Workshop on Quantum Entanglement at the Energy Frontier

25 Apr 2025, 10:00 → 27 Apr 2025, 12:00 Asia/Shanghai

W202 (School of Physics, Peking University)

Alim Ruzi (school of physics Peking Uniersity) , Chen Zhou (Peking University（北京大学）) , Hao Zhang (中国科学院高能物理研究所理论室) , Qiang Li (School of physics, Peking University) , Qing-Hong Cao (Peking University)

研究量子纠缠和验证贝尔不等式的破坏是近期在高能量前沿特别是高能对撞机上的热点领域之一。虽然高能对撞机的探测器并非特别优化来探测量子纠缠，高能对撞的高亮度高能量对量子纠缠的研究提供了新的研究途径。反之，量子纠缠也可能对超出标准模型的新物理提供了新的观测量和寻找方案。

兹定于2025年4月25日至4月27日【4月25日周五注册(在西206，同时有一个卫星会议 10am-4pm)、4月26日学术报告，4月27日自由讨论】在北京大学物理学院西202召开“高能量前沿的量子纠缠研讨会”：https://indico.ihep.ac.cn/event/24387/。 诚邀各位同行踊跃参加此次学术交流。会议由北京大学物理学院、北京大学高能物理研究中心主办。

本次会议不收注册费。住宿请自行安排。

The study of the quantum entanglement and testing Bell inequality violation can be another new subject for the high energy physics community. While detectors at high-energy colliders are not specifically designed to probe quantum entanglement, they have demonstrated surprising effectiveness in this task. This opens up exciting opportunities for novel measurements in quantum information science, as well as potential discoveries that could extend beyond the Standard Model.

The workshop on Quantum Entanglement at the Energy Frontier [Registration on April 25 (and also an open satellite meeting between 10am and 4pm in W206),  talks on April 26 in W202, and free discussions on April 27] offers a welcoming environment for physicists interested in Quantum Entanglement at the energy frontiers, inviting both experimental and theoretical communities to come together and share their latest findings. This workshop aims to facilitate discussions on ongoing and proposed experiments, as well as to encourage participants to consider future possibilities.

There is no registration fee for this workshop, and participants are responsible for their own food and accommodation fares.

QE2025_booklet.pdf

QE2025PKUposter.pdf

Friday, 25 April

1 Registration & Open Satellite meeting

Open Satellite meeting

Saturday, 26 April

2 Registration

Morning 1

Convener: Qiang Li (School of physics, Peking University)

3 Openning and Introduction

Speakers: Chen（辰） Zhou（周） (Peking University（北京大学）) , Qiang Li (School of physics, Peking University) , Qing-Hong Cao (Peking University)

PKMu_QE2025_PKU.pdf

QE2025_booklet

4 Quantum tomography at colliders

Particle colliders provide rich quantum systems for quantum information studies. Reconstructing the density matrix, known as quantum tomography, is the first step to studying quantum information at colliders. In this talk, I will revisit the recent developments of quantum tomography in different systems, including the spin states of massive or massless fermion pairs, and the flavor states of neutral meson pairs.

Speaker: Cheng Kun (University of Pittsburgh)

5 QE from the LHC ATLAS experiment

Speaker: Veljko Maksimovic (Institute of Physics Belgrade, Serbia)

6 Quantum Entanglement in particle physics: from physics to quantum information

I start with some histories regarding quantum entanglement in particle physics, and go on to discuss the usefulness of entangled states for particle physics and possibilities of quantum information processing in realms of particle physics.

Speaker: Prof. 郁 施 (中国科学技术大学上海研究院)

10:20 Coffee Break & Photo

Morning 2

Convener: Chen（辰） Zhou（周） (Peking University（北京大学）)

7 北京谱仪上的量子纠缠实验/ Quantum Entanglement Experiments at the Beijing Spectrometer

The nonlocality of quantum correlations is a fundamental feature of quantum theory. The benchmark for distinguishing quantum theory from local hidden variable theories (LHVT) is the testing of Bell's inequalities. Recent advances in photon entanglement experiments have made significant progress, addressing potential loopholes and observing significant violations of Bell's inequalities. However, these violations do not completely rule out LHVT. To further exclude LHVT, in addition to massless photon entanglement experiments, it is also necessary to conduct particle entanglement experiments under strong and weak interactions. In this report, the examination of quantum nonlocal correlations using entangled hyperon events from the Beijing Electron-Positron Collider is presented. By testing three Bell's inequalities, the experimental results exclude LHVT at a statistical significance level exceeding 5.2 standard deviations, indicating that quantum nonlocal correlations are a fundamental characteristic of basic interactions in the microscopic world.

