Search query: Investigation of exciton ground state in quantum dots via Hamiltonian diagonalization method

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abstract: We analyze the electron hole (exciton) ground state associated with the first peak in the optical absorption spectra of semiconductor quantum dots. We assume the effective mass approximation and a dot radius R on the order of the exciton Bohr radius aB. A Hamiltonian diagonalization method which accounts for the exciton's kinetic, direct Coulomb, and surface polarization energies is used. We obtain a representation of the exciton ground state wavefunction and a value for its energy using a basis set consisting of only three composite infinite spherical well wavefunctions. We discuss the precision obtained by this basis set by comparing with results from a much more extended basis set. Our results are used to predict the radius dependent energy of the first peak in visible light absorption spectra for CdSe quantum dots. Our analysis accurately describes the experimental data for dots with radii in the range aB
author_names: Zachary M Schultz

J M Essick
title: Investigation of exciton ground state in quantum dots via Hamiltonian diagonalization method
year: 2008

abstract: We propose an implementation of a universal set of one and two quantum bit gates for quantum computation using the spin states of coupled single electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a recently derived spin master equation incorporating decoherence caused by a prototypical magnetic environment. Dot array experiments that would provide an initial demonstration of the desired nonequilibrium spin dynamics are proposed.
author_names: Daniel Loss

David P DiVincenzo
title: Quantum computation with quantum dots
year: 1998

abstract: We demonstrated coherent control of a quantum two level system based on two electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. These techniques are based on rapid electrical control of the exchange interaction. Separating and later recombining a singlet spin state provided a measurement of the spin dephasing time, T2* of ~10 nanoseconds, limited by hyperfine interactions with the gallium arsenide host nuclei. Rabi oscillations of two electron spin states were demonstrated, and spin echo pulse sequences were used to suppress hyperfine induced dephasing. Using these quantum control techniques, a coherence time for two electron spin states exceeding 1 microsecond was observed.
author_names: Jason R Petta

A C Johnson

J M Taylor

E A Laird

Amir Yacoby

Mikhail D Lukin

Charles M Marcus

Micah P Hanson

Arthur C Gossard
title: Coherent Manipulation of Coupled Electron Spins in Semiconductor Quantum Dots
venue: Science
year: 2005

abstract: Transient nonlinear optical spectroscopy, performed on excitons confined to single GaAs quantum dots, shows oscillations that are analogous to Rabi oscillations in two level atomic systems. This demonstration corresponds to a one qubit rotation in a single quantum dot which is important for proposals using quantum dot excitons for quantum computing. The dipole moment inferred from the data is consistent with that directly obtained from linear absorption studies. The measurement extends the artificial atom model of quantum dot excitonic transitions into the strong field limit, and makes possible full coherent optical control of the quantum state of single excitons using optical pi pulses.
author_names: Todd H Stievater

Xiaoqin Li

Duncan Steel

Daniel Gammon

D Scott Katzer

D Park

Carlo Piermarocchi

Lu J Sham
title: Rabi oscillations of excitons in single quantum dots.
venue: Physical review letters
year: 2001

abstract: Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows one to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition from ionic bonding (for weak interdot tunnel coupling) to covalent bonding (for strong interdot tunnel coupling) in a double dot artificial molecule. This review is motivated by the relevance of double quantum dot studies for realizing solid state quantum bits.
author_names: Wilfred van der Wiel

