arXiv subjects

K. Koike

Publications and source records attributed to K. Koike.

11 recordsLinked to original sources

arXiv2024

Development of a bipolar 50 V output digital-to-analog converter system for ion-shuttling operations

The quantum charge-coupled device (QCCD) is one of the notable architectures to achieve large-scale trapped-ion quantum computers. To realize QCCD architecture, ions must be transported quickly while minimizing motional excitation. High-voltage sources are necessary to achieve such high-quality ion transport through a high secular frequency. In this study, we report the development of a field programmable gate array (FPGA)-based digital-to-analog converter (DAC) system with an output voltage range of +/-50 V and demonstrate its effectiveness in ion transport operations. The device provides 16-channel analog output, maximum update rate of 16 mega updates per second (MUPS), slew rate of 20 V/us, and bandwidth of > 200 kHz. By optimizing the voltage sets with quadratic programming, we experimentally confirmed that this DAC system can achieve more than twice the secular frequency attainable when its output range is restricted to +/-10 V, which is consistent with the fact that scaling all electrode voltages by a factor of 5 will scale the secular frequency by the square root of 5. Since the output range of many commercially available DACs is commonly limited to +/-10 V, this increase is effective for ion shuttling operations, such as transport, split and merge. The developed DAC system has potential to increase the speed of ion transport thereby reducing processing times in QCCD-based quantum computers.

quant-ph↗

arXiv2010

SiO Maser Spectra of V407 Cyg after the 2010 March Nova Outburst

We report on the time variation of SiO maser emission from the symbiotic stellar system V407 Cyg after the classical nova outburst on 2010 March 10. Although both the SiO $J=1$--0 $v=1$ and 2 lines at 43.122 and 42.821 GHz were found previously in the envelope of a mira in the binary system, only weak emission of the $J=1$--0 $v=2$ line has continuously been detectable after the nova outburst. The line profile exhibited a dramatic change several weeks after the burst; the component on the higher-velocity side of the systemic velocity disappeared two weeks after the burst, and a new persistent component appeared on the lower-velocity side later. These observations indicate that the SiO emitting regions are wiped out in a time scale of two weeks by the nova shock, but a part of the masing region is quickly replenished by cool molecular gases expelled by the mira pulsation.

astro-ph.SR↗

arXiv2010

SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk

We present the result of radio observations of red supergiants in the star cluster, Stephenson's #2, and candidates for red supergiants in the star clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and H$_2$O maser lines.The Stephenson's #2 cluster and nearby aggregation at the South-West contain more than 15 red supergiants. We detected one at the center of Stephenson's #2 and three in the south-west aggregation in the SiO maser line, and three of these 4 were also detected in the H2O maser line. The average radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with the other star clusters. In addition, mapping observations in the CO J=1--0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al.'s #122. It indicates that a time scale of gas expulsion differs considerably in individual clusters.

astro-ph.SR↗

arXiv2006

Centrosymmetric PbTe/CdTe quantum dots coherently embedded by epitaxial precipitation

A concept for the fabrication of highly symmetric quantum dots that are coherently embedded in a single crystalline matrix is demonstrated. In this approach, the formation of the quantum dots is induced by a transformation of an epitaxial 2D quantum well into an array of isolated precipitates with dimensions of about 25 nm. The formation process is driven by the immiscibility of the constituent materials resulting from their different lattice structures. The investigated PbTe/CdTe heterosystem combines two different cubic lattices with almost identical lattice constants. Therefore, the precipitated quantum dots are almost strain free and near thermodynamic equilibrium they exhibit the shape of small-rhombo-cubo-octahedrons. The PbTe/CdTe quantum dots, grown on GaAs substrates, display intense room temperature luminescence at wavelength around 3.2 micrometer, which makes them auspicious for applications in mid-infrared photonic devices.

cond-mat.mtrl-sci↗

arXiv2005

A Schematic Model of Leptons and Quarks Based on Majorana Partners

The possible extension of generation structure is investigated on the basis of a composite model, in which leptons and quarks are composed of rishons $T$ with charge 1/3 and purely neutral $V$. In this sub-system, we regard $V$ as the origin of Majorana particles. The seesaw mechanism implies the possible existence of heavy $V$, denoted as $V_B$ in addition to ordinary $V$, denoted as $V_s$. If we regard $V_B$ as a constitute block of leptons and quarks, a new generation scheme arises. This new scheme satisfies the anomaly-free condition.

