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Two-electron quantum dot in tilted magnetic fields: Sensitivity to the confinement model
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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2013 (English)In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 86, no 10, 430Article in journal (Refereed) Published
Abstract [en]

Semiconductor quantum dots are conventionally treated within the effective-mass approximation and a harmonic model potential in the two-dimensional plane for the electron confinement. The validity of this approach depends on the type of the quantum-dot device as well as on the number of electrons confined in the system. Accurate modeling is particularly demanding in the few-particle regime, where screening effects are diminished and thus the system boundaries may have a considerable effect on the confining potential. Here we solve the numerically exact two-electron states in both harmonic and hard-wall model quantum dots subjected to tilted magnetic fields. Our numerical results enable direct comparison against experimental singlet-triplet energy splittings. Our analysis shows that hard and soft wall models produce qualitatively different results for quantum dots exposed to tilted magnetic fields. Hence, we are able to address the sensitivity of the two-body phenomena to the modeling, which is of high importance in realistic spin-qubit design.

Place, publisher, year, edition, pages
2013. Vol. 86, no 10, 430
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-96095DOI: 10.1140/epjb/e2013-40677-xISI: 000325608100003OAI: oai:DiVA.org:su-96095DiVA: diva2:664194
Note

AuthorCount:5;

Available from: 2013-11-14 Created: 2013-11-11 Last updated: 2017-04-28Bibliographically approved
In thesis
1. Many-Body effects in Semiconductor Nanostructures
Open this publication in new window or tab >>Many-Body effects in Semiconductor Nanostructures
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Low dimensional semiconductor structures are modeled using techniques from the field of many-body atomic physics. B-splines are used to create a one-particle basis, used to solve the more complex many-body problems. Details on methods such as the Configuration Interaction (CI), Many-Body Perturbation Theory (MBPT) and Coupled Cluster (CC) are discussed. Results from the CC singles and doubles method are compared to other high-precision methods for the circular harmonic oscillator quantum dot. The results show a good agreement for the energy of many-body states of up to 12 electrons.

Properties of elliptical quantum dots, circular quantum dots, quantum rings and concentric quantum rings are all reviewed. The effects of tilted external magnetic fields applied to the elliptical dot are discussed, and the energy splitting between the lowest singlet and triplet states is explored for varying geometrical properties. Results are compared to experimental energy splittings for the same system containing 2 electrons.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2014. 44 p.
Keyword
coupled cluster, nanostructure, quantum dot, quantum ring, concentric quantum ring, many body pertubation theory
National Category
Nano Technology Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-102344 (URN)
Presentation
2014-04-25, FA31, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 16:05 (English)
Opponent
Supervisors
Available from: 2014-04-24 Created: 2014-04-02 Last updated: 2014-04-24Bibliographically approved
2. Confinement Sensitivity in Quantum Dot Spin Relaxation
Open this publication in new window or tab >>Confinement Sensitivity in Quantum Dot Spin Relaxation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum dots, also known as artificial atoms, are created by tightly confining electrons, and thereby quantizing their energies. They are important components in the emerging fields of nanotechnology where their potential uses vary from dyes to quantum computing qubits. Interesting properties to investigate are e.g. the existence of atom-like shell structures and lifetimes of prepared states.

Stability and controllability are important properties in finding applications to quantum dots. The ability to prepare a state and change it in a controlled manner without it loosing coherence is very useful, and in some semiconductor quantum dots, lifetimes of up to several milliseconds have been realized. Here we focus on dots in semiconductor materials and investigate how the confined electrons are effected by their experienced potential.

The shape of the dot will effect its properties, and is important when considering a suitable model. Structures elongated in one dimension, often called nanowires, or shaped as rings have more one-dimensional characteristics than completely round or square dots. The two-dimensional dots investigated here are usually modeled as harmonic oscillators, however we will also consider circular well models.

The effective potential confining the electrons is investigated both in regard to how elliptical it is, as well as how results differ when using a harmonic oscillator or a circular well potential. By mixing spin states through spin-orbit interaction transitioning between singlet and triplet states becomes possible with spin independent processes such as phonon relaxation. We solve the spin-mixing two-electron problem numerically for some confinement, and calculate the phonon transition rate between the lowest energy singlet and triplet states using Fermi's golden rule.

The strength of the spin-orbit interaction is varied both by changing the coupling constants, and by applying an external, tilted, magnetic field. The relation between magnetic field parameters and dot parameters are used to maximize state lifetimes, and to model experimental results.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2017. 64 p.
National Category
Nano Technology Other Physics Topics Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-142133 (URN)978-91-7649-809-5 (ISBN)978-91-7649-810-1 (ISBN)
Public defence
2017-06-08, sal FB55, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:15 (English)
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Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2017-05-16 Created: 2017-04-26 Last updated: 2017-05-16Bibliographically approved

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