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EXCITATION ENERGY TRANSFER IN QUANTUM-DOT SOLIDS

Ameenah N. Al‐Ahmadi

Published Jan 1, 2006• 0 citations
OpenAlex

Abstract

We study the dynamics of excitonic states in one dimensional, dimer and trimer, and two dimensional arrangements of colloidal quantum dots using a density-matrix approach.The dots are coupled via a dipole-dipole interaction akin to the Förster mechanism.Coherent oscillations of tuned donor dots are shown to appear as plateaus in the acceptor dots, and therefore in their optical response.This behavior provides one with an interesting and unique handle to monitor the quantum state of clusters in an eavesdroping arrangement.A trimer cluster in a symmetrical loop shows steady states in a shorter characteristic time than the typical radiative lifetime of the dots.Breaking the symmetry of the loop results again in damping oscillatory states in the donor dots and plateaus in the eavesdropping/acceptor dot.The use of realistic parameters allows direct comparison with recent experiments and indicates that coherent state monitoring is possible in real experiments.Estimates of the Förster coupling V F are obtained from a microscopic description of the exciton levels in the quantum dot.We present results for different materials CdS, CdSe, GaAs, and InP as function of dot features.V F shows a nonmonotonic variation with dot sizes and a maximum value that depends on the specific dot sizes, material parameters, and dot separation.We also study the effect of the orientation factor on coherent energy transfer from a donor quantum dot to an acceptor quantum dot by calculating the polarization of the acceptor dot.We study how the measurement of the ac-ceptor polarization can be used to determine the relative orientation between the donor-acceptor pair.We also find that Förster coupling between dots results in a polarization memory transfer.

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We study the dynamics of excitonic states in dimer and trimer arrangements of colloidal quantum dots using a density-matrix approach. The dots are coupled via a dipole-dipole interaction akin to the F\"orster mechanism. Coherent oscillations of tuned donor dots are shown to appear as plateaus in the acceptor dot, and therefore in its optical response. This behavior provides one with an interesting and unique handle to monitor the quantum state of the dimer, an ``eavesdroping arrangement.'' A trimer cluster in a symmetrical loop shows steady states in a shorter characteristic time than the typical radiative lifetime of the dots. Breaking the symmetry of the loop results again in damping oscillatory states in the donor dots and plateaus in the eavesdropping∕acceptor dot. The use of realistic parameters allows direct comparison with recent experiments and indicates that coherent-state monitoring is possible in real experiments.

