Defects for quantum information processing
The idea of utilizing quantum systems to perform complicated quantum mechanical simulations and calculations was raised by Richard Feynman in 1982. This basic idea has initiated new directions in many disciplines and influenced different fields of nowadays physics. By now it has been widely accepted that quantum computation and information processing applications may possess extraordinary features and of great importance for future technologies.
Research groups at the very frontiers of physics are actively working on explaining the behavior and creating viable designs of the building blocks, such as quantum bits (qubits), quantum gates, etc. of would-be quantum computers. One of the most promising candidates for the realization of a qubit is the spin of a single point defect in semiconductors and insulators which can be considered as a good compromise compared to the solution of other contenders and has great technical advantages because of the large amount of accumulated experiences with materials processing. The extraordinary properties of defects such as the famous NV center in diamond allow optical control of the electron and nuclear spins. With applying static and radio and microwave electromagnetic fields to them, several quantum operations have been carried out by these systems so far.
Furthermore, thanks to the achieved ultimate control of electron spins, these point defects often can be utilized as nanoscale sensing tools. High sensitivity of their finely-tuned properties to environmental perturbations is the key feature behind this idea. This recent field of research and application is often called as nanometrology.
Our group actively contributes to the development of these new fields by first-principles and analytical characterization of well-established point defects and promising candidates thereof.
Contents
Nitrogen-vacancy center in diamond
The nitrogen-vacancy (NV) center in diamond is a leading contender for realizing the solid state spin qubits concept in quantum information. Our group significantly contributed to the understanding of optical and magnetic properties of this defect, and is continuously investigating those as a function of external perturbations, temperature, surface effects or quantum confinement.
We successfully determined the hyperfine tensors of the nuclei with non-zero nuclei spins and identified the qubits realized by proximate 13C isotopes [1]Author: A. Gali, M. Fyta, E. KaxirasDoi: 10.1103/PhysRevB.77.155206
Journal: Phys. Rev. B
Month: Apr
Pages: 155206
Title: textitAb initio supercell calculations on nitrogen-vacancy center in diamond: Electronic structure and hyperfine tensors
Volume: 77
Year: 2008


Doi: 10.1103/PhysRevB.80.241204
Journal: Phys. Rev. B
Month: Dec
Pages: 241204
Title: Identification of individual isotopes of nitrogen-vacancy center in diamond by combining the polarization studies of nuclear spins and first-principles calculations
Volume: 80
Year: 2009


Doi: 10.1103/PhysRevB.88.075202
Journal: Phys. Rev. B
Pages: 075202
Title: Hyperfine coupling of point defects in semiconductors by hybrid density functional calculations: The role of core spin polarization
Volume: 88
Year: 2013


Doi: 10.1103/PhysRevB.79.235210
Journal: Phys. Rev. B
Month: Jun
Pages: 235210
Title: Theory of the neutral nitrogen-vacancy center in diamond and its application to the realization of a qubit
Volume: 79
Year: 2009


Doi: 10.1103/PhysRevLett.106.157601
Journal: Phys. Rev. Lett.
Month: Apr
Pages: 157601
Title: Dark States of Single Nitrogen-Vacancy Centers in Diamond Unraveled by Single Shot NMR
Volume: 106
Year: 2011


Doi: 10.1103/PhysRevLett.110.167402
Journal: Phys. Rev. Lett.
Pages: 167402
Title: Optically Controlled Switching of the Charge State of a Single Nitrogen-Vacancy Center in Diamond at Cryogenic Temperatures
Volume: 110
Year: 2013


Journal: Physical Review Letters
Month: oct
Number: 18
Pages: 186404
Title: Theory of Spin-Conserving Excitation of the N-V- Center in Diamond
Volume: 103
Year: 2009


Doi: 10.1088/1367-2630/13/2/025025
Journal: New Journal of Physics
Number: 2
Pages: 025025
Title: Properties of nitrogen-vacancy centers in diamond: the group theoretic approach
Volume: 13
Year: 2011


Doi: 10.1103/PhysRevB.81.041204
Journal: Phys. Rev. B
Month: Jan
Pages: 041204
Title: Excited states of the negatively charged nitrogen-vacancy color center in diamond
Volume: 81
Year: 2010


Doi: 10.1103/PhysRevB.89.075203
Journal: Phys. Rev. B
Pages: 075203
Title: Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects
Volume: 89
Year: 2014


Doi: 10.1103/PhysRevB.89.075203
Journal: Phys. Rev. B
Pages: 075203
Title: Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects
Volume: 89
Year: 2014


