Contextuality from the vacuum

TL;DR

The paper addresses whether contextuality can be harvested from the quantum vacuum by locally coupling two qutrit Unruh–DeWitt detectors to a massless scalar field in flat spacetime. It develops a relativistic quantum information protocol using Gaussian switching and spherical smearing to compute a two-qutrit state, quantifying contextuality with the contextual fraction $CF$ under Heisenberg–Weyl measurements, and validating the nonclassical resource via discrete Wigner negativity $N(\rho)$. The main results show $CF(\rho_D)>0$ and correlated $N(\rho_A)>0$, with HW detectors often outperforming SU(2) dynamics and two detectors outperforming single-detector magic harvesting, across a range of parameters and spacelike separations. This work situates contextuality as a harvestable resource from the quantum vacuum, linking it to Wigner negativity and offering new avenues for relativistic quantum information processing and quantum-resource engineering.

Abstract

Contextuality, a key resource for quantum advantage, describes systems in which the outcome of a measurement is not independent of other compatible measurements, in contrast to classical hidden-variable descriptions. We investigate the harvesting of contextuality from the vacuum of a quantum field using Unruh-DeWitt detectors. We show that localized interactions with the field can endow initially non-contextual detectors with contextuality with respect to Heisenberg-Weyl measurements, as quantified by contextual fraction. The harvested contextuality correlates with the emergence of Wigner function negativity, in agreement with known equivalences between these notions. Our results show that contextuality is a resource that can be extracted directly from the quantum vacuum and establish contextuality harvesting as a fundamental phenomenon in relativistic quantum information.

Figures (3)

• Figure 1: Contextual fraction (in (a)–(b)) and Wigner negativity (in (c)–(d)) normalized by the coupling constant squared as a function of the product of the detectors' gap and their interaction duration. As compared to the interaction time scale, the detector is "large" in (a) and (c) and "small" in (b) and (d).
• Figure 2: Contextual fraction (a) and Wigner negativity (b) (normalized by the squared coupling constant) as a function of $\Omega T$, both for the SU(2) and for the Heisenberg-Weyl qutrits. The plot is for small detectors in the spacelike regime; note, however, that the Wigner negativity is independent of the distance between the two detectors.
• Figure 3: Contextual fraction (a) and Wigner negativity (b) normalized by the squared coupling constant as a function of the product of the detectors' gap and their interaction duration. Here, instead of fixing $R/T$ and $d/T$, we fix $R\Omega$ and $d\Omega$.