Scientists at the U.S. Department of Energy's Brookhaven National Laboratory, along with collaborators, have developed a new method to explore quantum entanglement within protons using data from high-energy particle collisions. This approach employs quantum information science to understand how particle tracks from electron-proton collisions are influenced by entanglement inside protons.
The research highlights that quarks and gluons, which form the structure of a proton, experience quantum entanglement. Albert Einstein famously described this phenomenon as "spooky action at a distance," where particles can share information over significant distances. In protons, this entanglement occurs at extremely short distances — less than one quadrillionth of a meter — affecting all quarks and gluons in the proton.
The team's findings are published in the journal Reports on Progress in Physics (ROPP), summarizing six years of research. The study provides insight into how entanglement influences the distribution of stable particles emerging from particle collisions.
"Before we did this work, no one had looked at entanglement inside of a proton in experimental high-energy collision data," said physicist Zhoudunming (Kong) Tu. He explained that their findings have shifted the traditional view of protons as collections of quarks and gluons by introducing evidence that these components are entangled.
Future experiments at the Electron-Ion Collider (EIC), expected to open in the 2030s at Brookhaven Lab, will focus on exploring how being part of a larger nucleus affects proton properties using tools developed through this research.
The study employed quantum information science language and equations to predict how entanglement should impact particles from electron-proton collisions. Dmitri Kharzeev and Eugene Levin initially proposed these equations in 2017. "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," Kharzeev stated.
The researchers analyzed data from past experiments like those conducted at Europe's Large Hadron Collider and Hamburg's Hadron-Electron Ring Accelerator (HERA). Their analysis matched predictions perfectly, providing strong evidence for maximal entanglement among quarks and gluons within protons.
Understanding such statistical behavior offers insights into nuclear physics' complex questions, including why quarks and gluons remain confined within protons. Kharzeev noted that "Maximal entanglement inside the proton emerges as a consequence of strong interactions."
Tu emphasized how thinking about collective behavior could simplify understanding complex nuclear physics phenomena: "Particle collisions can be extremely complex... But this study shows that some outcomes... are determined by the entanglement within the protons before they collide."
Future studies aim to explore how being embedded within nuclei impacts proton behavior. "It will be very helpful to use the same tools to see the entanglement in a proton embedded in a nucleus," Tu said.
Martin Hentschinski from Universidad de las Américas Puebla commented on EIC science's focus on nuclear environment impacts: “The impact... is at the center." Co-author Krzysztof Kutak added their goal is "to push our understanding... to a new frontier."
This research received funding support from several entities including DOE Office Science Horizon 2020 program UDLAP Apoyos VAC 2024 Brookhaven Lab Directed Research Development program among others.