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arXiv:2507.15627 · Physica Scripta

Enhancing quantum discord in v-shaped plasmonic waveguides by quantum feedback

Huawei Zhao, Gen Li, Guo‐Feng Zhang

Published Dec 28, 2023• 2 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1088/1402-4896/ad1971

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Physica Scripta•Jul 31, 2019•4 citations
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.
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.
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.
The dynamics of two identical atoms is studied, which is resonantly coupled to a single-mode cavity under two different quantum feedback controls, i.e., the symmetric feedback control and the nonsymmetric feedback control. Correspondingly, the quantum discord of the system is induced to reach steady values under these two kinds of feedback controls. Furthermore, in some cases, the steady value of quantum discord of the system under symmetric feedback control is much larger than the steady value under nonsymmetric feedback control. The situation is just the opposite when the initial state is |eg〉. It is also found that the feedback is not good for getting a high discord when the initial state is in the form of Werner-like state (d = 0).
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.
We investigate the effect of quantum-jump-based feedback on the dynamics of quantum discord for two noninteracting two-level atoms coupled to a single mode of the cavity field with and without the rotating-wave approximation. It is found that the counterrotating terms can be helpful for generating steady states, and the value of steady-state quantum discord can be increased to approach 1 in the long-time limit by feedback controls. Furthermore, we also explore the influence of the time evolutions of mean excitation number in total systems and atomic subsystems on the quantum correlations and show that the enhancement of mean excitation number in atomic subsystems by feedback controls leads to the high value of steady-state quantum discord.
Abstract We investigate the dynamics of quantum discord between two colloidal quantum dots placed in the vicinity of nanoring with surface plasmons (SPs). We also analytically solve the corresponding master equation and show the influence of coupling strength and interdot distance on the dynamics of quantum discord. It is found that for an initial separable state, maximum quantum discord can be generated at a suitable interdot distance by the scattering of SPs in the metal nanoring resonator. Furthermore, for the initial correlated state, we observe that the decay and revivals of the quantum discord can be controlled by properly choosing the interdot distance and coupling strengths.