Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Chinese Physics C

Searching quantum entanglement in the pp → ZZ process*

Alim Ruzi, Youpeng Wu, Ran 然 Ding 丁, Qiang Li

Published Oct 15, 2025• 3 citations
Publisher

Abstract

Abstract Recent studies have shown that observing entangled particle states at a particle collider, such as the Large Hadron Collider (LHC), and testing the violation of Bell inequality in them can open up new research areas for studying high energy physics. We examine the presence of quantum entanglement in the process at leading order. We apply a generally recognized method, quantum state tomography, to reconstruct the spin density matrix of the joint ZZ system, through which all the relevant observables can be obtained. The angular distribution of the final leptons is obtained from simulated events using a Monte-Carlo program, which is used to reconstruct the spin density matrix. A non-zero value of the lower bound of the concurrence is measured with the simulated data. The numerical analysis shows that, with the luminosity corresponding to LHC Run 2+3, entanglement can be probed at the 2 level and up to the 3.75 level for High-Luminosity LHC data (3ab -1 ), revealing the possibility of finding quantum entanglement in real collider experiments.

DOI
10.1088/1674-1137/ae1374

Related papers

Searching Quantum Entanglement in $p\ p\to Z\ Z$ process

Alim Ruzi, Youpeng Wu, Ran Ding +1 more

Recent studies have shown that observing entangled particle states at a particle collider like Large Hadron Collider (LHC) and testing violation of Bell inequality in them can open up new research area for high energy physics study. We examine the presence of quantum entanglement in the $pp\to ZZ\to 4\ell$ process at leading order. We apply generally recognized method, quantum state tomography, to reconstruct spin density matrix of the joint $ZZ$ system, through which all the relevant observables can be obtained. The angular distribution of the final leptons are obtained from simulated events using Monte-Carlo program, which is used to reconstruct spin density matrix. Non-zero value of the lower bound of the concurrence is measured with simulated data. The numerical analysis shows that with the luminosity corresponding to LHC Run 2+3, entanglement can be probed at $2 σ$ level and up to 3.75$σ$ level for High-Luminosity LHC data ($3 \rm{ab}^{-1}$), revealing the possibility of finding quantum entanglement in real collider experiment.

arXiv:2506.16077•Jun 19, 2025•0 citations

Testing Bell inequalities and probing quantum entanglement at a muon collider

Alim Ruzi, Youpeng Wu, Ran Ding +3 more

A bstract A muon collider represents a promising candidate for the next generation of particle physics experiments after the expected end of LHC operations in the early 2040s. Rare or hard-to-detect processes at the LHC, such as the production of multiple gauge bosons, become accessible at a TeV muon collider. We present here the prospects of detecting quantum entanglement and the violation of Bell inequalities in H → ZZ → 4 ℓ events at a potential future muon collider. We show that the spin density matrix of the Z boson pairs can be reconstructed using the kinematics of the charged leptons from the Z boson decays. Once the density matrix is determined, it is straightforward to obtain the expectation values of various Bell operators and test the quantum entanglement between the Z boson pair. Through a detailed study based on Monte-Carlo simulation, we show that the generalized CGLMP inequality can be maximally violated, and testing Bell inequalities could be established with high significance.

arXiv:2408.05429•Journal of High Energy Physics•Oct 29, 2024•17 citations

Quantum tops at the LHC: from entanglement to Bell inequalities

Claudio Severi, C. Degli Esposti Boschi, Fabio Maltoni B +1 more

Abstract We present the prospects of detecting quantum entanglement and the violation of Bell inequalities in $$t\bar{t}$$ t t ¯ events at the LHC. We introduce a unique set of observables suitable for both measurements, and then perform the corresponding analyses using simulated events in the dilepton final state, reconstructing up to the unfolded level. We find that entanglement can be established at better than $$5 \sigma $$ 5 σ both at threshold as well as at high $$p_T$$ p T already in the LHC Run 2 dataset. On the other hand, only very high- $$p_T$$ p T events are sensitive to a violation of Bell inequalities, making it significantly harder to observe experimentally. By employing a sensitive and robust observable, two different unfolding methods and independent statistical approaches, we conclude that, at variance with previous estimates, testing Bell inequalities will be challenging even in the high luminosity LHC run.

arXiv:2110.10112•The European Physical Journal C•Apr 1, 2022•120 citations

Entanglement and Bell inequalities with boosted t t ¯

Zhongtian Dong, Dorival Gonçalves, Kyoungchul Kong +1 more

The Large Hadron Collider provides a unique opportunity to study quantum entanglement and violation of Bell inequalities at the highest energy available today. In this paper, we will investigate these quantum correlations with top quark pair production, which represents a system of two-qubits. The semileptonic top pair channel has a factor of 6 increase in statistics and easier reconstruction with respect to the dileptonic channel. Although measuring the spin polarization of the hadronic top quark is known to be challenging, our study indicates that it is feasible to reconstruct the spin density matrix of the two-qubit system using an optimal hadronic polarimeter. This is achieved with the aid of jet substructure techniques and NN-inspired reconstruction methods, which improve the mapping between subjets and quarks. We find that entanglement can already be observed at more than the 5 σ level with existing data, and violation of Bell inequalities may be probed above the 4 σ level at the HL-LHC with 3 ab − 1 of data. Published by the American Physical Society 2024

arXiv:2305.07075•Physical review. D/Physical review. D.•Jun 24, 2024•63 citations

