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A review of incompatibility in quantum information science (Topical Review Meeting #1)

2025年5月26日(月) 16:00 - 17:30

江守 陽規 (北海道大学 大学院情報科学院 博士課程)

As the first activity of the Quantum Foundation Study Group, we will hold a Topical Review Meeting. In quantum mechanics and quantum information science, the exploration of “quantumness” is of fundamental importance. One key concept that captures quantumness is “incompatibility”. In this meeting, I will give a review on incompatibility. If time permits, I would also like to introduce some of my recent research on this topic and engage in discussions with the participants.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Beyond-classical simulations using a quantum annealer

2025年5月23日(金) 10:00 - 11:15

Alberto Nocera (Senior Staff Scientist, Stewart Blusson Quantum Matter Institute, The University of British Columbia, Canada)

Join us for an electrifying online zoom talk featuring Dr. Alberto Nocera, the author of the groundbreaking Science article detailing D-Wave's quantum annealer outperforming classical supercomputers in simulating complex magnetic materials. D-Wave’s quantum annealer uses quantum annealing to efficiently solve optimization problems by finding low-energy states of complex systems. Unlike IBM and Quantinuum’s gate-based quantum computers, which are universal and execute algorithms via quantum circuits, D-Wave’s system is specialized but currently more scalable and practical for certain applications. While gate-based systems are still limited by noise and error rates, D-Wave’s annealer recently demonstrated a quantum advantage in simulating magnetic materials, outperforming classical supercomputers. This highlights a key difference: D-Wave excels in specific tasks today, while IBM and Quantinuum aim for broader, long-term quantum computational capabilities. Talk Abstract: Solving the equations governing the dynamics of interacting many-particle quantum systems is one of the biggest challenges in modern science. In 1982, Richard P. Feynman envisioned that the best way to emulate the behavior of many-particle quantum systems is to use another quantum system, starting the field of quantum simulation. Rather than seeking to solve the fundamental equations of quantum mechanics using conventional or classical computers, in quantum simulation one seeks to simulate a quantum system using an "analog device" mimicking its behavior, hoping to access solutions which are not easy to compute otherwise. In this talk, using the quantum annealing simulator device developed by D-Wave as a main tool, I will show that the use of tensor network methods has a key role in quantum simulation: besides benchmarking the quantum device, they can assess and help establishing its functionality beyond the classically simulatable regime [1].

会場: via Zoom

イベント公式言語: 英語

Stable homotopy theory of invertible quantum spin systems

2025年5月16日(金) 16:00 - 18:00

窪田 陽介 (京都大学 大学院理学研究科 准教授)

In the past decade, A. Kitaev proposed that the set of invertible gapped quantum spin systems would form an \Omega-spectrum. This conjecture is considered to have potentially significant application to the study of SPT phases. Recently, we give a mathematically rigorous realization of this proposal with the language of functional analysis and operator algebra. This gives a unified proof of a series of existing researches. The proof also suggests to understand Kitaev's proposal from the viewpoint of coarse geometry of metric spaces. This association leads us to the concept of localization flow.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Mini-Workshop on Neuro Science

2025年5月16日(金) 9:00 - 12:00

磯 暁 (理化学研究所 数理創造研究センター (iTHEMS) センター長)
磯村 拓哉 (理化学研究所 脳神経科学研究センター (CBS) 脳型知能理論研究ユニット ユニットリーダー)
豊泉 太郎 (理化学研究所 脳神経科学研究センター (CBS) 数理脳科学研究チーム チームディレクター)
岡ノ谷 一夫 (帝京大学 先端総合研究機構 教授)
入來 篤史 (帝京大学 先端総合研究機構 特任教授)
Gary Shiu (Professor, Department of Physics, University of Wisconsin-Madison, USA)

