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arXiv:2406.03976 · Reports on Progress in Physics

Observation of quantum entanglement in top quark pair production in proton–proton collisions at s = 13 TeV

CMS Collaboration, Aram Hayrapetyan, A. Tumasyan, Wolfgang Adam, Janik Walter Andrejkovic, T. Bergauer, S. Chatterjee, K. Damanakis, M. Dragicevic, André H. Hoang, Priya Sajid Hussain, Jeitler, Manfred, Natascha Krammer, A. Li, Dietrich Liko, I. Mikulec, J. Schieck, Schöfbeck, Robert, Dennis Schwarz, M. Sonawane, S. Templ, W. Waltenberger, C.-E. Wulz, X. Janssen, T. Van Laer, Pierre Van Mechelen A, Nordin Breugelmans, J. D’Hondt, Soumya Dansana, A. De Moor, M. Delcourt, Felix Heyen, S. Lowette, Inna Makarenko, D. Müller, S. Tavernier, M. Tytgat, G. P. Van Onsem, S. Van Putte, David Vannerom, B. Bilin, B. Clerbaux, Aloke Kumar Das, G. De Lentdecker, Hugues Evard, L. Favart, P. Gianneios, J. Jaramillo, Ali Khalilzadeh, Khan, Fakhri Alam, Kyeongpil Lee, M. Mahdavikhorrami, Andrea Malara, Santiago Rafael Paredes Saenz, Muhammad Aamir Shahzad, Laurent Thomas, Vanden Bemden, Max, Vander Velde, Catherine, Pascal Vanlaer, M. De Coen, Dobur, Didar, G. Gökbulut, Y. Hong, J. Knolle, Luka Lambrecht, David Marckx, Mota Amarilo, Kevin, Amrutha Samalan, K. Skovpen, N. Van Den Bossche, Jan van der Linden, Liam Wezenbeek, A. Benecke, Agni Bethani, G. Bruno, C. Caputo, De Favereau De Jeneret, Jerome, Christophe Delaere, Donertas, Izzeddin Suat, ANDREA GIAMMANCO, Ahmet Oguz Guzel, Sandhya Jain, Vincent Lemaître, Jindrich Lidrych, Paola Mastrapasqua, T. T. Tran, S. Wertz, Gilvan Augusto Alves, Alves Gallo Pereira, Miguel, E. Coelho, Correia Silva, Gilson, C. Hensel, T. Menezes De Oliveira, Clemencia Mora Herrera, Arthur M. Moraes, P. Rebello Teles, Mariana Soeiro, Vilela Pereira, Antonio, Aldá Júnior, Walter Luiz, Barroso Ferreira Filho, Mapse

Published Sep 23, 2024• 98 citations
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Abstract

Abstract Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark ( t t ¯ ) events produced in proton–proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb −1 . The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable D is derived from the top quark spin-dependent parts of the t t ¯ production density matrix and measured in the region of the t t ¯ production threshold. Values of D < − 1 / 3 are evidence of entanglement and D is observed (expected) to be − 0.480 − 0.029 + 0.026 ( − 0.467 − 0.029 + 0.026 ) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within t t ¯ pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.

