Details of a Researcher - Koike, Tatsuhiko

Koike, Tatsuhiko

写真a

Affiliation: Faculty of Science and Technology, Department of Physics （Yagami）

Position: Assistant Professor/Senior Assistant Professor

Related Websites

http://www.phys.keio.ac.jp/faculty/koike

External Links

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Career 【 Display / hide 】

1993.04

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1996.03

Tokyo Institute of Technology, 物理学科, JSPS postdoctoral fellow
1993.04

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1996.03

Tokyo Institute of Technology, 物理学科, JSPS postdoctoral fellow
1996.04

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2006.03

Department of Physics, Keio University, 物理学科, 助手
1996.04

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2006.03

Department of Physics, Keio University, 物理学科, 助手
2000.02

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2001.03

University of Maryland, JSPS postdoctoral fellow

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Academic Background 【 Display / hide 】

1991.03

The University of Tokyo, Faculty of Science, Department of Physics
1991.03

The University of Tokyo, Faculty of Science, Department of Physics

University, Graduated
1993.03

Tokyo Institute of Technology, Graduate School, Division of Science and Engineeri, 物理学
1993.03

Tokyo Institute of Technology, Graduate School, Division of Science and Engineeri, 物理学

Graduate School, Completed, Master's course
1996.03

Tokyo Institute of Technology, Graduate School, Division of Science and Engineeri, 物理学

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Academic Degrees 【 Display / hide 】

修士（理学）, Tokyo Institute of Technology, Coursework, 1993.03
博士（理学）, Tokyo Institute of Technology, Coursework, 1996.03

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Research Areas 【 Display / hide 】

Natural Science / Semiconductors, optical properties of condensed matter and atomic physics (Atomic/Molecular/Quantum Electronics, Plasma)
Natural Science / Semiconductors, optical properties of condensed matter and atomic physics (Atomic/Molecular/Quantum Electronics, Plasma)
Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics (Elementary Particle/Atomic Nucleus/Cosmic Ray/Space Physics)
Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics (Elementary Particle/Atomic Nucleus/Cosmic Ray/Space Physics)
Informatics / Theory of informatics (Fundamental Informatics)

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Books 【 Display / hide 】

Singularities in Geometry and Topology

KOIKE TATSUHIKO, European Mathematical Society, 2012

Scope: 51-69
爆発と凝集

原隆, 古池達彦, 東京大学出版会, 2006.02

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Papers 【 Display / hide 】

Nambu-Goto strings with a null symmetry and contact structure

Hiroshi Kozaki, Tatsuhiko Koike, Yoshiyuki Morisawa and Hideki Ishihara

Physical Review D （American Physical Society) 108 （ 8 ） 084069 2023.08

Research paper (scientific journal), Joint Work, Accepted, ISSN 24700010

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We study the classical dynamics of the Nambu-Goto strings with a null symmetry in curved spacetimes admitting a null Killing vector field. The Nambu-Goto equation is reduced to first-order ordinary differential equations and is always integrable in contrast to the case of non-null symmetries where integrability requires additional spacetime symmetries. It is found that in the case of null symmetry, an almost contact structure associated with the metric dual 1-form η of the null Killing vector field emerges naturally. This structure determines the allowed class of string worldsheets in such a way that the tangent vector fields of the worldsheet lie in ker dη. In the special case that the almost contact structure becomes a contact structure, its Reeb vector field completely characterizes the worldsheet. We apply our formulation to the strings in the pp-waves, the Einstein static universe and the Gödel universe. We also study their worldsheet geometry in detail.
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Quantum brachistochrone

Tatsuhiko Koike

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences （Royal Society Publishing) 380 （ 2239 ） 2022.12

Lead author, Last author, Corresponding author, ISSN 1364503X

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Quantum brachistochrone (QB) is a quantum analogue of classical brachistochrone (shortest path). It is a solution to the following problem: How can we perform a desired quantum operation (or obtain a desired final quantum state) most quickly, by a time-dependent Hamiltonian subject to given constraints? Finding QB is a fundamental problem in quantum mechanics in its own right. Moreover, it will be useful in the study of quantum information and quantum engineering, such as quantum speed limits and implementations of quantum computers. A general framework for finding QBs, called QB formalism, has been developed. It is based on Pontryagin's maximum principle. We review the basics of the QB formalism, give simple examples, and briefly discuss some related studies. This article is part of the theme issue 'Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives'.
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A general formulation of time-optimal quantum control and optimality of singular protocols

Wakamura Hiroaki, Koike Tatsuhiko

NEW JOURNAL OF PHYSICS （New Journal of Physics) 22 （ 7 ） 2020.07

ISSN 1367-2630

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We present a general theoretical framework for finding the time-optimal unitary evolution of the quantum systems when the Hamiltonian is subject to arbitrary constraints. Quantum brachistochrone (QB) is such a framework based on the variational principle, whose drawback is that it only deals with equality constraints. While inequality constraints can be reduced to equality ones in some situations, they usually cannot, especially when a drift field, an uncontrollable part, is present in the Hamiltonian. We first develop a framework based on Pontryagin's maximum principle (MP) in order to deal with inequality constraints as well. The new framework contains QB as a special case, and their detailed correspondence is given. Second, we address the problem of singular controls, which satisfy MP trivially so as to cause a trouble in determining the optimal protocol. To overcome this difficulty, we derive an additional necessary condition for a singular protocol to be optimal by applying the generalized Legendre-Clebsch condition. Third, we discuss general relations among the drift, the singular controls, and the inequality constraints. Finally, we demonstrate how our framework and results work in some examples. We also discuss the physical meaning of singular controls.
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Cohomogeneity-one-string integrability of spacetimes

