Change search
ReferencesLink to record
Permanent link

Direct link
Development of theoretical approaches for post-silicon information processing
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Despite knowing the fundamental equations in most of the physics research areas, still there is an unceasing need for theoretical method development, thanks to the more and more challenging problems addressed by the research community. The investigation of post-silicon, non-classical information processing is one of the new and rapidly developing areas that requires tremendous amount of theoretical support, new understanding, and accurate theoretical predictions. My thesis focuses on theoretical method development for solid-state quantum information processing, mainly in the field of point defect quantum bits (qubits) in silicon carbide (SiC) and diamond. Due to recent experimental breakthroughs in this field, there are diverse theoretical problems, ranging from functional development for accurate first principles description of point defects, through complete theoretical characterization of qubits, to the modeling and simulation of actual quantum information protocols, that are needed to be addressed. The included articles of this thesis cover the development of (i) hybrid-DFT+Vw approach for the first principles description of mixed correlated and uncorrelated systems, (ii) zero-field-splitting tensor calculation for solid-state quantum bit characterization, (iii) a comprehensive model for dynamic nuclear spin polarization of solid-state qubits in semiconductors, and (iv) group theoretical description of qubits and novel twodimensional materials for topologically protected states.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. , 74 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1792
National Category
Condensed Matter Physics Other Physics Topics Other Engineering and Technologies not elsewhere specified Computer Science Other Computer and Information Science
Identifiers
URN: urn:nbn:se:liu:diva-131853DOI: 10.3384/diss.diva-131853ISBN: 9789176856826 (Print)OAI: oai:DiVA.org:liu-131853DiVA: diva2:1034065
Public defence
2016-11-11, Plank, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2016-10-21Bibliographically approved
List of papers
1. Theoretical unification of hybrid-DFT and DFT plus U methods for the treatment of localized orbitals
Open this publication in new window or tab >>Theoretical unification of hybrid-DFT and DFT plus U methods for the treatment of localized orbitals
Show others...
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 3, 035146- p.Article in journal (Refereed) Published
Abstract [en]

Hybrid functionals serve as a powerful practical tool in different fields of computational physics and quantum chemistry. On the other hand, their applicability for the case of correlated d and f orbitals is still questionable and needs more considerations. In this article we formulate the on-site occupation dependent exchange correlation energy and effective potential of hybrid functionals for localized states and connect them to the on-site correction term of the DFT+ U method. The resultant formula indicates that the screening of the onsite electron repulsion is governed by the ratio of the exact exchange in hybrid functionals. Our derivation provides a theoretical justification for adding a DFT+ U-like on-site potential in hybrid-DFT calculations to resolve issues caused by overscreening of localized states. The resulting scheme, hybrid DFT+ V-w, is tested for chromium impurity in wurtzite AlN and vanadium impurity in 4H-SiC, which are paradigm examples of systems with different degrees of localization between host and impurity orbitals.

Place, publisher, year, edition, pages
American Physical Society, 2014
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-109879 (URN)10.1103/PhysRevB.90.035146 (DOI)000339974700005 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation "Isotopic Control for Ultimate Materials Properties"; Swedish Research Council (VR) Grants [621-2011-4426, 621-2011-4249]; Swedish Foundation for Strategic Research program SRL Grant [10-0026]; Swedish National Infrastructure for Computing Grants [SNIC 001/12-275, SNIC 2013/1-331]; "Lendulet program" of Hungarian Academy of Sciences; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]; Linnaeus Environment at Linkoping on Nanoscale Functional Materials (LiLi-NFM) - VR

Available from: 2014-08-28 Created: 2014-08-28 Last updated: 2016-10-11
2. Role of screening in the density functional applied to transition-metal defects in semiconductors
Open this publication in new window or tab >>Role of screening in the density functional applied to transition-metal defects in semiconductors
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 20Article in journal (Refereed) Published
Abstract [en]

We study selected transition-metal-related point defects in silicon and silicon carbide semiconductors by a range-separated hybrid density functional (HSE06). We find that HSE06 does not fulfill the generalized Koopmans' theorem for every defect, which is due to the self-interaction error in the functional in such cases. Restoring the so-called generalized Koopmans' condition with a simple correction in the functional can eliminate this error and brings the calculated charge transition levels remarkably close to the experimental data as well as to the calculated quasiparticle levels from many-body perturbation theory.

