Rochester physicists find ‘spooky action at a distance’ at CERN

Researchers have confirmed that quantum entanglement persists between top quarks, the heaviest fundamental particles known.

An experiment by a group of physicists led by University of Rochester physics professor Regina Demina has produced a significant result about quantum entanglement — an effect Albert Einstein called “spooky action at a distance.”

Entanglement is about the coordinated behavior of small particles that have interacted but then drifted apart. Measuring a property—such as the position or momentum or spin—of one of the separated pairs of particles immediately changes the results of the other particle, no matter how far the second particle is from its twin. In fact, the state of one entangled particle, or qubit, is inseparable from another.

Quantum entanglement is observed between stable particles, such as photons or electrons.

But Demina and her group broke new ground in that they found, for the first time, a persistent entanglement between unstable top quarks and their antimatter partners at distances farther than what can be covered by the transferred information. at the speed of light. Specifically, the researchers observed the spin correlation between the particles.

The particles therefore demonstrated what Einstein described as “tremorous action at a distance.”

A ‘new path’ for quantum exploration

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

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

CERN, located near Geneva, Switzerland, is the world’s largest particle physics laboratory. Producing top quarks requires the very high energies available at the Large Hadron Collider (LHC), which enables scientists to send high-energy particles whizzing around a 17-mile underground path at close to the speed of light.

The phenomenon of entanglement has become the foundation of an emerging field of quantum information science that has far-reaching implications in fields such as cryptography and quantum computing.

Top quarks, each as heavy as a gold atom, can only be produced in colliders such as the LHC, and so are unlikely to be used to build a quantum computer. But studies like those conducted by Demina and her group could shed light on how long entanglement persists, whether it is passed on to particle “daughters” or decay products, and what, if anything, ultimately breaks the entanglement.

Theorists believe that the universe was in a confused state after the initial phase of rapid expansion. The new result observed by Demina and her colleagues may help scientists understand what led to the loss of quantum coherence in our world.

Top quarks in long-range quantum relations

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

King Top receives word that his country is being invaded, so he sends messengers to tell all the people of his country to prepare to defend themselves. But then, Demina explains in the video, he changes his mind and sends messengers to order people to leave.

“He keeps rolling like this and nobody knows what his decision will be at the next moment,” says Demina.

No one, Demina continues to explain, except the leader of a village in this kingdom, who is known as “Anti-Top”.

“They know each other’s mood at any moment,” says Demina.

Demina’s research group consists of her and graduate student Alan Herrera and postdoctoral fellow Otto Hindrichs.

As a graduate student, Demina was on 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 US 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 a long history at CERN as part of the CMS collaboration, which brings together physicists from around the world. Recently, another Rochester team achieved an important milestone in measuring the weak mixing angle, a core component of the Standard Model of particle physics, which explains how the building blocks of matter interact.