Quantum entanglement and Bell inequality violation in semi-leptonic top decays

Tao Han, Matthew Low, Tong Arthur Wu

A bstract Quantum entanglement is a fundamental property of quantum mechanics. Recently, studies have explored entanglement in the $$ t\overline{t} $$ t t ¯ system at the Large Hadron Collider (LHC) when both the top quark and anti-top quark decay leptonically. Entanglement is detected via correlations between the polarizations of the top and anti-top and these polarizations are measured through the angles of the decay products of the top and anti-top. In this work, we propose searching for evidence of quantum entanglement in the semi-leptonic decay channel where the final state includes one lepton, one neutrino, two b -flavor tagged jets, and two light jets from the W decay. We find that this channel is both easier to reconstruct and has a larger effective quantity of data than the fully leptonic channel. As a result, the semi-leptonic channel is 60% more sensitive to quantum entanglement and a factor of 3 more sensitive to Bell inequality violation, compared to the leptonic channel. In 139 fb − 1 (3 ab −1 ) of data at the LHC (HL-LHC), it should be feasible to measure entanglement at a precision of ≲ 3% (0 . 7%). Detecting Bell inequality violation, on the other hand, is more challenging. With 300 fb −1 (3 ab −1 ) of integrated luminosity at the LHC Run-3 (HL-LHC), we expect a sensitivity of 1 . 3 σ (4 . 1 σ ). In our study, we utilize a realistic parametric fitting procedure to optimally recover the true angular distributions from detector effects. Compared to unfolding this procedure yields more stable results.

arXiv:2310.17696•Journal of High Energy Physics•Jul 22, 2024•57 citations

Testing Bell inequalities and probing quantum entanglement at CEPC

Youpeng Wu, Ruobing Jiang, Alim Ruzi +3 more

We study quantum entanglement and test violation of Bell-type inequality at the Circular Electron Positron Collider (CEPC), which is one of the most attractive future collides. It is a promising particle collider designed to search new physics, make Standard Model (SM) precision measurements, and serving as a Higgs factory. Our study is based on a fast simulation of the Z boson pair production from Higgs boson decay at s = 250 GeV . The detector effects are also included in the simulation. The spin density matrix of the joint Z Z system is parametrized using irreducible tensor operators and reconstructed from the spherical coordinates of the decay leptons. To test Bell inequalities, we construct observable quantities for the H → Z Z * process in CEPC by using the Collins-Gisin-Linden-Massar-Popescu (CGLMP) inequality, whose value is determined from the density matrix of the Z boson pairs. The sensitivity of the Bell inequality violation is observed with more than 1 σ and the presence of the quantum entanglement is probed with more than 2 σ confidence level.