Doi: 10.1103/PhysRevB.89.075203
Journal: Phys. Rev. B
Pages: 075203
Title: Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects
Volume: 89
Year: 2014


Recently, we have started to study the effect of different perturbations on the critical defect's properties.
Doi: 10.1103/PhysRevB.86.081406
Journal: Physical Review B
Pages: 081406
Title: Spin properties of very shallow nitrogen vacancy defects in diamond
Volume: 86
Year: 2012


Doi: 10.1038/nnano.2010.56
Journal: Nature Nanotechnology
Pages: 345-349
Title: Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds
Volume: 5
Year: 2010


Doi: 10.1021/nl501927y
Journal: Nano Letters
Month: july
Number: 8
Pages: 4772-4777
Title: Proper Surface Termination for Luminescent Near-Surface NV centers in Diamomnd
Volume: 14
Year: 2014


Doi: 10.1103/PhysRevB.90.235205
Journal: Phys. Rev. B
Month: Dec
Pages: 235205
Title: Pressure and temperature dependence of the zero-field splitting in the ground state of NV centers in diamond: A first-principles study
Volume: 90
Year: 2014


Silicon-vacancy center in diamond
In a cooperation with partners in Russia and Germany, we have taken part in the work [15]Author: Igor I. Vlasov, Andrey A. Shiryaev, Torsten Rendler, Steffen Steinert, Sang-Yun Lee, Denis Antonov, Márton Vörös, Fedor Jelezko, Anatolii V. Fisenko, Lubov F. Semjonova, Johannes Biskupek, Ute Kaiser, Oleg I. Lebedev, Ilmo Sildos, Philip. R. Hemme... moreDoi: 10.1038/nnano.2013.255
Journal: Nature Nanotechn.
Pages: 54-58
Title: Molecular-sized fluorescent nanodiamonds
Volume: 9
Year: 2014


Doi: 10.1038/nnano.2013.287
Journal: Nature nanotechnology
Number: 1
Pages: 16--17
Title: Fluorescent nanoparticles: Diamonds from outer space
Volume: 9
Year: 2014


Silicon carbide defects
The extraordinary properties of NV-center in diamond exhibit great potential for the investigation of point defect based quantum information processing systems. However, from the application point of view the extreme hardness of diamond may cause difficulties in fabrication and can hinder the spreading of possible applications. Among the first, our group proposed the idea of considering silicon carbide (SiC) as a new target of research, which is a device friendly material but may host promising defects for quantum information processing. The idea of using SiC to host solid state quantum bits supported by the combination of quantum mechanical calculations and group theory analysis was first openly suggested by Adam Gali at International Conference of SiC and Related Materials 2009 (Nürnberg, Germany, 2009) [17]Author: A. Gali, A. Gällström, N. Son, E. JanzénDoi: 10.4028/www.scientific.net/MSF.645-648.395
Journal: Mater. Sci. Forum
Pages: 395-397
Title: Theory of Neutral Divacancy in SiC: A Defect for Spintronics
Volume: 645-648
Year: 2010


Doi: 10.4028/www.scientific.net/MSF.645-648.395
Journal: Mater. Sci. Forum
Pages: 395-397
Title: Theory of Neutral Divacancy in SiC: A Defect for Spintronics
Volume: 645-648
Year: 2010


Doi: 10.1002/pssb.201046254
Journal: physica status solidi (b)
Number: 6
Pages: 1337--1346
Title: Time-dependent density functional study on the excitation spectrum of point defects in semiconductors
Volume: 248
Year: 2011


Doi: 10.1073/pnas.1003052107
Journal: Proceedings of the National Academy of Sciences
Number: 19
Pages: 8513-8518
Title: Quantum computing with defects
Volume: 107
Year: 2010


Doi: 10.1038/nature10562
Journal: Nature
Pages: 84-87
Title: Room temperature coherent control of defect spin qubits in silicon carbide
Volume: 479
Year: 2011


Investigation of new candidates in SiC is a rapidly developing direction of nowadays research. In this respect, the most actively studied defects in SiC are the divacancy, the silicon vacancy, and the carbon antisite-vacancy pair.
Divacancy
The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance (David Awschalom group at Chicago University) with ab initio simulations, we show that spin-spin interactions in 4H−SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10−6 strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%–36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields.
Physical Review Letters 112 187601 (2014). DOI:10.1103/PhysRevLett.112.187601
Carbon antisite-vacancy pair defects
In an international cooperation with Japanese and Australian colleagues, we supported the establishment and identification[21]Author: S. Castelletto, B. Johnson, V. Ivády, N. Stavrias, T. Umeda, A. Gali, T. OhshimaDoi: 10.1038/nmat3806
Journal: Nature materials
Number: 2
Pages: 151--156
Title: A silicon carbide room-temperature single-photon source
Volume: 13
Year: 2014


