Abstract This theoretical and numerical investigation explores the enhancement and preservation of quantum discord in quantum systems coupled through V-shaped plasmonic waveguides using advanced quantum feedback control techniques. We demonstrate that properly engineered quantum feedback can significantly improve quantum discord preservation, particularly in Werner states where we observe enhancements from zero to 0.38 under optimal conditions. The mechanism involves a sophisticated confinement of the quantum state within protected subspaces that are resilient against environmental decoherence. Through detailed theoretical modeling and extensive numerical simulations, we identified the key parameters governing this enhancement process, including waveguide geometry, emitter positioning, and feedback timing. Our results reveal three distinct quantum discord decay temporal regimes and establish optimal operating conditions for maximal quantum correlation preservation. The findings provide fundamental insights into quantum correlation dynamics in nanophotonic systems and practical guidelines for experimental implementations in quantum information processing applications, with particular relevance to room-temperature quantum technologies.
Abstract This theoretical and numerical investigation explores the enhancement and preservation of quantum discord in quantum systems coupled through V-shaped plasmonic waveguides using advanced quantum feedback control techniques. We demonstrate that properly engineered quantum feedback can significantly improve quantum discord preservation, particularly in Werner states where we observe enhancements from zero to 0.38 under optimal conditions. The mechanism involves a sophisticated confinement of the quantum state within protected subspaces that are resilient against environmental decoherence. Through detailed theoretical modeling and extensive numerical simulations, we identified the key parameters governing this enhancement process, including waveguide geometry, emitter positioning, and feedback timing. Our results reveal three distinct quantum discord decay temporal regimes and establish optimal operating conditions for maximal quantum correlation preservation. The findings provide fundamental insights into quantum correlation dynamics in nanophotonic systems and practical guidelines for experimental implementations in quantum information processing applications, with particular relevance to room-temperature quantum technologies.
Abstract We investigate the impact of a symmetric quantum feedback control on the quantum discord of the X state in V-shaped plasmonic waveguides. Under this feedback, the quantum discord of the Werner state is enhanced from 0 to 0.38. This value even continues to rise after reducing the decay rate of the atoms. Furthermore, we get the operational mechanism of feedback control through the evolution of the matrix elements. It confines the initial 4 × 4 matrix into a 3 × 3 subspace. As a result, the weights of each ground state in the quantum state change, which suppresses the degradation of Bell state. Lastly, we propose a direction for suggesting an improved feedback Hamiltonian.
This theoretical study presents a hybrid quantum system that combines the geometry of a T-shaped plasmonic waveguide with an embedded common cavity and applies quantum feedback control to enhance and preserve quantum discord between two quantum dots (QDs). Building upon previous work on entanglement generation in T-shaped waveguides and feedback-enhanced discord in V-shaped waveguides, we demonstrate that the T-shape geometry with its specific boundary conditions, coupled with active feedback, offers superior control over quantum correlations. The system consists of two QDs placed at strategic positions within the waveguide: one at the node and the other at the end of the finite arm, both embedded in a common cavity. We derive the system's dynamics using a real-space Hamiltonian approach and solve the time-independent Schrödinger equation to obtain scattering amplitudes. Quantum discord is then calculated for the two-QD subsystem. Our results show that by applying symmetric quantum feedback based on Wiseman-Milburn formalism, we can significantly enhance the steady-state quantum discord, achieving values up to [Formula: see text] for Werner states under optimal parameter conditions. We identify three distinct decay regimes for discord and demonstrate that parameters such as the phase accumulation ([Formula: see text], where [Formula: see text] is the plasmon wavevector) along the finite arm, providing cavity-QD couplings ([Formula: see text], [Formula: see text]), detunings ([Formula: see text], [Formula: see text]), and dipole-dipole interaction strength (f) provide multiple control knobs for tuning quantum correlations. This work provides a comprehensive framework for designing actively controlled nanophotonic quantum devices that leverage both plasmonic field enhancement and quantum feedback for robust quantum information processing at room temperature.
