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Scientific Reports

Quantum feedback-enhanced discord in T-shaped plasmonic waveguides with embedded cavity

HOSSEIN SADEGHI, Mehdi Mirzaee, Rezvan Zarei

Published Feb 23, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1038/s41598-026-41393-7

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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 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.
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).
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.
We propose a new model of a T-shaped quantum router composed of two InGaAs quantum dots and two coupled-cavity waveguides, where the quantum dots are embedded in an infinite coupled-cavity waveguide that serves as an incoming route, with one of the dots being placed at the junction. Based on the discrete scattering equations, we theoretically discuss the controllable transport behavior of a single photon in a hybrid system with one input and two outputs. The results show that the reflection, transmission, and transfer rates can be successfully adjusted by various parameters such as the transition energy of the quantum dots, the momentum of the incident photons, the coupling strength between the quantum dots and the waveguides, and detuning. The validity and control of the reflection, transmission, and transfer rates of the single photons in the T-shaped quantum router make it possible to design various quantum devices.
Abstract Using quantum discord (QD) and geometric quantum discord (GQD), quantum correlation dynamics is investigated for two coupled qubits within a multiqubit interacting system in the zero-temperature bosonic reservoir, under both weak and strong qubit-reservoir coupling regimes. The multiqubit system is connected with either a common bosonic reservoir (CBR) or multiple independent bosonic reservoirs (IBRs). In the CBR case, our findings indicate that both QD and GQD can be strengthened by increasing the number of qubits in the multiqubit system. Furthermore, we study the steady state QD and GQD in the strong coupling regime, and find that the stable value in the long-time limit is determined exclusively by the number of qubits. The evolution period of QD and GQD gets longer as the dipole–dipole interaction (DDI) strength increases, which helps prolong the correlation time and thus preserves the quantum correlation under the weak coupling regime. Further analysis reveals notable differences between the CBR and IBRs scenarios. In the IBRs case, the decay of QD and GQD becomes slower compared to the CBR case, with both measures tending to zero at a reduced rate. Moreover, GQD consistently exhibits lower values than QD in both scenarios. These findings provide valuable insights into the selection of appropriate correlation measurement techniques for quantifying quantum correlations.