Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P15: Focus Session: Spins in Semiconductors - Quantum Computing with Defects |
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Sponsoring Units: DMP GMAG FIAP Chair: Vlatcheslav Dobrivitski, Ames Laboratory/Iowa State University Room: D171 |
Wednesday, March 23, 2011 8:00AM - 8:36AM |
P15.00001: Quantum computing with defects Invited Speaker: The development of a quantum computer is contingent upon the identification and design of systems for use as qubits, the basic units of quantum information. One of the most promising candidates consists of a defect in diamond known as the nitrogen-vacancy (NV$^{-1})$ center, since it is an individually-addressable quantum system that can be initialized, manipulated, and measured with high fidelity at room temperature. While the success of the NV$^{-1}$ stems from its nature as a localized ``deep-center'' point defect, no systematic effort has been made to identify other defects that might behave in a similar way. We provide guidelines for identifying other defect centers with similar properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate systems. To elucidate these points, we compare electronic structure calculations of the NV$^{-1}$ center in diamond with those of several deep centers in 4H silicon carbide (SiC). Using hybrid functionals, we report formation energies, configuration-coordinate diagrams, and defect-level diagrams to compare and contrast the properties of these defects. We find that the N$_{C}$V$_{Si}^{-1}$ center in SiC, a structural analog of the NV$^{-1}$ center in diamond, may be a suitable center with very different optical transition energies. We also discuss how the proposed criteria can be translated into guidelines to discover NV analogs in other tetrahedrally coordinated materials.\\[4pt] [1] J. R. Weber, W. F. Koehl, J. B. Varley, A. Janotti, B. B. Buckley, C. G. Van de Walle, and D. D. Awschalom, Proc. Nat. Acad. Sci. \textbf{107}, 8513 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P15.00002: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P15.00003: Optical Control of Spatial Patterning of Nuclear Polarization in GaAs Jonathan King, Yunpu Li, Le Peng, Maria Tamargo, Carlos Meriles, Jeffrey Reimer We present new results on the optical polarization of nuclear spins in gallium arsenide. Previous work has identified the contact hyperfine interaction at shallow donors as the mechanism for helicity dependent nuclear polarization. We show a new regime, where donors are only partially occupied, where nuclear quadrupolar relaxation at shallow donors is the dominant mechanism. Since quadrupolar relaxation is helicity independent, the incident light polarization may be tuned such that the two relaxation mechanisms drive the nuclear spins to opposite signs of polarization. We show that incident light wavelength and power may be tuned to create spatial patterns of varying donor occupation in a single sample, which in turn creates a pattern of positive and negative nuclear polarization. We have developed an analytical mode which accurately describes the bulk NMR signal in terms of irradiation power and wavelength. We also present stray-field NMR imaging experiments showing direct observation of the patterned nuclear polarization. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P15.00004: Spin Orbit Interaction in Inversion-Symmetric Semiconductors: SrTiO3 and group IV Cuneyt Sahin, Giovanni Vignale, Michael E. Flatt\'e Low-energy effective spin-orbit Hamiltonians have proved effective at describing the effect of spin-orbit interactions on populations of polarized carriers in direct-gap semiconductors such as gallium arsenide. No similar low-energy Hamiltonians are available for materials with inversion symmetry, such as cubic oxides or group-IV semiconductors. In order to construct such low-energy Hamiltonians we have calculated the electronic band structure of strontium titanate, a perovskite material which has recently been used to make high-density two-dimensional electron gases, using a tight-binding electronic structure with atomic spin-orbit interactions. We have also calculated the band structures of several group-IV semiconductors, including germanium, silicon, and diamond. An expression for the effective spin-orbit interaction in the conduction band of these materials has been derived, and calculated for these materials. The symmetry properties of this effective spin-orbit interaction tensor will also be discussed. This work was supported by an ARO MURI. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:48AM |
