arXiv subjects

Takumi Ito

Publications and source records attributed to Takumi Ito.

31 records · Page 2Linked to original sources

arXiv2019

Diamonds in the Rough: Generating Fluent Sentences from Early-Stage Drafts for Academic Writing Assistance

The writing process consists of several stages such as drafting, revising, editing, and proofreading. Studies on writing assistance, such as grammatical error correction (GEC), have mainly focused on sentence editing and proofreading, where surface-level issues such as typographical, spelling, or grammatical errors should be corrected. We broaden this focus to include the earlier revising stage, where sentences require adjustment to the information included or major rewriting and propose Sentence-level Revision (SentRev) as a new writing assistance task. Well-performing systems in this task can help inexperienced authors by producing fluent, complete sentences given their rough, incomplete drafts. We build a new freely available crowdsourced evaluation dataset consisting of incomplete sentences authored by non-native writers paired with their final versions extracted from published academic papers for developing and evaluating SentRev models. We also establish baseline performance on SentRev using our newly built evaluation dataset.

cs.CL↗

arXiv2019

TEASPN: Framework and Protocol for Integrated Writing Assistance Environments

Language technologies play a key role in assisting people with their writing. Although there has been steady progress in e.g., grammatical error correction (GEC), human writers are yet to benefit from this progress due to the high development cost of integrating with writing software. We propose TEASPN, a protocol and an open-source framework for achieving integrated writing assistance environments. The protocol standardizes the way writing software communicates with servers that implement such technologies, allowing developers and researchers to integrate the latest developments in natural language processing (NLP) with low cost. As a result, users can enjoy the integrated experience in their favorite writing software. The results from experiments with human participants show that users use a wide range of technologies and rate their writing experience favorably, allowing them to write more fluent text.

cs.CL↗

arXiv2018

Difference in charge and spin dynamics in a quantum dot-lead coupled system

We analyze time evolution of charge and spin states in a quantum dot coupled to an electric reservoir. Utilizing high-speed single-electron detection, we focus on dynamics induced by the first-order tunneling. We find that there is a difference between the spin and the charge relaxation: the former appears slower than the latter. The difference depends on the Fermi occupation factor and the spin relaxation becomes slower when the energy level of the quantum dot is lowered. We explain this behavior by a theory which includes the first-order tunneling processes. We conduct detailed comparison of the experiment and the theory with changing the energy of the quantum dot levels, and the theory can reproduce the experimental results.

cond-mat.mes-hall↗

arXiv2018

Four single-spin Rabi oscillations in a quadruple quantum dot

Scaling up qubits is a necessary step to realize useful systems of quantum computation. Here we demonstrate coherent manipulations of four individual electron spins using a micro-magnet method in a quadruple quantum dot - the largest number of dots used for the single spin control in multiple quantum dots. We observe Rabi oscillations and electron spin resonance (ESR) for each dot and evaluate the spin-electric coupling of the four dots, and finally discuss practical approaches to independently address single spin control in multiple quantum dot systems containing even more quantum dots.

cond-mat.mes-hall↗

arXiv2016

Tunneling induced spin dynamics in a quantum dot-lead hybrid system

Semiconductor quantum dots (QDs) offer a platform to explore the physics of quantum electronics including spins. Electron spins in QDs are considered good candidates for quantum bits in quantum information processing, and spin control and readout have been established down to a single electron level. We use these techniques to explore spin dynamics in a hybrid system, namely a QD coupled to a two dimensional electronic reservoir. The proximity of the lead results in relaxation dynamics of both charge and spin, the mechanism of which is revealed by comparing the charge and spin signal. For example, higher order charge tunneling events can be monitored by observing the spin. We expect these results to stimulate further exploration of spin dynamics in QD-lead hybrid systems and expand the possibilities for controlled spin manipulations.

cond-mat.mes-hall↗

arXiv2016

Detection and control of charge states in a quintuple quantum dot

A semiconductor quintuple quantum dot with two charge sensors and an additional contact to the center dot from an electron reservoir is fabricated to demonstrate the concept of scalable architecture. This design enables formation of the five dots as confirmed by measurements of the charge states of the three nearest dots to the respective charge sensor. The gate performance of the measured stability diagram is well reproduced by a capacitance model.These results provide an important step towards realizing controllable large scale multiple quantum dot systems.

