Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X19: Theory and Simulations of Defect Spin Qubits in SemiconductorsInvited Session
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Sponsoring Units: DCOMP Chair: Adam Gali, Hungarian Academy of Sciences Room: 278-279 |
Friday, March 17, 2017 8:00AM - 8:36AM |
X19.00001: Simulations of defect spin qubits in piezoelectric semiconductors Invited Speaker: Hosung Seo In recent years, remarkable advances have been reported in the development of defect spin qubits in semiconductors for solid-state quantum information science and quantum metrology. Promising spin qubits include the nitrogen-vacancy center in diamond, dopants in silicon, and the silicon vacancy and divacancy spins in silicon carbide. In this talk, I will highlight some of our recent efforts devoted to defect spin qubits in piezoelectric wide-gap semiconductors for potential applications in mechanical hybrid quantum systems [1-3]. In particular, I will describe our recent combined theoretical and experimental study on remarkably robust quantum coherence found in the divancancy qubits in silicon carbide. We used a quantum bath model combined with a cluster expansion method to identify the microscopic mechanisms behind the unusually long coherence times of the divacancy spins in SiC. Our study indicates that developing spin qubits in complex crystals with multiple types of atom is a promising route to realize strongly coherent hybrid quantum systems. I will also discuss progress and challenges in computational design of new spin defects for use as qubits in piezoelectric crystals such as AlN and SiC, including a new defect design concept using large metal ion - vacancy complexes. Our first principles calculations include DFT computations using recently developed self-consistent hybrid density functional theory and large-scale many-body GW theory. [1] H. Seo, A. L. Falk, P. V. Klimov, K. C. Miao, G. Galli, and D. D. Awschalom, Nature Communications 7, 12935 (2016). [2] H. Seo, M. Govoni, and G. Galli, Scientific Reports 6, 20803 (2016). [3] W. F. Koehl, H. Seo, G. Galli and D. D. Awschalom, MRS Bulletin 40, 1146 (2015). [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 9:12AM |
X19.00002: First-principles theory on dynamic spin polarization of nuclei in solids Invited Speaker: Viktor Ivády Nuclear spins’ weak coupling to external degrees of freedom not only implies long relaxation times, which makes nuclei attractive for quantum bit (qubit) applications, but causes serious difficulties in individual nuclear spin initialization and read-out. Nuclear spin polarization is traditionally achieved by high magnetic field at low temperatures in static processes, which generally give rise to only minor population difference between the different spin states. Dynamic nuclear polarization (DNP) processes, which utilize the coupling of electron and nuclear spins to realize polarization transfer from the easy-to-address electron spin to the nuclear spin, can be implemented by point defect spin qubits in conventional semiconducting material to achieve outstandingly high nuclear spin polarization for a small number of nuclei at room temperatures. Recently, $99\pm 1$% nuclear spin polarization was reported by important qubits, such as the NV center in diamond and the divacancy in silicon carbide (SiC). In my talk, I shortly review the electronic structure and spin Hamiltonian of the most important point defect qubits, discuss first principles techniques for the determination of spin coupling strengths, such as the hyperfine coupling and zero-field-splitting, as well as introduce the model of the dynamic nuclear spin polarization. Through this model, I examine the role of electron state lifetimes and spin relaxation times as well as the possibility of radio-frequency-free bi-directional nuclear spin polarization of distinct nuclear spin for advanced nuclear spin initialization control. [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:48AM |
X19.00003: Marshak Lectureship: Vibrational properties of isolated color centers in diamond Invited Speaker: Audrius Alkauskas In this talk we review our recent work on first-principles calculations of vibrational properties of isolated defect spin qubits and single photon emitters in diamond. These properties include local vibrational spectra, luminescence lineshapes, and electron-phonon coupling. They are key in understanding physical mechanisms behind spin-selective optical initialization and read-out, quantum efficiency of single-photon emitters, as well as in the experimental identification of as yet unknown centers. We first present the methodology to calculate and analyze vibrational properties of effectively isolated defect centers. We then apply the methodology to the nitrogen-vacancy and the silicon-vacancy centers in diamond. First-principles calculations yield important new insights about these important defects. Work performed in collaboration with M. W. Doherty, A. Gali, E. Londero, L. Razinkovas, and C. G. Van de Walle. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:24AM |
X19.00004: Transition-Metal Dopants in Tetrahedrally Bonded Semiconductors Invited Speaker: Victoria Kortan Single and few defects can control the properties of nanomagnetic systems and thus are of great importance to nanometer scale systems [1]. Diamond provides an advantageous system to study these defects due to its extended spin coherence times [2], the presence of optically addressable spin centers and the progress that has been made with ion implantation [3]. The negatively charged nitrogen vacancy center is an especially attractive optically addressable spin center in diamond and there have been many impressive experimental demonstrations of optical spin initialization, manipulation, coupling and read-out [4]. Also of interest are transition-metal dopants with partially-filled d-levels which offer the possibility of electrical manipulation due to their large spin-orbit interaction [5,6]. These partially-filled d-levels split in symmetry of the diamond lattice into e and t$_{2}$ symmetry states. These two states are predicted to have different spatial extents [4,5] and this in turn affects the exchange interaction between pairs of spin centers. Using an spds* tight-binding model [7] and a Green’s function-based Koster Slater technique (as in [8]) we calculate the exchange interaction between pairs of transition metal spin centers and compare these with the exchange interaction between pairs of negatively charged nitrogen vacancy centers [9]. The exchange interaction is comparable between the two and suggests the relevance of transition metal spin centers in diamond. I acknowledge collaborations with C. Sahin and M. E. Flatt\’e. This work was supported in part by an AFOSR MURI. [1] P. Koenraad \& M.E. Flatt\'e, Nat. Mat. 10, 91 (2011). [2] G. Balasubramanian, et. al. Nature Materials 8, 383 (2009). [3] D. M. Toyli, et. al. Nano Letters 10, 3168 (2010). [4] F. Jelezko \& J. Wrachtrup. Phys Status Solidi A 203, 3207 (2006). [5] T. Chanier, et. al. Europhys. Lett. 99, 67006 (2012). [6] T. Chanier, et. al. Phys. Rev. B 86, 085203 (2012). [7] J.-M. Jancu, et. al. Phys. Rev. B 57, 6493 (1998). [8] J.-M. Tang \& M. E. Flatt\’e. Phys. Rev. Lett. 92, 047201 (2004). [9] V. R. Kortan et al., Phys. Rev. B 93, 220402(R) (2016). [Preview Abstract] |
Friday, March 17, 2017 10:24AM - 11:00AM |
X19.00005: The physics and technology of Nitrogen-vacancy centers Invited Speaker: Marcus Doherty The nitrogen-vacancy (NV) center in diamond is a leading platform for the development of quantum microscopy, computing and communication technologies. Its applications stem from its rich optical, spin and charge physics that is becoming well understood. Recently, a number of similar defects in diamond and other materials have been identified. These defects exhibit properties that are potentially superior to the NV center’s for specific quantum applications, but are yet to be fully understood. In this presentation, I will briefly review the physics and applications of the NV center before reporting the development of new first principles techniques for modelling its optical, spin and charge dynamics and decoherence processes. These techniques support deeper understanding of the NV center and the design of NV quantum devices, as well as the rapid identification and characterization of emerging defects for quantum technologies. [Preview Abstract] |
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