Scientists have used high-energy particle collisions to peer inside protons, the particles that sit inside the nuclei of all atoms. This has revealed for the first time that quarks and gluons, the building blocks of protons, experience the phenomenon of quantum entanglement.
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despite Einstein’s skepticism about entanglement, this “spooky” phenomenon has been verified over and over again. Many of those verifications have concerned testing increasing distances over which entanglement can be demonstrated. This new test took the opposite approach, investigating entanglement over a distance of just one quadrillionth of a meter, finding it actually occurs within individual protons.
The team found that the sharing of information that defines entanglement occurs across whole groups of fundamental particles called quarks and gluons within a proton.
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To probe the inner structure of protons, scientists looked at high-energy particle collisions that have occurred in facilities like the Large Hadron Collider (LHC). When particles collide at extremely high speeds, other particles stream away from the collision like wreckage flung away from a crash between two vehicles.
This team used a technique developed in 2017 that applies quantum information science to electron-proton collisions to determine how entanglement influences the paths of particles streaming away. If quarks and gluons are entangled with protons, this technique says that should be revealed by the disorder, or “entropy,” seen in the sprays of daughter particles.
“Think of a kid’s messy bedroom, with laundry and other things all over the place,” Tu said. “In that disorganized room, the entropy is very high.”
The contrast to this is a low-entropy situation which is akin to a neatly tidied and sorted bedroom in which everything is organized in its proper place. A messy room indicates entanglement, if you will.
“For a maximally entangled state of quarks and gluons, there is a simple relation that allows us to predict the entropy of particles produced in a high-energy collision,” Brookhaven Lab theorist Dmitri Kharzeev said in the statement. “We tested this relation using experimental data.”
The interior of the Large Hadron Collider is within which protons and other particles are collided at high speeds. (Image credit: Robert Lea)
To investigate how “messy” particles get after a collision, the team first turned to data generated by proton-proton collisions conducted at the LHC. Then, in search of “cleaner” data, the researchers looked to electron-proton collisions carried out at the Hadron-Electron Ring Accelerator (HERA) particle collider from 1992 to 2007.
This data was delivered by the H1 team and its spokesperson as well as Deutsches Elektronen-Synchrotron (DESY) researcher Stefan Schmitt after a three-year search through HERA results.
Comparing HERA data with the entropy calculations, the team’s results matched their predictions perfectly, providing strong evidence that quarks and gluons inside protons are maximally entangled.
“Entanglement doesn’t only happen between two particles but among all the particles,” Kharzeev said. “Maximal entanglement inside the proton emerges as a consequence of strong interactions that produce a large number of quark-antiquark pairs and gluons.”
The revelation of maximal entanglement of quarks and gluons within protons could help reveal what keeps these fundamental particles bound together with the building blocks of atomic nuclei.
