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Significant results have been achieved in the research of solid-state quantum bits, which are the building blocks of a future implementation of the quantum computer. Diamond is a known host of solid-state qubits and single-photon emitters. Nitrogen-vacancy center (NV) stands out among these qubits in terms of robustness of optical spin readout and initialization. The microscopic mechanism behind the observed optical spin polarization was revealed by ab initio first-principles calculations. A new method was developed and implemented to describe the so-called highly-correlated electronic states in this and similar quantum bits that play a crucial role in the spin polarization process. Furthermore, the interaction between nearby NV quantum bit and acceptor defects was analyzed by the use of first-principles wavefunctions, and a novel mechanism for the decoherence of the quantum bit was revealed that may play an important role in the properties of near-surface NV quantum sensors. In addition, the ab initio magneto-optical spectrum of Group-IV--Vacancy color centers was calculated in diamond, and a new spin Hamiltonian was established in which the electron spin and the phonons are strongly coupled (see Fig. 2) that has an impact in the quantum communication applications of these quantum bits.
Figure 2. Schematic diagram of the photoexcitation of the negatively charged Group-IV—vacancy color centers in diamond. The Jahn-Teller unstable ground state (2Eg) state is photoexcited to the Jahn-Teller unstable excited state (2Eu) by absorbing a photon, and emits a red-shifted photon in the decay process. The so-called Jahn-Teller energy (EJT) in the corresponding states is also depicted.
Furthermore, we studied nanosystems that are promising in biomarker and solar cell applications. The silicon nanoparticles (Si NPs) are very promising in various emerging technologies and for fundamental quantum studies of semiconductor nanocrystals. Heavily boron and phosphorus co-doped fluorescent Si NPs can be fabricated with diameters of a few nanometers. However, very little is understood about the structure and origin of the vibration and optical spectra of these NPs. By means of first-principles simulations, various spectroscopic quantities can be computed and compared to the corresponding experimental data. We characterized the size-dependent photoluminescence and Raman spectra of dopant-free Si NPs and found good agreement with the experiments (see Fig. 3). Based on these encouraging results, we utilized the same methodology to study the Raman and PL spectra of 10 randomly generated, heavily co-doped Si NP models (where we have chosen stable dopant configurations), and found that the results are in good agreement with the experimental spectra. These results imply that we could identify the dopant configurations in small Si NPs that are responsible for the observed photoluminescence, infrared vibration and Raman spectra.
Grants
EU H2020 No. DLV-820394: Asteriqs- Advancing Science and Technology through diamond Quantum Sensing (Adam Gali, 2017-2021)
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Figure 3. The calculated photoluminescence emission spectra and resonant Raman spectra of hydrogen-terminated, pristine Si nanocrystals with diameters in the region of 1.1-2.8 nm. For the PL spectra, black and red curves correspond to 0 K and 300 K, respectively. For the Raman spectra, black curves correspond to the full spectra, while green curves correspond to the projected Raman spectra where the outermost layer of Si atoms and H atoms is excluded from the projection.
NKFIH-NN-118161: JST V4: Nanophotonics with metal – group-IV-semiconductor nanocomposites: From single nanoobjects to functional ensembles (NaMSeN, A. Gali, 2016-2018)
NKFIH NVKP_16-1-2016-0152958: Development of fluorescent dyes and microscope for the treatment of epilepsy, (Femtonics Ltd., Wigner participant: A. Gali, 2017-2019)
NKFIH NKP-2017-1.2.1-NKP-2017-00001 National Quantumtechnology Program: Creation and distribution of quantum bits and development of quantum information networks (A. Gali, 2017-2021) NKFIH-NN-127889: EU QuantERA project: Scalable Electrically Read Diamond Spin Qubit Technology for Single Molecule Imagers (A. Gali, 2018-2021)
NKFIH-127902: EU QuantERA project: Spin-based nanolytics - Turning today's quantum technology research frontier into tomorrow's diagnostic devices (A. Gali, 2018-2021)
International cooperation
Pontificia Universidad Católica de Chile (Santiago de Chile, Chile), Biophysics with color centers in diamond and related materials (J. R. Maze)
RMIT (Melbourne, Australia), Color centers in SiC nanoparticles for bioimaging (S. Castalletto) University of Melbourne (Melbourne, Australia), Single-photon emitters in SiC devices (B.C.