cond-mat.mes-hall↗

arXiv2015

Single-electron Spin Resonance in a Quadruple Quantum Dot

Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of the electron spin resonance is possible.

cond-mat.mes-hall↗

arXiv2011

Exploring Supersymmetric Model with Very Light Gravitino at the LHC

The low-scale gauge mediation scenario of supersymmetry breaking predicts very light gravitino, which makes the next lightest supersymmetric particle (NLSP) quasi stable. We study the LHC phenomenology of the case that the NLSP is the stau. When the mass of the gravitino is of the order of 10eV, the decay length of stau is about 0.1--1 mm, so that it decays before reaching the first layer of the inner silicon detector. We show, however, that, with utilizing the impact parameter of tau-jets from the stau decay, it is possible to determine the mass spectrum of sparticles precisely. It is also possible to estimate the lifetime of the stau by observing distribution of the impact parameter.

hep-ph↗

arXiv2011

Identifying the Origin of Longevity of Metastable Stau at the LHC

In the framework of the supersymmetric standard model, the lighter stau often becomes long-lived. Such longevity of the stau is realized in three well-motivated scenarios: (A) the stau is the next-to-lightest supersymmetric particle (NLSP) and the gravitino is the lightest supersymmetric particle (LSP), (B) the stau is the LSP and R-parity is slightly violated, and (C) the stau is NLSP, the neutralino is the LSP, and the their masses are degenerate. We study the event topology and the decay of the stopping stau at the hadron calorimeter at the LHC, and show that it is possible to identify the reason why the stau becomes long-lived.

hep-ph↗

arXiv2010

Squark Mass Measurement in the Long-lived Stau Scenario at the LHC

The long-lived stau scenario is an interesting possibility at the LHC. We study squark mass measurements in this scenario; in particular, we show that left- and right-handed squark masses are both measurable. In SUSY events, multiple jets are expected, which become a source of combinatorial backgrounds. In order to reduce such backgrounds a hemisphere analysis is applied, and we discuss mass measurements of squarks in decay modes of left-handed squark into quark + (neutral / charged) Wino and also right-handed squark into quark + Bino.

hep-ph↗

arXiv2010

Spin and Chirality Determination of Superparticles with Long-Lived Stau at the LHC

Long-lived stau shows up in various supersymmetric models, like gauge-mediated supersymmetry (SUSY) breaking model. At the LHC experiment, long-lived stau is useful not only for the discovery of SUSY signals but also for the study of the detailed properties of superparticles. We discuss a method to obtain information on spins and chiralities of superparticles in the framework with long-lived stau. We also show that such a study can be used to distinguish SUSY model from other models of new physics, like the universal extra dimension model.

hep-ph↗

arXiv2009

Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC

In supersymmetric scenarios with a long-lived stau, the LHC experiments provide us with a great environment for precise mass measurements of superparticles. We study a case in which the mass differences between the lightest stau and other sleptons are about 10 GeV or larger, so that the decay products of heavier sleptons are hard enough to be detected. We demonstrate that the masses of neutralinos, sleptons, and squarks can be measured with a good accuracy.

hep-ph↗

arXiv2008

Long-Lived Unstable Superparticles at the LHC

In various models of supersymmetry (SUSY), the lightest superparticle in the minimal SUSY standard model sector, which we call MSSM-LSP, becomes unstable. Then, we may observe the decay of the MSSM-LSP in the detector at the LHC experiment. We show that the discovery of such a decay process (and the determination of the lifetime of the MSSM-LSP) may be possible at the LHC even if the decay length of the MSSM-LSP is much longer than the size of the detector; sizable number of the MSSM-LSPs decay inside the detector if the lifetime is shorter than 0.01-1 millisec. We also discuss the implications of the study of the MSSM-LSP decay for several well-motivated SUSY models.

hep-ph↗