Masahito Hayashi's Research Group

I am the Presidential Chair Professor in School of Data Science, The Chinese University of Hong Kong, Shenzhen, and Chief Research Scientist in Shenzhen International Quantum Academy. Also, I am an IEEE Fellow, an AAIA Fellow, and an IMS Fellow. My research interests include classical and quantum information theory and classical and quantum statistical inference. My full CV is available here.

Short Biography

Masahito Hayashi received the B.S. degree from the Faculty of Sciences, Kyoto University, Japan, in 1994, and the M.S. and Ph.D. degrees in mathematics from Kyoto University, Japan, in 1996 and 1999, respectively. He worked in Kyoto University as a Research Fellow of the Japan Society of the Promotion of Science (JSPS) from 1998 to 2000, and worked in the Laboratory for Mathematical Neuroscience, Brain Science Institute, RIKEN from 2000 to 2003, and worked in ERATO Quantum Computation and Information Project, Japan Science and Technology Agency (JST) as the Research Head from 2000 to 2006. He worked in the Graduate School of Information Sciences, Tohoku University as Associate Professor from 2007 to 2012. In 2012, he joined the Graduate School of Mathematics, Nagoya University as Professor. He worked in the Shenzhen Institute for Quantum Science and Engineering, Southern University of Science and Technology as Chief Research Scientist from 2020 to 2023. In 2023, he joined School of Data Science, The Chinese University of Hong Kong, Shenzhen as Professor and was granted as Presidential Chair Professor. He also joined Shenzhen International Quantum Academy as Chief Research Scientist.

Also, he worked in Centre for Quantum Technologies, National University of Singapore as Visiting Research Associate Professor from 2009 to 2012 and as Visiting Research Professor from 2012 to now. He also worked in Shenzhen Institute for Quantum Science and Engineering, Southern University of Science and Technology, China as a Visiting Professor from 2018 to 2020, and in Center for Quantum Computing, Peng Cheng Laboratory, China as a Research Scientist from 2019 to 2020.

In 2011, he received Information Theory Society Paper Award (2011) for “Information-Spectrum Approach to Second-Order Coding Rate in Channel Coding”. In 2016, he received the Japan Academy Medal from the Japan Academy and the JSPS Prize from Japan Society for the Promotion of Science. In 2017, he was promoted to IEEE Fellow. In 2022, he was promoted to AAIA Fellow and IMS Fellow. In 2023, he was selected as the Best Scientist in the Field of Mathematics and Best Scientist in the Field of Engineering and Technology in the top scientists ranking released by He was also selected for the Annual Science Influence Ranking and Lifetime Science Influence Ranking in Elsevier’s Top 2% Global Scientists Rankings. Besides, he was honored with the APS Outstanding Referee from the American Physical Society in 2023.

Representative Works

M. Hayashi, Quantum Information Theory: Mathematical Foundation, Graduate Texts in Physics, Springer (2017). (First Edition: M. Hayashi, Quantum Information: An Introduction, Springer (2006)).

Assuming only elementary knowledge, this monograph explains many advanced topics in quantum information, quantum channel coding, quantum data compression, and quantum entanglement, etc., including original achievements.

M. Hayashi, “Information spectrum approach to second-order coding rate in channel coding,” IEEE Transactions on Information Theory, Vol. 55, No. 11, 4947–4966 (2009).

Using the information-spectrum method, this paper established the systematic method for second order theory for the channel coding. Then, this paper resolved the second order coding rate for AWGN channel and channel coding with energy constraint that had been unsolved for 47 years. Although this problem was discussed by Polyanskiy, H. V. Poor, and S. Verdú (2010), this paper preceded them by one year. Due to the strength of this approach, many subsequent papers of the second order employ the proposed systematic method. Also, this paper clarifies the difference between the second order analysis and Gallager bound. Due to the above seminal contributions, this paper was awarded the 2011 IEEE Information Theory Society Paper Award.

M. Hayashi and H. Nagaoka, “General formulas for capacity of classical-quantum channels,” IEEE Transactions on Information Theory, Vol. 49, No. 7, 1753–1768 (2003).

Non-commutativity causes several kinds of difficulties in quantum information theory. To overcome this problem, this paper derived a novel matrix inequality, which has often been referred to as the Hayashi-Nagaoka inequality in many papers for quantum information theory. This result brings us the quantum version of the information spectrum method. As another contribution, this paper revealed two useful relations between channel coding and the binary hypothesis testing. One is the relation between existence of a good channel code and the binary hypothesis testing. The other is the relation between the optimal performance of channel code and the binary hypothesis testing. Due to their generality, both relations were used to several papers of channel coding, including the paper for the second order rate of channel coding.

M. Tomamichel and M. Hayashi, “A Hierarchy of Information Quantities for Finite Block Length Analysis of Quantum Tasks,” IEEE Transactions on Information Theory, Vol. 59, No. 11, 7693 – 7710 (2013).

This paper established the foundation of finite-length theory of quantum system. This paper also derived the second order analysis for secure key generation and data compression with side-information in the quantum setting.

M. Hayashi, “General non-asymptotic and asymptotic formulas in channel resolvability and identification capacity and its application to wire-tap channel,” IEEE Transactions on Information Theory, Vol. 52, No. 4, 1562-1575 (2006).

This paper pointed out the clear connection between the wire-tap channel coding and the channel resolvability. Using this connection, this paper derived an explicit exponent for leaked information by using Arimoto’s exponents. Also, combining the information spectrum approach, this paper revealed the capacity formula of general sequence of degraded wire-tap channels. Since this connection is a very powerful tool for wire-tap channel, many papers for wire-tap channel followed this idea to construct codes for wire-tap channel. Further, this paper proved the conjecture for resolvability capacities for general sequence of channel, which had been an open problem proposed by Han-Verdu in 1993 (13 years).

M. Hayashi, “Exponential decreasing rate of leaked information in universal random privacy amplification,” IEEE Transactions on Information Theory, Vol. 57, No. 6, 3989–4001 (2011).

This paper addresses security analysis when hash functions are applied. It applies hash function to wiretap channel, and constructs a practical code with small encoding and decoding time in finite-length setting. The proposed method can achieve the optimal asymptotic rate for secure key generation.

M. Hayashi, K. Iwama, H. Nishimura, R. Raymond, and S. Yamashita, “Quantum Network Coding,” 24th International Symposium on Theoretical Aspects of Computer Science (STACS 2007), Aachen, Germany; 22-24 February 2007.

The study for quantum network coding was studied by this paper. This paper proposed a non-trivial network code over quantum butterfly network.

M. Hayashi, “Prior entanglement between senders enables perfect quantum network coding with modification,” Physical Review A, Vol.76, 040301(R) (2007).

This paper proposed a quantum network code on quantum butterfly network. The proposed protocol has been experimentally implemented by Prof. Pan’s group in USTC.

Y. Yang, G. Chiribella, and M. Hayashi, “Attaining the Ultimate Precision Limit in Quantum State Estimation,” Communications in Mathematical Physics, vol. 368(1), 223 – 293 (2019).

This paper formalizes quantum state estimation with nuisance parameters. It clarifies the ultimate precision limit in quantum state estimation.

M. Hayashi, T. Morimae, “Verifiable measurement-only blind quantum computing with stabilizer testing,” Physical Review Letters, vol. 115, 220502 (2015).

This paper initialized the verification of measurement-based quantum computer.