Scientists have observed for the first time that quantum interference—a wave-like interaction between particles related to the strange quantum phenomenon of entanglement—occurs between two types of particles. The discovery could help physicists understand what’s going on inside the nucleus.
Particles act as both particles and waves. Interference is the ability of the wave-like action of one particle to dampen or amplify the action of another quantum particle. For example, two boats crossing a lake. Overlapping waves can add together to form a large wave, or they can cancel each other out and the wave disappears. This interference occurs because of one of the strange aspects of quantum physics, entanglement, predicted in the 1930s and experimentally observed since the 1970s. Entanglement links the quantum states of multiple particles so that one measurement correlates with that of another, even if one is on Jupiter and the other is in the vestibule.
Dissimilar particles can become entangled, but until now it was not known that these mismatched entangled particles would interfere with each other. This is because some interference measurements rely on two wave particles that are indistinguishable from each other. Imagine two photons, or particles of light, from two separate light sources. If we detect these photons, we have no way of determining which photon was which, and therefore which source each one came from. Thanks to the quantum laws governing these very small particles, this ambiguity is actually measurable: all possible histories of two identical photons interfere with each other, creating a new wave-like behavior on the particle. Create a pattern.
However, these patterns usually do not occur even when two different particles are entangled. Since it is possible to distinguish these particles, there is no mystery about their history and therefore no interference between these different possible worlds. That is, to date.
For the first time, physicists have discovered interference between two different subatomic particles. The researchers made the observations at the Relativistic Heavy Ion Collider (RHIC), a giant particle accelerator at Brookhaven National Laboratory on Long Island. This discovery expands the way we understand entanglement and provides new opportunities to use it to study the world of elementary particles.
Ohio State University physicist James Daniel Brandenburg said: A member of the RHIC STAR experiment where a new phenomenon was observed. This makes him 10 to 100 times more accurate than previous measurements of high-energy nuclei.
RHIC is designed to bombard heavy ions such as gold nuclei. In this case, however, researchers were concerned with near misses rather than collisions. When the gold nucleus passes through the collider at near-light speed, it creates an electromagnetic field that produces photons. If two gold nuclei approach each other but do not collide, photons can ping the adjacent nuclei. Vanderbilt University physicist and STAR collaborator Raghav Kunnawalkam Elayavalli says these near misses were previously considered background noise. But seeing the close call “opened up a whole new field of physics that was initially inaccessible,” says Kunnawalkam Elayavalli.
When a photon bounces off a neighboring gold ion nucleus, it creates a very short-lived particle called rho. This particle rapidly decays into two particles called pions, one positively charged and one negatively charged.
Positive pions can interfere with other positive pions caused by other atom flybys. Negative pions can interfere with other negative pions. Up to this point, it is a textbook. But then things get weird. The positive and negative pions are intertwined and interfere with each other. “What they do is stylistically different in interesting ways,” says Jordan Kotler, a postdoctoral fellow in theoretical physics at the Harvard Society of Fellows.. The two-step effect of entanglement and interference doesn’t violate the fundamental rules of quantum mechanics, says Kotler, but is a “smarter” way to squeeze new information out of these particles.
In particular, the photons act like tiny lasers, scanning the nuclei of colliding gold ions. These interactions allow researchers to study the quarks that make up protons and neutrons in atoms, and subatomic particles such as gluons that hold quarks together. Physicists still don’t fully understand how protons acquire properties such as mass and spin (the quantum version of angular momentum) from this stew of entangled particles.
By measuring the momentum of the pion, researchers can get a picture of the density of the object the photon bounced off of. In this case, the subatomic particles that make up the nucleus of the ion. Previous attempts to make this type of measurement with other types of particles at high speeds have led to frustratingly blurry images.
However, STAR scientists recently discovered that the photons in these experiments are polarized. This means that their electric field moves in a certain direction. This polarization is transmitted to pions and enhanced by quantum interference, says Yoshitaka Hatta, a physicist at Brookhaven National Laboratory. He was not involved in this research. Accurately calculating polarization essentially allows researchers to subtract the “blur” from nuclear measurements, resulting in a more accurate image. “You can really see the difference between where protons are in the nucleus and where neutrons are in the nucleus,” says Brandenberg. Protons, he says, tend to cluster in the center, surrounded by a neutron “skin.”
Beyond nuclear size, there are other details that this technique can reveal. For example, the proton spin exceeds the spin of the quarks that make up the proton. This means that there is something unknown within the proton that accounts for the remaining spin. Brandenberg says the gluons that hold the quarks together are likely the culprits, but scientists haven’t yet found a good way to understand what they’re trying to do. , new techniques may allow us to see gluon spins and other properties more clearly.
“What’s very exciting is that these modern experiments push the boundaries of our understanding of both quantum mechanics and measurement, breaking new ground in both theory and experiment,” Kotler said. say.
