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arXiv:1808.03990 · Physical review. D/Physical review. D.

Entanglement harvesting in double-layer graphene by vacuum fluctuations in a microcavity

Juan Sebastián Ardenghi

Published Aug 8, 2018• 19 citations
arXivHTMLPDF

Abstract

The aim of this work is to study the entanglement harvesting between two graphene layers inside a planar microcavity. Applying time-dependent perturbation theory it is shown that nonclassical correlations between electrons in different layers are obtained through the exchange of virtual photons. Considering different initial states of the electrons and the vacuum state of the electromagnetic field, the negativity measure that quantifies the entanglement is computed through the photon propagator for time scales smaller than the light-crossing time of the double layer. The results are compared with those obtained for hydrogenic probes and pointlike Unruh-DeWitt detectors, showing that for different initial states, entangled $X$ states and more general entangled reduced matrices are obtained, which enlarge the classification of bipartite quantum states.

DOI
10.1103/physrevd.98.045006

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The aim of this work is to study the entanglement harvesting between two graphene layers inside a planar microcavity. Applying time-dependent perturbation theory it is shown that nonclassical correlations between electrons in different layers are obtained through the exchange of virtual photons. Considering different initial states of the electrons and the vacuum state of the electromagnetic field, the negativity measure that quantifies the entanglement is computed through the photon propagator for time scales smaller than the light-crossing time of the double layer. The results are compared with those obtained for hydrogenic probes and pointlike Unruh-DeWitt detectors, showing that for different initial states, entangled XXX states and more general entangled reduced matrices are obtained, which enlarge the classification of bipartite quantum states.
Abstract We analyze the entanglement generation of a system composed of two decoupled rotated graphene layers inside a planar microcavity. By considering the electromagnetic field of the cavity in the vacuum state and using time-dependent perturbation theory it is possible to obtain the range of geometric parameters at which the quantum states of electrons in different layers are entangled. By employing the negativity measure, correlations between layers are obtained for time scales smaller than the light-crossing time of the layers. It is shown that the negativity measure is modulated by the rotation angle between layers, allowing manipulation of X states. Finally, an experimental protocol is analyzed in order to detect non-causal effects between layers, by allowing back-voltage switching functions in the two layers with supports that do not overlap in time. By turning off the second-back voltage at a time smaller than the light-crossing time, it is possible to obtain correlations between layers through the independent interaction with virtual photons. The exchange of virtual photons implies that the propagator can be nonzero outside the light cone and this non-causal propagation can create entangled quantum states.
We study the entanglement harvesting between two identical buckled honeycomb lattices placed inside a planar microcavity. By applying time dependent perturbation theory, we obtain quantum correlations between both layers induced by the cavity field. Considering the vacuum state as the initial state of the cavity field and tracing out the time-evolved degrees of freedom, we analyze the entanglement formation using the concurrence measure. We show that the concurrence depends on the virtual photon exchanged and the positions of the layer through the interlayer photon propagator. Furthermore, we find that the formation of entanglement between equal energy electrons tends to be enhanced when they move in perpendicular directions. Our results indicate that a buckled honeycomb structure and a large spin-orbit interaction favor the entanglement harvesting.
We examine the non-Markovian dynamics and the generation of quantum coherence and entanglement within a triple-layer graphene (TLG) system embedded in a planar microcavity. Using time-dependent perturbation theory, we derive an exact analytic solution for the system and demonstrate how the confined electromagnetic field mediates quantum correlations between the graphene layers. We employ three complementary measures; the relative entropy of coherence (REC) to quantify quantum coherence, the tangle to assess tripartite entanglement, and a non-Markovianity measure derived from the REC to characterize quantum memory effects. Our analysis reveals that these quantum resources exhibit remarkable sensitivity to various control parameters. Specifically, we demonstrate that the number of cutoff modes, the spatial positioning of the layers, the momentum parameter, and the interlayer rotation angles provide effective control over coherence, entanglement, and memory effects. We further show that these measures exhibit an exceptional sensitivity to the rotation angle between the layers. Ultimately, our results establish cavity-confined TLG as a highly tunable platform for exploring vacuum-mediated quantum phenomena, providing a framework for the precise manipulation of quantum correlations in graphene-based photonic and optoelectronic devices.
So far, entanglement harvesting has been extensively studied in free space setups. Here, we provide a detailed analytical and numerical analysis of entanglement harvesting in cavities. Specifically, we adiabatically couple the quantized electromagnetic field to two identical Gaussian detectors located on the symmetry axis of a cylindrical cavity. Our numerical investigations reveal a strong dependence on the cavity length, while showing invariance under changes in the cavity radius in regimes of maximal entanglement. Moreover, we identify different scalings of the detector system parameters for entanglement inside and outside the light cone. Finally, we uncover a strong dependence of the harvested correlations on the cavity induced parity of the electromagnetic field.
It is a well-known fact that, in recent times, entanglement harvesting from the quantum field is being rigorously investigated further in flat and different curved backgrounds. The usually understood formulation studies the possibility of two uncorrelated Unruh-DeWitt detectors getting entangled over time due to the effects of quantum vacuum fluctuations. Our current work presents a thorough formulation to realize the entanglement harvesting from nonvacuum background fluctuations. In particular, we further consider single excitation field states and a pair of inertial detectors, respectively, in (1+11+11+1) and (1+31+31+3) dimensions for this investigation. Our main observation asserts that entanglement harvesting is suppressed compared to the vacuum fluctuations in this situation. Our other observations confirm a nonzero individual detector transition probability in this background and vanishing entanglement harvesting for parallel comoving detectors. We look into the characteristics of the harvested entanglement and discuss its dependence on different system parameters.
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.