In recognition of important achievements toward progress in physics, the Physical Society of Japan (JPS) annually selects outstanding papers from among original research articles published in the Journal of the Physical Society of Japan, Progress of Theoretical Physics, Progress of Theoretical and Experimental Physics, and JPS Conference Proceedings. The selection committee has chosen five papers for the 2025 award from 15 nominations, covering 14 unique papers, submitted by the editors of the JPS journals and representatives of the 16 divisions of the JPS.

The 2025 award ceremony will be held at noon on September 18, 2025.

The titles of the five selected papers, together with their citations, follow below:

Exponential Speedup of Quantum Annealing by Inhomogeneous Driving of the Transverse Field

J. Phys. Soc. Jpn.87, 023002 (2018)

https://doi.org/10.7566/JPSJ.87.023002.

Yuki Susa, Yu Yamashiro, Masayuki Yamamoto, and Hidetoshi Nishimori

Quantum annealing, a new quantum computing technology originating in Japan, has attracted much attention, especially from the viewpoint of a fast-solution method for combinatorial optimization problems for which to find optimal solutions is essentially difficult. This method is an original method proposed by the author’s group and has already been commercially implemented and applied to many problems. This method seeks an optimal solution adiabatically by gradually reducing the transverse magnetic field from a trivial ground state under a strong transverse magnetic field. However, this method cannot be applied if there is a level crossing in the process. If there is a pseudo-crossing of levels corresponding to a first-order phase transition, the adiabatic process becomes practically difficult. Managing this problem has been one of the most important issues, and many studies have been continued. In this paper, they take up a mean-field Ising model with many-body interactions as a simple, typical, and easy-to-analyze mathematical model which shows a quantum first-order phase transition in the annealing process, although the model itself is a somewhat peculiar model. They discover that it is possible to bypass the end point (critical point) of the first-order phase transition on the phase diagram by manipulating a spatial inhomogeneous external magnetic field, and they actually show a concrete method to avoid it. This result represents an important breakthrough in this type of problem, and many attempts are being made to construct protocols for quantum annealing on a real machine based on the results of this paper. The results of this paper provided progress in the field of quantum annealing and have attracted great interest not only in this field but also in various other fields of physics. For these reasons, this paper is worthy of Outstanding Paper Award from the JPS.

Orbital Magnetism of Bloch Electrons I. General Formula

J. Phys. Soc. Jpn.84, 124708 (2015)

https://doi.org/10.7566/JPSJ.84.124708.

Masao Ogata and Hidetoshi Fukuyama

Orbital susceptibility as an external response of itinerant electrons is a fundamental and important quantity. It is experimentally measurable and has been an important target of research for a long time. The present paper is based on the compact and generic formula in terms of Green’s functions that was discovered in 1971 by one of the authors. On the other hand, orbital susceptibility especially for the multiband Bloch states due to the periodic potential in a crystal has been focused recently from a modern viewpoint. The authors derived a formula of orbital susceptibility starting from the above compact formula in terms of Bloch wave functions. The paper showed that orbital susceptibility contains four terms: (1) Landau-Peierls susceptibility, (2) interband contribution, (3) Fermi surface contribution, and (4) contribution from occupied states. Physical meaning of them is clarified, and consistency of the results to other works has been also discussed. The results presented in the paper give a generic and compact basis for the study of magnetic response of itinerant electrons and motivates research in related fields of condensed matter physics. For these findings, this paper deserves the Outstanding Paper Award from the JPS.

Chiral Soliton Lattice Formation in Monoaxial Helimagnet Yb(Ni_1-xCux)₃Al₉

J. Phys. Soc. Jpn. 86, 124702 (2017)

https://doi.org/10.7566/JPSJ.86.124702.

Takeshi Matsumura, Yosuke Kita, Koya Kubo, Yugo Yoshikawa, Shinji Michimura, Toshiya Inami, Yusuke Kousaka, Katsuya Inoue, and Shigeo Ohara

“Chirality” is an old and well-known concept proposed by Lord Kelvin. In the last decade, chirality and related phenomena in various materials have attracted much attention in materials science. In chiral crystals, a nontrivial magnetic order emerges due to the effect of the Dzyaloshinskii-Moriya interaction: skyrmions and chiral soliton lattices are typical examples. The latter has been observed in a transition metal compound CrNb₃S₆. However, the chiral soliton lattice had not been demonstrated in f-electron materials.

This paper reports on a study of resonant X-ray scattering for heavy fermion materials Yb(Ni_1-xCu_x)₃Al₉, in which previous magnetization measurements suggested the existence of a chiral soliton lattice. For the first time, the authors have proved the existence of the chiral soliton lattice structures. They have revealed the magnetic structures of the materials by magnetic reflection in the resonant X-ray diffraction: The direction of rotation of the helical spin structure is altered by the left- or right-handedness of the crystal, and higher harmonic components of the propagation vectors increase with applied magnetic field. Moreover, some differences were found in the properties of the soliton lattice from those of d-electron systems. These results stimulate research on magnetic structures induced by chirality and may contribute to the understanding of chirality in nature. This paper, therefore, deserves the Outstanding Paper Award from the JPS.

The mean square radius of the neutron distribution and the skin thickness derived from electron scattering

Prog. Theor. Exp. Phys. 2021, 013D02

https://doi.org/10.1093/ptep/ptaa177.

Haruki Kurasawa, Toshimi Suda, and Toshio Suzuki

To obtain the density distribution of protons and neutrons in nuclei is an important issue not only in nuclear physics but also in astrophysics. Especially in neutron-rich nuclei, the “neutron skin thickness,” which arises from the difference between the neutron root-mean-square radius (rms) and the proton rms, is a key in determining the radius and maximum mass of a neutron star. The proton density distribution in the nucleus can be determined with high precision with “electron scattering” by electromagnetic interactions. On the other hand, the neutron density distribution has been measured by nuclear reactions. However, the density distribution is strongly dependent on models employed. Therefore, observed neutron density distribution is less reliable.

In this paper, the authors pointed out that the neutron distribution is sensitive to the fourth-order moment of the charge density distribution obtained by electron scattering and shown for the first time in the world that the radius of neutron distribution by electron scattering can be extracted with a method that is less dependent on the model. This is an epoch-making paper that pioneered the derivation of skin thickness with less model dependence. This research will contribute to the development of research not only in nuclear physics but also in astrophysics. This paper deserves the Outstanding Paper Award from the JPS.

Global inconsistency, ’t Hooft anomaly, and level crossing in quantum mechanics

Prog. Theor. Exp. Phys. 2017, 113B05

https://doi.org/10.1093/ptep/ptx148.

Yuta Kikuchi and Yuya Tanizaki

Anomaly in quantum field theory is known as the phenomenon that classical symmetry is broken by quantization. More broadly, it is also used to study the low-energy dynamics of the theory through the condition that global symmetry transformation must be reacted universally independent of its energy scale ('t Hooft anomaly matching).

This paper is about the “global inconsistency,” which further extends the concept of anomaly. When a theory has a kind of anomaly under the transformation of its parameter, such as the theta parameter in quantum chromodynamics, its analysis may be used to constrain its low-energy dynamics, the vacuum structure in particular. This paper represents a pioneering study that shows this possibility explicitly using a solvable quantum mechanics model.

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