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.
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.
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.
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.
This study investigates the emergency effects of coupling two superconducting-charge-qubits on thermal equilibrium nonlocality behaviors, including Bell inequality violation (BIV) nonlocality and uncertainty-induced (UI) quantum nonlocality beyond logarithmic negativity entanglement (LN entanglement). Thermal entangled two superconducting-charge-qubits states can exhibit UI-quantum nonlocality without BIV nonlocality, highlighting the hierarchical relationship between these resources. Increasing Josephson-qubit energies enhances resistance to degradation at high temperatures. Large differences in Josephson-qubit energies amplify the degradation temperature for nonlocalities. Coupling of the two qubits improves robustness, preservation, and thermal interval of maximal and partial nonlocalities. The temperatures for sudden death of entanglement depend on Josephson qubit energies, their difference, and mutual coupling. Finally, we explore the symmetrical dependence of thermal two superconducting-qubit nonlocality on Josephson-qubit energies and mutual qubit coupling.
Abstract In this paper, we address the dynamics of nonclassical correlation, quantified by local quantum uncertainty (LQU) in a two-qubit system subjected to classical environmental noise when the initial states of system are prepared in a specific class of Bell states. Two different configurations of the local noisy environment are examined. In the first case, we consider a system of two independently qubits, each locally interacting with its classical random noise, whereas in the second case we consider only one of qubits subject to a classical random noise. Our results show that the dynamics of LQU is strongly related to both the dephasing and relaxation factors. The behaviors of LQU in above two cases exhibit similar variation, with monotonic decay in the weak coupling region, while revivals in the strong coupling region depending on the ratio of the switching rate and coupling strength to the qubit. By controlling this ratio, long-time survival of LQU is obtained. Therefore, our results may open an interesting perspective in using of the long-time survival of quantum correlations for practical applications in quantum information science.
This study examines the influence of temperature and Josephson energy on the quantum properties of superconducting qubits, specifically Bell non-locality and quantum coherence. Our results demonstrate that increasing temperature induces a degradation of both of these essential properties for quantum computing. In contrast, Josephson energy is revealed to be an adjustable parameter allowing for the modulation of non-locality and coherence. However, we observe a trade-off in the simultaneous optimization of these two quantum resources via Josephson energy. This study underscores the crucial importance of thermal control and precise engineering of qubit parameters for the development of high-performance and robust superconducting quantum technologies.
The generated nonlocal correlations of two superconducting-charge (SCC) qubits including uncertainty-induced nonlocality (UIN), Bell-Horodecki nonlocality, and negativity’s entanglement have been explored by intrinsic decoherence model. An initial separable two SCC-qubits state to study the generation of nonlocal correlations. By adjusting the intrinsic decoherence intensity and the two superconducting-qubits interaction parameters (of Josephson energies, the mutual two SCC-qubits coupling energy, and the difference between the Josephson SCC-qubit energies), we can control the produced maximum Bell-Horodecki nonlocality, UIN, and entanglement, which their dynamics align with the hierarchy principle. It is found that the generations of two-qubit states, having Bell-Horodecki nonlocality, UIN, and negativity entanglement, by the interactions of two SCC-qubits depend on their interaction parameters and intrinsic decoherence. For weak mutual two SCC-qubits coupling energy and the Josephson SCC-qubit energies with a slight difference between the Josephson SCC-qubit energies, the generated two SCC-qubit state has strong nonlocal correlation dynamics. The mutual coupling energy for two SCC-qubits can enhance the generation of weak nonlocal correlation dynamics when there is a significant difference between the Josephson SCC-qubit energies. Controlling Josephson energy, mutual coupling, and the energy difference of SCC-qubits can improve nonlocal correlations’ robustness against intrinsic decoherence.