Place, publisher, year, edition, pages
American Physical Society, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-93859 (URN)10.1103/PhysRevB.87.205201 (DOI)000318521500002 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research||Swedish Research Council||Swedish Energy Agency||Swedish National Infrastructure for Computing|SNIC 011/04-8SNIC001-10-223|Knut & Alice Wallenberg Foundation||EU||European Science Foundation for Advanced Concepts in ab-initio Simulations of Materials||

Available from: 2013-06-11 Created: 2013-06-11 Last updated: 2016-10-11
3. Pressure and temperature dependence of the zero-field splitting in the ground state of NV centers in diamond: A first-principles study
Open this publication in new window or tab >>Pressure and temperature dependence of the zero-field splitting in the ground state of NV centers in diamond: A first-principles study
Show others...
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 23, 235205- p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen-vacancy centers in diamond (NV) attract great attention because they serve as a tool in many important applications. The NV center has a polarizable spin S = 1 ground state and its spin state can be addressed by optically detected magnetic resonance (ODMR) techniques. The m(S) = 0 and m(S) = +/- 1 spin levels of the ground state are separated by about 2.88 GHz in the absence of an external magnetic field or any other perturbations. This zero-field splitting (ZFS) can be probed by ODMR. As this splitting changes as a function of pressure and temperature, the NV center might be employed as a sensor operating at the nanoscale. Therefore, it is of high importance to understand the intricate details of the pressure and temperature dependence of this splitting. Here we present an ab initio theory of the ZFS of the NV center as a function of external pressure and temperature including detailed analysis on the contributions of macroscopic and microscopic effects. We found that the pressure dependence is governed by the change in the distance between spins as a consequence of the global compression and the additional local structural relaxation. The local structural relaxation contributes to the change of ZFS with the same magnitude as the global compression. In the case of temperature dependence of ZFS, we investigated the effect of macroscopic thermal expansion as well as the consequent change of the microscopic equilibrium positions. We could conclude that theses effects are responsible for about 15% of the observed decrease of ZFS.

Place, publisher, year, edition, pages
American Physical Society, 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113573 (URN)10.1103/PhysRevB.90.235205 (DOI)000346860700002 ()
Note

Funding Agencies|NIIF Supercomputer center [1090]; EU [270197, 611143]; Hungarian Academy of Sciences; Knut and Alice Wallenberg Foundation; Swedish National Infrastructure for Computing [SNIC 001/12-275, SNIC 2013/1-331]; Conicyt (Chile) Fondecyt [1141185, PIA ACT1108, PIA ACT1112]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University

Available from: 2015-01-23 Created: 2015-01-23 Last updated: 2016-10-11
4. Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Open this publication in new window or tab >>Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Show others...
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 11, 115206- p.Article in journal (Refereed) Published
Abstract [en]

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2015
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-121891 (URN)10.1103/PhysRevB.92.115206 (DOI)000361370600003 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation "Isotopic Control for Ultimate Materials Properties"; Swedish Research Council (VR) [621-2011-4426, 621-2011-4249]; Swedish Foundation for Strategic Research program SRL [10-0026]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]; Swedish National Infrastructure for Computing Grants [SNIC 2013/1-331]; "Lendulet program" of Hungarian Academy of Sciences

Available from: 2015-10-13 Created: 2015-10-12 Last updated: 2016-10-11
5. Optical Polarization of Nuclear Spins in Silicon Carbide
Open this publication in new window or tab >>Optical Polarization of Nuclear Spins in Silicon Carbide
Show others...
2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 24, 247603- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate optically pumped dynamic nuclear polarization of Si-29 nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. The 99% +/- 1% degree of polarization that we observe at room temperature corresponds to an effective nuclear temperature of 5 mu K. By combining ab initio theory with the experimental identification of the color centers optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-120166 (URN)10.1103/PhysRevLett.114.247603 (DOI)000356407600010 ()
Note

