Details of a Researcher - Ohashi, Yoji

Ohashi, Yoji

写真a

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

Position: Professor

Related Websites

http://www.phys.keio.ac.jp/faculty/yohashi/index-jp.html

External Links

Career 【 Display / hide 】

1994.04

-

1995.03

日本学術振興会特別研究員（大阪大学基礎工学部）
1995.04

-

1998.04

筑波大学物理学系助手
1998

佐賀大学理工学部非常勤講師（併任、集中講義）
1998.05

-

2006.03

筑波大学物理学系講師
1999

佐賀大学理工学部非常勤講師（併任、集中講義）

Academic Background 【 Display / hide 】

1989.03

慶應義塾大学, Faculty of Science and Engineering, 物理学科

University, Graduated
1994.03

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

Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide 】

博士（理学）, Tokyo Institute of Technology, Coursework, 1994.03

Books 【 Display / hide 】

Encyclopedia of Condensed Matter Physics, 2nd edition

Y. Ohashi, Elsevier, 2023.10, Page： vol. 3, 10-21

Scope: BEC-BCS crossover in ultracold atomic gases and neutron stars, Contact page： Volume 3 , 10-21 , Accepted
- Access to Document (DOI)
Foundations of Quantum Mechanics in the Light of New Technology

S. Tsuchiya, and Y. Ohashi, World Scientific, 2009

Scope: 37-40
Foundations of Quantum Mechanics in the Light of New Technology

Y. Ohashi, and N. Fukushima, World Scientific, 2009

Scope: 18-23
RECENT PROGRESS IN MANY-BODY THEORIES

Y. Ohashi, World　Scientific, 2006

Scope: 18-23, 37-40
科学大辞典（第２版）

OHASHI Yoji, 丸善, 2005

Scope: 項目執筆

Papers 【 Display / hide 】

Engineering nonequilibrium superconducting phases in a voltage-driven superconductor under an external magnetic field

Taira Kawamura, Yoji Ohashi

Annalen der Physik (Wiley) e2500102(1-14) 2025.06

Accepted
- Access to Document (DOI)
Nuclear Spin-Lattice Relaxation Rate in Odd-Frequency Superconductivity

Shumpei Iwasaki,Yoji Ohashi

J. Phys. Soc. Jpn. (JPSJ) 94 ( 3 ) 034707(1-11) 2025.03

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00319015

　View Summary

We theoretically investigate the temperature dependence of nuclear spin–lattice relaxation rate T1-1 in bulk odd-frequency superconductivity. For a model odd-frequency pairing interaction, we first evaluate the superconducting order parameter, within the framework of the combined path-integral formalism with the saddle-point approximation. We then calculate T1-1 below the superconducting phase transition temperature Tc, to see how the odd-frequency pairing affects this physical quantity. In the odd-frequency p-wave state, while the so-called coherence peak is suppressed as in the even-frequency p-wave case, T1-1 is found to exhibit the Korringa-law-like behavior (T1-1 / T) except just below Tc, even without impurity scatterings. In the odd-frequency s-wave case, the behavior of T1-1 is found to be sensitive to the detailed spin structure of the superconducting order parameter: In a case, T1-1 is enhanced far below Tc, being in contrast to the conventional (even-frequency) s-wave BCS case, where the coherence peak appears just below Tc. We also show that the calculated T1-1 in the odd-frequency p-wave case well explains the recent experiment on CeRh0.5Ir0.5In5, where the possibility of odd-frequency p-wave superconductivity was recently suggested experimentally.
- Access to Document (DOI)
Shear viscosity and hierarchical structure of matter

Daichi Kagamihara, Munekazu Horikoshi, Chiho Nonaka, Yoji Ohashi, Kenta Shigaki

European Physical Journal A (Springer) 2025

Accepted
Equation of State of Quantum Cluster Matter

Munekazu Horikoshi, Yoji Ohashi, and Daichi Kagamihara

European Physical Journal A (Springer) 2025

Accepted
Nonequilibrium BCS-BEC crossover and unconventional FFLO superfluid in a strongly interacting driven-dissipative Fermi gas

Taira Kawamura, Yoji Ohashi

AAPPS Bulletin (AAPPS) 34 ( 1 ) 31(1-3) 2024.11

Research paper (scientific journal), Joint Work, Accepted, ISSN 02182203

　View Summary

We present a theoretical review of the recent progress in non-equilibrium BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover physics. As a paradigmatic example, we consider a strongly interacting driven-dissipative two-component Fermi gas where the non-equilibrium steady state is tuned by adjusting the chemical potential difference between two reservoirs that are coupled with the system. As a powerful theoretical tool to deal with this system, we employ the Schwinger-Keldysh Green’s function technique. We systematically evaluate the superfluid transition, as well as the single-particle properties, in the non-equilibrium BCS-BEC crossover region, by adjusting the chemical potential difference between the reservoirs and the strength of an s-wave pairing interaction associated with a Feshbach resonance. In the weak-coupling BCS side, the chemical potential difference is shown to imprint a two-step structure on the particle momentum distribution, leading to an anomalous enhancement of pseudogap, as well as the emergence of exotic Fulde-Ferrell-Larkin-Ovchinnikov-type superfluid instability. Since various non-equilibrium situations have recently been realized in ultracold Fermi gases, the theoretical understanding of non-equilibrium BCS-BEC crossover physics would become increasingly important in this research field.
- Access to Document (DOI)

