CMS Collaboration Discovers Quantum Entanglement in Top Quarks

Researchers from the **CMS Collaboration** at **CERN** have made a significant breakthrough by observing quantum entanglement in top quark-antiquark pairs. This discovery sheds light on the intricate behavior of quantum particles at extremely small scales, offering new insights into the fundamental principles of quantum mechanics.

Quantum entanglement describes a phenomenon where the states of two particles become interconnected, meaning a change in one instantaneously affects the other, regardless of the distance separating them. This concept, often referred to by **Albert Einstein** as “spooky action at a distance,” has previously been observed in systems involving atoms, electrons, and photons. The latest findings, derived from data collected in **2016** at the **Large Hadron Collider (LHC)**, extend this understanding to top quarks, the heaviest known fundamental particles.

During experiments conducted at energies of **13 TeV**, protons were collided, resulting in the production of top quark pairs as predicted by **Quantum Chromodynamics**. Both the top quark and its antiquark decay almost instantaneously, making their study particularly challenging. The CMS team focused on events where two leptons, such as electrons or muons, were detected with opposite charges and high momentum. These leptons originate from the decay of the top quark and antiquark, carrying vital information about their parent particles, including their spin.

To investigate entanglement, researchers employed an observable known as **D**, which quantifies the correlation between the spins of the top quark and antiquark. A value of D less than **-1/3** serves as a clear indicator of quantum entanglement. The CMS results showed a value that lies more than five standard deviations below this threshold, thus confirming the existence of entanglement in top quark-antiquark pairs. This finding enriches the understanding of quantum systems under extreme energy conditions.

Previously, the **ATLAS Collaboration** reported the first observation of entanglement among more stable particles reconstructed post-hadronization. In contrast, the CMS measurement operates at the parton level, focusing on the behavior of quarks and gluons before they form composite particles. This distinct approach provides a complementary perspective on the quantum state, enhancing the overall knowledge of particle physics.

This groundbreaking work not only validates the principles of quantum mechanics at the highest energies and shortest timescales but also establishes particle colliders like the LHC as essential platforms for exploring quantum information science. The observation of quantum entanglement in top quark pair production marks a critical advancement in understanding the fundamental forces that govern the universe.

As research continues, these findings are expected to inspire further investigations into the complexities of quantum mechanics and the fundamental constituents of matter. The implications of such breakthroughs could extend beyond theoretical physics, potentially influencing various fields, including quantum computing and communication technologies.