First principles investigation of solid state defects acting as quantum bits

Nima Ghafari Cherati, Gergő Thiering, Ádám Gali

Point defects in diamond may act as quantum bits. Recently, oxygen-vacancy related defects have been proposed to the origin of the so-called ST1 color center in diamond that can realize a long-living solid-state quantum memory. Motivated by this proposal we systematically investigate oxygen-vacancy complexes in diamond by means of first principles density functional theory calculations. We find that all the considered oxygen-vacancy defects have a high-spin ground state in their neutral charge state, which disregards them as an origin for the ST1 color center. We identify a high-spin metastable oxygen-vacancy complex and characterize their magneto-optical properties for identification in future experiments.

Michael Hanks, Michael Trupke, William J. Munro +1 more

Viktor Ivády

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+V w 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 two-dimensional materials for topologically protected states.v vi First of all, I would like to thank my main supervisor, Prof. Igor Abrikosov, and my co-supervisors, Prof. Adam Gali and Prof. Erik Janzén, for their great guidance and helpfulness over the years.I appreciate and thank the numerous advice, the valuable discussions and the inspiring ideas.I am particularly grateful to all of them for providing and maintaining an unusual working agreement through which I can experience and learn much more than I could imagine before.Furthermore, I am thankful to Prof. Adam Gali for launching me on my career, helping from the beginning, and for involving me in several collaborations as well as to Prof. Igor Abrikosov for showing me numerous theoretical techniques, guiding me towards method development studies, and for supporting during my PhD studies.I would like to thank all of the members of our Swedish and Hungarian groups for creating a friendly and helpful atmosphere and for always being open for discussions.I am also very grateful to all of my collaborators, particularly from

Dafei Jin

Donald R. Hamann

F.J. Gonzalez, Diego Tancara, Hossein T. Dinani +2 more

Abstract Understanding defect-phonon interactions in solid-state devices is crucial for improving our current knowledge of quantum platforms. In this work, we develop first-principles calculations for a defect composed of two spin- 1 / 2 particles that interact with phonon modes in a one-dimensional lattice. We follow a bottom-up approach that begins with a dipolar magnetic interaction to ultimately derive the spectral density function and time-local master equation that describes the open dynamics of the defect. We provide theoretical and numerical analysis for the non-Markovian (NM) features of the defect-phonon dynamics induced by a pure dephasing channel acting on the Bell basis. Finally, we analyze two measures of NM based on the canonical rates and Coherence, shedding more light on the role of the spectral density function and temperature; and envisioning experimental realizations.