Papers, etc., Registered in KOARA 【 Display / hide 】

Research to elucidate the formation process of strongly correlated many-body systems using high tunability of ultracold Fermi gas

Ohashi, Yoji

科学研究費補助金研究成果報告書 2021
Theoretical study on neutron-star cooling mechanism by using non-equilibrium Fermi gas superfluids

Ōhashi, Yōji

科学研究費補助金研究成果報告書 2018
Theoretical studies on the realization of a p-wave superfluid fermi gas by using a synthetic gauge field

Ohashi, Yoji

科学研究費補助金研究成果報告書 2015
Superfluid fluctuations in the BCS-BEC crossover regime of a trapped Fermi gas

Ohashi, Yoji

科学研究費補助金研究成果報告書 2012

Reviews, Commentaries, etc. 【 Display / hide 】

室温超伝導の研究開発動向と実現の可能性

大橋洋士

車載テクノロジー (（株）技術情報協会) 2024.04

Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media), Single Work, Lead author, Last author, Corresponding author
BCS-BEC クロスオーバー

大橋洋士

数理科学 (サイエンス社) 58 ( 6 ) 21 - 27 2020.06

Article, review, commentary, editorial, etc. (scientific journal), Single Work
フェルミ原子ガス超流動と中性子星内部状態への応用

大橋洋士

日本物理学会誌 (日本物理学会) 73 ( 12 ) 842 - 851 2018.12

Article, review, commentary, editorial, etc. (scientific journal), Single Work
「Superfluid Fermi atomic gas as a quantum simulator for the study of neutron-star equation of state」（P. van Wyk, H. Tajima, D. Inotani, A. Ohnishi, and Y. Ohashi, Physical Review A 97, 013601(1-13) (2018). ）の紹介記事

大橋洋士

慶應義塾大学理工学部 (慶應義塾大学理工学部) 2018.04

Single Work
フェルミ原子ガス超流動のBCS-BECクロスオーバー理論と中性子星状態方程式への挑戦

大橋洋士、Pieter van Wyk, 田島裕之

原子核研究 61 ( 1 ) 70 - 84 2016.09

Article, review, commentary, editorial, etc. (scientific journal), Joint Work

Presentations 【 Display / hide 】

Nuclear spin-lattice relaxation rate and ultrasound attenuation rate in odd-frequency superconductivity

Shumpei Iwasaki and Yoji Ohashi

30th International Conference on Low Temperature Physics (LT30) (Bilbao Exhibition Centre, Spain ) ,

2025.08
,
Poster presentation, International Union of Pure and Applied Physics (IUPAP)
Strong-Coupling Properties of a 2D-3D mixed dimensional Fermi atomic gas

Haruka Takeda, Shumpei Iwasaki, and Yoji Ohashi

30th International Conference on Low Temperature Physics (LT30) (Bilbao Exhibition Centre, Spain ) ,

2025.08
,
Poster presentation, International Union of Pure and Applied Physics (IUPAP)
BCS-rashbon BEC crossover in a superfluid gas of Fermi atoms with an anti-centrosymmetric spin-orbit interaction

Yusuke Okajima, Koki Takemoto, Shumpei Iwasaki, and Yoji Ohashi

30th International Conference on Low Temperature Physics (LT30) (Bilbao Exhibition Centre, Spain ) ,

2025.08
,
Poster presentation, International Union of Pure and Applied Physics (IUPAP)
Ultrasound attenuation in odd-frequency superconductivity

岩崎舜平, 大橋洋士

日本物理学会 (オンライン開催) ,

2025.03
,
Oral presentation (general), 日本物理学会
The non-centrosymmetric superfluidity of a spin-orbit coupled ultracold Fermi gas

Yusuke Okajima, Koki Takemoto, Shumpei Iwasaki, Yoji Ohashi

日本物理学会 (オンライン開催) ,

2025.03
,
Oral presentation (general), 日本物理学会

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

Theoretical study of superfluid ordering process in the BCS-BEC crossover regime of an ultracold Fermi gas

2022.04

-

2025.03

MEXT,JSPS, Grant-in-Aid for Scientific Research, 基盤研究(C), Principal investigator
BCS-BECクロスオーバー領域におけるフェルミ原子ガスの超流動秩序化過程の解明

