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Laser Physics

Quantum correlations and thermal coherence in a two-superconducting charge qubit system

Mourad Benzahra, Mostafa Mansour, Mansoura Oumennana, Samira Elghaayda

Published May 23, 2023• 20 citations
Publisher

Abstract

Abstract Superconducting charge qubits represent a cutting-edge technology in the field of quantum computing, offering a promising platform for quantum processing. This study delves into the behaviors of thermal coherence and quantum correlations within a two-superconducting charge qubit system coupled by a fixed capacitance. Specifically, we investigate the effects of thermal noise on entanglement (measured by concurrence), nonclassical correlations (quantified by local quantum uncertainty), and quantum coherence (measured by correlated coherence) within the two-superconducting charge qubit capacitively coupled. Our analysis takes into account the interplay between the equilibrium temperature of the reservoir and various system parameters. Our findings demonstrate that an increase in temperature leads to a decrease in coherence and quantum correlations within the considered system. However, the behavior of these quantum resources is heavily dependent on the system parameters, and a careful selection of these parameters can help mitigate the negative effects of absolute temperature. Additionally, we observe that local quantum uncertainty and correlated coherence are more resilient than thermal entanglement to rising temperatures. These results provide insight into how a two-superconducting charge qubit system can be optimized for achieving quantum advantages.

DOI
10.1088/1555-6611/acd4ae

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Abstract Superconducting charge qubits represent a cutting-edge technology in the field of quantum computing, offering a promising platform for quantum processing. This study delves into the behaviors of thermal coherence and quantum correlations within a two-superconducting charge qubit system coupled by a fixed capacitance. Specifically, we investigate the effects of thermal noise on entanglement (measured by concurrence), nonclassical correlations (quantified by local quantum uncertainty), and quantum coherence (measured by correlated coherence) within the two-superconducting charge qubit capacitively coupled. Our analysis takes into account the interplay between the equilibrium temperature of the reservoir and various system parameters. Our findings demonstrate that an increase in temperature leads to a decrease in coherence and quantum correlations within the considered system. However, the behavior of these quantum resources is heavily dependent on the system parameters, and a careful selection of these parameters can help mitigate the negative effects of absolute temperature. Additionally, we observe that local quantum uncertainty and correlated coherence are more resilient than thermal entanglement to rising temperatures. These results provide insight into how a two-superconducting charge qubit system can be optimized for achieving quantum advantages.
This study investigates the progression of thermal entanglement and quantum coherence in a system composed of two superconducting charge qubits connected through a fixed capacitor. Superconducting materials play a central role in modern quantum technologies due to their ability to sustain coherent states over long timescales, making them an ideal platform for quantum information processing. We employ metrics such as logarithmic negativity and relative entropy of coherence to precisely evaluate these quantum resources. In particular, we analyze how thermal noise affects entanglement and quantum coherence in this capacitively coupled system. A central aspect of this work is the interaction between the reservoir's temperature at equilibrium and various intrinsic parameters of the system. The results show that increasing temperature leads to a gradual degradation of entanglement and coherence. However, these quantum resources are highly sensitive to system variables, and careful tuning of these variables can reduce the harmful impact of absolute temperature. These findings offer promising perspectives for optimizing two-qubit superconducting charge systems, with the aim of enhancing their robustness and fully exploiting the advantages offered by quantum technologies.
By considering the local quantum uncertainty (LQU) as a measure of quantum correlations, the thermal evolution of a two-qubit-superconducting system is investigated. We show that the thermal LQU can be increased by manipulating the Hamiltonian parameters such as the mutual coupling and Josephson energies, however, it undergoes sudden transitions at specific temperatures. Furthermore, a detailed analysis is presented regarding the impact of decohering channels on thermal LQU. This controllable LQU in engineering applications can disclose the advantage enabled in the superconducting charge qubits for designing quantum computers and quantum batteries.
We investigate thermal quantum correlations in a system of two coupled superconducting spin qubits described by an effective Andreev spin-qubit Hamiltonian in the presence of spin-orbit interaction. Using Local Quantum Fisher Information (LQFI) and Local Quantum Uncertainty (LQU) as quantum-correlation quantifiers, we analyze the effects of the superconducting phase difference, tunneling amplitude, spin-orbit coupling, and temperature on the nonclassical properties of the system. Analytical expressions for the thermal density matrix are obtained and employed to evaluate both quantities. Our results show that quantum correlations decrease monotonically with increasing temperature, while stronger tunneling and spin-orbit interaction significantly enhance their robustness. Moreover, the superconducting phase introduces a pronounced periodic behavior through the modulation of the effective exchange couplings, leading to constructive and destructive interference regimes that strongly influence the correlations. By analyzing the energy spectrum of the effective Hamiltonian, we demonstrate that the enhancement of quantum correlations is closely associated with an increased energy gap between the ground and first excited states, which suppresses thermal excitations and stabilizes the correlated ground state. Furthermore, LQFI is consistently larger than LQU throughout the investigated parameter space, reflecting its higher sensitivity to quantum fluctuations and local parameter estimation. These findings reveal the microscopic mechanism governing thermal quantum correlations in Andreev spin qubits and highlight the important roles of phase engineering, spin-orbit interaction, and tunneling in protecting quantum resources in hybrid superconducting quantum devices.
Abstract This study explores the dynamics of a two-qubit superconducting charge system, a prevalent technology in quantum computing. We utilize logarithmic negativity and local quantum Fisher information to gauge the entanglement and correlations within this system. Our findings indicate a significant influence of temperature on the system, leading to a reduction in both measures. However, adjusting system parameters can enhance these quantum quantifiers. Furthermore, we note that the local quantum Fisher information exhibits greater resilience to temperature-induced degradation compared to logarithmic negativity.
Abstract In this work, the thermal quantum correlations in two coupled double semiconductor charge qubits are investigated. This is carried out by deriving analytical expressions for both the thermal concurrence and the correlated coherence. The effects of the tunneling parameters, the Coulomb interaction, and the temperature on the thermal entanglement and on the correlated coherence are studied in detail. It is found that the Coulomb potential plays an important role in the thermal entanglement and in the correlated coherence of the system. The results also indicate that the Coulomb potential can be used for significant enhancement of the thermal entanglement and quantum coherence. One interesting aspect is that the correlated coherence capture all the thermal entanglement at low temperatures, that is, the local coherences are totally transferred to the thermal entanglement. Finally, the role played by thermal entanglement and the correlated coherence responsible for quantum correlations are focused on. It is shown that in all cases, the correlated coherence is more robust than the thermal entanglement so that quantum algorithms based only on correlated coherence may be more robust than those based on entanglement.
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.