High-energy Collisions Demonstrate Bell Inequality Violations, Extending Quantum Entanglement Studies to Energies over Ten Orders of Magnitude Higher

The fundamental nature of quantum entanglement, a phenomenon once considered a paradox, now fuels advancements in quantum technologies and challenges our understanding of reality. Emidio Gabrielli from the University of Trieste and colleagues are pioneering research into entanglement within the extreme environment of high-energy particle collisions, a realm previously unexplored. Building on the Nobel Prize-winning work demonstrating entanglement with photons, this research investigates how entanglement manifests at energies vastly exceeding those of previous experiments, and in the presence of powerful forces governing particle interactions. This work represents a significant step towards understanding the limits of quantum mechanics and potentially revealing new physics beyond our current models, while also offering unique opportunities to reconstruct quantum states using collider detectors.

Experimentally, violations of Bell inequalities, which challenge Einstein’s principle of local realism, were first observed in low-energy entangled photon systems by A. Aspect, J. F. Clauser, and A.Zeilinger, achievements for which they were awarded the Nobel Prize in Physics. Particle colliders offer a unique setting for probing quantum information theory, operating at energies that are over ten orders of magnitude higher than those of previous experiments and in the presence of electroweak and strong interactions. Additionally, collider detectors offer unique advantages for reconstructing quantum states via quantum state tomography. This chapter reviews key theoretical and experimental.

Top Quark, Higgs, and Quantum Information Studies

This collection of references focuses on research in high-energy physics, particularly concerning the top quark, Higgs boson, quantum information, and collider physics. Many papers investigate top quark production, decay, spin correlations, and its potential to reveal new physics. A significant portion centers on Higgs boson production, decay, especially to W bosons and tau particles, and precise measurements of its properties, including the search for CP violation. Increasingly, researchers are exploring how quantum information concepts, like entanglement, discord, and Bell inequalities, can be applied to study particle physics processes, representing a relatively new and exciting area of investigation.

The references also highlight studies of the Standard Model and searches for deviations that might indicate new physics, often employing Effective Field Theory. Computational tools like PYTHIA, DELPHES, and PDF4LHC are frequently cited, demonstrating the importance of simulation and analysis in these studies. This collection reveals a growing trend towards utilizing quantum information theory to enhance our understanding of particle interactions and search for phenomena beyond the Standard Model. The increasing number of papers exploring the connection between quantum information theory and particle physics is particularly striking.

Traditionally, particle physics has focused on measuring energies, momenta, and decay rates. Now, researchers are asking if concepts like entanglement and Bell inequalities can better characterize particle interactions and reveal new physics. This represents a significant paradigm shift. Precise measurements of particle properties are also crucial, as the LHC has provided a wealth of data, but further precision is needed to probe for new physics, a goal of future colliders like the ILC, CEPC, and FCC. The top quark and Higgs boson are particularly interesting because they are the most massive particles in the Standard Model.

Their interactions are sensitive to new physics, making them excellent probes for beyond-the-Standard-Model phenomena. Effective Field Theory is a powerful tool for parameterizing new physics in a model-independent way, and many studies use it to analyze experimental data and constrain the parameters of new physics models. The references to future colliders highlight their importance for advancing our understanding of particle physics, as they are designed to provide higher energies and luminosities, allowing for more precise measurements and the discovery of new particles. In summary, this is a comprehensive collection that reflects the current state of research in high-energy physics, with a growing emphasis on the intersection of quantum information and particle physics.

Probing Quantum Non-Locality at High Energies

This work demonstrates that testing for quantum non-locality, traditionally performed with low-energy photons and atoms, is also possible within the high-energy environment of particle colliders. By utilizing quantum state tomography, reconstructing particle properties from decay product distributions, researchers can infer polarization and investigate entanglement even with unpolarized beams and detectors. This approach opens a new avenue for probing fundamental quantum mechanics at energy scales far exceeding those previously accessible. While current collider experiments cannot fully meet the stringent requirements for device-independent tests of non-locality, they can effectively probe non-locality in a device-specific manner.

The authors acknowledge this limitation, noting that existing and planned experiments fall short of the ideal setup for eliminating all potential loopholes. Nevertheless, this research establishes a pathway for leveraging collider data to explore entanglement and test the boundaries of quantum mechanics, potentially offering insights into physics beyond the Standard Model through entanglement-sensitive observables. Future work will likely focus on refining these techniques and pushing the boundaries of accessible energy scales to further investigate the implications of quantum non-locality in high-energy physics.