hep-ph↗

arXiv2004

On the Weak Decay of Composite System based on Majorana Partners

In a composite model of leptons and quarks, composite particles with heavy Majorana particles appear provided that the V-rishon is regarded as a Majorana particle. In this paper, the decay mode of such "Majorana partners" is isestigated. It is shown that the life time of Majorana partners are fairly long. Our model suggests that a new mechanism of proton decay is possible, where the X and Y bosons in GUTs are not necessary.

hep-ph↗

arXiv2004

Possible Chandra-Mechanism for Generation Bound

In the generation structure, the quark mass increases extremely rapidly with the increase of generation index, and there is the bound for generation number. The ground for this bound is investigated on the basis of a certain kind of composite model of leptons and quarks, in which they are supposed to be composed of sub-constituents with fermi statistics. Possible Chandrasekhar-like mechanism for generation bound is proposed.

hep-ph↗

arXiv2004

Photo-Luminescence and Possible Forsterite nanoparticles Model of Extended Red Emission

Possible forsterite nanoparticle model of the Extended Red Emission(ERE) is proposed on the basis of photo-luminescence of forsterite after gamma-ray and neutron irradiation. Forsterite exhibits interesting thermoluminescence spectrum similar to ERE of Red Rectangle after irradiation in low temperature. It is shown that the forsterite after thermoluminescence is over exhibits photo-luminescence(PL) when Ultraviolet ray is irradiated. The structure of PL spectrum is almost similar to that of thermoluminescence. In order to explain small variations of the peak position of wavelength of ERE spectrum, possible nanoparticle model of forsterite is investigated. Our model is consistent to the ISO observation data in near and middle infrared region, which suggest the existence of forsterite.

astro-ph↗

arXiv2002

Thermoluminescence of Simulated Interstellar Matter after Gamma-ray Irradiation

Interstellar matter is known to be strongly irradiated by radiation and several types of cosmic ray particles. Simulated interstellar matter, such as forsterite $\rm Mg_{2}SiO_{4}$, enstatite $\rm MgSiO_{3}$ and magnesite $\rm MgCO_{3}$ has been irradiated with the $\rm ^{60}Co$ gamma-rays in liquid nitrogen, and also irradiated with fast neutrons at 10 K and 70 K by making use of the low-temperature irradiation facility of Kyoto University Reactor (KUR-LTL. Maximum fast neutron dose is $10^{17}n_f{\rm /cm^{2}}$). After irradiation, samples are stored in liquid nitrogen for several months to allow the decay of induced radioactivity. We measured the luminescence spectra of the gamma ray irradiated samples during warming to 370K using a spectrophotometer. For the forsterite and magnesite, the spectra exhibit a rather intense peak at about 645 -- 655 nm and 660 nm respectively, whereas luminescence scarcely appeared in olivine sample. The spectra of forsterite is very similar to the ERE of the Red Rectangle.

astro-ph↗

arXiv2001

Generation Structure and Proton Decay Problem

Possible generation structure is investigated. We considere alternative possibility of combination of leptons and quarks to compose each generation, where the combination of $(ν_τ,τ)$ and $(u,d)$ compose a generation. Our model exhibits the hierarcy structure after sea-saw mechanism provived that possible existence of realistic right-handed neutrinos are taken into account. Then, in the GUTs model based on our scheme, possible inter-generation properties are examined together with the classification of gauge bosons. It is shown that if our scheme is realized, the proton decay exhibits different mode from ordinary one.

hep-ph↗

arXiv2000

On the Family of Pentagonal curves of genus 6 and associated modular forms on the Ball

In this article we study the inverse of the period map for the family $\mathcal{F}$ of complex algebraic curves of genus 6 equipped with an automorphism of order 5. This is a family with 2 parameters, and is fibred over a certain type of Del Pezzo surace. The period satisfies the hypergeometric differential equation for Appell's $F_1({3/5},{3/5},{2/5},{6/5})$ of two variables after a certain normalization of the variable parameter. This differential equation and the family $\mathcal{F}$ are studied by G. Shimura (1964), T. Terada (1983, 1985), P. Deligne - G.D. Mostow (1986) and T. Yamazaki- M. Yoshida(1984). Recently M. Yoshida presented a new approch using the concept of configration space. Based on their results we show the representation of the inverse of the period map in terms of Riemann theta constants. This is the first variant of the work of H. Shiga (1981) and K. Matsumoto (1989, 2000) to the co-compact case.

math.AG↗