Silvano De Franceschi

Jeroen Elzerman

Toshimasa Fujisawa

Seigo Tarucha

L P Kouwenhoven
title: Electron transport through double quantum dots
year: 2002

abstract: The canonical example of a quantum mechanical two level system is spin. The simplest picture of spin is a magnetic moment pointing up or down. The full quantum properties of spin become apparent in phenomena such as superpositions of spin states, entanglement among spins, and quantum measurements. Many of these phenomena have been observed in experiments performed on ensembles of particles with spin. Only in recent years have systems been realized in which individual electrons can be trapped and their quantum properties can be studied, thus avoiding unnecessary ensemble averaging. This review describes experiments performed with quantum dots, which are nanometer scale boxes defined in a semiconductor host material. Quantum dots can hold a precise but tunable number of electron spins starting with 0, 1, 2, etc. Electrical contacts can be made for charge transport measurements and electrostatic gates can be used for controlling the dot potential. This system provides virtually full control over individual electrons. This new, enabling technology is stimulating research on individual spins. This review describes the physics of spins in quantum dots containing one or two electrons, from an experimentalist's viewpoint. Various methods for extracting spin properties from experiment are presented, restricted exclusively to electrical measurements. Furthermore, experimental techniques are discussed that allow for 1 the rotation of an electron spin into a superposition of up and down, 2 the measurement of the quantum state of an individual spin, and 3 the control of the interaction between two neighboring spins by the Heisenberg exchange interaction. Finally, the physics of the relevant relaxation and dephasing mechanisms is reviewed and experimental results are compared with theories for spin orbit and hyperfine interactions. All these subjects are directly relevant for the fields of quantum information processing and spintronics with single spins i.e. single spintronics.
author_names: Ronald Hanson

L P Kouwenhoven

Jason R Petta

Seigo Tarucha

Lieven M K Vandersypen
title: Spins in few electron quantum dots
year: 2007

abstract: Single spins trapped in self assembled quantum dots present rich opportunities for studying their quantum mechanical properties. This Review surveys their optical properties, and the techniques for initializing, manipulating and reading out single spin qubits in these structures. Self assembled quantum dots have excellent photonic properties. For instance, a single quantum dot is a high brightness, narrow linewidth source of single photons. Furthermore, the environment of a single quantum dot can be tailored relatively easily using semiconductor heterostructure and post growth processing techniques, enabling electrical control of the quantum dot charge and control over the photonic modes with which the quantum dot interacts. A single electron or hole trapped inside a quantum dot has spintronics applications. Although the spin dephasing is rather rapid, a single spin can be manipulated using optical techniques on subnanosecond timescales. Optical experiments are also providing new insights into old issues, such as the central spin problem. This Review provides a snapshot of this active field, with some indications for the future. It covers the basic materials and optical properties of single quantum dots, techniques for initializing, manipulating and reading out single spin qubits, and the mechanisms that limit the electron spin and hole spin coherence.
author_names: Richard John Warburton
title: Single spins in self assembled quantum dots
venue: 2008 34th European Conference on Optical Communication
year: 2008

abstract: The properties of quasi two dimensional semiconductor quantum dots are reviewed. Experimental techniques for measuring the electronic shell structure and the effect of magnetic fields are briefly described. The electronic structure is analyzed in terms of simple single particle models, density functional theory, and "exact" diagonalization methods. The spontaneous magnetization due to Hund's rule, spin density wave states, and electron localization are addressed. As a function of the magnetic field, the electronic structure goes through several phases with qualitatively different properties. The formation of the so called maximum density droplet and its edge reconstruction is discussed, and the regime of strong magnetic fields in finite dot is examined. In addition, quasi one dimensional rings, deformed dots, and dot molecules are considered. (Less)
author_names: S M Reimann

Matti Manninen
title: Electronic structure of quantum dots
year: 2002

abstract: We measure a dephasing time of several hundred picoseconds at low temperature in the ground state transition of strongly confined InGaAs quantum dots, using a highly sensitive four wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non Lorentzian line shape with a lifetime limited zero phonon line and a broadband from elastic exciton acoustic phonon interactions.
author_names: Paola Borri

Wolfgang W Langbein

S Schneider

Ulrike Woggon

Roman Sellin

D Ouyang

Dieter H Bimberg
title: Ultralong dephasing time in InGaAs quantum dots.
venue: Physical review letters
year: 2001

abstract: Quantum dots (QDs) are a unique type of nanocrystalline semiconductor whose electronic and optical properties are dependent on the size and shape of the dots. Diameters of these particles can range from about 2 10 nm, on the order of 10 50 atomic lengths6. The small size of the particle gives a high ratio of surface to volume, so their properties fall somewhere between that of individual molecules and bulk semiconductors Quantum dots can be single elements (such as silicon, germanium, etc. or compounds (CdSe, CdS, etc.)6.
author_names: Elliott H Lieb

Jan philip Solovej
title: Quantum Dots
year: 1993