The inside of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider. Rochester physicists working on the detector have observed that the spin entanglement between top quarks and top antiquarks persists at long distances and high speeds. Credit: CERN
Researchers have confirmed that quantum entanglement persists between top quarks, the heaviest known fundamental particles.
Physicists have demonstrated quantum entanglement in top quarks and their antimatter partners, a discovery made at CERN. This finding extends the behavior of entangled particles to distances beyond the reach of light-speed communication and opens new avenues for investigating quantum mechanics at high energies.
An experiment by a group of physicists led by University of Rochester physics professor Regina Demina has produced a significant result involving quantum entanglement – an effect Albert Einstein called “spooky action at a distance.”
Entanglement involves the coordinated behavior of tiny particles that interact but then separate. Measuring properties – such as position, momentum or spin – of one of the separated pairs of particles immediately changes the results of the other particle, regardless of how far the second particle has drifted from its twin. In fact, the state of one entangled particle, or qubit, is inextricably linked to 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 discovering for the first time that the entanglement between unstable top quarks and their antimatter partners persists at greater distances than what can be covered by information transferred at the speed of light. Specifically, the researchers observed spin correlation between the particles.
Therefore, the particles demonstrated what Einstein described as “spooky action at a distance.”
A ‘new path’ for quantum exploration
The finding was reported by the Compact Muon Solenoid (CMS) Collaboration at the European Center for Nuclear Research, or CERN, where the experiment was conducted.
“Confirming quantum entanglement between the heaviest fundamental particles, the top quarks, has opened a new avenue to explore the quantum nature of our world at energies far beyond what is accessible,” the report said.
CERN, located near Geneva, Switzerland, is the world’s largest particle physics laboratory. The production of top quarks requires very high energies accessible via the Large Hadron Collider (LHC), allowing scientists to spin high-energy particles at almost the speed of light along a 27-kilometer underground track.
Quantum information science and future applications
The phenomenon of entanglement has become the basis of a rapidly growing field of quantum information science that has broad implications in areas such as cryptography and quantum computers.
Top quarks, each as heavy as one atom of gold, can only be produced at colliders, such as LHC, and so is unlikely to be used to build a quantum computer. But studies like those by Demina and her group can shed light on how long the entanglement lasts, whether it is passed on to the particles’ “daughters” or to decay products, and what, if anything, ultimately breaks 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 relations
Demina recorded a video for CMS’s social media channels to explain her group’s results. 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 in his country to prepare for defense. But then, Demina explains in the video, he changes his mind and sends messengers to order the people to stand down.
“He keeps going around like this, and no one knows what his decision will be the next moment,” Demina says.
No one, Demina explains further, except the leader of a village in this kingdom known as ‘Anti-Top’.
“They know each other’s state of mind at all times,” says Demina.
Demina’s research group consists of herself, graduate 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 in Rochester, Demina co-led a team of scientists from across the U.S. who built a tracking device that played a key role in the 2012 discovery of the Higgs boson—an elementary particle that helps determine the origin of mass in the universe to declare.
Researchers from Rochester have a long history at CERN as part of the CMS Collaboration, which brings together physicists from around the world. Recently, another team from Rochester achieved a major milestone in measuring the electroweak mixing angle, a crucial part of the Standard Model of particle physics, which explains how the building blocks of matter interact.