Self-assembly of parallel atomic wires and periodic clusters of silicon on a vicinal Si(111) surface

Silicon self-assembly at step edges in the initial stage of homoepitaxial growth on a vicinal Si(111) surface is studied by scanning tunneling microscopy (STM). The resulting atomic structures change dramatically from a parallel array of 0.7 nm wide wires to one dimensionally aligned periodic clusters of the diameter ~ 2 nm and periodicity 2.7 nm in the very narrow range of growth temperatures between 400 and 300 C. These nanostructures are expected to play an important role in future development of silicon quantum computers. Mechanisms leading to such distinct structures are discussed.Comment: Accepted for publication in Phys. Rev. Lett. Numbers of pages and figures are 13 and 3, respectivel

Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the ms = \pm1 sub-levels differ significantly from that of the ms =0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor 29Si nuclear spin. We measure the coherence time of the 29 Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance.Comment: 5 pages, 4 figure

NOP132 is required for proper nucleolus localization of DEAD-box RNA helicase DDX47

Previously, we described a novel nucleolar protein, NOP132, which interacts with the small GTP binding protein RRAG A. To elucidate the function of NOP132 in the nucleolus, we identified proteins that interact with NOP132 using mass spectrometric methods. NOP132 associated mainly with proteins involved in ribosome biogenesis and RNA metabolism, including the DEAD-box RNA helicase protein, DDX47, whose yeast homolog is Rrp3, which has roles in pre-rRNA processing. Immunoprecipitation of FLAG-tagged DDX47 co-precipitated rRNA precursors, as well as a number of proteins that are probably involved in ribosome biogenesis, implying that DDX47 plays a role in pre-rRNA processing. Introduction of NOP132 small interfering RNAs induced a ring-like localization of DDX47 in the nucleolus, suggesting that NOP132 is required for the appropriate localization of DDX47 within the nucleolus. We propose that NOP132 functions in the recruitment of pre-rRNA processing proteins, including DDX47, to the region where rRNA is transcribed within the nucleolus

Association of the GTP-Binding Protein Gtr1p With Rpc19p, a Shared Subunit of RNA Polymerase I and III in Yeast Saccharomyces cerevisiae

Yeast Gtr1p and its human homolog RRAG A belong to the Ras-like small G-protein superfamily and genetically interact with RCC1, a guanine nucleotide exchange factor for Ran GTPase. Little is known regarding the function of Gtr1p. We performed yeast two-hybrid screening using Gtr1p as the bait to find interacting proteins. Rpc19p, a shared subunit of RNA polymerases I and III, associated with Gtr1p. The association of Gtr1p with Rpc19p occurred in a GTP-form-specific manner. RRAG A associated with RPA16 (human Rpc19p homolog) in a GTP-form-specific manner, suggesting that the association is conserved during evolution. Ribosomal RNA and tRNA synthesis were reduced in the gtr1Δ strain expressing the GDP form of Gtr1p, but not the GTP form of Gtr1p. Gel-filtration studies revealed an accumulation of the smaller Rpc19p-containing complex, but not of A135, in the gtr1Δ strain. Here, we propose that Gtr1p is involved in RNA polymerase I and III assembly by its association with Rpc19p and could be a mediator that links growth regulatory signals with ribosome biogenesis

Study on electron spin control method for high-sensitivity diamond quantum sensor

Study on electron spin control method for high-sensitivity diamond quantum sensorThe 4th International Forum on Quantum Metrology and Sensin

Effect of P1 concentration on NV centers created by electron beam irradiation

1. IntroductionNegatively charged nitrogen-vacancy (NV-) center in diamond is expected as quantum sensor to measure small changes in physical quantities, such as magnetic and electric field, temperature, strain, etc. The quantum sensors with high sensitivity require diamond containing high concentration of NV centers. Electron irradiation is a good method to create high concentration of NV centers. The high energy electrons knock carbon atoms out of the diamond lattice, creating vacancies. Annealing an irradiated diamond causes all the vacancies to become mobile and subsequently trapped by substituted nitrogen (P1 centers), forming NV centers. It is known that the process of NV center creation depends on the initial P1 concentrations, and the irradiation fluence dependence at low initial P1 concentrations below 1 ppm is still uncleared. In this study,we irradiate samples with different initial P1 concentrations, especially low concentration, and estimate the fluence dependency of the charge state and the amount of created NV centers.2. ExperimentsThe diamonds synthesized by High Pressure and High Temperature (HPHT) and Chemical Vapor Deposition (CVD) were used. The initial concentration of P1 was in the range from 40 ppb to 100 ppm. 2 MeV electrons were irradiated with a fluence up to 2E18 cm-2 at room temperature. Then, the samples were annealed at1000℃ for 2 hours to create NV center. The concentration of P1 was measured by Electron Spin Resonance (ESR) using JES-X330 (JEOL). The ratio between NV0 and NV- was estimated from photoluminescence (PL) spectrum measurement obtained using LabRAM HR Evolution (HORIBA). All these measurements wereperformed at room temperature.3. Results & DiscussionIn the case of type Ib HPHT diamond containing initial P1 concentration of ~100 ppm, the most of NV centers are thought to be NV-, and PL measurement revealed that only NV- was detected when the fluence of 2E18 cm-2. P1 center acts as electron donor, and provide electron to NV0. In contrast to high P1 concentration,an appreciable fraction of NV center is present as NV0 for samples with low initial P1 concentration (~ 10 ppm). We examined the relationship between the concentration of P1 and the fluence, using HPHT diamonds with initial P1 concentration of ~0.8 ppm. The concentration of P1 decreased to ~0.3 ppm when the fluence of 1.5E17 cm-2. This result suggests that P1 centers of ~0.5 ppm change to either NV center or positively charged substitutional nitrogen. PL spectrum when the fluence of 1.5×1017 cm-2, shows that both NV0 and NVarecreated. The ratio of NV- to NV0 decreased as irradiation fluence, to be 0.70 after irradiated with 1.0×1017 cm-2 and 0.53 after irradiated with 1.5E17 cm-2. It is noted that NV0 was formed even though P1 center which can act as electron donor to NV0 center remains. Similar results were observed for CVD diamonds with initial P1 concentration of ~40 ppb. The adequate fluence to maximize NV- concentration for diamonds containing low P1 concentration will be discussed by examining the fluence dependency of the charge state and total amount of NV center.New Diamond and Nano Carbons 2020/202

Storing quantum information for 30 seconds in a nanoelectronic device

The spin of an electron or a nucleus in a semiconductor(1) naturally implements the unit of quantum information-the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices(2). The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms(3), or charge and spin fluctuations arising from defects in oxides and interfaces(4). For materials such as silicon, enrichment of the spin-zero Si-28 isotope drastically reduces spin-bath decoherence(5). Experiments on bulk spin ensembles in Si-28 crystals have indeed demonstrated extraordinary coherence times(6-8). However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual P-31 electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered Si-28 substrate. The P-31 nuclear spin sets the new benchmark coherence time (>30 s with Carr-Purcell-Meiboom-Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5 s, and detailed noise spectroscopy(9) indicates that-contrary to widespread belief-it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement

Crossed broadband coplanar-waveguide circuits for extension of the spin dephasing time T2* of NV-center ensembles in bulk diamonds

広帯域の交差コプレーナー導波路を用いてT2*を伸長した結果を報告する。第68回　応用物理学会春季学術講演