Johnson)
University of Pittsburgh (USA), Prof. W. J. Choyke experimental group, SiC (nano)particles University of Linköping (Sweden), Prof. Erik Janzén experimental group, point defects in SiC Harvard University (USA), Prof. Michael Lukin experimental group, defects for quantum computing
University of Chicago (USA), Prof. David D. Awschalom experimental group, SiC defects for quantum computing
University of Stuttgart (Germany), Prof. Jörg Wrachtrup experimental group, defects for quantum computing
University of Ulm (Germany), Prof. Fedor Jelezko experimental group, defects for quantum computing
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Hasselt University (Belgium), Prof. Milos Nesladek experimental group, defects in diamond Kaunas University of Technology (Lithuania), Dr. Audrius Alkauskas theoretician group, defects in diamond and SiC
University of Erlangen-Nürnberg (Germany), Dr. Michel Bockstedte theoretician group, defects in diamond and SiC
University of Kobe (Japan), Prof. Minoru Fujii experimental group, Si nanoparticles
Charles University (Czech Republic), Prof. Jan Valenta experimental group, Si nanoparticles Slovakian Academy of Sciences (Slovakia), Prof. Ivan Štich theoretician group, quantum Monte Carlo methods in Si nanoparticles
Warsaw University of Technology (Poland), Prof. Romuald B. Beck experimental group, Si layers and devices
University of Mainz (Germany), Prof. Dmitrii Budker experimental group, diamond defects University of Saarland (Germany), Prof. Christoph Becher experimental group, diamond defects
Racah Institute of Physics, The Hebrew University of Jerusalem (Israel), solid-state quantum bits (Alex Retzker)
National Institutes for Quantum and Radiological Science and Technology (Japan), solid-state quantum bits (Takeshi Ohshima)
Materials Modeling and Development Laboratory, National University of Science and Technology “MISIS,” (Russia), solid-state quantum bits (Igor A. Abrikosov)
Institute for Experimental Physics II, Universität Leipzig, solid-state quantum bits (Jan Meijer) Universität Wien (Vienna, Austria), Silicon carbide quantum bits (Michael Trupke)
Publications
Articles
1. Abdi M, Chou JP, Gali Á, Plenio MB: Color centers in hexagonal boron nitride monolayers: A group theory and ab initio analysis. ACS PHOTONICS 5:5 1967-1976 (2018)
2. Beke D, Fučíková A, Jánosi TZ, Károlyházy Gy, Somogyi B, Lenk S, Krafcsik O, Czigány Z, Erostyák J, Kamarás K, Valenta J, Gali Á: Direct observation of transition from solid-state to molecular-like optical properties in ultrasmall silicon carbide nanoparticles. J PHYS CHEM C 122:46 26713-26721 (2018)
3. Bockstedte M, Schutz F, Garratt T, Ivády V, Gali Á: Ab initio description of highly correlated states in defects for realizing quantum bits. NPJ QUANTUM MATER 3:
31/1-6 (2018)
4. Chou JP, Bodrog Z, Gali Á: First-principles study of charge diffusion between proximate solid-state qubits and its implications on sensor applications. PHYS REV LETT 120:13 136401/1-5 (2018)
5. Davidsson J, Ivády V, Armiento R, Son NT, Gali Á, Abrikosov IA: First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC. NEW J PHYS 20: 023035/1-14 (2018)
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6. Ivády V, Davidsson J, Son NT, Ohshima T, Abrikosov IA, Gali Á: Ab initio theory of Si-vacancy quantum bits in 4H and 6H-SiC. MATER SCI FORUM 924: 895-900 (2018) 7. Ivády V, Abrikosov IA, Gali Á: First principles calculation of spin-related quantities for
point defect qubit research. NPJ COMPUT MATER 4:1 76/1-13 (2018)
8. Lindner S, Bommer A, Muzha A, Krueger A, Gines L, Mandal S, Williams O, Londero E, Gali Á, Becher C: Strongly inhomogeneous distribution of spectral properties of silicon-vacancy color centers in nanodiamonds. NEW J PHYS 20:11 115002/1-14 (2018)
9. Londero E, Thiering G, Razinkovas L, Gali Á, Alkauskas A: Vibrational modes of negatively charged silicon-vacancy centers in diamond from ab initio calculations.
