Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B39: Invited Session: Silicon-based Quantum Information Processing |
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Sponsoring Units: DCMP Chair: Michael Flatte, University of Iowa Room: Mile High Ballroom 2A-3A |
Monday, March 3, 2014 11:15AM - 11:51AM |
B39.00001: Building quantum states at the silicon surface using dangling bonds Invited Speaker: Steven Schofield Scanning tunnelling microscopes can be used to deterministically introduce atomic-scale defects in semiconductors [1-3], and this is considered a promising route toward the fabrication of a solid-state quantum computer. Here, we investigate the properties of deep centre defects created in the hydrogen terminated silicon (001) surface by removing individual hydrogen atoms to form dangling bonds (DBs). We demonstrate that pairs, linear chains, and two dimensional structures of individual DBs form quantum dot type states with probability density maxima between the missing H atom sites. By using the STM tip as an electrostatic gate to control which states contribute to the STM image, we suggest the origin of these surprising and previously unobserved states are first excited states of the individual DBs [1]. Our results show that quantum states can be fabricated on silicon with atomic-scale precision, and suggest a general model of quantum state fabrication using other passivated semiconductor surfaces. \\[4pt] [1] Schofield et al., Nature Commun. 4, 1649 (2013)\\[0pt] [2] Schofield et al., PRL 91, 136104 (2003).\\[0pt] [3] Koenraad et al., Nature Mater. 10, 91, (2011) [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:27PM |
B39.00002: A single dopant atom in silicon sees the light Invited Speaker: Sven Rogge Optical access to a single qubit is very attractive since it allows for readout with unprecedented high spectral resolution and long distance coupling. Substantial progress has been demonstrated for nitrogen-vacancy centers in diamond (Bernien, Nature, 2013). Optical access to qubits in silicon been an important goal but has to date only been achieved in the ensemble limit (Steger, Science, 2012). Here, we present the photoionization of an individual erbium dopant in silicon (Yin, Nature, 2013). A single-electron transistor is used as a single-shot charge detector to observe the resonant ionization of a single atom as a function of photon energy. This allows for optical addressing and electrical detection of individual erbium dopants with exceptionally narrow line width. The hyperfine coupling is clearly resolved which paves the way to single shot readout of the nuclear spin. This hybrid approach is a first step towards an optical interface to dopants in silicon. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 1:03PM |
B39.00003: Qubit control in phosphorus doped silicon nanowires Invited Speaker: Adam Gali Quantum confinement can turn thin silicon nanowires (SiNWs) to wide band gap material where the large surface-to-volume ratio indicates that its electronic structure may be tailored by surface termination. Here we show an example how these properties of thin SiNWs may be utilized to host quantum bits. A phosphorus (P) donor has been extensively studied in bulk silicon to realize the concept of Kane quantum computers. In most cases the quantum bit was realized as an entanglement between the donor electron spin and the nonzero nuclei spin of the donor impurity mediated by the hyperfine coupling between them. The donor ionization energies and the spin-lattice relaxation time limited the temperatures to a few kelvin in these experiments. Here, we demonstrate by means of ab initio density functional theory calculations that quantum confinement in thin SiNWs results in (i) larger excitation energies of donor impurity and (ii) a sensitive manipulation of the hyperfine coupling by external electric field. We propose that these features may allow to realize the quantum bit (qubit) experiments at elevated temperatures with a strength of electric fields applicable in current field-effect transistor technology. We also show that the strength of quantum confinement and the presence of strain induced by the surface termination may significantly affect the ground and excited states of the donors in thin SiNWs, possibly allowing an optical read-out of the electron spin [1]. Another forms of donor-related defects as potential qubits will be also discussed.\\[4pt] Work done in collaboration with Binghai Yan, Max Planck Institute for Chemical Physics of Solids, Dresden, and Riccardo Rurali, Institut de Ci\`encia de Materials de Barcelona (ICMAB-CSIC).\\[4pt] [1] Binghai, Rurali, Gali, Nano Letters, 12, 3460 (2012). [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:39PM |
B39.00004: Physics of high field magnetic white dwarf stars -- relevance to silicon quantum information applications? Invited Speaker: Ben Murdin Shallow donor impurities in silicon, once frozen out at low temperature, share many properties in common with free hydrogen atoms [1]. They have long been the subject of spectroscopic investigation, but it is only very recently [2,3] that it has been possible to investigate the time-domain dynamics of orbital excitations such as the 1s to 2p, due to the difficulty of obtaining short, intense pulses in the relevant wavelength range. These new techniques make shallow donors, and also acceptors [4], attractive for studying atomic physics effects, and for applications in quantum information. We have measured the population dynamics [2] of electrons orbiting around phosphorus impurities in commercially-available silicon, and shown that the lattice relaxation lifetime is about 200ps, only 1 order of magnitude shorter than the radiative lifetime of free hydrogen. Recently we also showed that high magnetic fields can introduce enormous changes in the electron wavefunction [1], and that easily available fields could be used for spatial control of the Rydberg orbital, and hence the overlap with adjacent atoms. A spin off benefit of the analogy with free hydrogen, is that we can use the results to better understand the spectroscopy of free hydrogen atoms on the surface of white dwarf stars where the magnetic field can be as high as one gigagauss.\\[4pt] [1] BN Murdin et al Nature Communications 4, 1469 (2013);\\[0pt] [2] NQ Vinh, et al, Proc Nat Acad Sci USA 105, 10649 (2008);\\[0pt] [3] PT Greenland, et al Nature 465, 1057 (2010);\\[0pt] [4] NQ Vinh, et al Phys Rev X 3, 011019 (2013). [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 2:15PM |
B39.00005: Engineered defect spin states in silicon carbide for sensing and computation Invited Speaker: Abram Falk Crystal defects can confine isolated electronic spins and are promising candidates for solid-state quantum bits. Alongside research efforts focusing on nitrogen-vacancy centers in diamond, an alternative approach seeks to identify and control new spin systems with an expanded set of technological capabilities, a strategy that could ultimately lead to ``designer'' spins with tailored properties. We show that the 4H, 6H and 3C polytypes of silicon carbide are all hosts for optically addressable spin states, including states in all three whose long quantum coherence times persist up to room temperature\footnote{A. L. Falk, B. B. Buckley, G. Calusine, W. F. Koehl, V. V. Dobrovitski, C. A. Zorman, P. X.-L. Feng, D. D. Awschalom. Polytype control of spin qubits in SiC. \textit{Nat. Commun.}, {\bf 4}, 1819 (2013)} and states with highly spin-dependent photoluminescence. Atomic-scale sensing with SiC defects is also an exciting and developing area of research, particularly since the polar character of the Si-C bond enhances the sensitivity of defect spin transitions to electric fields. We show that SiC defects can be used for high-sensitivity electric- and strain- field measurements\footnote{ A. L. Falk, P. V. Klimov, B. B. Buckley, V. Iv\'{a}dy, W. F. Koehl, I. A. Abrikosov, \'{A}. Gali, and D. D. Awschalom. Strain and electric field sensing with defect spins in SiC. \textit{Submitted} (2013).} and controlled on the nanometer scale through electrically driven spin resonance.\footnote{P. V. Klimov, A. L. Falk, B. B. Buckley, D. D. Awschalom, Electrically driven spin resonance in SiC color centers. \textit{ArXiv}:1310.4844 (2013).} Moreover, we use double electron-electron resonance to measure magnetic dipole interactions between spin states occupying inequivalent lattice sites of the same crystal. Together with the distinct spin transition energies of such inequivalent states, these interactions provide a route to dipole-coupled networks of separately addressable spins. [Preview Abstract] |
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