Welcome to Ryuji Takagi’s website!

I am a faculty member at the University of Tokyo working on quantum information theory. My research interests lie in the quantitative understanding of the power of quantum resources in quantum information processing tasks, and how those quantities provide insights into operational aspects of quantum mechanics and related physical phenomena.

I obtained my Ph.D. in Physics at the Massachusetts Institute of Technology under the guidance of Seth Lloyd and Isaac Chuang. Before joining the University of Tokyo, I was a Lee Kuan Yew Research Fellow at Nanyang Technological University Singapore, where I worked in the group led by Mile Gu.

News

October 15, 2025
Our work “Symmetric Channel Verification for Purifying Noisy Quantum Channels” has been published in PRX Quantum. Joint work with Kento Tsubouchi, Yosuke Mitsuhashi, and Nobuyuki Yoshioka.

Ocotber 15, 2025
Our work “Classical simulation and quantum resource theory of non-Gaussian optics” has been published in Quantum. Joint work with Oliver Hahn.

October 7, 2025
Our work “Recovery of the second law in fully quantum thermodynamics” has been posted on arXiv. Joint work with Naoto Shiraishi.

September 5, 2025
Our work “Quantum algorithms for Uhlmann transformation” has been posted on arXiv. Joint work with Takeru Utsumi, Yoshifumi Nakata, and Qisheng Wang

August 28, 2025
Our work “Measuring non-Gaussianity with correlation” has been posted on arXiv. Joint work with Oliver Hahn.

August 1, 2025
Our work “Universal tradeoff relations between resource cost and irreversibility of channels: General-resource Wigner-Araki-Yanase theorems and beyond” has been posted on arXiv. Joint work with Hiroyasu Tajima, Koji Yamaguchi, and Yui Kuramochi.

May 7, 2025
Our work “Quantum Dynamic Programming” has been published in Physical Review Letters. Joint work with Jeongrak Son, Marek Gluza, and Nelly Ng.

April 29, 2025
Our work “Gibbs-Preserving Operations Requiring Infinite Amount of Quantum Coherence” has been published in Physical Review Letters. Joint work with Hiroyasu Tajima.

April 18, 2025
Our work “Universal work extraction in quantum thermodynamics” has been posted on arXiv. Joint work with Kaito Watanabe.

March 17, 2025
Our work “Symmetric channel verification for purifying noisy quantum channels” has been posted on arXiv. Joint work with Kento Tsubouchi, Yosuke Mitsuhashi, and Nobuyuki Yoshioka.

February 18, 2025
Our work “Bridging Magic and Non-Gaussian Resources via Gottesman-Kitaev-Preskill Encoding” has been published in PRX Quantum. Joint work with Oliver Hahn and Giulia Ferrini.

December 18, 2024
Our work “Black Box Work Extraction and Composite Hypothesis Testing” has been published in Physical Review Letters. Joint work with Kaito Watanabe. Press release is here (in Japanese).

October 6, 2024
Our work “Mixed-state additivity properties of magic monotones based on quantum relative entropies for single-qubit states and beyond” has been published in Quantum. Joint work with Roberto Rubboli and Marco Tomamichel.

July 8, 2024
Our work “Black box work extraction and composite hypothesis testing” has been posted on arXiv. Joint work with Kaito Watanabe.

June 22, 2024
Our work “When quantum memory is useful for dense coding” has been published in Letters in Mathematical Physics (Special Issue Honoring Mary Beth Ruskai). Joint work with Masahito Hayashi.

June 11, 2024
Our work “Bridging magic and non-Gaussian resources via Gottesman-Kitaev-Preskill encoding” has been posted on arXiv. Joint work with Oliver Hahn and Giulia Ferrini.

May 2, 2024
Our work “Arbitrary Amplification of Quantum Coherence in Asymptotic and Catalytic Transformation” has been published in Physical Review Letters. Joint work with Naoto Shiraishi.

April 11, 2024
Our work “Classical simulation and quantum resource theory of non-Gaussian optics” has been posted on arXiv. Joint work with Oliver Hahn, Giulia Ferrini, and Hayata Yamasaki.

April 9, 2024
Our works “Every Quantum Helps: Operational Advantage of Quantum Resources Beyond Convexity” and its companion paper “Robustness and weight resource measures without convexity restriction: Multicopy witness and operational advantage in static and dynamical quantum resource theories” have been published in Physical Review Letters and Physical Review A. Joint work with Kohdai Kuroiwa, Gerardo Adesso, and Hayata Yamasaki.

April 5, 2024
Our work “Gibbs-preserving operations requiring infinite amount of quantum coherence” has been posted on arXiv. Joint work with Hiroyasu Tajima.

March 15, 2024
Our work “Quantum Dynamic Programming” has been posted on arXiv. Joint work with Jeongrak Son, Marek Gluza, and Nelly Ng.

February 3, 2024
Our works “Virtual Qunatum Resource Distillation” and its companion paper “Virtual quantum resource distillation: General framework and applications” have been published in Physical Review Letters and Physical Review A. Joint work with Xiao Yuan, Bartosz Regula, and Mile Gu.

November 23, 2023
Our work “Universal Sampling Lower Bounds for Quantum Error Mitigation” has been published in Physical Review Letters. Joint work with Hiroyasu Tajima and Mile Gu. See here for the release from the University of Tokyo and here for the article from Nikkei (Japanese newspaper).

October 13, 2023
Our works “Every quantum helps: Operational advantage of quantum resources beyond convexity” and its companion paper “Robustness and weight resource measures without convexity restriction: Multicopy witness and operational advantage in static and dynamical quantum resource theories” have been posted on arXiv. Joint work with Kohdai Kuroiwa, Gerardo Adesso, and Hayata Yamasaki.