Morisawa Y, Hasegawa S, Koike T, Ishihara H

Classical and Quantum Gravity （Classical and Quantum Gravity) 36 （ 15 ） 2019.07

Joint Work, ISSN 02649381

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© 2019 IOP Publishing Ltd. A classical string whose world sheet shares a one-dimensional symmetry with the spacetime is called cohomogeneity-one (C1). We propose C1-string integrability, i.e. integrability of all C1 strings in the spacetime, as a class of hidden symmetry of a spacetime. The C1 string may probe symmetry which is not probed by a particle. We present a simple, systematic procedure for finding constants of motion of a C1 string and examining C1 string integrability of a spacetime. We apply the framework to some physically important spacetimes such as AdS5, AdS5 × S5, and AdS5 × Tp,q. C1 strings and C1-string integrability may be useful for a prior examination of general string integrability of a highly symmetric spacetime since, among the examples above, all C1 string integrable spacetimes are string-integrable, and the previously obtained chaotic string solutions in those or other spacetimes are of class C1.
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Disturbance by optimal discrimination

Ryuitiro Kawakubo and Tatsuhiko Koike

Physical Review A （American Physical Society) 97 （ 3 ） 032102 (5pp) 2018.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 24699926

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© 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. We discuss the disturbance by measurements which unambiguously discriminate between given candidate states. We prove that such an optimal measurement necessarily changes distinguishable states indistinguishable when the inconclusive outcome is obtained. The result was previously shown by Chefles [Phys. Lett. A 239, 339 (1998)PYLAAG0375-960110.1016/S0375-9601(98)00064-4] under restrictions on the class of quantum measurements and on the definition of optimality. Our theorems remove these restrictions and are also applicable to infinitely many candidate states. Combining with our previous results, one can obtain concrete mathematical conditions for the resulting states. The method may have a wide variety of applications in contexts other than state discrimination.
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Presentations 【 Display / hide 】

Time optimization of quantum gates by quantum brachistchrone

Kaoru Ono, Hiroshi Sato, Tatsuhiko Koike

Spring Meeting 2024, Physical Society of Japan (online) ,

2024.03
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Oral presentation (general), Physical Society of Japan
Quantum brachistochrone and Pontryagin's maximum principle

Tatsuhiko Koike

重力と量子で紡ぐ宇宙 (公共の宿しきぶ温泉湯楽里) ,

2023.08
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Oral presentation (invited, special), 斉田浩見、樽家篤史、野田宗佑、吉野裕高、柳哲文
等質余次元1物体から量子最速曲線まで

古池達彦

相対論と重力研究の現在，過去・未来 (大阪市立大学) ,

2022.03
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Oral presentation (invited, special)
A generalization of quantum brachistochrone

Hiroaki Wakamura, Tatsuhiko Koike

第21回「特異点と時空、および関連する物理」研究会 (秋田市) ,

2019.12
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Oral presentation (general), 特異点研究会組織委員会
量子系での時間最適制御の一般論と特異的な制御

若村浩明, 川久保龍一郎, 古池達彦

日本物理学会2019年秋季大会 (岐阜大学柳戸キャンパス) ,

2019.09
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Oral presentation (general), 日本物理学会

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

時間最適量子制御の基礎理論と特異制御に関する研究

2020.04

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2023.03

MEXT,JSPS, Grant-in-Aid for Scientific Research, 古池達彦, Grant-in-Aid for Scientific Research (C), Principal investigator

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本課題研究の目的は量子系を素速く精確に制御する方法を明らかにすることである。制御とは系を所望の状態に保ったり変化させることを指す。量子系を自在に制御するためには外場や測定の影響を理解する必要がある。特に、最適制御の研究は量子ダイナミクスの限界を明らかにするという基礎研究のみならず、情報処理への応用という面でも意義が大きい。例えば現在の量子計算機においては、量子状態が壊れてしまう前にできるだけ多くの計算を行うことをが必須である。研究代表者は、従来から時間最適制御を変分原理により求める方法を開発してきた。それは「量子最速曲線法」と呼ばれている。昨年度は、時間最適量子制御に対する基礎理論を構築・確立した。与えられた制限下で所望の量子操作を最速に行う方法を求める理論である。これを、量子最速曲線法を「ポントリャーギン最大値原理」という手法で拡張することで実現した。その結果、従来扱えなかった不等式拘束条件を扱えるようになり、理論および応用上遭遇するほぼ全ての状況に適用可能となった。
本年度は、確立された理論を実際に応用すべく研究を継続中である。特に、我々の方法を用いれば既存の方法を越えた計算速度を実現可能であることを示すための研究を遂行中である。特に、本学量子計算センターで利用可能な量子計算機実機への具体的応用をシミュレート中である。一方、確立した量子最速曲線理論の周知および普及にも資するべく、理論を招待公演にて紹介し、国外専門誌において来年度出版予定の招待論文を執筆中である。コロナ禍で多少の遅れが生じているが、研究の基礎段階の遂行および若手の研究協力者の育成を進めることができた。

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Awards 【 Display / hide 】

Teshima Memorial Doctoral Thesis Award

KOIKE TATSUHIKO, 1996.03, 手島工業教育資金団, Renormalization group analysis of critical behaviour in gravitational collapse

Type of Award： Award from publisher, newspaper, foundation, etc.
Teshima Memorial Doctoral Thesis Award

HKOIKE TATSUHIKO, HR, 1996.03, 手島工業教育資金団, Renormalization group analysis of critical behaviour in gravitational collapse

Type of Award： Award from publisher, newspaper, foundation, etc.
Teshima Memorial Doctoral Thesis Award

KOIKE TATSUHIKO, 1996.03, 手島工業教育資金団, Renormalization group analysis of critical behaviour in gravitational collapse

Type of Award： Award from publisher, newspaper, foundation, etc.