Nuclear physicists have found a way to peer into the deepest recesses of atomic nuclei, according to a new study.
The discovery was made possible by the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York, which can collide gold ions at nearly the speed of light. It led to the discovery of a new type of quantum entanglement.
The term quantum entanglement describes an invisible connection that connects distant objects; No matter how far apart they are in space, they affect each other. That is, when two particles are quantum-level entangled, by measuring the quantum state of one of the particles, you can instantly know the quantum state of the other, wherever it may be. For example, if one particle is “heads,” using a coin analogy, scientists can immediately see that the other particle is “tails,” no matter where it is in the universe.
Theoretical physicist Albert Einstein once dismissed the phenomenon of quantum entanglement as “spooky action at a distance,” but Daniel Brandenburg, co-author of the study and professor of physics at Ohio State University, said there is a need to learn more about this codependent relationship learn fundamental to understanding the mysteries of the world around us.
“Entanglement is one of the defining characteristics that makes quantum mechanics so different from the kind of physics that usually happens around us,” he said.
The study of how photons and electrons interact with and affect matter, quantum mechanics, is the foundation on which many technologies – such as quantum computing and quantum chemistry – are built. Despite these advances, scientists previously believed that only particles of the same kind were capable of quantum interference: photons could only interfere with photons, and neutrons with neutrons. That is, until now.
This new study, published in the journal Science Advances, describes how a team of researchers – dubbed the STAR Collaboration – used the RHIC to uncover a form of quantum entanglement, showing that particles of all kinds can interact with each other, leading to interference in a variety of different patterns.
“For the first time, we have caused different types of particles to interfere, although it was previously thought that this was not possible in quantum mechanics,” says Brandenburg. Using the collider like a large 3D digital camera, the researchers used light to track the particles that escaped from the center of the machine once the atoms collided and captured high-resolution, two-dimensional images, much like a PET scan for imaging can be used and measure changes in the human body.
This method allowed the researchers to map the arrangement of gluons – glue-like particles that act as a binding force for quarks, the particles inside the protons and neutrons inside atomic nuclei. These interactions produced a subatomic particle called a pion, which by measuring the speed and angles at which light strikes the collider, the researchers could essentially use as a microscope to look inside atomic nuclei in ways never before seen.
“With these quantum mechanical tricks, we can achieve a level of precision that would otherwise not be possible,” says Brandenburg. “This precision allowed us to actually see where the protons and neutrons are within a single gold core.”
This novel result was achieved in part thanks to a discovery made by Brandenburg about two years ago, called the Breit-Wheeler process, which describes how light can be converted into matter and antimatter. Building on the physics of this earlier discovery, the team was able to view the interior of the nucleus on a scale from one-tenth to one-hundredth the size of a single proton.
“It’s incredibly small,” said Brandenburg.
The findings could eventually help advance research in several areas, from quantum computing to astrophysics, he said.
Brandenburg, whose interest in nuclear physics originally began in astronomy, notes that studying the inner workings of atomic nuclei could also allow astrophysicists to discern aspects such as a star’s stability, size, density, and even how it formed, since all matter is interrelated connected is. “By doing this work here on Earth, we’re helping to actually better understand things that are far out in the universe,” Brandenburg said.
In the future, the team hopes to expand their work by mapping the depths of other types of quantum objects.
“One of the big questions in our field is how we understand the properties of this fundamental building block of matter,” he said. “The discovery of this new type of entanglement allows us to test these ideas for the first time.”
This work was supported by the Office of Nuclear Physics within the US Department of Energy Office of Science, the US National Science Foundation, the National Natural Science Foundation of China, and others.