[Program] 9:00am – 9:05am Satoshi Iso (iTHEMS RIKEN) “Opening Remarks” 9:05am – 9:35am Takuya Isomura (CBS RIKEN) “Triple equivalence integrates neural network dynamics, statistical inference, and computation” 9:45m – 10:15am Taro Toyoizumi (CBS RIKEN) “Chaotic neural dynamics facilitate probabilistic computations through sampling” 10:25am – 10:55am Kazuo Okanoya (Teikyo University) “Brain topography and auditory processing in birds and rats” 11:05am – 11:30am Atsushi Iriki (Teikyo University, iTHEMS RIKEN) “From Classical to Quantum: Rethinking Science, Consciousness, and Civilization” 11:30am – Gary Shiu (University of Wisconsin) “Summary: Mathematical Science and Brain” Followed by a seminar 2:00pm – 3:30pm Prof. Gary Shiu (University of Wisconsin) Topology and Brain Science Room 359, 3rd floor, Main Research Building, RIKEN

会場: 理化学研究所 和光キャンパス 研究本館3階 345-347 (メイン会場) / via Zoom

イベント公式言語: 英語

On IR/UV divergence of inflationary decoherence

2025年4月22日(火) 14:00 - 15:30

佐野 文哉 (東京科学大学 博士課程)

Supported by observational evidence indicating that cosmological scalar perturbations were nearly Gaussian at the beginning of the universe, it is anticipated that the origin of these perturbations is quantum fluctuations. Consequently, cosmic inflation provides a valuable laboratory for testing the quantum nature with/of gravity. Evaluation of the quantumness of the primordial perturbations is an inevitable step for the purpose. However, quantum states of the perturbations are suffered from IR/UV divergence, resulting in fully classical states. In this presentation, I will first review the evaluation of the quantum coherence in de Sitter spacetime as a measure of quantumness, and then show how to regularize the divergence.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Gauge subtleties and the finiteness of loop corrections beyond slow roll

2025年4月3日(木) 14:00 - 15:30

Danilo Artigas (京都大学 大学院理学研究科 物理学・宇宙物理学専攻 物理学第二教室 学振特別研究員PD)

The early universe undergoes a phase of exponential expansion called inflation, under which quantum fluctuations are amplified and later seed cosmological structures. A long-standing question is whether interactions of these quantum fields may significantly affect the n-point statistics of cosmological observables. These corrections are known as loop corrections. Recently, Kristiano and Yokoyama claimed that, in scenarios beyond slow-roll inflation, the one-loop correction of super-Hubble fluctuations could become non-negligible and violate cosmological-perturbation theory. This result is highly debated, and in this talk we will use a non-linear approach known as delta N formalism to evaluate these loop corrections. We find the existence of loop corrections for modes close to the Hubble scale, however, these corrections are quickly suppressed for long-wavelength modes. We also show how the result of Kristiano and Yokoyama may arise when truncating the perturbative expansion, and how this result depends on the chosen gauge.

会場: セミナー室 (359号室)

イベント公式言語: 英語

Omega Meson from Lattice QCD

2025年4月2日(水) 15:00 - 16:00

Haobo Yan (Ph.D. Student, School of Physics, Peking University, China)

The three-body problem, renowned for its unsolvable nature in celestial mechanics and homonymous science fiction, is not only solvable in the quantum realm regarding spectra but also offers profound insights into QCD. In this talk, I will present the first-ever lattice calculation of the resonance parameters for the lightest hadron decaying into three particles, the -meson. By mapping finite-volume energy levels to infinite-volume scattering amplitude, a pole position trajectory is obtained that, when extrapolated to the physical point, shows good agreement with the experiment.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Stability of nonsingular black holes

2025年3月27日(木) 15:00 - 16:30

辻川 信二 (早稲田大学 理工学術院 先進理工学研究科 物理学及応用物理学専攻 辻川研究室 教授)

