Browsing by Author "Ramirez, Hanz Y."

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Effects of electrostatic environment on the electrically triggered production of entangled photon pairs from droplet epitaxial quantum dots
(2019-02-07)
Ramirez, Hanz Y.
;
Chou, Ying-Lin
;
Cheng, Shun-Jen
;
電子物理學系
;
Department of Electrophysics
Entangled photon pair generation is a crucial task for development of quantum information based technologies, and production of entangled pairs by biexciton cascade decays in semiconductor quantum dots is so far one of the most advanced techniques to achieve it. However, its scalability toward massive implementation requires further understanding and better tuning mechanisms to suppress the fine structure splitting between polarized exciton states, which persists as a major obstacle for entanglement generation from most quantum dot samples. In this work, the influence of electrostatic environment arising from electrically biased electrodes and/or charged impurities on the fine structure splitting of GaAs/AlGaAs droplet epitaxial quantum dots is studied, by means of numerical simulations considering a realistic quantum dot confining potential and electron-hole exchange interaction within a multiband k.p framework. We find that reduction of the fine structure splitting can be substantially optimized by tilting the field and seeding impurities along the droplet elongation axis. Furthermore, our results provide evidence of how the presence of charged impurities and in-plane bias components, may account for different degrees of splitting manipulation in dots with similar shape, size and growth conditions.
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots
(2010-02-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
The effects of electron-hole (e-h) symmetry breaking on the optical fine structure splitting (FSS) of single excitons in individual InGaAs/GaAs self-assembled quantum dots are experimentally and theoretically studied. The measured FSSs of small InGaAs/GaAs self-assembled quantum dots show a monotonic decrease wills increasing emission energy and eventually almost vanish (<= 10 mu eV) in the high energy regime. A theory based on 3D asymmetric parabolic model for e-h exchange interaction in combination with 3D finite difference simulations for Ga-diffused InGaAs/GaAs QDs is developed to explore the underlying physics. The reduced FSSs in the high emission energy regime are shown closely related to the e-h wave function symmetry breaking which is especially significant in highly Ga-diffused quantum dots. The Ga-diffusion induced e-h asymmetry reduces the e-h wave function overlap and results in the feature of reduced fine energy splitting. (c) 2009 Elsevier Boy. All rights reserved.
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots (vol 42, pg 1155, 2010)
(2010-11-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots (vol 42, pg 1155, 2010)
(2010-11-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
Solid-state emitter embedded in a microcavity under intense excitation: A variational master-equation approach
(2018-11-26)
Gomez-Sanchez, Oscar J.
;
Ramirez, Hanz Y.
;
電子物理學系
;
Department of Electrophysics
In this work, dissipative effects from a phonon bath on the resonance fluorescence of a solid-state two-level system embedded in a high-quality semiconductor microcavity and driven by an intense laser are investigated. Within the density operator formalism, we derive a variational master equation valid for broader ranges of temperatures, pumping rates, and radiation-matter couplings than previous studies. From the obtained master equation, fluorescence spectra for various thermal and exciting conditions are numerically calculated and compared to those computed from weak coupling and polaronic master equations, respectively. Our results evidence the breakdown of those rougher approaches under increased temperature and strong pumping.
Theory of electron-hole exchange interaction in double quantum dots
(2009-04-01)
Ramirez, Hanz Y.
;
Cheng, Shun-Jen
;
Chang, Chih-Pin
;
電子物理學系
;
Department of Electrophysics
A theory of electron-hole exchange interaction in vertically stacked double quantum dots is developed. This theory was built up from the full interaction Hamiltonian of two coupled dots, taking into account both of the macroscopic and microscopic natures of particle wave functions. In the basis of S-type Fock-Darwin orbitals, compact formulations for electro-hole exchange terms responsible for the fine structure splitting of spin exciton states as functions of material parameters, geometric structure of dots, and the strength of external field are explicitly derived. Significant reduction of the splitting, down to 50% of the magnitude of such energy in single dot case, is observed as the system is switched into the near-resonance regime. (C) WILEY-VCH Verlage GmbH & Co. KGaA, Weinheim
Tunneling Effects on Fine-Structure Splitting in Quantum-Dot Molecules
(2010-05-21)
Ramirez, Hanz Y.
;
Cheng, Shun-Jen
;
電子物理學系
;
Department of Electrophysics
We theoretically study the effects of bias-controlled interdot tunneling in vertically coupled quantum dots on the emission properties of spin excitons in various bias-controlled tunneling regimes. As a main result, we predict substantial reduction of optical fine-structure splitting without any drop in the optical oscillator strength for the coupled dots with high tunneling rates. This special reduction diminishes the distinguishability of polarized decay paths in cascade emission processes suggesting the use of stacked quantum-dot molecules as entangled photon-pair sources.