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Physica Scripta

Work extraction, dynamics of quantum coherence and quantum correlations between two superconducting qubits

Elhabib Jaloum, Mohamed Amazioug

Published Apr 25, 2025• 8 citations
Publisher

Abstract

Abstract We investigate quantum coherence, quantum correlations (steering, entanglement, and geometric quantum discord (GQD)), and quantum thermodynamics between two superconducting qubits, examining both steady and dynamical states. Our findings reveal that GQD is more robust to thermal effects than entanglement, which surpasses steerability in robustness. We also show that quantum correlations are more sensitive to thermal noise than coherence. The impact of coupling and Josephson energies on these quantum properties is analyzed. Moreover, we investigate these resources in Markovian and in non-Markovian regimes. Finally, we discuss and compare the extracted work and efficiency in relation to quantum coherence and correlations, focusing on the influence of thermal noise, Josephson energy, and coupling energy.

DOI
10.1088/1402-4896/add0f2

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Abstract We investigate quantum coherence, quantum correlations (steering, entanglement, and geometric quantum discord (GQD)), and quantum thermodynamics between two superconducting qubits, examining both steady and dynamical states. Our findings reveal that GQD is more robust to thermal effects than entanglement, which surpasses steerability in robustness. We also show that quantum correlations are more sensitive to thermal noise than coherence. The impact of coupling and Josephson energies on these quantum properties is analyzed. Moreover, we investigate these resources in Markovian and in non-Markovian regimes. Finally, we discuss and compare the extracted work and efficiency in relation to quantum coherence and correlations, focusing on the influence of thermal noise, Josephson energy, and coupling energy.
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We investigate the interplay between quantum thermodynamics, quantum correlations, and quantum coherence within the framework of the Unruh-DeWitt (UdW) detector model. By analyzing both the steady and dynamical states of various quantum resources (including steerability, entanglement, quantum discord, and coherence), we study how these resources evolve under Markovian and non-Markovian environments. Furthermore, we investigate the impact of both the Unruh temperature and the energy levels on three key quantum phenomena: thermodynamic evolution, quantum correlations, and quantum coherence, considering different initial state preparations. The hierarchical structure relating quantum correlations and quantum coherence is determined. We further examine the thermodynamic performance of a quantum heat engine, highlighting the influence of memory effects and classical correlations on heat exchange, work extraction, and efficiency. Our results reveal that non-Markovian dynamics can enhance the preservation of quantum correlations and improve the engine's efficiency compared to purely Markovian regime. These findings provide insights into the role of quantum correlations and quantum coherence in quantum thermodynamic processes and open avenues for optimizing quantum devices operating in relativistic or open-system settings.
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Coherence arises from the superposition principle, where it plays a central role in quantum mechanics. In Phys. Rev. Lett. 114, 210401 (2015), it has been shown that the freezing phenomenon of quantum correlations beyond entanglement is intimately related to the freezing of quantum coherence (QC). In this paper, we compare the behavior of entanglement and quantum discord with quantum coherence in two different subsystems (optical and mechanical). We use respectively the entanglement of formation (EoF) and the Gaussian quantum discord (GQD) to quantify entanglement and quantum discord. Under thermal noise and optomechanical coupling effects, we show that EoF, GQD and QC behave in the same way. Remarkably, when entanglement vanishes, GQD and QC remain almost unaffected by thermal noise, keeping nonzero values even for high-temperature, which is in concordance with Phys. Rev. Lett. 114, 210401 (2015). Also, we find that the coherence associated with the optical subsystem is more robust — against thermal noise — than those of the mechanical subsystem. Our results confirm that optomechanical cavities constitute a powerful resource of QC.
We investigate the time evolutions of purity, coherence and entanglement in two superconducting qubits coupled through Josephson junctions. The system is modeled by coupling strength, energy, Josephson energy and phase difference. Meanwhile, the structure is under the action of thermal field and classical Ornstein–Uhlenbeck (OU) noise. According to our findings, quantum correlations are notably developed governed by the system parameters. Purity and entanglement generally increase for the energetic qubit regimes. The state’s entanglement and purity degrade with increased coupling strength and temperature. On the other hand, the optimal preservation of quantum correlations reqires the adjustment to intermediate Josephson energies ([Formula: see text]) and phase differences ([Formula: see text]). The coherence measurement shows completely opposite traits compared to the entanglement and purity in the system. These results reveal that quantum states need proper parametrization for the considered state while providing optimization for the higher performance of superconducting qubits in quantum information processing.
We analyze the dynamics of both entanglement and quantum discord (QD) in a system of two non-interacting flux-qubits initially prepared in a Bell's state and subjected to either static or random telegraph noises (RTNs). Both independent and common sources of system-environment coupling are considered either in the Markovian or non-Markovian regime and the results are compared to those of ordinary qubits. Under suitable conditions, both entanglement and QD are more robust in flux-qubit systems than classical ones. In the Markovian regime where the decay is monotonic, they are both stronger in different environment coupling than in common coupling, while the opposite is found in the non-Markovian regime where the dynamics is stressed by sudden death and revival phenomena, more robust in qubits than in flux-qubits under dynamical RTN. Weakness of revival amplitudes is interpreted as a noise spectrum-related induced interaction affecting quantum features of the system, while energy level non-degeneracy (at zero-splitting) of flux-qubits induces a phase factor that set conditions under which entangled states can be experimentally witnessed in flux-qubit systems. Note that the energy levels non-degeneracy has no particular effect on other entanglement measures apart from entanglement witnesses.