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Communications in Theoretical Physics

Nonclassical correlations in two-dimensional graphene lattices

Hao Wang

Published Feb 26, 2024• 5 citations
Publisher

Abstract

Abstract We investigate nonclassical correlations via negativity, local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) for two-dimensional graphene lattices. The explicitly analytical expressions for negativity, LQU and LQFI are given. The close forms of LQU and LQFI confirm the inequality between the quantum Fisher information and skew information, where the LQFI is always greater than or equal to the LQU, and both show very similar behavior with different amplitudes. Moreover, the effects of the different system parameters on the quantified quantum correlation are analyzed. The LQFI reveals more nonclassical correlations than LQU in a two-dimensional graphene lattice system.

DOI
10.1088/1572-9494/ad2d51

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Abstract Many measures of quantum correlations have been introduced so far, and now their properties are carefully studied both theoretically and experimentally. The most important among them are quantum entanglement and quantum discord. Recently, it was shown that the Wigner–Yanase skew information and quantum Fisher information also can serve as measures of nonclassical correlations. These discordlike measures are called local quantum uncertainty (LQU) and interferometric power or local quantum Fisher information (LQFI), correspondingly. In this paper the behavior of LQU and LQFI is considered at thermal equilibrium of the two-qubit Heisenberg models in the absence and presence of an external magnetic field; these cases correspond to the Bell-diagonal and general X states, respectively.
This research delves into the influence of intrinsic decoherence on the behavior of quantum correlations and coherence between two interacting qubits in a graphene-based system. To evaluate the amount of nonclassical correlations in the system, we employ local quantum uncertainty (LQU), and to assess quantum coherence we use the relative entropy of coherence [Formula: see text] and [Formula: see text]-norm [Formula: see text]. We assume that the system is initially prepared in an extended-Werner-like (EWL) state, and we investigate how these quantifiers evolve over time and examine their sensitivity to various graphene layer system parameters, mixture parameter of the initial state and the intrinsic decoherence rate. Our results indicate that by adjusting the wave number operators, decreasing the intrinsic decoherence rate, and increasing the initial state mixing parameter, it is possible to enhance both quantum correlations and coherence within the two-dimensional honeycomb lattice system. In addition, we found that quantum coherence is more resilient to intrinsic decoherence than LQU, moreover, the [Formula: see text]-norm is more robust than the relative entropy of coherence.
Abstract This study explores the dynamic evolution of non-classical correlations and coherence within a two-dimensional graphene layer, examining its vulnerability to intrinsic decoherence. We use local quantum uncertainty (LQU) to quantify the level of quantum correlations, while assessing quantum coherence using the l1l_1l1​ l 1 -norm ( Cl1C_{l_1}Cl1​​ C l 1 ) and relative entropy of coherence ( CrC_rCr​ C r ). We investigate how these quantum estimators respond to various parameters of the graphene system, including wavenumber operators, the initial-state mixing parameter, and intrinsic decoherence factor. Our results demonstrate that adjusting the wavenumber operators, increasing the purity parameter, and reducing the intrinsic decoherence rate can enhance both quantum coherence and correlations in the graphene layer system. Furthermore, we observe that Cl1C_{l_1}Cl1​​ C l 1 and CrC_{r}Cr​ C r exhibit greater resilience to intrinsic decoherence compared to LQU.
We derive the compact closed forms of local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) for hybrid qubit-qutrit axially symmetric (AS) states. This allows us to study the quantum correlations in detail and present some essentially novel results for spin-(1/2, 1) systems, the Hamiltonian of which contains ten independent types of physically important parameters. As an application of the derived formulas, we study the behavior of these two quantum correlation measures at thermal equilibrium. New features are observed in their behavior that are important for quantum information processing. Specifically, cascades of sudden changes in the behavior of LQU and LQFI are found with a smooth change in temperature or interaction parameters. Interestingly, in some cases, sudden transitions are observed in the behavior of LQU but not in LQFI, and vice versa. Moreover, our compact formulas open a way to apply them to other problems, for instance, when investigating the environmental effects on quantum correlations in open systems.
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In this paper, a two-spin-1/2 particle coupled via dipolar interaction with the interplay of antisymmetric Dzyaloshinskii–Moriya and symmetric Kaplan–Shekhtman–Entin–Wohlman–Aharony interactions is considered at thermal equilibrium. The local quantum uncertainty and local quantum Fisher information are investigated as the pairwise nonclassical correlations quantifiers. The effects of the different system parameters on the quantified quantum correlation are analyzed in detail. Our results showed that the two studied thermal quantum correlation measures have similar qualitative behavior as well as quantitative sometimes. Also, it is shown that the quantumness of correlations is lost as the temperature rises sufficiently. Nevertheless, the antisymmetric and symmetric contributions of spin-orbit coupling considerably improve the amount of quantum correlations. Our analysis emphasized also that the local quantum uncertainty is bounded by local quantum Fisher information.