PHYS REV B 98:3 035306/1-9 (2018)
10. Londero E, Bourgeois E, Nesladek M, Gali Á: Identification of nickel-vacancy defects by combining experimental and ab initio simulated photocurrent spectra. PHYS REV B 97:24 241202/1-6 (2018)
11. Magnusson B, Nguyen TS, Csóré A, Gallstrom A, Ohshima T, Gali Á, Ivanov IG:
Excitation properties of the divacancy in 4H-SiC. PHYS REV B 98:19 195202/1-15 (2018)
12. Mihalyuk AN, Bondarenko LV, Tupchaya AY, Gruznev DV, Chou J-P, Hsing R, Wei C-M, Zotov AV, Saranin AA: Double-atomic layer of Tl on Si(111): Atomic arrangement and electronic properties. SURF SCI 668: 17-22 (2018)
13. Rose BC, Thiering G, Tyryshkin AM, Edmonds AM, Markham ML, Gali Á, Lyon SA, De Leon NP: Strongly anisotropic spin relaxation in the neutral silicon vacancy center in diamond. PHYS REV B 98:23 235140/1-11 (2018)
14. Somogyi B, Bruyer E, Gali Á: Photoluminescence, infrared, and Raman spectra of co-doped Si nanoparticles from first principles. J CHEM PHYS 149:15 154702/1-12 (2018) 15. Tang W, Sun M, Yu J, Chou J-P: Magnetism in non-metal atoms adsorbed
graphene-like gallium nitride monolayers. APPL SURF SCI 427: 609-612 (2018)
16. Thiering G, Gali Á: Theory of the optical spin-polarization loop of the nitrogen-vacancy center in diamond. PHYS REV B 98:8 085207/1-12 (2018)
17. Thiering G, Gali Á: Ab initio magneto-optical spectrum of group-IV vacancy color centers in diamond. PHYS REV X 8:2 021063/1-17 (2018)
18. Udvarhelyi P, Gali Á: Ab initio spin-strain coupling parameters of divacancy qubits in silicon carbide. PHYS REV APP 10:5 054010/1-6 (2018)
19. Udvarhelyi P, Shkolnikov VO, Gali Á, Burkard G, Palyi A: Spin-strain interaction in nitrogen-vacancy centers in diamond. PHYS REV B 98:7 075201/1-13 (2018)
20. Ulbricht R, Dong S, Gali Á, Meng S, Loh Z-H: Vibrational relaxation dynamics of the nitrogen-vacancy center in diamond. PHYS REV B 97:22 220302/1-6 (2018)
21. Valenta J, Fujii M, Gali Á, Nesladek M: Silicon, germanium, diamond and carbon nanostructures and their nanocomposites with other materials. PHYS STATUS SOLIDI B 255:10 1870135/1-1 (2018)
22. Zhou Y, Wang Z, Rasmita A, Kim S, Berhane A, Bodrog Z, Adamo G, Gali Á, Aharonovich I, Gao W-B: Room temperature solid-state quantum emitters in the telecom range.
SCI ADV 4:3 eaar3580/1-6 (2018)
23. Zhuang Y, Chou J-P, Chen HYT, Hsu YY, Hu CW, Hu A, Chen TY: Atomic scale Pt decoration promises oxygen reduction properties of Co@Pd nanocatalysts in alkaline electrolytes for 310k redox cycles. SUSTAIN ENERG FUELS 2:5 946-957 (2018)
See also: S-C.22, S-Q.1
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