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Nonlocal Advantage of Quantum Coherence in Top Quarks

Saurabh Rai, Jitendra Kumar

TL;DR

This paper addresses the nonlocal advantage of quantum coherence (NAQC) in top–antitop ($t\bar{t}$) quark pairs produced at high energy. It advances a two-qubit density-matrix framework and applies two NAQC measures based on the $l_{1}$-norm and the relative entropy of coherence to both fully differential parton-level states and a toy hadron-level mixture, mapping NAQC as a function of kinematic variables $\theta$ and $\beta$ and exploring angular averages. The study finds that NAQC is most pronounced in the gluon-fusion channel $gg \to t\bar{t}$, with NAQC regions shrinking as hadronic mixing increases; angular-averaged NAQC is reduced but remains detectable in the $gg$ channel and is basis-independent. Overall, NAQC provides a novel quantum-information-based diagnostic for collider processes, offering a complementary probe for testing the Standard Model and searching for new physics scenarios.

Abstract

There is a growing interest in investigating top-quark systems using tools from quantum information theory. A key peculiarity of the top quark is that it decays before hadronization or spin decorrelation occurs, thereby preserving its spin information. This unique property enables direct access to spin correlations, making the top quark an ideal candidate for probing fundamental quantum correlations in high-energy physics processes. A wide range of concepts from quantum information theory, such as entanglement, Bell nonlocality, quantum steering, quantum discord, and fidelity, have been investigated in this context. Several of these measures have been employed as diagnostic tools to test the Standard Model and to search for possible signatures of physics beyond. However, the $\textit{nonlocal advantage of quantum coherence}$ (NAQC) has remained largely unexplored in this context. In this work, we present a detailed investigation of the NAQC in top quark pair production. We employ two complementary NAQC measures based on the $l_{1}$-norm and the relative entropy of coherence. We also study the effect of angular averaging on these measures. Our findings reveal rich coherence structures and highlight NAQC as potentially a novel and complementary quantum signature in high-energy physics systems.

Nonlocal Advantage of Quantum Coherence in Top Quarks

TL;DR

This paper addresses the nonlocal advantage of quantum coherence (NAQC) in top–antitop () quark pairs produced at high energy. It advances a two-qubit density-matrix framework and applies two NAQC measures based on the -norm and the relative entropy of coherence to both fully differential parton-level states and a toy hadron-level mixture, mapping NAQC as a function of kinematic variables and and exploring angular averages. The study finds that NAQC is most pronounced in the gluon-fusion channel , with NAQC regions shrinking as hadronic mixing increases; angular-averaged NAQC is reduced but remains detectable in the channel and is basis-independent. Overall, NAQC provides a novel quantum-information-based diagnostic for collider processes, offering a complementary probe for testing the Standard Model and searching for new physics scenarios.

Abstract

There is a growing interest in investigating top-quark systems using tools from quantum information theory. A key peculiarity of the top quark is that it decays before hadronization or spin decorrelation occurs, thereby preserving its spin information. This unique property enables direct access to spin correlations, making the top quark an ideal candidate for probing fundamental quantum correlations in high-energy physics processes. A wide range of concepts from quantum information theory, such as entanglement, Bell nonlocality, quantum steering, quantum discord, and fidelity, have been investigated in this context. Several of these measures have been employed as diagnostic tools to test the Standard Model and to search for possible signatures of physics beyond. However, the (NAQC) has remained largely unexplored in this context. In this work, we present a detailed investigation of the NAQC in top quark pair production. We employ two complementary NAQC measures based on the -norm and the relative entropy of coherence. We also study the effect of angular averaging on these measures. Our findings reveal rich coherence structures and highlight NAQC as potentially a novel and complementary quantum signature in high-energy physics systems.
Paper Structure (11 sections, 28 equations, 3 figures)

This paper contains 11 sections, 28 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Formalism
  3. Top Quarks as Two-Qubit Systems
  4. Nonlocal Advantage of Quantum Coherence
  5. NAQC in top quarks
  6. Fully differential final states
  7. NAQC at parton level
  8. NAQC at hadron level
  9. Angular-averaged final states
  10. Conclusion
  11. Acknowledgement

Figures (3)

  • Figure 1: NAQC measure in the $q\bar{q}$-initiated process (left panel) and the $gg$-initiated process (right panel) for top-antitop quark pair production. The top panel shows the measure based on the $l_1$-norm of coherence ($C^{\text{na}}_{l_1}$), while the bottom panel shows the measure based on the relative entropy ($C^{\text{na}}_{\text{re}}$).
  • Figure 2: Investigation of NAQC in top-antitop quark pair production using a toy hadronic process with various mixing parameter $f$.
  • Figure 3: NAQC measures for angular-averaged $\rho_{gg}$ state. The horizontal gray and black dashed lines indicate the threshold values of NAQC based on the $l_{1}$-norm and relative entropy measures, respectively. The vertical dotted lines mark the corresponding bounds on $\beta$ for each measure.