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Physica Scripta

Dynamics of quantum discord between two quantum dots placed near a nanoring surface plasmons

Abdul Basit, Hamad Ali, Misbah Qurban, Fazal Badshah, Qing He, Guo-Qin Ge

Published Jul 31, 2019• 4 citations
Publisher

Abstract

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.

DOI
10.1088/1402-4896/ab374f

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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.
We study the systems of two and three quantum dots positioned near a metallic nanoring having a surface plasmon in a particular mode. Interaction of surface plasmon with quantum dots generates entanglement between quantum dots as well as among the incident and reflected modes of the surface plasmons. We show that the maximum amount of entanglement is generated among two initially unentangled quantum dots separated by distance and with interaction parameter , while entanglement among two counter-propagating modes of the surface plasmons can be generated with interdot distance and interaction parameter , where k and μ are the propagation vector and coupling constant, respectively. In case of three quantum dots, the maximum entanglement among the quantum dots is obtained at kd = mπ /3 and Finally, the scheme is straightforwardly generalized to generate quantum entanglement among N quantum dots as well as among two counter-propagating modes of the surface plasmon due to their interactions with quantum dots.
We investigate coherent single surface-plasmon transport in a metal nanowire strongly coupled to two colloidal quantum dots. Analytical expressions are obtained for the transmission and reflection coefficients by solving the corresponding eigenvalue equation. Remote entanglement of the wave functions of the two quantum dots can be created if the interdot distance is equal to a multiple half-wavelength of the surface plasmon. Furthermore, by applying classical laser pulses to the quantum dots, the entangled states can be stored in metastable states that are decoupled from the surface plasmons.
Generating entangled states is a vital ingredient for quantum information engineering. Here, we investigate the entanglement generation between two quantum dots coupled to nanoring surface plasmons with asymmetric coupling strength g(1) and g(2). The dynamics of concurrence C is obtained by solving the corresponding master equation. High entanglement can be generated at appropriate times through the scatterings of the incident field and its scattered field. Furthermore, we find that maximum entanglement can be created when r≡g(1)/g(2) is the ratio of odd numbers. Contrary to intuition, relative high entanglement (C≃1) can remain even if the ratio r is far off the required values, which is useful in real experiments.
We study the dynamics of quantum coherence and quantum correlations in two semiconductor double-dot molecules separated by a distance and indirectly coupled via a transmission line resonator. Dominant dissipation processes are considered. The numerical results show the sudden death of entanglement and the robustness of quantum discord to sudden death. Furthermore, the results indicate the dephasing processes in our model can lead in the revival and decay of coherence and discord with the absence of entanglement for certain initial states. By observing the dynamics of coherence versus discord for different initial states, we find that the similarities and differences of coherence and discord are not only related to the dependance of discord on optimizing the measurement set, but more importantly to the coherences in individual qubits which are captured by the adopted coherence measure.
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.