Speaker: Ping Ronggang (高能所)

8 Bell Inequality Violation of Light Quarks in Back-to-Back Dihadron Pair Production at Lepton Colliders

Spin correlations between particles produced at colliders provide valuable insights for quantum information studies. While traditional studies of quantum information at colliders are typically limited to massive particles with perturbative decay, we propose an innovative method to explore the Bell inequality in massless quark pair systems by analyzing the azimuthal correlations in back-to-back $\pi^+\pi^-$ dihadron pair production at lepton colliders. Revisiting the Belle data, we have shown the potential to detect Bell inequality violation of light quarks by introducing an additional angular cut, achieving a significance of 2.5 $\sigma$ even in the worst-case scenario of 100\% correlated systematic uncertainties in each bins. The significance substantially exceeds $5\sigma$ when considering uncorrelated systematic uncertainties. Our approach opens avenues for exploring spin quantum information in the non-perturbative aspect and leverages existing data for quantum information research.

Speaker: Prof. Bin Yan (IHEP)

9 Parity and Environmental Effects on Quantum Entanglement and Bell Tests

Symmetries exhibit the beauty of nature, while their breaking reflects the reality of our Universe. In this talk, I will discuss how parity violation affects Bell tests by quantifying its impact on quantum entanglement and the violation of the Bell inequality, using spin-half bipartite systems as an illustration. On the other hand, spins interact with the environment, causing a decoupling effect that tends to disentangle the bipartite systems. This environmental effect, however, has been largely overlooked in the past but will be discussed in detail in this talk.

This talk is based on https://arxiv.org/abs/2409.15418

Speaker: Yong Du (IMP CAS)

10 Entanglement and beyond: Quantum information properties of on-shell scattering

Recently it has been noticed that many familiar quantum field theories (QFTs) may minimize or maximize the amount of entanglement in a scattering process. Studying the quantum information (QI) properties of final states for on-shell scattering will help establish whether fundamental physics can be formulated in terms of QI principles. We first present a universal relation between final state entanglement entropy and (semi)-inclusive cross sections. This implies a growing behavior of the entanglement entropy in the very high energy limit, which hints at a connection between micro- and macroscopic physics. We then go beyond the concept of entanglement and consider the notion of magic, which quantifies the computational advantage of quantum states over classical algorithms. A novel bound for magic in 2-qubit systems is derived, which suggests new connections between magic and entanglement as well as other principles in QFTs.

Speaker: Zhewei Yin (Northwestern University & Argonne National Lab)

12:30 Lunch

Afternoon 1

Convener: Alim Ruzi (school of physics Peking Uniersity)

11 Rigidity of Quantum Nonlocality in Device-Independent Self-Testing of Qutrit Systems

The quantum rigidity of Bell nonlocality in device-independent self-testing scenarios for qutrit systems is established using the sum-over-squares method. It is demonstrated that when the quantum upper bound of the generalized Bell inequality is achieved, the underlying entangled state is required to be maximally entangled, and the measurement observables are uniquely specified.

Speaker: Dr Chon-Fai Kam (University at Buffalo in New York)

12 News from the “Quantum Observables for Collider Physics” Workshop, Italy

Speakers: Alim Ruzi (school of physics Peking Uniersity) , Leyun Gao (Peking University)

Italy QE workshop

13 Dihadron spin correlations in unpolarized high energy collisions (remote talk)

The emergence of spin correlations through quantum entanglement in unpolarized high-energy collisions offers a unique opportunity to investigate spin-dependent fragmentation functions, even with unpolarized experiments. In a series of studies [1-5], we investigated the longitudinal and transverse spin correlations of back-to-back dihadrons produced in unpolarized $e^+e^-$, $pp$ and $ep$ collisions. We demonstrate the phenomenological application of quantum entanglements.