P15.00005: Excited-State Spin Manipulation and Intrinsic Nuclear Spin Memory using Single Nitrogen-Vacancy Centers in Diamond Invited Speaker: Nitrogen vacancy (NV) center spins in diamond have emerged as a promising solid-state system for quantum information processing and precision metrology at room temperature. Understanding and developing the built-in resources of this defect center for quantum logic and memory is critical to achieving these goals. In the first case, we use nanosecond duration microwave manipulation to study the electronic spin of single NV centers in their orbital excited-state (ES) [1]. We demonstrate ES Rabi oscillations and use multi-pulse resonant control to differentiate between phonon-induced dephasing, orbital relaxation, and coherent electron-nuclear interactions. A second resource, the nuclear spin of the intrinsic nitrogen atom, may be an ideal candidate for a quantum memory due to both the long coherence of nuclear spins and their deterministic presence. We investigate coherent swaps between the NV center electronic spin state and the nuclear spin state of nitrogen using Landau-Zener transitions performed outside the asymptotic regime [2]. The swap gates are generated using lithographically fabricated waveguides that form a high-bandwidth, two-axis vector magnet on the diamond substrate. These experiments provide tools for coherently manipulating and storing quantum information in a scalable solid-state system at room temperature. \\[4pt] [1] G. D. Fuchs, V. V. Dobrovitski, D. M. Toyli, F. J. Heremans, C. D. Weis, T. Schenkel, and D.D. Awschalom, \textit{Nat. Phys.} \textbf{6}, 668 (2010). \\[0pt] [2] G. D. Fuchs, G. Burkard, P. Klimov, and D. D. Awschalom, \textit{in preparation}. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P15.00006: Dynamic Jahn-Teller Effect in Negatively Charged Nitrogen-Vacancy Center in Diamond Tesfaye Abtew, Peihong Zhang The negatively charged nitrogen-vacancy (NV) center in diamond has attracted much research interest recently owing to its desirable optical properties and long spin coherent lifetime. The ground state of NV$^{- }$center has a $^{3}$A$_{2}$ symmetry, which can be optically excited, to a $^{3}$E state. The excited state is orbitally degenerate therefore should experience either static or dynamic Jahn-Teller (JT) effects. We use accurate first-principles methods to study structural and electronic properties of the NV$^{-}$ center in diamond both in the ground and excited states. Our results indicate that the excited state of the NV$^{-}$ center is indeed a dynamic JT system. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P15.00007: Using Adiabatic Pulses for the Control of Nitrogen Impurities in Diamond Zhi-Hui Wang, G. de Lange, R. Hanson, V.V. Dobrovitski High-fidelity quantum control and dynamical decoupling of the NV center in diamond has been recently demonstrated [1]. Efficiently manipulating the spin bath of nitrogen atoms (P1 centers) can add new freedom to the control of NV centers, and can map out the properties of the bath. However, the electron spins of P1 centers have a broad spectrum, and it is difficult to implement accurate rotations uniformly over the whole spectrum. We show that the adiabatic pulses (AP) provide an efficient tool for the bath control. The internal bath dynamics imposes very moderate limitations on the AP parameters so that P1 centers can be controlled with good ($>90$\%) fidelities. The shape of AP can be tailored to the spectral density of the bath for optimized performance. We show how, by manipulating P1 centers, spin echo and dynamical decoupling of the NV center can be achieved in efficient manner. \\[4pt] [1] G. de Lange et al., Science {\bf 330}, 60 (2010); B. Naydenov et al., arXiv:1008.1953 (2010); C. A. Ryan et al., arXiv:1008.2197 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P15.00008: Nanofabrication of single spins and spin arrays in diamond D.M. Toyli, G.D. Fuchs, D.J. Christle, D.D. Awschalom, C.D. Weis, T. Schenkel The properties of isolated nitrogen vacancy (NV) centers in diamond make them a promising solid-state qubit candidate for spin-based quantum information processing. However, scaling this system to multi-qubit NV center devices requires methods to accurately place single NV centers in pure diamond substrates. To address this challenge we have developed a method for fabricating single NV centers on 50 nm length scales based on ion implantation and electron beam lithography.