Entangled two-proton emission from 16Ne and its sensitivity to diproton correlation

Abstract

We discuss how the spin correlation, which reflects the quantum entanglement between two fermions, can serve as a probe of diproton correlation in the two-proton ($2p$) emission. We investigated the 16Ne nucleus using the time-dependent three-body (14O + 2p) model, and found that the $2p$-spin correlation exceeded the limit of local-hidden-variable (LHV) theory when the initial state had a spin-singlet diproton configuration. In contrast, for other configurations, it was remarkably reduced. This suggests that a strong initial diproton correlation is essential to generate a spin correlation nearly identical to that of a pure spin-singlet diproton. Such sensitivity indicates that $2p$-spin correlation can serve as a sensitive probe of diproton configurations, which could facilitate future studies on quantum entanglement and spin-dependent phenomena in atomic nuclei as well as in broader multi-fermion systems.

Figures (6)

• Figure 1: Spin correlation of the pure $S_{12}=0$ and spherical $S_{12}=1$ states. The limit of LHV theory reads $S(\Phi) =2$1969CHSH.
• Figure 2: Density distribution of $2p$ state at $t=0$ for $^{16}$Ne. For convention of plotting variables, see Refs. 2014Oishi2017Oishi2023Pfutzner_rev. Same distributions in the sequential and angular-symmetric cases are also plotted.
• Figure 3: Decaying probability $P_{\rm decay} (t)$ from the diproton-dominant initial state of $^{16}$Ne. The $S_{12}=0$ ratio is also plotted. Same results in the sequential and angular-symmetric cases are compared. Note that their time scales are different.
• Figure 4: (Top) Spin correlations $S(\Phi = \pi /4)$ calculated for the time-dependent decaying states of $^{16}$Ne. In the sequential case, its time is scaled by $10$, due to the short life time. (Bottom) $S(\Phi)$ evaluated when $P_{\rm decay} (t) \cong 0.0068$.
• Figure 5: Time-dependent decaying-density distributions in the $2p$ emission of $^{16}$Ne. See Ref. 2025Oishi_16Ne for plotting methods.