We conduct a theoretical study of the bistable optical response of a nanoparticle heterodimer comprised of a closely spaced semiconductor quantum dot and a metal nanoparticle. The bistable nature of the response results from the interplay between the quantum dot's optical nonlinearity and its selfaction (feedback) originating from the presence of the metal nanoparticle. The feedback is governed by a complex valued coupling parameter G = G R + iG I . We calculate the bistability phase diagram within the system's parameter space: spanned by G R , G I , and , the latter being the detuning between the driving frequency and the transition frequency of the quantum dot. Additionally, switching times from the lower stable branch to the upper one (and vice versa) are calculated as a function of the intensity of the driving field. The conditions for bistability to occur can be realized, for example, for a heterodimer comprised of a closely spaced CdSe (or CdSe/ZnSe) quantum dot and a gold nanosphere. © 2013 AIP Publishing LLC. [http://dx

Tailoring optical response of a hybrid comprising a quantum dimer emitter strongly coupled to a metallic nanoparticle Nugroho, Bintoro S.; Malyshev, V.A.; Knoester, Jasper IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Publication date: 2015Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Nugroho, B. S., Malyshev, V. A., & Knoester, J. (2015). Tailoring optical response of a hybrid comprising a quantum dimer emitter strongly coupled to a metallic nanoparticle. Physical Review B, 92(16), [165432]. DOI: 10.1103/PhysRevB.92.165432 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We study theoretically the optical response of a nanohybrid comprising a symmetric quantum dimer emitter coupled to a metal nanoparticle (MNP). The interactions between the exitonic transitions in the dimer and the plasmons in the MNP lead to interesting effects in the composite's input-output characteristics for the light intensity and the absorption spectrum, which we study in the linear and nonlinear regimes. We find that the exciton-plasmon hybridization leads to optical bistability and hysteresis for the one-exciton transition and enhancement of excitation for the two-exciton transition. The latter leads to a significant decrease in the field strength needed to saturate the system. In the linear regime, the absorption spectrum has a dispersive (Fano-like) line shape. The spectral position and shape of this spectrum depend on the detuning of the dimer's one-exciton resonance relative to the plasmon resonance and the ratio of the exciton-plasmon coupling constant to the exciton dephasing rate. When the applied field intensity to the nonlinear regime is increased, the Fano-like singularities in the absorption spectra are smeared and they disappear due to saturation of the dimer, which leads to the MNP dominating the spectrum. The above effects, for which we provide physical explanations, allow one to tailor the Fano-like shape of the absorption spectrum, by changing either the detuning or the input power.

Tho-photon Rabi oscillations hold potential for quantum computing and quantum information processing, because during a Rabi cycle a pair of entangled photons may be created. We theoretically investigate the onset of this phenomenon in a heterodimer comprising a semiconductor quantum dot strongly coupled to a metal nanoparticle. Two-photon Rabi oscillations in this system occur due to a coherent two-photon process involving the ground-to-biexciton transition in the quantum dot. The presence of a metal nanoparticle nearby the quantum dot results in a self-action of the quantum dot via the metal nanoparticle, because the polatization state of the latter depends on the quantum state of the former. The interparticle interaction gives rise to two principal effects: (i) -enhancement of the external field amplitude and (ii) -renormalization of the quantum dot's resonance frequencies and relaxation rates of the off-diagonal density matrix elements, both depending on the populations of the quantum dot's levels. Here, we focus on the first effect, which results in interesting new features, in particular, in an increased number of Rabi cycles per pulse as compared to an isolated quantum dot and subsequent growth of the number of entangled photon pairs per pulse. We also discuss the destructive role of radiative decay of the excitonic states on two-photon Rabi oscillations for both an isolated quantum dot and a heterodimer.

We theoretically investigate the nonlinear optical response of a heterodimer comprising a semiconductor quantum dot strongly coupled to a metal nanoparticle. The quantum dot is considered as a three-level ladder system with ground, one-exciton, and biexction states. As compared to the case of a two-level quantum dot model, adding the third (bi-exciton) state produces fascinating effects in the optical response of the hybrid system. Specifically, we demonstrate that the system may exhibit picosecond and subpicosecond self-oscillations and quasi-chaotic behaviour under single-frequency continuous wave excitation. An isolated semiconductor quantum dot does not show such features. The effects originate from competing one-exciton and bi-exciton transitions in the semiconductor quantum dot, triggered by the self-action of the quantum dot via the metal nanoparticle. The key parameter that governs the phenomena mentioned is the ratio of the self-action strength and the bi-exciton shift. The self-oscillation regime can be achieved in practice, in particular, in a heterodimer comprised of a closely spaced ZnS/ZnSe core-shell quantum dot and a spherical silver nanoparticle. The results may have applications in nanodevices for generating trains of ultrashort optical pulses.

