Cosmological Expansion Induces Interference Between Communication and Entanglement Harvesting

TL;DR

This work investigates how spacetime expansion affects entanglement harvesting and communication-mediated correlations for two localized detectors interacting with a conformally coupled massless scalar field in de Sitter spacetime. By decomposing the detector entanglement into harvesting and communication contributions using Wightman function symmetries and Feynman propagators, the authors analyze two detector models: expanding-with-Universe and fixed proper size. They find that cosmological expansion induces nontrivial interference between harvesting and communication, which can suppress entanglement for rapidly expanding (expanding) detectors, while fixed-size detectors can retain significant entanglement under the same conditions. The results reveal that expansion reshapes the balance between harvesting and communication, with detector internal cohesion playing a key role in whether entanglement can persist in expanding universes, and they illuminate the importance of time-reversal symmetry-breaking effects in relativistic quantum information in cosmological backgrounds.

Abstract

We investigate the interplay between genuine entanglement harvesting and communication mediated correlations for local particle detectors in expanding cosmological spacetimes. Focusing on a conformally coupled scalar field in de Sitter spacetime, we analyze how spacetime expansion induces interference between these two sources of entanglement when the detectors are in causal contact. We compare two physically distinct detector models: detectors whose spatial profile expands with the Universe, and detectors whose proper size remains fixed despite cosmological expansion. We find that the lack of time-reversal symmetry in cosmological settings generically leads to constructive or destructive interference between communication mediated correlations and harvested field correlations, dramatically affecting the entanglement that detectors can acquire. In particular, rapid expansion can suppress entanglement entirely for expanding detectors through destructive interference, even when both communication and field correlations are individually large, whereas detectors that maintain a fixed proper size remain capable of acquiring significant entanglement. Our results show that cosmological expansion qualitatively reshapes the balance between communication and harvesting, and that the detector internal cohesion (whether it expands with the Universe or not) plays a crucial role in determining whether detectors' entanglement can survive in rapidly expanding universes.

Figures (7)

• Figure 1: Results for the negativity ($\mathcal{N}$) and communication-assisted negativity ($\mathcal{N}^{-}$) in de Sitter spacetime as a function of the coordinate distance $d$ between the centers of the spatial smearings of the detectors and the time delay $\Delta \eta = \eta(t_{\textsc{b}}) - \eta(t_{\textsc{a}} = 0) = \eta(t_{\textsc{b}})$ between the centers of the switching functions. In plots (a), (b) we use $\Omega T = 4$, whereas in (c), (d) we have $\Omega T = 6$. In all cases, we set $H T = 0.1$, $\sigma/T = 0.1$. The red, dashed-dotted lines represent the light cones described by $\Delta \eta = \pm d$.
• Figure 2: Results for the negativity ($\mathcal{N}$) and communication-assisted negativity ($\mathcal{N}^{-}$) in de Sitter spacetime as a function of the coordinate distance $d$ between the centers of the spatial smearings of the detectors and the time delay $\Delta \eta = \eta(t_{\textsc{b}}) - \eta(t_{\textsc{a}} = 0) = \eta(t_{\textsc{b}})$ between the centers of the switching functions. In plots (a), (b) we use $\Omega T = 4$, and in (c)-(d) we have $\Omega T = 6$. In all cases, we set $\sigma/T = 1$ and $H T = 0.1$. The red, dashed-dotted lines represent the light cones described by $\Delta \eta = \pm d$.
• Figure 3: Negativity $\mathcal{N}$ and its different sources $|\mathcal{M}^{\pm}|$ as a function of the coordinate time delay $\Delta t = t_{\textsc{b}} - t_{\textsc{a}} = t_{\textsc{b}}$ between the detectors, for a fixed energy gap $\Omega T = 6$ and different comoving distances (a) $d/T = 2$ and (b) $d/T = 4$. The solid, vertical yellow lines represent the light cones of detector A emanating from the event $(0, \bm x_{\textsc{a}})$. The pink vertical rectangles on the left denote the region of approximate lightlike communication, with detector B in the past of detector A. Analogously, the blue vertical rectangle on the right denotes the region of approximate lightlike communication, with detector B in the future of detector A. The size of the detectors is taken as $\sigma/T = 0.1$, and the Hubble parameter is $H T = 0.1$.
• Figure 4: Negativity $\mathcal{N}$ and its different sources $|\mathcal{M}^{\pm}|$ as a function of the coordinate time delay $\Delta t = t_{\textsc{b}} - t_{\textsc{a}} = t_{\textsc{b}}$ between the detectors, for a fixed energy gap $\Omega T = 6$ and comoving distance $d/T = 2$, and different Hubble parameters (a) $H T = 0.2$, (b) $H T = 0.3$, and (c) $H T = 0.4$. The solid, vertical yellow lines represent the light cones of detector A emanating from the event $(0, \bm x_{\textsc{a}})$. The pink vertical rectangles on the left denote the region of approximate lightlike communication, with detector B in the past of detector A. Analogously, the blue vertical rectangle on the right denotes the region of approximate lightlike communication, with detector B in the future of detector A. The size of the detectors is taken as $\sigma/T = 0.1$.
• Figure 5: Negativity ($\mathcal{N}$) as a function of the coordinate time delay $\Delta t = t_{\textsc{b}} - t_{\textsc{a}} = t_{\textsc{b}}$ between the detectors, for a fixed energy gap $\Omega T = 6$ and comoving distance $d/T = 2$, and different Hubble parameters $H T \in \{0.1, 0.2, 0.3, 0.4, 0.5\}$. Each column represents a different detector model: in the first column (plot a) we have detectors that expand with the Universe, i.e, detectors with a constant $\sigma$. In the second column (plot b) we consider detectors that keep their size by scaling their effective size according to $\sigma(t) = \sigma/a(t)$. In both scenarios, we fix $\sigma/T=1$.