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Journal of Russian Laser Research

Quantum Coherence and Degree of Mixedness for a System of Two Superconducting Qubits Under Decohe\rence Conditions

Zainab Mufarreh Elqahtani, S. Abdel‐Khalek, K. Berrada

Published Mar 1, 2022• 6 citations
Publisher
DOI
10.1007/s10946-022-10031-8

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In a model consisting of two superconducting charge qubits (SC-Qs), we study how the Josephson energy (JE) and temperature have an influence on the coherence, the degree of mixedness, and the nonclassical correlation. In this example, we show how the quantumness metrics change depending on the JE and the temperature. We also show that the number of quantifiers can be controlled by appropriate selection of the JE of the SC-Q and temperature effect. Additionally, we determine the optimal conditions required to enhance and preserve the coherence and maintain the level of coherence in the existence of temperature variations. We observe important quantum phenomena, i.e., coherence trapping and the quantum correlation trapping. Furthermore, we explain the variations in the coherence based on the degree of mixedness in the superconducting qubit state.
In this work, superposition of spin coherent states composed of two qubits is formed and by calculating the geometric measure of mixing of the system introduced in this work, the degree of mixedness of the studied state is investigated. In the following, the changes in the entanglement of the introduced state are studied by using the negativity measure. Finally, by drawing the appropriate plots, according to the influential parameters in this system, we examine the maximum and the minimum of the changes in the mixedness and entanglement and also their relationship to the mixed system consisting of two-qubit spin coherent states. It was observed that for maximizing α, when the changes of parameters indicate the purity of the state, the entanglement of the system reaches its maximum value for two-qubit systems. Also, for all values of coherence parameter, the entanglement decreases when mixedness of the system increases.
In this paper, we quantitatively examine the dynamics of quantum resources, such as quantum coherence, degree of mixedness, fidelity, and the atomic entropy squeezing, in a quantum system of a two-level atom (TLA) driven by a phase noise laser (PNL) within the context of non-Markovian dynamics. The [Formula: see text] norm is used to quantify coherence, linear entropy to measure the degree of TLA mixedness, and entropy to detect the atomic squeezing. We demonstrate how these quantum resources can be controlled through a suitable selection of model parameters. Furthermore, we provide the optimal conditions required to manipulate these quantum resources based on changes in the damping coupling. Finally, we discuss the relationships among the quantum resources in the present quantum model.