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).
Though this experiment didn’t create a disruption of physical space and time in the way we might
understand the term “wormhole” from science fiction, calculations from the experiment
showed that qubits traveled from one system of entangled particles to another in a model
of gravity.
This experiment performed on the Sycamore quantum processor device at Google opens the
doors to future experiments with quantum computers to probe ideas from string theory and gravitational
physics.
The research paper is published in the journal Nature.
A wormhole is a bridge between two remote spacetime regions.
In the classical general theory of relativity, nothing is allowed to pass through the wormhole.
In 2019, Harvard University’s Daniel Jafferis and his collaborators suggested a wormhole
could be traversable when created by entangled black holes.
These physicists discovered a quantum mechanism to make a wormhole traversable by introducing
a direct interaction between the distant spacetime regions, using a simple quantum dynamical
system of fermions.
The researcher says that in their work, they also used these entangled quantum systems
to produce this kind of ‘wormhole teleportation’ using quantum computing and were able to confirm
the results with classical computers.
In this experiment, researchers sent a signal “through the wormhole” by teleporting
a quantum state from one quantum system to another on the Sycamore 53-qubit quantum processor.
To do so, the research team needed to determine entangled quantum systems that behaved with
the properties predicted by quantum gravity — but that were also small enough to run
on today’s quantum computers.
A central challenge for this work was to find a simple enough many-body quantum system that
preserves gravitational properties.
To achieve this, the team used techniques from machine learning, taking highly interacting
quantum systems and gradually reducing their connectivity.
The output of this learning process produced many examples of systems with behavior consistent
with quantum gravity, but each instance only required around 10 qubits — a perfect size
for the Sycamore processor.
Once the researchers identified these 10-qubit systems, the team inserted a qubit into one
system, applied an energy shockwave across the processor, and then observed this same
information on the other quantum system on the processor.
The team measured how much quantum information passed from one quantum system to the other
depending on the type of shockwave applied, negative or positive.
The researcher says that they showed that if the wormhole is propped open for long enough
time by the negative energy shockwaves, a causal path is established between the two
quantum systems.
The qubit inserted into one system is indeed the same that appears on the other system.
The team then verified these and other properties with classical computer calculations.
This new work opens up the possibility of future quantum gravity experiments with larger
quantum computers and more complicated entangled systems.
This work doesn’t replace direct observations of quantum gravity, for example from detections
of gravitational waves using the Laser Interferometer Gravitational wave Observatory (LIGO)