Quantum Discord in de-Sitter Axiverse

TL;DR

This work investigates quantum correlations in a string-theory–motivated $3+1$-dimensional de Sitter Axiverse by quantifying quantum discord between causally disconnected regions in an open vs global chart framework. The authors construct the Bunch-Davies vacuum, perform Bogoliubov transformations to relate BD states to open-chart vacua, and compute reduced-density matrices, entanglement negativity, and logarithmic negativity for various mode configurations. A key finding is that increasing open-chart curvature diminishes entanglement, yet quantum discord remains nonzero even when entanglement vanishes, with maximal discord occurring near conformal and massless axion limits and enhanced discord at small momentum. The results illuminate how nonclassical correlations persist in curved spacetime with string-theoretic axions, suggesting robustness of quantum correlations beyond entanglement and potential implications for early-universe cosmology and observational probes. Analytic expressions in limiting cases and detailed constructions of ground, excited, and maximally entangled states underpin the results and point to future exploration in non-Bunch-Davies vacua, decoherence, and squeezed-state dynamics.

Abstract

In this work, we compute quantum discord between two causally independent areas in $3+1$ dimensions global de Sitter Axiverse to investigate the signs of quantum entanglement. For this goal, we study a bipartite quantum field theoretic setting driven by an Axiverse that arises from the compactification of Type IIB strings on a Calabi-Yau three fold. We consider a spherical surface that separates the interior and exterior causally unconnected subregions of the spatial slice of the global de Sitter space. The Bunch-Davies state is the most straightforward initial quantum vacuum that may be used for computing purposes. Two observers are introduced, one in an open chart of de Sitter space and the other in a global chart. The observers calculate the quantum discord generated by each detecting a mode. The relationship between an observer in one of the two Rindler charts in flat space and another in a Minkowski chart is comparable to this circumstance. We see that when the curvature of the open chart increases, the state becomes less entangled. Nevertheless, we see that even in the limit when entanglement vanishes, the quantum discord never goes away.

Figures (8)

• Figure 3.1: Geometry of open chart.
• Figure 3.2: Axion potential with respect to the field obtained from Type IIB String Theory compactification.
• Figure 4.1: Logarithmic negativity (${\cal LN}(\nu)/{\cal LN}(\nu=1/2)$) with mass parameter squared ($\nu^2$) for both $f_p=0$ and small $f_p\neq 0$.
• Figure 4.2: Entanglement negativity (${\cal N}(\nu)/{\cal N}(\nu=1/2)$) with mass parameter squared ($\nu^2$) for both $f_p=0$ and small $f_p\neq 0$.
• Figure 8.1: Logarithmic negativity vs mass parameter for a specified momentum mode.