2022.04

-

2025.03

Grant-in-Aid for Scientific Research, Research grant, Principal investigator
強相関量子多体状態の形成過程をフェルミ原子気体の高い操作性を使い解明する研究

2019.04

-

2022.03

Grant-in-Aid for Scientific Research, Research grant, Principal investigator
物質の階層変化および状態変化に伴う普遍的物理

2018.06

-

2023.03

Grant-in-Aid for Scientific Research, Research grant, Coinvestigator(s)
エクサスケール計算機を想定した量子モデルシミュレーションに対する並列化・高速化

2018.04

-

2021.03

Grant-in-Aid for Scientific Research, Research grant, Coinvestigator(s)

Works 【 Display / hide 】

大学院集中講義

OHASHI Yoji

京都大学,

2017.11
,
Other, Single

　View Details

フェルミ原子ガス超流動におけるＢＣＳ－ＢＥＣクロスオーバー
長崎国際テレビ開局25周年記念特別番組「アインシュタイン美しい国日本を旅する」監修（物理学）

大橋洋士

長崎国際テレビ：2015年10月18日(日)15:00～16:25、BS日テレ：2015年11月1日(日)16:00～17:25,

2015.10
,
Other, Single
研究分野を変えた時のこと

大橋洋士

三田評論 No 1187, 2015年3月号：Researcher's Eye,

2015.03

-

Present
,
Other, Single
大学院集中講義

OHASHI Yoji

東京大学,

2015.02
,
Other, Single

　View Details

フェルミ原子ガス超流動の物理
SFC科学入門講座

OHASHI Yoji

慶應義塾湘南藤沢高等学校,

2014.03
,
Other, Single

　View Details

量子の世界と超伝導

Awards 【 Display / hide 】

2020年秋季日本物理学会学生優秀発表賞

河村泰良（研究室研究生)[花井亮、大橋洋士], 2020.09, 日本物理学会, 非平衡定常状態にあるフェルミ超流動の安定性解析 [研究室研究生]
KEKオンライン研究会「熱場の量子論とその応用」ポスター賞

河村泰良（研究室研究生)[大橋洋士], 2020.08, 熱場の量子論とその応用2020, 非平衡フェルミ原子気体の超流動状態の性質 [研究室研究生]
日本物理学会学生優秀発表賞（領域１、2019秋）

真辺幸喜（研究室学生Ｄ１)[真辺幸喜、大橋洋士], 2019.11, 日本物理学会, 調和トラップ中の冷却Bose-Fermi混合気体における光原子分光スペクトル

Type of Award： Award from Japanese society, conference, symposium, etc.
理研シンポジウム・iTHEMS研究会「熱場の量子論とその応用」ポスター賞

真辺幸喜（研究室学生M2)[真辺幸喜、猪谷太輔、大橋洋士], 2018.08, 熱場の量子論とその応用2018, 強結合冷却Bose-Fermi混合気体の１粒子励起における質量インバランス効果[研究室院生]
藤原賞

田島裕之（研究室学生D3), 2017.03, 慶應義塾大学, フェルミ原子ガス超流動の熱力学的性質の理論研究に対して[研究室院生]

Courses Taught 【 Display / hide 】

THERMODYNAMICS AND STATISTICAL MECHANICS

2025
STATISTICAL MECHANICS 1

2025
PHYSICS D

2025
PHYSICS C

2025
LITERATURE OF PHYSICS

2025

Courses Previously Taught 【 Display / hide 】

凝縮系物理学特論

Keio University

2014.04

-

2015.03
,
Autumn Semester, Lecture, Within own ｆaculty
熱統計力学第1

Keio University

2014.04

-

2015.03
,
Spring Semester, Lecture, Within own ｆaculty

Media Coverage 【 Display / hide 】

:世紀の大発見！？「室温超伝導」

テレ東Biz, テレ東Biｚ　理系通信, 2023.08

　View Summary

最近、LK-99と呼ばれる物質において「室温超伝導が実現したのではないか」との発表があり大きな話題になっているが、その信ぴょう性や疑問点、室温超伝導の可能性について、配信番組中で専門的観点からコメントを与えた。

Memberships in Academic Societies 【 Display / hide 】

日本物理学会,

1991.09

-

Present

Committee Experiences 【 Display / hide 】

2023.04

-

2024.03

令和5年度知識集約型社会を支える人材育成委員会, 大橋洋士
2022.04

-

2023.03

令和4年度知識集約型社会を支える人材育成委員会, 大橋洋士
2022

カルカッタ大学博士審査外部委員（2件）, インド　カルカッタ大学
2021.12

-

2022.03

研究業績審査委員会専門委員, 日本原子力研究開発機構
2021.06

-

2025.05

AAPPS Bulltin board editor, Association of Asia Pacific Physics Society