quantumTANGO: Quantum Information with Top Quarks and Higgs Bosons
The discovery of the Higgs boson in 2012 using the ATLAS and CMS experiment at the Large Hadron Collider (LHC) was a tremendous achievement in particle physics. This discovery confirmed the Higgs field, a part of the Standard Model of particle physics responsible for giving mass to all fundamental particles. Since then, the Higgs boson and its properties have been extensively studied for about ten years to see if the Standard Model’s predictions about the nature of the Higgs hold up as more data from the Large Hadron Collider (LHC) is gathered.
The 27km long LHC, the largest particle accelerator in the world, operates by accelerating beams of protons or heavy ions to nearly the speed of light and then colliding them head-on. These high-energy collisions create conditions similar to those that existed shortly after the Big Bang, allowing exploring matter’s properties under extreme conditions.
ATLAS aims to address some of the most profound questions in particle physics, such as studying the Higgs boson properties, investigating dark matter and dark energy, and exploring physics beyond the Standard Model.
Among these research areas, the Higgs boson is remarkable because it gives other elementary particles their mass. It is like the “celestial glue” that holds the universe together. If the Higgs boson’s properties differed slightly, it would significantly affect our understanding of the structure of matter, the fundamental forces, and the universe’s evolution. It would require rethinking and revising our current theories, leading to exciting new avenues of exploration and potential breakthroughs in our understanding of the fundamental laws of nature.
Observing and studying Higgs bosons directly at experiments like the ATLAS detector is challenging because they exist only fleetingly before decaying into other lighter particles. Therefore, the study of these Higgs boson decays, in particular, offers a unique opportunity to investigate several fundamental principles of particle physics, amongst them, quantum entanglement.
In the realm of quantum mechanics, the concept of quantum entanglement is a mind-bending principle that even Albert Einstein found perplexing. It refers to a unique phenomenon in which two or more particles become correlated to make their properties inseparably linked. Imagine you have two particles, let us call them Particle A and Particle B. When they become entangled, it is as if they develop a mysterious connection, no matter how far apart they are. If you measure the properties of Particle A, like its spin or polarisation, the state of Particle B instantly becomes linked to it, even if it is on the other side of the universe!
This mind-boggling connection persists even when vast distances separate the particles. It is as if they are communicating faster than the speed of light, violating the classical understanding of physics.
Einstein called this phenomenon “spooky action at a distance” because it challenges our intuitive notions of cause and effect.
It represents a striking difference between how we classically perceive the world around us and quantum mechanics’ true underlying non-classical nature.
In so-called tabletop experiments, quantum entanglement has been observed in various low-energy systems, such as pairs of electrons or photons. This discovery has paved the way for new types of quantum experiments, leading to the emergence of modern technologies like quantum cryptography and quantum computing. The outstanding contributions of Alain Aspect, John F. Clauser, and Anton Zeilinger in the field of quantum information science have been recognised through the prestigious 2022 Nobel Prize in Physics.
The “QuantumTango” project aims to merge our extensive high-energy particle physics knowledge at the LHC with the latest advancements in quantum information theory. By regarding quantum entanglement as a potent tool for studying the fundamental principles of quantum mechanics, we plan to investigate this phenomenon’s presence (or absence) in the decays of Higgs bosons produced at the LHC. Furthermore, we will be conducting these experiments at energy levels that are several orders of magnitude higher than any achieved in the laboratory thus far.
Several decay particles can be chosen to perform these experiments at the LHC. The most-likely decay of the Higgs boson into a pair of heavy quarks, known as “bottom” quarks, is not a practical signature for detection due to the vast number of background processes producing quarks. Conversely, the decay of the Higgs boson into pairs of photons provides an unambiguous signal in the ATLAS detector, but it only occurs 0.2% of the time and involves virtual quantum corrections that could disrupt the entanglement conditions. Therefore, to balance event reconstruction quality and the number of candidate Higgs events, the QuantumTango project will focus on the decay of Higgs bosons into multiple charged leptons through intermediate production of W± and Z0 bosons.
The project aims to construct experimental observables based on theoretical frameworks developed during a quantumTANGO workshop to identify an optimal discriminator between the entangled and null hypotheses. A multivariate analysis approach, supported by modern machine learning techniques, will be employed to distinguish candidate Higgs events from other background processes in the Standard Model, such as the pair production of W± and Z0 bosons. A significant aspect of this project will be translating these LHC-specific and technical findings into the language and formalism of the broader field of quantum information theory, paving the way for future LHC quantum information research endeavors.
“I am excited for the opportunity to study such a fundamental quantum mechanical effect at a large-scale experiment like ATLAS together with Jonathan.”
“The benefits of collaborative research form the very foundation of modern experimental particle physics, I hope we are able to take the same philosophies into this project to help us gain a deeper understanding of the intriguing intersection of quantum information theory and high energy particle physics.”
Steffen Korn is a physicist with a keen interest in high-energy research, mainly focused on the ATLAS experiment at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. His current work involves conducting high-energy-physics analyses at ATLAS, specifically emphasising the top-boson coupling in processes such as the associated production of a top quark pair and a Z or Higgs boson.
Utilising machine learning techniques, Steffen Korn applies advanced computational methods to reconstruct and classify events, enhancing the precision and efficiency of their research and contributing to the broader understanding of high-energy phenomena.
As a member of the II Physics Institute at the University of Göttingen, Steffen Korn actively collaborates with fellow physicists and researchers exploring the Higgs boson’s properties within the quantum entanglement framework. Investigating the intricate interplay between quantum phenomena and particle interactions contributes to the ongoing exploration of fundamental physics possible.
Jonathan Jamieson received his PhD from the University of Glasgow in 2022, working as part of the ATLAS collaboration at the Large Hadron Collider (LHC) at CERN. His doctoral research focussed on studying the top-quark, the heaviest fundamental particle in the universe, improving the precision of high energy measurements and setting limits on possible new physics effects.
As a research associate at the same institute he has contributed to our understanding of the properties of the top-quark via novel measurements of its mass, improving simulated collision events, as well as studying quantum effects in both the Top and Higgs sectors. Jonathan has also been the Top UK convenor for the ATLAS experiment since October 2022 which sees him representing the physics interests of multiple UK-based research institutions.