Doi: 10.1038/nphys2858
Journal: Nature Physics
Number: 2
Pages: 93--94
Title: Optical materials: Silicon carbide goes quantum
Volume: 10
Year: 2014


Doi: 10.1038/nphoton.2013.375
Journal: Nature Photonics
Number: 2
Pages: 88--90
Title: Optical materials: Silicon carbide's quantum aspects
Volume: 8
Year: 2014


Nature Materials 13 151-156 (2014) DOI:10.1038/nmat3806
Doi: 10.1021/nn502719y
Journal: ACS Nano
Note: PMID: 25036593
Number: 8
Pages: 7938-7947
Title: Room Temperature Quantum Emission from Cubic Silicon Carbide Nanoparticles
Volume: 8
Year: 2014


ACS Nano 8 7938-7947 (2014). DOI:10.1021/nn502719y
Silicon-vacancy
Adam Gali has been shown by ab initio calculations that the negatively charged silicon vacancy (Si-vacancy) can be associated with the Tv2a and related photoluminescence centers with possessing S=3/2 spin [25]Author: A. GaliDoi: 10.4028/www.scientific.net/MSF.717-720.255
Journal: Mater. Sci. Forum
Pages: 255-258
Title: Excitation Properties of Silicon Vacancy in Silicon Carbide
Volume: 717-720
Year: 2012


Doi: 10.1557/jmr.2011.431
Journal: J. Mater. Res.
Pages: 897-909
Title: Excitation spectrum of point defects in semiconductors studied by time-dependent density functional theory
Volume: 27
Year: 2012


In collaboration with German (Jörg Wrachtrup group at Stuttgart University) and Swedish (Erik Janzén group at Linköping University) researchers, we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology. Our study is highlighted in a News and Views article from Nature Materials.
Nature Materials 15 164-168 (2015). DOI:10.1038/nmat4145
P-donor in ultrathin Si nanowires
Doi: 10.1021/nl300816t
Journal: Nano Letters
Note: PMID: 22694292
Number: 7
Pages: 3460-3465
Title: Ab Initio Study of Phosphorus Donors Acting as Quantum Bits in Silicon Nanowires
Volume: 12
Year: 2012


