Information transfer through “spooky action at a distance” at the Large Hadron Collider

The interior of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider. Rochester physicists working on the detector have observed spin entanglement between top quarks and top antiquarks that persists over large distances and high speeds. Image credit: CERN

Researchers have confirmed that quantum entanglement exists between top quarks, the heaviest known elementary particles.

Physicists have demonstrated the quantum entanglement of top quarks and their antimatter partners. This discovery was made at CERNThis discovery extends the behavior of entangled particles to distances beyond the reach of light-speed communication and opens new avenues for studying quantum mechanics at high energies.

An experiment by a group of physicists led by Regina Demina, professor of physics at the University of Rochester, has produced a significant result related to quantum entanglement – ​​an effect that Albert Einstein called “spooky action at a distance”.

Entanglement involves the coordinated behavior of tiny particles that have interacted with each other but have then moved apart. Measuring properties – such as position, momentum, or spin – of one of the separated pairs of particles instantly changes the results of the other particle, regardless of how far the second particle has moved from its twin. In fact, the state of one entangled particle, or qubit, is inseparable from the other.

Breakthrough in particle physics

Quantum entanglement has been observed between stable particles such as photons or electrons.

But Demina and her group broke new ground by finding for the first time that the entanglement between unstable top quarks and their antimatter partners persists over distances greater than what can be bridged by information traveling at the speed of light. Specifically, the researchers observed a spin correlation between the particles.

The particles thus demonstrated what Einstein described as “spooky action at a distance.”

A “new path” for quantum research

The finding was reported by the Compact Muon Solenoid (CMS) Collaboration at the European Center for Nuclear Research (CERN), where the experiment was conducted.

“The confirmation of quantum entanglement between the heaviest elementary particles, the top quarks, has opened a new way to explore the quantum nature of our world at energies far beyond what is accessible,” the report says.

CERN, near Geneva in Switzerland, is the world’s largest particle physics laboratory. The production of top quarks requires very high energies, which are available at the Large Hadron Collider (LHC). This allows scientists to rotate high-energy particles at almost the speed of light on a 27-kilometer-long underground track.

Quantum information science and future applications

The phenomenon of entanglement has become the basis of an emerging field of quantum information science, which has far-reaching implications for areas such as cryptography and Quantum computing.

Top quarks, each as heavy as a atom Gold particles, which can only be produced in colliders like the LHC, are therefore unlikely to be used to build a quantum computer. However, studies like those by Demina and her group can shed light on how long entanglement lasts, whether it is passed on to the particles’ “daughters” or decay products, and what, if anything, ultimately resolves the entanglement.

Theorists believe that the universe was in an entangled state after its initial phase of rapid expansion. The new result observed by Demina and her researchers could help scientists understand what led to the loss of quantum connection in our world.

Top quarks in quantum long-distance relationships

Demina recorded a video for CMS’s social media channels to explain her group’s result, using the analogy of an indecisive king of a faraway land, whom she called “King Top.”

King Top learns that his country is under attack. He sends messengers to tell everyone in his country to prepare for defense. But then, as Demina explains in the video, he changes his mind and sends messengers to tell people to stand back.

“He is constantly wavering between his views and no one knows what his decision will be in the next moment,” says Demina.

Nobody, Demina explains, except the leader of a village in this kingdom known as the “Anti-Top.”

“They know what state of mind the other is in at all times,” says Demina.

Demina’s research group consists of herself, doctoral student Alan Herrera and postdoctoral fellow Otto Hindrichs.

As a graduate student, Demina was part of the team that discovered the top quark in 1995. Later, as a faculty member at Rochester, Demina co-led a team of scientists from across the United States that built a tracking device that played a key role in the 2012 discovery of the Higgs boson—an elementary particle that helps explain the origin of mass in the universe.

Rochester researchers have long been part of the CMS collaboration at CERN, which brings together physicists from around the world. Recently, another Rochester team achieved a major milestone in measuring the electroweak mixing angle, a crucial component of the Standard Model of particle physics that explains how the building blocks of matter interact.