Two-photon absorption holds potential for many practical applications. We theoretically investigate the onset of this phenomenon in a semiconductor quantum dot-metallic nanoshell composite subjected to a resonant CW excitation. Two-photon absorption in this system may occur in two ways: incoherent-due to a consecutive ground-to-one-exciton-to-biexciton transition-and coherent-due to a coherent two-photon process, involving the direct ground-to-biexciton transition in the quantum dot. The presence of the nanoshell nearby the quantum dot gives rise to two principal effects: (i) renormalization of the applied field amplitude and (ii) renormalization of the resonance frequencies and radiation relaxation rates of the quantum dot, both depending on the quantum dot level populations. We show that in the perturbation regime, when the excitonic levels are only slightly populated, each of these factors may give rise to either suppression or enhancement of the two-photon absorption. The complicated interplay of the two determines the final effect. Beyond the perturbation regime, it is found that the two-photon absorption experiences a drastic enhancement, which occurs independently of the type of excitation, either into the one-exciton resonance or into the two-photon resonance. Other characteristic features of the twophoton absorption of the composite, emerging from the coupling between both nanoparticles, are bistability and self-oscillations.

AbstrakTelah dilakukan studi teoretik untuk mempelajari respons optik semiconductor quantum dot (SQD) yang dieksitasi dengan cahaya monokromatik. SQD yang ditinjau dimodelkan sebagai three-level system bertipe V. Perhitungan teoretik dilakukan menggunakan pendekatan semiklasik dengan memperlakukan SQD sebagai objek kuantum yang berinteraksi dengan medan elektromagnetik klasik. Formalisme density matrix digunakan dalam perumusan SQD dengan faktor damping yang diperhitungkan melalui operator Lindblad. Dari hasil perhitungan, diperoleh bahwa selain frekuensi medan pengeksitasi, frekuensi Rabi ikut menentukan kebergantungan respons optik SQD terhadap intensitas. Sementara, dinamika respons optik SQD (kebergantungan populasi terhadap waktu) menunjukkan bahwa frekuensi osilasi populasi meningkat seiring dengan meningkatnya intensitas medan pengeksitasi. Hasil perhitungan menunjukkan bahwa pada intensitas medan pengeksitasi rendah ( = 10 Wcm −2 ) , spektrum serapan SQD menunjukkan bentuk kurva Lorentzian, sedangkan pada intensitas medan pengeksitasi tinggi ( = 1000 Wcm −2 ), spektrum serapan SQD melebar berbentuk Gaussian akibat power broadening.Kata kunci: quantum dot, density matrix, respons optik, three-level system

Telah dilakukan studi teoretis untuk mempelajari osilasi Rabi pada heterodimer yang terdiri dari semiconductor quantum dot (SQD) dan metal nanoparticle (MNP). SQD dimodelkan sebagai two-level system dan ditinjau dengan formalisme density matrix sedangkan MNP dimodelkan secara klasik dan dikarakterisasi dengan nilai polarisabilitasnya. Respon optik diamati untuk sistem yang diiluminasi dengan medan osilatif yang terpolarisasi linear pada arah paralel sumbu penghubung SQD-MNP. Persamaan gerak density matrix sistem diselesaikan secara numerik menggunakan Runge-Kuta-Fehlberg (RKF 45).  Hasil yang diperoleh menunjukkan bahwa hibridisasi SQD-MNP dapat menimbulkan interaksi yang menyebabkan terjadinya pergeseran frekuensi transisi resonansi dan perubahan laju dephasing pada sistem. Efek kopling tersebut terlihat dominan dan menjadi faktor utama dalam modifikasi osilasi Rabi ketika sistem dieksitasi dengan laser berintensitas rendah, I = 1 W/cm^2. Hibridisasi juga menyebabkan timbulnya medan induksi dari MNP yang berperan pada modifikasi osilasi Rabi saat sistem dieksitasi dengan laser berintensitas lebih tinggi, I = 10 W/cm^2. Efek modifikasi yang diamati dapat dikontrol dengan mengubah jarak pisah SQD-MNP.

The properties of GaAs material in zinc blende type was calculated using Hiroshima Linear Plane Wave program based on the Density Functional Theory. This calculation aims to determine electronic properties of GaAs material are based on Density of States and energy band structure. This simulation’s results are DOS shows that hybridization of s orbital of Ga with s orbital of As provides covalent properties. The simulation of energy band structure from GaAs material indicates that semiconductor properties of GaAs is direct band gap. The energy band gap results obtained for GaAs is 0.80 eV. The computational result of the energy band gap calculation form HiLAPW has better accuracy and prediction with good agreement within reasonable acceptable errors when compared to some other DFT programs and the results of the experimental obtained.