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  • Open Access

Quantum simulation of strong charge-parity violation and the Peccei-Quinn mechanism

Le Bin Ho*

  • Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan and Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

  • *Contact author: binho@fris.tohoku.ac.jp
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Phys. Rev. D 113, 074507 – Published 9 April, 2026

DOI: https://doi.org/10.1103/yx1t-mkgp

Abstract

Quantum chromodynamics (QCD) admits a topological θ¯ term that violates charge-parity (CP) symmetry, yet experiments indicate that θ¯ is extremely small. To investigate this problem in a controlled setting, we derive a Hamiltonian formulation of QCD through a (1+1)-dimensional Schwinger-model analog. Fermionic and gauge degrees of freedom are encoded into qubits using Jordan-Wigner and quantum-link mappings, yielding a compact Pauli Hamiltonian that preserves the essential topological vacuum structure. Ground states are prepared using a feedback-based quantum optimization protocol, providing access to the vacuum energy on few-qubit simulators. We observe vacuum minima at θ¯=0 and 2π, consistent with the continuum QCD expectations within the accessible regime. Upon coupling to a dynamical axion field, the system relaxes to θeff=0, realizing the Peccei-Quinn mechanism within a minimal quantum simulation. These results demonstrate how quantum simulation can probe CP violation and its dynamical resolution in gauge theories.

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Phys. Rev. D 113, 074507– Published 9 April, 2026
  • Received 15 January 2026
  • Accepted 23 March 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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