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arXiv:1609.04732 · Physical Review B

Entanglement of two qubits mediated by a localized surface plasmon

Khachatur Nerkararyan, Sergey I. Bozhevolnyi

Published Jul 10, 2015• 0 citations
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Abstract

We investigate relaxation dynamics in the system of two identical quantum dipole emitters (QDEs) located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. Considering one QDE to be brought into an optically active excited state and weakly coupled to the resonant LSP, we show that a stable superposition state of two QDEs is formed during the transition time, which is much shorter than the QDE spontaneous decay time and determined by the efficiency of resonant interaction between the QDEs and induced LSP. It is elucidated that the superposition state is established as a result of redistribution of the energy of the initially excited QDE so that the corresponding steady-state QDE fields induced at the MNP site cancel each other. The degree of steady-state entanglement characterized by the concurrence is found dependent only on the ratio of distances between the QDEs and the MNP, reaching its maximum value of $\ensuremath{\sim}0.65$, when the separation between the MNP and the initially excited QDE is larger by $\ensuremath{\sim}20%$ than the distance from the other QDE to the MNP.

DOI
10.1103/physrevb.92.045410

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We investigate relaxation dynamics in the system of two identical quantum dipole emitters (QDEs) located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. Considering one QDE to be brought into an optically active excited state and weakly coupled to the resonant LSP, we show that a stable superposition state of two QDEs is formed during the transition time, which is much shorter than the QDE spontaneous decay time and determined by the efficiency of resonant interaction between the QDEs and induced LSP. It is elucidated that the superposition state is established as a result of redistribution of the energy of the initially excited QDE so that the corresponding steady-state QDE fields induced at the MNP site cancel each other. The degree of steady-state entanglement characterized by the concurrence is found dependent only on the ratio of distances between the QDEs and the MNP, reaching its maximum value of \ensuremath∼0.65\ensuremath{\sim}0.65\ensuremath∼0.65, when the separation between the MNP and the initially excited QDE is larger by \ensuremath∼20\ensuremath{\sim}20%\ensuremath∼20 than the distance from the other QDE to the MNP.
We investigate the relaxation dynamics of a quantum dipole emitter (QDE), e.g., a molecule or quantum dot, located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. A generic three-level QDE, which is pumped with an external laser pulse and thereby brought into an optically active excited state, is considered to be weakly coupled to the resonant LSP described by a coherent state. It is shown that, under the condition of the QDE-MNP characteristic relaxation time being much shorter than that of the QDE in free space but much longer than the LSP lifetime, the QDE relaxation dynamics can be described analytically and feature, in general, non-exponential decay with complicated transient behaviour. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. It is also shown that energy dissipation in the QDE-MNP system is relatively weak with the probability of the photon emission being ∼0.75, a number which, rather surprisingly, does not explicitly depend on the metal absorption characteristics. A large number of QDE-MNP system parameters in our analytical description open new possibilities for controlling quantum emitter dynamics.
We investigate relaxation dynamics of a quantum dipole emitter (QDE), e.g., a molecule or quantum dot, located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. It is shown that under the condition of the QDE-MNP characteristic relaxation time being much shorter than that of the QDE in free-space but much longer than the LSP lifetime. It is also shown that energy dissipation in the QDE-MNP system is relatively weak with the probability of the photon emission being about 0.75, a number which, rather surprisingly, does not explicitly depend on the metal absorption characteristics. The degree of entanglement measured by the concurrency takes the maximum value, while the distances between the QDEs and metal ball approximately are equal.
We investigate excitation dynamics in the system of a quantum dipole emitter (QDE) coupled to a located nearby metal nanoparticle (MNP), which exhibits a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition, in the presence of a strong external resonant electromagnetic field. Considering the QDE-field interactions in the regime of strong QDE-field coupling, we show that the feedback provided by the MNP on the QDE (due to the LSP excitation with the field generated by the dipole moment of the QDE transition) influences significantly the coherent process of Rabi oscillations, resulting in the occurrence of additional satellite frequencies in the radiation spectrum scattered by the QDE-MNP configuration. The relative ratio of high harmonics depends strongly on the QDE-MNP separation, an important characteristic feature that can be used for observing this effect and can be exploited, for example, for controlling distances at the nanoscale.
The presence of a metal nanoparticle (MNP) near a quantum dipole emitter, when a localized surface plasmon mode is excited via the resonant coupling with an excited quantum dipole, dramatically changes the relaxation dynamics: an exponential decay changes to step-like behavior. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. A large number of system parameters in our analytical description opens new possibilities for controlling quantum emitter dynamics.
We theoretically investigate a general scheme for determining quantum entanglement of two detuned quantum dots (QDs) mediated by plasmon nanoparticle for weakly driven dissipative systems. By adiabatically eliminating the field operators, an effective model is proposed to find the underlying mechanism for this determination. Two specific hybrid systems composed of two QDs and a metallic nanoparticle (MNP) are considered. In the QD-MNP-QD system, the concurrence maxima generated by the detunings are several times larger than those in the resonance condition because of the robust superposition between the two separated entangled states. However, in the MNP-QD-QD system, the detunings generally reduce entanglement because the dipole-dipole interaction strongly suppresses the superposition of the entangled states. Moreover, the plateau of large concurrence exists for a broad range of parameters in both cases. The scheme is robust to dissipative systems and paves the way to improve entanglement in quantum information devices at the nanoscale.
We explore the entanglement generation between two dipole emitters via a hybrid photonic-plasmonic resonant structure which consists of two metal nanoparticles (MNPs) and a high-QQQ whispering-gallery-mode (WGM) microcavity. Because the coupling strength between the dipole emitter and the cavity can be substantially enhanced with the help of MNPs and maintained by the WGM cavity, the maximum entanglement plateau between two dipole emitters can be deterministically created even in the presence of the spontaneous emission of the dipole emitters and the decay induced by the microcavity and MNPs. The width of the plateau depends on the coupling strengths (or the radii of the MNPs) and the initial state, but is insensitive to the dipole-cavity detuning. These results are useful in real experiments.