DOI
10.1088/1361-6633/ad7e4d

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Abstract Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark ( t t ¯ ) events produced in proton–proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb −1 . The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable D is derived from the top quark spin-dependent parts of the t t ¯ production density matrix and measured in the region of the t t ¯ production threshold. Values of D < − 1 / 3 are evidence of entanglement and D is observed (expected) to be − 0.480 − 0.029 + 0.026 ( − 0.467 − 0.029 + 0.026 ) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within t t ¯ pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.
Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark (t¯t) events produced in proton–proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb−1 . The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable D is derived from the top quark spin-dependent parts of the t¯t production density matrix and measured in the region of the t¯t production threshold. Values of D < −1/3 are evidence of entanglement and D is observed (expected) to be −0.480+0.026 −0.029 (−0.467+0.026 −0.029) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within t¯t pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.
Abstract Entanglement is a key feature of quantum mechanics1–3, with applications in fields such as metrology, cryptography, quantum information and quantum computation4–8. It has been observed in a wide variety of systems and length scales, ranging from the microscopic9–13 to the macroscopic14–16. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top–antitop quark events produced at the Large Hadron Collider, using a proton–proton collision dataset with a centre-of-mass energy of √s = 13 TeV and an integrated luminosity of 140 inverse femtobarns (fb)−1 recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable D, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top–antitop quark production threshold, at which the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D = −0.537 ± 0.002 (stat.) ± 0.019 (syst.) for 340 GeV<mttˉ<380 GeV340\,{\rm{GeV}} < {m}_{t\bar{t}} < 380\,{\rm{GeV}}340GeV<mttˉ​<380GeV 340 GeV < m t t ¯ < 380 GeV . The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.
Entanglement is a key feature of quantum mechanics1,2,3^{1,2,3}1,2,3, with applications in fields such as metrology, cryptography, quantum information and quantum computation4,5,6,7,8^{4,5,6,7,8}4,5,6,7,8. It has been observed in a wide variety of systems and length scales, ranging from the microscopic9,10,11,12,13^{9,10,11,12,13}9,10,11,12,13 to the macroscopic14,15,16^{14,15,16}14,15,16. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top–antitop quark events produced at the Large Hadron Collider, using a proton–proton collision dataset with a centre-of-mass energy of s=13 TeV\sqrt{s} = 13\text{ TeV}s​=13 TeV and an integrated luminosity of 140 inverse femtobarns (fb)−1140\text{ inverse femtobarns (fb)}^{-1}140 inverse femtobarns (fb)−1 recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable DDD, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top–antitop quark production threshold, at which the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D=−0.537±0.002 (stat.)±0.019 (syst.)D = -0.537 \pm 0.002 \text{ (stat.)} \pm 0.019 \text{ (syst.)}D=−0.537±0.002 (stat.)±0.019 (syst.) for . The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.
Entanglement is a key feature of quantum mechanics1–3, with applications in fields such as metrology, cryptography, quantum information and quantum computation4–8. It has been observed in a wide variety of systems and length scales, ranging from the microscopic9–13 to the macroscopic14–16. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top–antitop quark events produced at the Large Hadron Collider, using a proton–proton collision dataset with a centre-of-mass energy of √s = 13 TeV and an integrated luminosity of 140 inverse femtobarns (fb)−1 recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable D, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top–antitop quark production threshold, at which the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D = −0.537 ± 0.002 (stat.) ± 0.019 (syst.) for 340GeV
Measurements of top quark properties in CMS: ttˉt\bar{t}ttˉ spin density matrix, quantum entanglement and quantum magic
Polarization and spin correlation measurements of top quark-antiquark (ttˉt\bar{t}ttˉ) pairs provide tests of the standard model, but also new ways to test quantum mechanics with unstable particles at highest energies ever produced in a laboratory. Recent ttˉt\bar{t}ttˉ spin correlation measurements and the tests they enable, made with the CMS detector at the CERN LHC Run 2, are presented. The measurements summarized include the full spin density matrix measurement of top quark pairs using events with a single lepton and jets in the final state. Spin correlation measurements in specific phase space regions allow the observation of the entanglement phenomenon, and the measurement of quantum magic. From the measured spin correlation at the ttˉt\bar{t}ttˉ production threshold and high ttˉt\bar{t}ttˉ mass, entanglement is observed with a large fraction of the ttˉt\bar{t}ttˉ decays being spacelike separated. The observation of entanglement in ttˉt\bar{t}ttˉ events with two high transverse momentum leptons of opposite charge is also presented. Finally, the first TeV-scale experimental measurement of quantum magic, an important variable for the characterization of quantum states in quantum information science, is presented. These measurements provide one of the first connections between quantum information science and particle physics, and show the potential of collider experiments in the studies of the foundations of quantum mechanics.