Magic is the quantum resource allowing a quantum computer to perform operations that cannot be simulated efficiently by classical computation. As such, generating magic in a quantum system is crucial for achieving quantum advantage. This article shows that magic can be harvested by a three-level Unruh-DeWitt detector (a qutrit) interacting with a quantum field in an initial vacuum state. While the idea of extracting resources from Quantum Field Theories (QFT) was born from the harvesting of entanglement, our result extends the protocol to evolve a qutrit from a nonmagical state to a magical one, making it possible to generate magic from QFT.
Magic is the quantum resource allowing a quantum computer to perform operations that cannot be simulated efficiently by classical computation. As such, generating magic in a quantum system is crucial for achieving quantum advantage. This article shows that magic can be harvested by a three-level Unruh-DeWitt detector (a qutrit) interacting with a quantum field in an initial vacuum state. While the idea of extracting resources from Quantum Field Theories (QFT) was born from the harvesting of entanglement, our result extends the protocol to evolve a qutrit from a nonmagical state to a magical one, making it possible to generate magic from QFT.
Magic is a quantum resource characterising quantum advantage. It is required for fault-tolerant application of non-Clifford gates, which may yield algorithms faster than their classical counterparts. Magic generation is therefore a concept of great importance. In this thesis, we present a novel method of generating magic by interaction with bosonic systems. Most notably, we show that it is possible to generate magic by interaction with a quantum scalar field in the vacuum state and with a single quantum harmonic oscillator. This work was inspired by the concept of entanglement harvesting, where two space-like separated probes become entangled when coupled to a quantum field. As a continuation of this, we show that another resource, specifically magic, may also be harvested by interaction with a quantum field. This is done for both a point-like and a spatially smeared detector. As a corollary, we study a simpler case of magic generation using the Jaynes–Cummings model for a qutrit. After presenting the relevant methods for numerical simulations, this interaction is simulated for various initial states and values of the relevant parameters. These simulations demonstrate magic generation to be possible through interaction with a quantum harmonic oscillator as well. We use mana as the resource monotone evaluating the magic of a state. Mana is defined through the negativity of the discrete Wigner function, which is only defined for odd-dimensional systems. Hence, we will employ a quantum system with three levels, a qutrit, to study magic generation of this kind. When considering interaction with a quantum field, this qutrit will function as a three-level Unruh–DeWitt detector.
Quantum contextuality is the notion that certain measurement scenarios do not admit a global description of their statistics and has been implicated as the source of quantum advantage in a number of quantum information protocols. It has been shown that contextuality generalizes the concepts of nonlocal entanglement and magic and is an equivalent notion of nonclassicality to Wigner negativity. In this paper, the protocol of contextuality harvesting is introduced, and it is shown that Unruh-DeWitt models are capable of harvesting quantum contextuality from the vacuum of a massless scalar quantum field. In particular, it is shown that gapless systems can be made to harvest contextuality given a suitable choice of measurements. The harvested contextuality is also seen to behave similarly to harvested magic and can be larger in magnitude for specific parameter regimes. An Unruh-DeWitt qubit-qutrit system is also investigated, where it is shown that certain tradeoffs exist between the harvested contextuality of the qutrit and the harvested entanglement between the systems and that there are regimes where the two resources can both be present. Some of the tools of contextuality, namely the contextual fraction, are also imported and used as general measures for any form of harvested contextuality, including nonlocal entanglement and magic. Additionally, new criteria for genuine harvesting are put forward that also apply to individual systems, revealing new permissible harvesting parameter regimes.
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.
The harvesting of quantum resources from the vacuum state of a quantum field is a central topic in relativistic quantum information. While several proposals for the harvesting of entanglement from the quantum vacuum exist, less attention has been paid to other quantum resources, such as nonstabilizerness, commonly dubbed magic and quantified by the stabilizer R\'enyi entropy (SRE). In this work, we show how to harvest SRE from the vacuum state of a massless field, using accelerated Unruh-DeWitt detectors in Minkowski spacetime. In particular, one can harvest a particular nonlocal form of SRE that cannot be erased by local unitary operations. This nonlocal SRE is a fundamental quantity to study the interplay between entanglement and nonstabilizer resources. We conclude our work with an analysis of the Clauser-Horne-Shimony-Holt inequalities: when restricting to stabilizer measurements, i.e., Pauli measurements, one cannot extract a violation from the quantum field.
Abstract We examine in (2+1)-dimensional anti-de Sitter (AdS) space the phenomena of entanglement harvesting — the process in which a pair of detectors (two-level atoms) extract entanglement from a quantum field through local interactions with the field. We begin by reviewing the Unruh-DeWitt detector and its interaction with a real scalar field in the vacuum state, as well as the entanglement harvesting protocol in general. We then examine how the entanglement harvested by a pair of such detectors depends on their spacetime trajectory, separation, spacetime curvature, and boundary conditions satisfied by the field. The harvested entanglement is interpreted as an indicator of field entanglement between the localized regions where the detectors interact with the field, and thus this investigation allows us to probe indirectly the entanglement structure of the AdS vacuum. We find an island of separability for specific values of the detectors’ energy gap and separation at intermediate values of the AdS length for which entanglement harvesting is not possible; an analogous phenomena is observed in AdS4, to which we compare and contrast our results. In the process we examine how the transition probability of a single detector, as a proxy for local fluctuations of the field, depends on spacetime curvature, its location in AdS space, and boundary conditions satisfied by the field.
Abstract We implement the entanglement harvesting protocol, in which two Unruh–DeWitt detectors become entangled through local interactions with a quantum field, for the first time in the vicinity of a black hole. Our study, focusing on the BTZ black hole, reveals that black holes inhibit entanglement harvesting. For two detectors with fixed proper separation along the radial direction, we demonstrate that the entanglement harvested rapidly falls to zero as the detectors move closer to the horizon. This effect is a combination of black hole radiation and gravitational redshift, both generic properties of horizons, suggesting it is a general result for black holes.