Nano Letters 12 3460-3465 (2012). DOI:10.1021/nl300816t
Bibliography
[1] | A. Gali, M. Fyta, E. Kaxiras: Phys. Rev. B, 77, 155206 (2008). textitAb initio supercell calculations on nitrogen-vacancy center in diamond: Electronic structure and hyperfine tensors | ![]() ![]() |
[2] | A. Gali: Phys. Rev. B, 80, 241204 (2009). Identification of individual isotopes of nitrogen-vacancy center in diamond by combining the polarization studies of nuclear spins and first-principles calculations | ![]() ![]() |
[3] | K. Szász, T. Hornos, M. Marsman, A. Gali: Phys. Rev. B, 88, 075202 (2013). Hyperfine coupling of point defects in semiconductors by hybrid density functional calculations: The role of core spin polarization | ![]() ![]() |
[4] | A. Gali: Phys. Rev. B, 79, 235210 (2009). Theory of the neutral nitrogen-vacancy center in diamond and its application to the realization of a qubit | ![]() ![]() |
[5] | G. Waldherr, J. Beck, M. Steiner, P. Neumann, A. Gali, T. Frauenheim, F. Jelezko, J. Wrachtrup: Phys. Rev. Lett., 106, 157601 (2011). Dark States of Single Nitrogen-Vacancy Centers in Diamond Unraveled by Single Shot NMR | ![]() ![]() |
[6] | P. Siyushev, H. Pinto, M. Vörös, A. Gali, F. Jelezko, J. Wrachtrup: Phys. Rev. Lett., 110, 167402 (2013). Optically Controlled Switching of the Charge State of a Single Nitrogen-Vacancy Center in Diamond at Cryogenic Temperatures | ![]() ![]() |
[7] | Á. Gali, J. Erik, P. Deák, K. Georg, K. Efthimios: Physical Review Letters, 103, 186404 (2009). Theory of Spin-Conserving Excitation of the N-V- Center in Diamond | ![]() ![]() |
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[9] | Y. Ma, M. Rohlfing, A. Gali: Phys. Rev. B, 81, 041204 (2010). Excited states of the negatively charged nitrogen-vacancy color center in diamond | ![]() ![]() |
[10] | P. Deák, B. Aradi, M. Kaviani, T. Frauenheim, A. Gali: Phys. Rev. B, 89, 075203 (2014). Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects | ![]() ![]() |
[11] | B. Ofori-Okai, S. Pezzagna, K. Chang, M. Loretz, R. Schirhagl, Y. Tao, B. Moores, K. Groot-Berning, J. Meijer, C. Degen: Physical Review B, 86, 081406 (2012). Spin properties of very shallow nitrogen vacancy defects in diamond | ![]() ![]() |
[12] | C. Bradac, T. Gaebel, N. Naidoo, M. Sellars, J. Twamley, L. Brown, A. Barnard, T. Plakhotnik, A. Zvyagin, J. Rabeau: Nature Nanotechnology, 5, 345-349 (2010). Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds | ![]() ![]() |
[13] | M. Kaviani, P. Deák, B. Aradi, T. Frauenheim, J. Chou, A. Gali: Nano Letters, 14, 4772-4777 (2014). Proper Surface Termination for Luminescent Near-Surface NV centers in Diamomnd | ![]() ![]() |
[14] | V. Ivády, T. Simon, J. R. Maze, I. A. Abrikosov, A. Gali: Phys. Rev. B, 90, 235205 (2014). Pressure and temperature dependence of the zero-field splitting in the ground state of NV centers in diamond: A first-principles study | ![]() ![]() |
[15] | Igor I. Vlasov, Andrey A. Shiryaev, Torsten Rendler, Steffen Steinert, Sang-Yun Lee, Denis Antonov, Márton Vörös, Fedor Jelezko, Anatolii V. Fisenko, Lubov F. Semjonova, Johannes Biskupek, Ute Kaiser, Oleg I. Lebedev, Ilmo Sildos, Philip. R. Hemmer, Vitaly I. Konov, Adam Gali , Jörg Wrachtrup: Nature Nanotechn., 9, 54-58 (2014). Molecular-sized fluorescent nanodiamonds | ![]() ![]() |
[16] | C. Becher: Nature nanotechnology, 9, 16-17 (2014). Fluorescent nanoparticles: Diamonds from outer space | ![]() ![]() |
[17] | A. Gali, A. Gällström, N. Son, E. Janzén: Mater. Sci. Forum, 645-648, 395-397 (2010). Theory of Neutral Divacancy in SiC: A Defect for Spintronics | ![]() ![]() |
[18] | A. Gali: physica status solidi (b), 248, 1337-1346 (2011). Time-dependent density functional study on the excitation spectrum of point defects in semiconductors | ![]() ![]() |
[19] | J. R. Weber, W. F. Koehl, J. B. Varley, A. Janotti, B. B. Buckley, C. G. Van de Walle, D. D. Awschalom: Proceedings of the National Academy of Sciences, 107, 8513-8518 (2010). Quantum computing with defects | ![]() ![]() |
[20] | W. F. Koehl, B. B. Buckley, F. J. Heremans, G. Calusine, D. D. Awschalom: Nature, 479, 84-87 (2011). Room temperature coherent control of defect spin qubits in silicon carbide | ![]() ![]() |
[21] | S. Castelletto, B. Johnson, V. Ivády, N. Stavrias, T. Umeda, A. Gali, T. Ohshima: Nature materials, 13, 151-156 (2014). A silicon carbide room-temperature single-photon source | ![]() ![]() |
[22] | I. Aharonovich, M. Toth: Nature Physics, 10, 93-94 (2014). Optical materials: Silicon carbide goes quantum | ![]() ![]() |
[23] | A. Boretti: Nature Photonics, 8, 88-90 (2014). Optical materials: Silicon carbide's quantum aspects | ![]() ![]() |
[24] | S. Castelletto, B. C. Johnson, C. Zachreson, D. Beke, I. Balogh, T. Ohshima, I. Aharonovich, A. Gali: ACS Nano, 8, 7938-7947 (2014). Room Temperature Quantum Emission from Cubic Silicon Carbide Nanoparticles | ![]() ![]() |
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[27] | B. Yan, R. Rurali, Á. Gali: Nano Letters, 12, 3460-3465 (2012). Ab Initio Study of Phosphorus Donors Acting as Quantum Bits in Silicon Nanowires | ![]() ![]() |