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Physical Review A

Nanoshell-mediated robust entanglement between coupled quantum dots

Jabir Wali Hakami, Muhammad Suhail Zubairy

Published Feb 16, 2016• 44 citations
Publisher

Abstract

The exact entanglement dynamics in a hybrid structure consisting of two quantum dots (QDs) in the proximity of a metal nanoshell is investigated. Nanoshells can enhance the local density of states, leading to a strong-coupling regime where the excitation energy can coherently be transferred between the QDs and the nanoshell in the form of Rabi oscillations. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the QDs and the surface of the shell. The loss of the system is greatly reduced even when the QDs are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation. Our protocol allows for an on-demand, fast, and almost perfect entanglement even at strong carrier-phonon interaction where other systems fail.

DOI
10.1103/physreva.93.022320

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The exact entanglement dynamics in a hybrid structure consisting of two quantum dots (QDs) in the proximity of a metal nanoshell is investigated. Nanoshells can enhance the local density of states, leading to a strong-coupling regime where the excitation energy can coherently be transferred between the QDs and the nanoshell in the form of Rabi oscillations. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the QDs and the surface of the shell. The loss of the system is greatly reduced even when the QDs are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation. Our protocol allows for an on-demand, fast, and almost perfect entanglement even at strong carrier-phonon interaction where other systems fail.
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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.
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Although the enhanced near fields produced by plasmon resonances in metal nanoparticles can enable strong local light-matter interactions, the strong dissipation of plasmon resonances would seem to be incompatible with quantum-mechanical phenomena such as entanglement. Counter to this intuition, the dissipation can in fact lead to the production of transient entanglement between the occupation states of dots coupled to a common plasmonic system. Building on previous results that showed entanglement between pairs of dots, we scale to larger systems of two, three, and more closely spaced dots. Moreover, we show that tuning the degree of coupling between each dot and the common plasmonic nanostructure enables entanglement to be created in the case where the entire system begins in its ground state and is excited by a single laser pulse. Entanglement is achieved without the need for the dots to be individually addressable, and without the need for controlled quantum gates, postselective measurements, or engineering of the dissipative environment. Through analytical solutions and numerical simulation of a model Hamiltonian based on a cavity-quantum-electrodynamics approach, we determine system configurations that maximize pairwise entanglement among the quantum dots, illustrating in principle the potential for true “quantum plasmonics.
We propose a scheme for achieving ultrastrong slow light in a hybrid nanosystem consisting of a metallic nanoshell (MNS), a semiconductor quantum dot (SQD), and a cell membrane. The MNS is composed of a metallic inner core and a dielectric outer shell. We derive the analytical expressions for the linear susceptibility and group velocity index under the multipole approximation. It is shown that the amplitudes and positions of the absorption peaks, as well as the group velocity index, depend strongly on the exciton-pump detuning, MNS-SQD distance, dielectric shell thickness, and exciton-phonon coupling strength. Especially, the amplitude of the characteristic absorption peak associated with the cell membrane can be enhanced by over 2200 times by only tuning the exciton-phonon coupling strength within an extremely narrow range. In an intermediate exciton-phonon coupling regime, the group velocity index rises abruptly from 86.13 to 2.87 × 10 11 with the pump intensity varied from 10 GHz 2 to 22.41 GHz 2 . Furthermore, we demonstrate that the precise monitoring of the cellular carcinogenesis degree can be realized by detecting the fast-to-slow light switching point, with the corresponding proportion of cancerous cells as low as 1.71%. Our findings exhibit broad application prospects in optical signal amplifiers and biosensors.