References
[1] Probing the longitudinal spin transfer via dihadron polarization correlations in unpolarized $e^+e^-$ and $pp$ collisions; H.C. Zhang, S.Y. Wei; Phys.Lett.B839, 137821 (2023).
[2] Correlations of dihadron polarization in central, peripheral and ultraperipheral heavy-ion collisions; X. Li, Z.X. Chen, S. Cao, S.Y. Wei; Phys.Rev.D 109, 014035 (2024).
[3] Dihadron helicity correlation in photon-nucleus collisions; Z.X. Chen, H. Dong, S.Y. Wei; Phys.Rev.D 110, 056040 (2024).
[4] Transverse spin correlation of back-to-back dihadron in unpolarized collisions; L. Yang, Y.K. Song, S.Y. Wei; arXiv:2410.20917.
[5] Helicity correlation of neighboring dihadron; F. Huang, T. Liu, Y.K. Song, S.Y. Wei; arXiv:2412.00394.

Speaker: Prof. Shu-yi Wei (Shandong University)

14 TBD (remote talk)

Speaker: Prof. Juan Antonio Aguilar-Saavedra (Madrid, IFT.)

15:10 Coffee Break

Afternoon 2

15 Machine Learning for Parton-Level Studies of Quantum Entanglement Using pp→ττ

Quantum entanglement is a hallmark feature of quantum mechanics, manifesting as correlations between subsystems that cannot be fully described without one another, regardless of spatial separation. While entanglement has been observed in processes such as $pp \rightarrow t \bar{t}$ and thoroughly analyzed in Higgs decay channels ($H \rightarrow VV$) at the Large Hadron Collider (LHC), it remains comparatively underexplored in the $pp \rightarrow \tau \tau$ system. In this study, we adapt OmniLearn, a foundational model for solving all jet physics tasks, to reconstruct the neutrino information in the final state of $pp \rightarrow \tau \tau$ system, which is an essential step toward probing quantum entanglement in this channel. Good neutrino reconstruction has reached now, which is the key to the following steps in the reconstruction level study.

Speaker: Baihong Zhou (Tsung-Dao Lee Institute, Shanghai Jiao Tong Univ. (CN))

16 A first test on spooky actions between free-traveling charged lepton pairs

Quantum entanglement is a cornerstone of quantum mechanics. While entanglement between confined electron pairs is well-studied, free-traveling electron pairs remain largely unexplored due to significant challenges in spin measurement. We hereby propose a novel theory-assisted quantum entanglement test for free-traveling electron-positron pairs through polarization correlation measurements. The entangled pairs are generated in a GeV-scale positron on-target experiment, approaching a Bell state theoretically. Then their polarization correlation is measured at two secondary scattering targets, where a high event rate can be achieved and the unique behavior of the Bell state theoretically known in prior helps verify the entanglement.

Based primarily on: arXiv:2411.12518 and arXiv:2502.07597

Speaker: Mr Leyun Gao (Peking University)

17 Probing quantum decoherence through data from B meson decays

The time evolution of the neutral B mesons determines key parameters in flavor physics. While their behavior is generally studied under the assumption of perfect quantum coherence, interactions with the surrounding environment can introduce decoherence. The influence of such environmental effects on neutral meson systems can be effectively described using the open quantum system framework. This decoherence can obscure the extraction of critical parameters, such as the oscillation frequency $\Delta m$ and the $ CP $-violating parameter $ \sin 2\beta $. Utilizing the available experimental data, we present the first combined analysis of mixing asymmetry and $ CP $-asymmetry measurements for $ B_d $-mesons, revealing that $ \lambda_d $ is non-zero with a significance of approximately $ 6 \,\sigma $. Furthermore, we establish the first experimental constraints on the decoherence parameter $ \lambda_s $ for $ B_s $-mesons, confirming its non-zero value at $ 3 \,\sigma $.

Speaker: Neetu Raj Singh Chundawat (高能所)

18 entanglement autodistillation from baryon decays

We study the spin-entangled mixed state of a spin-(\frac{1}{2}) baryon-antibaryon pair produced in the process (e^+e^-\to J/\psi,\psi' \to B\bar{B}). We show that the spin entanglement of the system can increase after the process that a baryon decays to a spin-(\frac{1}{2}) baryon and a spin-0 meson, an anti-baryon decays to a spin-(\frac{1}{2}) anti-baryon and a spin-0 meson.

Speaker: 海龙 丰 (华中科技大学)

19 Fully charmed tetraquark decays and their quantum entanglement effects

Speaker: 凯文 陈 (Nanjing Normal University)