Funding Agencies|Air Force Office of Scientific Research (AFOSR); AFOSR Multidisciplinary Research Program of the University Research Initiative; National Science Foundation; Material Research Science and Engineering Center; Knut and Alice Wallenberg Foundation "Isotopic Control for Ultimate Materials Properties"; Lendulet program of the Hungarian Academy of Sciences; National Supercomputer Center in Sweden

Available from: 2015-07-13 Created: 2015-07-13 Last updated: 2016-10-11
6. A silicon carbide room-temperature single-photon source
Open this publication in new window or tab >>A silicon carbide room-temperature single-photon source
Show others...
2014 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 13, no 2, 151-156 p.Article in journal (Refereed) Published
Abstract [en]

Over the past few years, single-photon generation has been realized in numerous systems: single molecules(1), quantum dots(2-4), diamond colour centres5 and others(6). The generation and detection of single photons play a central role in the experimental foundation of quantum mechanics(7) and measurement theory(8). An efficient and high-quality single-photon source is needed to implement quantum key distribution, quantum repeaters and photonic quantum information processing(9). Here we report the identification and formation of ultrabright, room-temperature, photostable single-photon sources in a device-friendly material, silicon carbide (SiC). The source is composed of an intrinsic defect, known as the carbon antisite-vacancy pair, created by carefully optimized electron irradiation and annealing of ultrapure SiC. An extreme brightness (2 x 10(6) counts s(-1)) resulting from polarization rules and a high quantum efficiency is obtained in the bulk without resorting to the use of a cavity or plasmonic structure. This may benefit future integrated quantum photonic devices(9).

Place, publisher, year, edition, pages
Nature Publishing Group, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-104643 (URN)10.1038/nmat3806 (DOI)000330182700020 ()
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2016-10-11
7. Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Open this publication in new window or tab >>Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Show others...
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 15Article in journal (Refereed) Published
Abstract [en]

We investigated the structural and electrical properties of 2D MXene sheets by means of firstprinciples density functional theory (DFT) calculations. To describe the Kohn-Sham states, plane wave basis set and projector augmented wave method (PAW) were used as implemented in the Vienna ab initio Simulation Package (VASP). We applied PBE parameterization of the generalized gradient approximation of the exchange and correlation energy functional to account for many-body effects of the interacting electron system. Convergent sampling of the Brillouin-zone was achieved by a Γ-centered 15×15×1 grid. In order to model a single sheet of MXene we ensured at least 30 Å vacuum between the periodically repeated sheets. For the structural optimization 1×10−3 eV/Å force criteria was used. The relativistic spin-orbit coupling effects were also included in our simulations regarding band structure and density of states.

Keyword
Cone-point, MAX phase, MXene, Dirac fermion, Spin-orbit coupling
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113761 (URN)10.1103/PhysRevB.92.155142 (DOI)000363512700002 ()
Available from: 2015-05-01 Created: 2015-01-30 Last updated: 2016-10-11Bibliographically approved

Open Access in DiVA

Development of theoretical approaches for post-silicon information processing(5479 kB)34 downloads
File information
File name FULLTEXT01.pdfFile size 5479 kBChecksum SHA-512
696eb8d6f12a475bed35251aa48a70dcf47ea92b1e85ef0029f04ce0c96561d8c0118d06c93078b3201379f66bf021b3abb5811ffdc20a69273656c72061d3c8
Type fulltextMimetype application/pdf
omslag(4640 kB)17 downloads
File information
File name COVER01.pdfFile size 4640 kBChecksum SHA-512
20148cc7206c95dc4f3e48e3fca9130955a69d08328ad523024347b071b141ac1acd4ffe2667a173dfebddcdc9e6c0b42eaff89302a55c07063e655ff8bbce16
Type coverMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Ivády, Viktor
By organisation
Theoretical PhysicsFaculty of Science & Engineering
Condensed Matter PhysicsOther Physics TopicsOther Engineering and Technologies not elsewhere specifiedComputer ScienceOther Computer and Information Science

Search outside of DiVA

GoogleGoogle Scholar
Total: 34 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 248 hits
ReferencesLink to record
Permanent link

Direct link