arXiv:2410.17025•Physical review. D/Physical review. D.•Feb 6, 2025•16 citations
Abstract Recent studies have shown that observing entangled particle states at a particle collider, such as the Large Hadron Collider (LHC), and testing the violation of Bell inequality in them can open up new research areas for studying high energy physics. We examine the presence of quantum entanglement in the process at leading order. We apply a generally recognized method, quantum state tomography, to reconstruct the spin density matrix of the joint ZZ system, through which all the relevant observables can be obtained. The angular distribution of the final leptons is obtained from simulated events using a Monte-Carlo program, which is used to reconstruct the spin density matrix. A non-zero value of the lower bound of the concurrence is measured with the simulated data. The numerical analysis shows that, with the luminosity corresponding to LHC Run 2+3, entanglement can be probed at the 2 level and up to the 3.75 level for High-Luminosity LHC data (3ab -1 ), revealing the possibility of finding quantum entanglement in real collider experiments.
Searching Quantum Entanglement in p p→Z Zp\ p\to Z\ Zp p→Z Z process
Recent studies have shown that observing entangled particle states at a particle collider like Large Hadron Collider (LHC) and testing violation of Bell inequality in them can open up new research area for high energy physics study. We examine the presence of quantum entanglement in the pp→ZZ→4ℓpp\to ZZ\to 4\ellpp→ZZ→4ℓ process at leading order. We apply generally recognized method, quantum state tomography, to reconstruct spin density matrix of the joint ZZZZZZ system, through which all the relevant observables can be obtained. The angular distribution of the final leptons are obtained from simulated events using Monte-Carlo program, which is used to reconstruct spin density matrix. Non-zero value of the lower bound of the concurrence is measured with simulated data. The numerical analysis shows that with the luminosity corresponding to LHC Run 2+3, entanglement can be probed at 2σ2 σ2σ level and up to 3.75σσσ level for High-Luminosity LHC data (3ab−13 \rm{ab}^{-1}3ab−1), revealing the possibility of finding quantum entanglement in real collider experiment.
A bstract A muon collider represents a promising candidate for the next generation of particle physics experiments after the expected end of LHC operations in the early 2040s. Rare or hard-to-detect processes at the LHC, such as the production of multiple gauge bosons, become accessible at a TeV muon collider. We present here the prospects of detecting quantum entanglement and the violation of Bell inequalities in H → ZZ → 4 ℓ events at a potential future muon collider. We show that the spin density matrix of the Z boson pairs can be reconstructed using the kinematics of the charged leptons from the Z boson decays. Once the density matrix is determined, it is straightforward to obtain the expectation values of various Bell operators and test the quantum entanglement between the Z boson pair. Through a detailed study based on Monte-Carlo simulation, we show that the generalized CGLMP inequality can be maximally violated, and testing Bell inequalities could be established with high significance.
Abstract We present the prospects of detecting quantum entanglement and the violation of Bell inequalities in ttˉt\bar{t}ttˉ t t ¯ events at the LHC. We introduce a unique set of observables suitable for both measurements, and then perform the corresponding analyses using simulated events in the dilepton final state, reconstructing up to the unfolded level. We find that entanglement can be established at better than 5σ5 \sigma 5σ 5 σ both at threshold as well as at high pTp_TpT​ p T already in the LHC Run 2 dataset. On the other hand, only very high- pTp_TpT​ p T events are sensitive to a violation of Bell inequalities, making it significantly harder to observe experimentally. By employing a sensitive and robust observable, two different unfolding methods and independent statistical approaches, we conclude that, at variance with previous estimates, testing Bell inequalities will be challenging even in the high luminosity LHC run.
The Large Hadron Collider provides a unique opportunity to study quantum entanglement and violation of Bell inequalities at the highest energy available today. In this paper, we will investigate these quantum correlations with top quark pair production, which represents a system of two-qubits. The semileptonic top pair channel has a factor of 6 increase in statistics and easier reconstruction with respect to the dileptonic channel. Although measuring the spin polarization of the hadronic top quark is known to be challenging, our study indicates that it is feasible to reconstruct the spin density matrix of the two-qubit system using an optimal hadronic polarimeter. This is achieved with the aid of jet substructure techniques and NN-inspired reconstruction methods, which improve the mapping between subjets and quarks. We find that entanglement can already be observed at more than the 5 σ level with existing data, and violation of Bell inequalities may be probed above the 4 σ level at the HL-LHC with 3 ab − 1 of data. Published by the American Physical Society 2024
A bstract Quantum entanglement is a fundamental property of quantum mechanics. Recently, studies have explored entanglement in the tt‾ t\overline{t} tt t t ¯ system at the Large Hadron Collider (LHC) when both the top quark and anti-top quark decay leptonically. Entanglement is detected via correlations between the polarizations of the top and anti-top and these polarizations are measured through the angles of the decay products of the top and anti-top. In this work, we propose searching for evidence of quantum entanglement in the semi-leptonic decay channel where the final state includes one lepton, one neutrino, two b -flavor tagged jets, and two light jets from the W decay. We find that this channel is both easier to reconstruct and has a larger effective quantity of data than the fully leptonic channel. As a result, the semi-leptonic channel is 60% more sensitive to quantum entanglement and a factor of 3 more sensitive to Bell inequality violation, compared to the leptonic channel. In 139 fb − 1 (3 ab −1 ) of data at the LHC (HL-LHC), it should be feasible to measure entanglement at a precision of ≲ 3% (0 . 7%). Detecting Bell inequality violation, on the other hand, is more challenging. With 300 fb −1 (3 ab −1 ) of integrated luminosity at the LHC Run-3 (HL-LHC), we expect a sensitivity of 1 . 3 σ (4 . 1 σ ). In our study, we utilize a realistic parametric fitting procedure to optimally recover the true angular distributions from detector effects. Compared to unfolding this procedure yields more stable results.
We study quantum entanglement and test violation of Bell-type inequality at the Circular Electron Positron Collider (CEPC), which is one of the most attractive future collides. It is a promising particle collider designed to search new physics, make Standard Model (SM) precision measurements, and serving as a Higgs factory. Our study is based on a fast simulation of the Z boson pair production from Higgs boson decay at s = 250 GeV . The detector effects are also included in the simulation. The spin density matrix of the joint Z Z system is parametrized using irreducible tensor operators and reconstructed from the spherical coordinates of the decay leptons. To test Bell inequalities, we construct observable quantities for the H → Z Z * process in CEPC by using the Collins-Gisin-Linden-Massar-Popescu (CGLMP) inequality, whose value is determined from the density matrix of the Z boson pairs. The sensitivity of the Bell inequality violation is observed with more than 1 σ and the presence of the quantum entanglement is probed with more than 2 σ confidence level.