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arXiv:2602.10203

Cosmological Expansion Induces Interference Between Communication and Entanglement Harvesting

Matheus H. Zambianco, Adam Teixidó-Bonfill, Eduardo Martín-Martínez

quant-phgr-qchep-thSubmitted Feb 10, 2026• Announced Feb 12, 2026

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.

Journal reference: Phys. Rev. D 113, 085023 (2026)
DOI: 10.1103/vfb8-3z93
Comments: 14 pages, 7 figures, 1 appendix

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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.

We revisit the entanglement harvesting protocol when two detectors are in causal contact. We study the role of field-mediated communication in generating entanglement between the two detectors interacting with a quantum field. We provide a quantitative estimator of the relative contribution of communication versus genuine entanglement harvesting. For massless scalar fields in flat spacetime, we show that when two detectors can communicate via the field, the detectors do not really harvest entanglement from the field, and instead they get entangled only via the field-mediated communication channel. In other words, in these scenarios the entanglement harvesting protocol is truly ``harvesting entanglement'' from the field only when the detectors are not able to communicate. In contrast, for massive scalar fields both communication and genuine harvesting contribute equally to the bipartite entanglement when the detectors are causally connected. These results emphasize the importance of taking into account the causal relationships between two parties involved in this relativistic quantum information protocol before we can declare that it is truly entanglement harvesting.

We study entanglement harvesting in general

d

-dimensional conformal field theories using pointlike Unruh-DeWitt detectors coupled to scalar primary operators. This extends standard harvesting protocols beyond free fields to interacting conformal theories and arbitrary spatial dimensions. We find that increasing the operator scaling dimension suppresses both negativity and mutual information, reflecting the faster decay of correlations. For holographic CFTs, we show that bulk effective field theory enables a separation between field-harvested and communication-mediated entanglement. We also derive asymptotic, closed-form approximations that agree well with numerical results.

A quantum communication protocol between harmonic oscillator detectors, interacting with a quantum field, is developed in a cosmological expanding background. The aim is to see if the quantum effects arising in an expanding universe, such as the cosmological particle production, could facilitate the communication between two distant parts or if they provide an additive noisy effect. By considering a perfect cosmic fluid, the resulting expansion turns out to increase the classical capacity of the protocol. This increasing occurs for all the cosmological expansions unless the latter is sharpened just before the receiver's detector interacts with the field. Moreover, the classical capacity turns out to be sensible to the barotropic parameter

w

of the perfect fluid and to the coupling between the field and the scalar curvature $\ensuremath{\xi}$. As a consequence, by performing this protocol, one can achieve information about the cosmological dynamics and its coupling with a background quantum field.

We consider Unruh–Wald qubit detector model adopted for the far future region of an exactly solvable

1+1

dimensional scalar field theory in a toy model of Robertson–Walker expanding spacetime. It is shown that the expansion of the spacetime in its history enhances the decoherence of the qubit coupled with a scalar field. Moreover, we consider two entangled qubits, each locally coupled with a scalar field. The expansion of the spacetime in its history degrades the entanglement between the qubits, and it can lead to entanglement’s sudden death if the initial entanglement is small enough. The details depend on the parameters characterizing the expansion of the spacetime. This work, on a toy model, suggests that the history of the spacetime might be probed through the coherent and entanglement behavior of the future detectors of quantum fields. In the present toy model, the two cosmological parameters can be determined from the quantum informational quantities of the detectors.