August 25, 2023
Our work “Alchemy of quantum coherence: Arbitrary amplification in asymptotic and catalytic coherence manipulation” has been posted on arXiv. Joint work with Naoto Shiraishi.

July 18, 2023
Our work “Mixed-state additivity properties of magic monotones based on quantum relative entropies for single-qubit states and beyond” has been posted on arXiv. Joint work with Roberto Rubboli and Marco Tomamichel.

June 21, 2023
Our work “When quantum memory is useful for dense coding” has been posted on arXiv. Joint work with Masahito Hayashi.

April 1, 2023
I have moved to the Department of Basic Science at the University of Tokyo.

March 9, 2023
I gave an invited talk at APS March Meeting on quantum error mitigation. The talk information is here.

March 5, 2023
I am serving as a program committee member for Beyond IID 11 in Information Theory conference. The submission deadline is March 10, 2023.

March 3, 2023
Our work “Virtual quantum resource distillation” has been posted on arXiv. Joint work with Xiao Yuan, Bartosz Regula, and Mile Gu.

February 7, 2023
Our work “Universal trade-off structure between symmetry, irreversibility, and quantum coherence in quantum processes” has been presented at QIP 2023 as a contributed talk by Hiroyasu Tajima.

February 1, 2023
I am serving as a program committee member for TQC 2023 conference. The submission deadline is February 13, 2023.

October 20, 2022
I gave an invited talk on our work “Correlation in Catalysts Enables Arbitrary Manipulation of Quantum Coherence” at the Third Kyoto Workshop on Quantum Information, Computation, and Foundation.

September 26, 2022
I served as a program committee member for Beyond IID 10 in Information Theory conference.

September 22, 2022
Our work “Fundamental limits of quantum error mitigation” has been published in npj Quantum Information. Joint work with Suguru Endo, Shintaro Minagawa, and Mile Gu.

August 22, 2022
Our work “Universal sample lower bounds for quantum error mitigation” has been posted on arXiv. Joint work with Hiroyasu Tajima and Mile Gu.

June 23, 2022
Our work “Universal trade-off structure between symmetry, irreversibility, and quantum coherence in quantum processes” has been posted on arXiv. Joint work with Hiroyasu Tajima and Yui Kuramochi.

June 13, 2022
Our work “Correlation in Catalysts Enables Arbitrary Manipulation of Quantum Coherence” has been published in Physical Review Letters. Joint work with Naoto Shiraishi.

March 24, 2022
I gave an invited talk at Quantum Information Entropy in Physics on some of our recent progress in general quantum resource theories.

March 23, 2022
Our work “One-Shot Yield–Cost Relations in General Quantum Resource Theories” has been published in PRX Quantum. Joint work with Bartosz Regula and Mark M. Wilde.

October 6, 2021
Preprint “One-shot yield–cost relations in general quantum resource theories” has been posted on arXiv. Joint work with Bartosz Regula and Mark M. Wilde.

September 27, 2021
I gave three lightning talks at Beyond IID conference.

September 10, 2021
Preprint “Fundamental limits of quantum error mitigation” has been posted on arXiv. Joint work with Suguru Endo, Shintaro Minagawa, and Mile Gu.

September 1, 2021
I gave talks at AQIS 2021 on “One-Shot Manipulation of Dynamical Quantum Resources” and “Correlation in catalysts enables arbitrary manipulation of quantum coherence“.

August 20, 2021
My paper “Optimal resource cost for error mitigation” has been published in Physical Review Research.

August 9, 2021
Our paper “Operational applications of the diamond norm and related measures in quantifying the non-physicality of quantum maps” has been published in Quantum. Joint work with Bartosz Regula and Mile Gu.

August 5, 2021
Our paper “One-Shot Manipulation of Dynamical Quantum Resources” has been published in Physical Review Letters. Joint work with Bartosz Regula.

July 20, 2021
Our paper “Fundamental limitations on distillation of quantum channel resources” has been published in Nature Communications. Joint work with Bartosz Regula.

July 7, 2021
I gave a talk at TQC 2021 on “One-shot manipulation of dynamical quantum resources”. Pre-recorded talk can be found here.

June 23, 2021
Preprint “Correlation in catalysts enables arbitrary manipulation of quantum coherence” has been posted on arXiv. Joint work with Naoto Shiraishi

May 13, 2021
Preprint “Enhancing quantum models of stochastic processes with error mitigation” has been posted on arXiv. Joint work with Matthew Ho and Mile Gu

March 18, 2021
Companion papers on quantification of infinite-dimensional quantum resources have been published in Physical Review Letters and Physical Review A.
– Short version: “Operational Quantification of Continuous-Variable Quantum Resources”
– Full version: “Framework for resource quantification in infinite-dimensional general probabilistic theories”
Joint work with Bartosz Regula, Ludovico Lami, and Giovanni Ferrari

February 15, 2021
Preprint “Operational applications of the diamond norm and related measures in quantifying the non-physicality of quantum maps” has been posted on arXiv.
Joint work with Bartosz Regula and Mile Gu

February 5, 2021
My coauthor Bartosz Regula gave a talk at QIP 2021 on our work “Fundamental limitations on quantum channel manipulation”.

December 3, 2020
Preprint “One-shot manipulation of dynamical quantum resources” has been posted on arXiv. Joint work with Bartosz Regula.

October 22, 2020
Preprint “Fundamental limitations on quantum channel manipulation” has been posted on arXiv. Joint work with Bartosz Regula.