arXiv:2507.12513 · Physical Review Letters

Quantum Tomography in Neutral Meson and Antimeson Systems

Kun Cheng, Tao Han, Matthew Low, Tong Arthur Wu

Published Mar 25, 2026• 1 citation

Abstract

The flavor space of particles produced in collider environments contains informative quantum correlations. We present a systematic approach for constructing the complete flavor density matrix for a meson and antimeson system (MM[over ¯]) in the Bloch vector space at a given time t, which can be at or after production. We point out that the B_{s}^{0} and K^{0} systems are superior to the B_{d}^{0} and D^{0} systems for quantum tomography because of their flavor oscillation and decay properties. Performing quantum tomography for the MM[over ¯] system can facilitate the study of production mechanisms, decoherence phenomena, quantum information variables, and potential new sources of CP violation.

DOI: 10.1103/t9vg-hk6c

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arXiv:2507.12513 · Physical Review Letters

Quantum Tomography in Neutral Meson and Antimeson Systems

Kun Cheng, Tao Han, Matthew Low, Tong Arthur Wu

Published Mar 25, 2026• 1 citation

arXiv HTML PDF

Abstract

DOI: 10.1103/t9vg-hk6c

Related papers

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arXiv:1707.01638The European Physical Journal CDec 30, 201728 citations

B

- and

D

- mesons into two scalar octets of SU(3) flavor space. We briefly discuss the quantum properties of these states, including entanglement, contextuality, and nonlocality. Additionally, we demonstrate a comparable approach for spin-1 final states by employing a density matrix describing states in the space of helicities. The significance of CP violation obtained through this method is consistently comparable, and often surpasses that obtained using only single, or combinations of, asymmetries.

Qubit-Qutrit Quantum Tomography of hadronic

Λφ

and

ΛK^{\ast 0}

systems

Quantum-information observables have emerged in recent years as new tools in nuclear and particle physics, from entanglement in top-quark pairs to spin correlations in

Λ\barΛ

production. Extending these studies to unequal-spin hadronic final states poses a fundamental challenge: the

6\times6

density matrix of a qubit-qutrit system contains 35 independent spin parameters, but the decays of

ΛV

pairs, with

V=φ

K^{*0}

, provide access to only 23 due to the hidden vector polarization from the strong decay. In this Letter, we formulate a qubit-qutrit quantum tomography (QQQT) technique for these spin-

\tfrac{1}{2}\otimes1

systems and establish exact criteria for entanglement certification from the \textit{incomplete} density matrix. Compared with the

Λ\barΛ

system, QQQT of

Λφ

and

ΛK^{*0}

provides a new probe of nonperturbative QCD hadronization, enabling a direct comparison of the spin evolution of entangled quark pairs produced from the vacuum as they hadronize into a baryon or a vector meson.

Quantum detection of CP violation in the

t\bar{t}

system: tomography

We develop a quantum-tomographic framework for determining whether possible CP-odd effects in

t\bar t

events originate in production, in decay, or in both. In the narrow-width approximation, the process

I\to t\bar t\to b\ell^+ν\,\bar b\ell^-\barν

factorises into a production density matrix and top and antitop decay density matrices. We extend the standard tomography procedure to a general anomalous

Wtb

vertex and derive the corresponding angular distributions. Polar-angle distributions retain their usual tomographic form, up to modifications of the spin-analysing powers, and can therefore be used to reconstruct the production density matrix and test its CP properties. By contrast, dedicated azimuthal observables involving the

b

--lepton decay planes contain characteristic sine modulations that provide linear probes of possible new CP-violating interactions in the decay vertex. Combining the two classes of observables gives a systematic strategy for separating sources of CP violation in production and in decay. We illustrate the resulting angular signatures for representative

t\bar t

production scenarios at hadron and lepton colliders.

Quantum detection of CP violation in the

t\bar{t}

system: production

We investigate how possible new CP-violating top-quark interactions are encoded in the quantum state of a produced

t\bar t

pair. We derive analytic expressions for the production density matrix in several benchmark channels relevant to hadron, lepton and photon colliders. In a common spin basis, we identify two characteristic CP-odd structures in the Fano--Bloch decomposition: a difference between the top and antitop polarisation vectors and an antisymmetric component of the spin-correlation matrix. We construct observables that directly probe these structures and study how quantum information measures, including discord, concurrence, magic and trace distance, respond to CP-even and CP-odd SMEFT contributions. Finally, using current measurements and future collider projections, we assess the sensitivity of these observables to possible new sources of CP violation in top-quark production. This establishes the production-level framework whose experimental reconstruction is developed in a companion paper.

\chi ^{2}

statistic will be a global minimum: There are no isolated local minima. This property with an automated implementation of positivity promises to mitigate issues relating to multiple minima and convention dependence that have been problematic in previous work on angular distributions.