Exploring quantum observables at the LHC

Project Information

QUANTUMLHC

Grant agreement ID: 101107121

DOI

10.3030/101107121

Project closed

EC signature date 21 March 2023

Start date 2 October 2023

End date 1 October 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 188 590,08

Coordinated by

ALMA MATER STUDIORUM - UNIVERSITA DI BOLOGNA
Italy

Periodic Reporting for period 1 - QUANTUMLHC (Exploring quantum observables at the LHC)

Reporting period: 2023-10-02 to 2025-10-01

Summary of the context and overall objectives of the project

Our world is made of fundamental particles that interact through a small set of basic forces. Understanding how these particles behave is essential for uncovering the deeper structure of the universe. The Large Hadron Collider (LHC) at CERN collides protons at unprecedented energies, offering a unique opportunity to test the limits of our understanding of physics. As experimental precision increases, however, new ideas and methods are needed to extract as much information as possible from the data.
This project addressed that challenge by introducing a new way of analysing particle collisions: applying concepts and tools from quantum information science to high-energy physics. Quantum information is the field that studies how quantum systems store and process information, forming the basis of technologies such as quantum computing. Despite the fact that particles produced at the LHC are inherently quantum objects, these techniques had rarely been used to study them.
The main objective of the project was to explore whether quantum-information-inspired observables—such as quantum entanglement—can be measured directly using the particles produced in LHC collisions. In this framework, the particles produced in a collision are treated as physical realisations of qubits, the fundamental units of quantum information.
By building this innovative bridge between two previously separate research areas, the project aimed to open a new window on the subatomic world and propose fresh directions for addressing some of the biggest open questions in particle physics, such as the nature of dark matter and the origin of the asymmetry between matter and antimatter.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project carried out a broad scientific programme aimed at developing and applying quantum-inspired methods to the study of particle collisions at the LHC. These activities combined theoretical research, numerical simulations, and the development of new data-analysis tools. The work can be grouped into two main areas.
Investigating top-quark final states: the project developed a dedicated analysis strategy to reconstruct quantum observables in events containing highly energetic top quarks, enabling the study of quantum entanglement at the highest energies ever explored. The work focused on a challenging final state in which one of the top quarks decays hadronically, producing a complex pattern of particles difficult to reconstruct. The project addressed this by exploring multiple approaches, including techniques to identify jets originating from charm quarks. The analysis was applied to simulated LHC data to estimate the feasibility of measuring entanglement and observing violations of Bell’s inequalities in this channel. The same framework was also used to investigate whether quantum observables could enhance searches for physics beyond the Standard Model.
Investigating diboson final states: the project also studied several processes that produce pairs of electroweak bosons, with the goal of reconstructing their full spin-density matrix and extracting quantum observables. These reconstructed quantities were then used to assess the possibility of measuring entanglement in non-resonant diboson pairs at the LHC, to explore their sensitivity to potential new physics, and to quantify the impact of higher-order processes.In particular, the project examined additional diagrams—such as rare processes contributing to final states like H→e⁺e⁻μ⁺μ⁻—that are experimentally indistinguishable from the main channels under study. While these contributions are always present in real collider data, they are often neglected in simulations. The project showed that such higher-order processes can significantly affect the reconstruction of quantum observables. This behaviour was analysed in detail, leading to the development of an adaptation strategy that makes it possible to reliably quantify entanglement even when these additional contributions are included, as is the case in real experimental data.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

This project has significantly advanced a new research direction at the intersection of quantum information science and particle physics. It generated concrete scientific results, reusable software tools, and helped strengthen an emerging international community working at this frontier. The main outcomes can be grouped into three categories.
New methods and tools to study quantum observables at colliders: the project introduced several innovative analysis strategies that enable the reconstruction and interpretation of quantum observables in LHC processes. This includes detailed methods tailored to specific final states, such as top-quark pairs and pairs of electroweak bosons produced directly in proton–proton collisions or through intermediate Higgs bosons.
The project also opened the possibility to study quantum observables in new topologies by exploiting the identification of jets originating from charm quarks. In addition, it uncovered important limitations of standard reconstruction approaches in processes involving a Z boson in the final state and proposed solutions to overcome them.
Long-term methodological contributions and reuse: the software developed to achieve the project objectives—including tools for reconstructing quantum observables in diboson and top-quark final states—is publicly available. It can be used directly or serve as a reference for similar analyses, supporting future research in this area. Several follow-up studies are already building upon these tools to explore quantum observables at colliders, highlighting the long-term value of the project’s methodological contributions.
Building a strong community in the QI–HEP research area: beyond its technical achievements, the project played a key role in shaping the rapidly expanding QI–HEP research landscape. Supported by the MSCA fellowship, the fellow took on a leadership role within the community, initiating collaborations and contributing to the development of shared research directions. One of the project-related publications was produced as input to the European Strategy for Particle Physics, where the fellow served as one of the coordinators, demonstrating the project’s influence on the strategic evolution of the field.