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Journal of Physics A Mathematical and Theoretical•May 30, 2012•0 citations
We study the dynamics of excitonic states in one dimensional, dimer and trimer, and two dimensional arrangements of colloidal quantum dots using a density-matrix approach.The dots are coupled via a dipole-dipole interaction akin to the Förster mechanism.Coherent oscillations of tuned donor dots are shown to appear as plateaus in the acceptor dots, and therefore in their optical response.This behavior provides one with an interesting and unique handle to monitor the quantum state of clusters in an eavesdroping arrangement.A trimer cluster in a symmetrical loop shows steady states in a shorter characteristic time than the typical radiative lifetime of the dots.Breaking the symmetry of the loop results again in damping oscillatory states in the donor dots and plateaus in the eavesdropping/acceptor dot.The use of realistic parameters allows direct comparison with recent experiments and indicates that coherent state monitoring is possible in real experiments.Estimates of the Förster coupling V F are obtained from a microscopic description of the exciton levels in the quantum dot.We present results for different materials CdS, CdSe, GaAs, and InP as function of dot features.V F shows a nonmonotonic variation with dot sizes and a maximum value that depends on the specific dot sizes, material parameters, and dot separation.We also study the effect of the orientation factor on coherent energy transfer from a donor quantum dot to an acceptor quantum dot by calculating the polarization of the acceptor dot.We study how the measurement of the ac-ceptor polarization can be used to determine the relative orientation between the donor-acceptor pair.We also find that Förster coupling between dots results in a polarization memory transfer.
We study the dynamics of excitonic states in dimer and trimer arrangements of colloidal quantum dots using a density-matrix approach. The dots are coupled via a dipole-dipole interaction akin to the F\"orster mechanism. Coherent oscillations of tuned donor dots are shown to appear as plateaus in the acceptor dot, and therefore in its optical response. This behavior provides one with an interesting and unique handle to monitor the quantum state of the dimer, an ``eavesdroping arrangement.'' A trimer cluster in a symmetrical loop shows steady states in a shorter characteristic time than the typical radiative lifetime of the dots. Breaking the symmetry of the loop results again in damping oscillatory states in the donor dots and plateaus in the eavesdropping∕acceptor dot. The use of realistic parameters allows direct comparison with recent experiments and indicates that coherent-state monitoring is possible in real experiments.
The theory of coherent energy transfer in nanocrystal (NC) systems is generalised for multi-exciton states. We study the effect of the Forster coupling between two individual semiconductor nanocrystals on the pump and induced Rabi oscillations (ROs). The relevant excitonic states in an isolated NC can be described by an effective four-state system, consisting of the ground state, the exciton state, the biexciton state and the triexciton state. The dynamics of a single donor-acceptor pair is described using a density matrix approach that incorporates dipole coupling to multi-exciton states. Our study shows that for short pulse the multi-exciton states play an important role in the dynamics. We also show that the amplitude and the period of the ROs in both dots are heavily influenced by Forster coupling strength. The quality factor of the induced ROs in the acceptor yields information on the energy transfer rate between the two dots. We present result for a variety of sample materials and realistic structure parameters.
Abstract The analytical solution of the system consisting of donor-acceptor double quantum dots of approximately the same size, located inside a high-quality cavity is studied. The double quantum dots interact with the same phonon fields within the cavity, as well as with a single-mode electromagnetic field. The effect of the modified Förster interaction strength coefficient on the atomic occupation probabilities, ρ11(t), ρ22(t), the atomic population inversion ρz(t), the von Neumann entropy, the information entropies H(σx), H(σy) and H(σz), quantum Fisher information (FI ) and quantum coherence (Qc) of this system are investigated. The results clearly show that the modified Förster interaction strength coefficient (Ω) plays a pivotal role in controlling the dynamics of the coupled quantum dot system, where the interaction between quantum dots accelerates energy transfer and information exchange processes within the system. Hence, under the influence of the Förster interaction, which occurs when the donor’s emission spectrum overlaps with the acceptor’s absorption spectrum, a quantum tunneling current is generated between the two quantum dots using photons from negatively charged excitons. Also, the ability to control the degree of entanglement through Ω provides a mechanism to tune the properties of the quantum system.
We have studied energy transfer and photoluminescence in donor and acceptor quantum dots embedded in a nonlinear photonic crystal. The quantum dots are interacting with each other via the dipole-dipole interaction. The nonlinear photonic crystal modifies the dielectric constant of the hybrid system. Using the density matrix method, it is found that the energy transfer and photoluminescence in the donor quantum dot can be controlled by a pump field due to the nonlinearity of the photonic crystal. Additionally, our theoretical calculations agree with recent experiments. This hybrid system can be used to fabricate ultrafast switching and sensing nanodevices.
We provide a theoretical study for the dynamical behavior of two-photon Rabi oscillations in two coupled quantum dots. Each dot is a three-level quantum system (ground, one-exciton, and biexciton states). We describe the optical dynamics within the density matrix formalism framework. The two-photon Rabi oscillations are found to be significantly affected by the strength of the interdot dipolar interaction. Using a detuned laser pulse with an exciton state of the driven quantum dot in our numerical simulations, a direct coherent excitation between the biexciton states can be established, but whether Rabi oscillations can be observed depend mainly on the strength of the dipolar interaction and bandwidth of the excitation laser. When the strength of the dipolar coupling is less than the excitation laser bandwidth, the time-dependent populations of the various two biexciton states of the system exhibit coherent oscillations with several frequencies. However, as we increase the dipolar coupling strength, the population transfer between the quantum dots levels amazingly becomes forbidden, and the excitation gets trapped at the initial state. The reduction of the influence of the dipolar interaction leads to a manipulation of two-photon Rabi oscillation in an ultrashort timescale (∼ps), opening possibilities to achieve ultrafast quantum state control and quantum logic gate generation.
We investigate the entanglement dynamics of excitons confined in two adjacent quantum dots, which we describe through their algebraic properties using in the z -direction. We use two explicit forms of coherent states: the Perelomov and Barut–Girardello states to represent the electronic component of the excitonic state in the z -direction. Our results show that in a coherent state basis, the concurrence of an excitonic-qubit pair shows subtle variations which are dependent on the algebraic parameters of the group. These variations also appear in the classical and quantum correlations, present in the qubit–qubit density matrix that is associated with the purely Förster-coupled excitonic-qubit pair. A brief discussion of a plausible experimental technique of detecting excitonic coherent states is provided. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to 'Coherent states: mathematical and physical aspects'.