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Azimuthal angular entanglement between decaying particles in ultra-peripheral ion collisions

Spencer R. Klein

Abstract

Ultra-peripheral collisions (UPCs) involving relativistic heavy ions are a unique laboratory to study quantum correlations. The intense electromagnetic fields generate high rates of photonuclear interactions, including events involving multiple photon exchange. Multiple photon exchange can result in the production of multiple vector mesons and/or nuclear excitations. These interactions share a common impact parameter, so the photons have the same linear polarization. The shared polarization entangles the particles, leading to unique quantum correlations. The decays of these vector excitations are sensitive to this polarization, allowing for the study of these correlations. This letter will compare classical and quantum calculations of the correlations between these azimuthal directions. The two approaches predict vert different angular correlations. The differences are akin to those seen with polarized photons in tests of Bells inequality. Uniquely, UPC photoproduction can produce final states containing three or more particles, all entangled with the same polarization. These more complex states exhibit additional unique phenomenology, allowing new tests of multi-particle entanglement.

Azimuthal angular entanglement between decaying particles in ultra-peripheral ion collisions

Abstract

Ultra-peripheral collisions (UPCs) involving relativistic heavy ions are a unique laboratory to study quantum correlations. The intense electromagnetic fields generate high rates of photonuclear interactions, including events involving multiple photon exchange. Multiple photon exchange can result in the production of multiple vector mesons and/or nuclear excitations. These interactions share a common impact parameter, so the photons have the same linear polarization. The shared polarization entangles the particles, leading to unique quantum correlations. The decays of these vector excitations are sensitive to this polarization, allowing for the study of these correlations. This letter will compare classical and quantum calculations of the correlations between these azimuthal directions. The two approaches predict vert different angular correlations. The differences are akin to those seen with polarized photons in tests of Bells inequality. Uniquely, UPC photoproduction can produce final states containing three or more particles, all entangled with the same polarization. These more complex states exhibit additional unique phenomenology, allowing new tests of multi-particle entanglement.
Paper Structure (9 equations, 2 figures)

This paper contains 9 equations, 2 figures.

Figures (2)

  • Figure 1: (top) The geometry for UPC photoexcitation to a giant dipole resonance (GDR) state. At closest approach, the two nuclei ("A") are separated by $\vec{b}$. One of them emits a photon $\gamma$ with polarization $\vec{E}$ parallel to $\vec{b}$ which strikes the other nucleus, exciting it to a GDR, which then decays, emitting a single neutron ("n"). Perpendicular to the beam direction, the neutron makes an angle $\theta$ with respect to $\vec{b}$. (bottom) The geometry for UPC photoproduction of a $\rho^0$ (in red), almost immediately followed by its decay to $\pi^+\pi^-$.
  • Figure 2: Comparison of the classical-calculation and quantum-calculation azimuthal angular distributions for two vector particles produce in a single UPC interaction.