\footnote{D. M. Toyli \emph{et al.}, Nano Lett. 10, 3168 (2010).} Secondary ion mass spectroscopy measurements facilitate depth profiling of the implanted nitrogen to provide three-dimensional characterization of the NV center spatial distribution. Finally, electron spin resonance measurements of single NV centers, including temperature-dependent spin coherence measurements, suggest a pathway for optimizing single spin coherence in future devices. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P15.00009: Nuclear spin diffusion in semiconductor quantum wells Ionel Tifrea, Tom D. Kim We analyze the nuclear spin diffusion effect in semiconductor quantum wells in connection with dynamical nuclear polarization under optical pumping. The natural confinement provided by the particular geometry of quantum well structures is responsible for a position dependent nuclear spin relaxation time and a reduced nuclear spin diffusion. In particular, we consider the case of GaAs quantum wells within GaAlAs barriers and analyze the nuclear spin diffusion for As nuclei. Our results, obtained for different nuclear spin diffusion constants, show that nuclear spin diffusion has a relatively small effect on the overall polarization of As nuclei in these structures. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P15.00010: Single-shot electrical readout of an ensemble nuclear spin memory in silicon Dane R. McCamey, J. van Tol, G. W. Morley, C. Boehme Storing information in spin is widely recognized as a promising technological driver. However, the ability to interact with, and thus control electron spin implies a reasonable coupling to the environment, and thus a limited spin lifetime. This problem can be overcome by using nuclear spins for long term information storage even though mapping nuclear spin information onto device currents has remained challenging. Here, we report on an electrically readable nuclear spin memory implemented using phosphorus donors in silicon [1]. Donor electron spins can be used to encode logical information, which is then transferred to the nuclei. The state can be stored in the nuclear spin and then read out electrically via the hyperfine coupling with the electron. We show that information can be stored in the nuclear spin for longer than 100 seconds, that the information can be read back single shot, and that repetitive measurement does not degrade the stored information. Other nuclei, such as the spin 1/2 $^{29}$Si, can also be used, pointing to the possibility of a nuclear spin memory register. [1] D. R. McCamey, J. van Tol, G. W. Morley and C. Boehme. Science, in press (2010) [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P15.00011: Nuclear spin phase transition in the presence of interacting two-dimensional electrons Robert \.{Z}ak, Dmitrii Maslov, Daniel Loss The recent study of the RKKY interaction between localized moments, e.g., nuclear spins of Ga and As atoms in a GaAs heterostructure, mediated by interacting two-dimensional electrons, has shown a possibility of polarizing nuclear spins at currently accessible temperatures [1]. This ferromagnetic phase transition is governed by: (i) anisotropy of the electron spin susceptibility, $\chi$, in the presence of Rashba spin-orbit interaction (RSOI) and (ii) nonanalyticity in momentum dependence of $\chi$. In this talk I will argue that on top of the anisotropy in $\chi$ caused by the RSOI at zero momentum [2], the momentum dependence of $\chi$ is anisotropic itself: while the linear scaling of $\chi_{zz}$ with momentum saturates at the energy scale set by the RSOI, that of the $\chi_{xx}=\chi_{yy}$ continues through this energy scale (in this way it resembles the temperature and magnetic field dependence of $\chi$ in the presence of the RSOI [2]). The effect of the renormalization of the backscattering amplitude in the Cooper channel will be taken into account as well. In the end I will elaborate on possible implications of our results for the stability and nature of the nuclear spin ordered phase. References: [1] P.~Simon and D.~Loss, PRL {\bf 98}, 156401 (2007), P.~Simon, B.~Braunecker, and D.~Loss, PRB {\bf 77}, 045108 (2008); [2] R.~A.~\.Zak, D.~Maslov, and D.~Loss, PRB {\bf 82}, 115415 (2010). [Preview Abstract] |
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