Abstract Quantum teleportation fundamentally depends on shared quantum correlations between spatially separated parties. Although entanglement is widely recognized as the primary resource enabling teleportation, quantum discord represents a more general form of nonclassical correlations that can persist even when entanglement is absent. We provide a thorough analysis combining analytical and numerical evaluations of quantum discord, negativity, and concurrence across varying noise parameters. The study includes simulations under both ide-alized and realistic noisy conditions, incorporating depolarizing noise models alongside experimentally relevant constraints. To improve quantum fidelity and accurately characterize quantum correlations in noisy environments, advanced error mitigation techniques—such as measurement error correction and zero-noise extrapolation—are applied. In this study, we focus on teleportation protocols utilizing two-qubit Werner states, which constitute a significant class of noisy mixed states modeling imperfect entanglement. We systematically examine how the teleportation fidelity varies as a function of the Werner mixing parameter λ and investigate its relationship with the corresponding quantum discord. Our findings indicate that quantum discord remains strictly greater than zero even in parameter regions where entanglement vanishes, emphasizing the role of discord in sustaining quantum advantages in teleportation schemes exposed to noise and imperfections. This highlights the importance of considering non-entanglement quantum correlations for a comprehensive understanding of teleportation resources in realistic settings.
Abstract In this present manuscript, we explore the possibility to preserve and manipulate of classical and quantum correlations initially present in a system of qubits, where each qubit is immersed in a cavity that is interacted with another cavity as an engineered environment. We consider the qubit entropy, entanglement of formation, quantum discord, and classical correlation for Markovian and non-Markovian regimes. We find that the correlations can be maintained and enhanced during the dynamics, which is a useful dynamical feature, by adjusting the strength coupling constant between cavities for weak- and strong- coupling regime (W- and S-CR). In particular, we have found that, for the case of perfect cavities, high values of correlations can be achieved during the evolution with respect to the strength coupling between cavities. The obtained results can provide more hints for future studies on the control of correlations with optimal conditions. By a specific selection of the model parameters, long-time preservation of correlations can be achieved without being affected by the decoherence.
This paper studies quantum discord of two qutrits coupled to their own environments independently and coupled to the same environment simultaneously under quantum-jump-based feedback control. Our results show that spontaneous emission, quantum feedback parameters, classical driving, initial state, and detection efficiency all affect the evolution of quantum discord in a two-qutrit system. We find that under the condition of designing proper quantum-jump-based feedback parameters, quantum discord can be protected and prepared. In the case where two qutrits are independently coupled to their own environments, classical driving, spontaneous emission, and low detection efficiency have negative effect on the protection of quantum discord. For different initial states, it is found that the evolution of quantum discord under the control of appropriate parameters is similar. In the case where two qutrits are simultaneously coupled to the same environment, the classical driving plays a positive role in the generation of quantum discord, but spontaneous emission and low detection efficiency have negative impact on the generation of quantum discord. Most importantly, we find that the steady discord depends on feedback parameters, classical driving, and detection efficiency, but not on the initial state.
Abstract Exploring strategies to protect quantum correlations from the detrimental effects of their surroundings is crucial in the field of quantum computing and information sciences. For this purpose, we consider a simple engineered environment consisting of two noninteracting separated qubits, each embedded in a single-mode lossy cavity which is further connected to another lossy cavity. We investigate the dynamics and protection of quantum discord for the initially maximum entangled state in the weak and strong coupling regimes between the qubits and their corresponding cavities. It is found that the quantum discord can be preserved efficiently for a much longer time by adjusting the hopping strengths between the two coupled cavities. In addition, if the secondary cavity is perfect then a stationary quantum discord between the two qubits arises after certain damping oscillations. Interestingly, the magnitude of the stationary quantum discord can be maximized by increasing the coupling strengths of the two cavities.