We show that nonsingular black holes (BHs) realized in nonlinear electrodynamics are always prone to Laplacian instability around the center because of a negative squared sound speed in the angular direction. This is the case for both electric and magnetic BHs, where the instability of one of the vector-field perturbations leads to enhancing a dynamical gravitational perturbation in the even-parity sector. Thus, the background regular metric is no longer maintained in a steady state. We also generalize our analysis to the case in which a scalar field is present besides the U(1) gauge field and find no explicit examples of linearly stable nonsingular BHs. Our results suggest that the construction of regular BHs without instabilities is generally challenging within the scheme of classical field theories.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Third Workshop on Density Functional Theory: Fundamentals, Developments, and Applications (DFT2025)

2025年3月25日(火) - 27日(木)

The density functional theory (DFT) is one of the powerful methods to solve quantum many-body problems, which, in principle, gives the exact energy and density of the ground state. The accuracy of DFT is, in practice, determined by the accuracy of an energy density functional (EDF) since the exact EDF is still unknown. Currently, DFT has been used in many communities, including nuclear physics, quantum chemistry, and condensed matter physics, while the fundamental study of DFT, such as the first principle derivations of an accurate EDF and methods to calculate many observables from obtained densities and excited states, is still ongoing. However, there has been little opportunity to have interdisciplinary communication. On December 2022, we had the first workshop on this series (DFT2022) at Yukawa Institute for Theoretical Physics, Kyoto University, and several interdisciplinary discussions and collaborations were started. On February 2024, we had the second workshop on this series (DFT2024) at RIKEN Kobe Campus, and more stimulated discussion occured. To keep and extend collaborations, we organize the third workshop. Since the third workshop, we extend the scope of the workshop to the development and application of DFT as well. In this workshop, the current status and issues of each discipline will be shared towards solving these problems by meeting together among researchers in mathematics, nuclear physics, quantum chemistry, and condensed matter physics. This workshop mainly comprises lectures/seminars on cutting-edge topics and discussion, while sessions composed of contributed talks are also planned.

会場: 融合連携イノベーション推進棟（IIB） 8階 / via Zoom

イベント公式言語: 英語

A Century of Quantum Mechanics

2025年3月24日(月) 14:00 - 15:30

ゴードン・ベイム (Professor Emeritus, University of Illinois, USA)

This is a RIKEN iTHEMS - The Univ. of Tokyo, Phys. Dept. Joint Seminar. This year, 2025, the "International Year of Quantum Science and Technology (IYQ)," is the 100th anniversary of the "formal" start of quantum mechanics, the description of the microscopic world. 1925 is the year in which Werner Heisenberg and others formulated "matrix mechanics," and physicists began to understand how to accurately predict microscopic phenomena. In this talk I will describe how quantum mechanics came about, starting with physicists in the late nineteenth century trying to understand the colors of hot metals and other hot objects, noting crucial advances leading to the fully developed wave and matrix quantum mechanics in the mid 1920's, to steps towards understanding real materials, culminating with spectacular applications such as smartphones, scarcely a century later.

会場: 東京大学 理学部4号館 1220号室 (メイン会場) / via Zoom

イベント公式言語: 英語

The puzzle of angular momentum conservation in beta decay and related processes.

2025年3月21日(金) 14:00 - 15:30

ゴードン・ベイム (Professor Emeritus, University of Illinois, USA)

This is a iTHEMS-FQSP joint seminar. We ask the question of how angular momentum is conserved in a number of related processes, from elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon; to scattering of a fully relativistic spin-1/2 particle by a central potential; to inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus, where the final spin is in a different direction than that of the neutrino – an apparent change of angular momentum. The apparent non-conservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in direction in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Asymptotically flat black hole spacetimes with multiple injections

2025年3月14日(金) 15:30 - 17:00

齊藤 佑太 (日本大学 大学院理工学研究科 物理学専攻 博士課程)

In quantum gravity, Hawking radiation presents several fundamental problems. One of the problems is the black hole (BH) information paradox, in which the entanglement entropy (EE), which quantifies quantum entanglement, exceeds its upper bound. In the absence of the paradox, EE follows the Page curve. Recent progress has been made in resolving this paradox using the island formula, a method for computing EE that successfully reproduces the expected Page curve. In this approach, a portion of the black hole interior is treated as part of the radiation region. Meanwhile, an alternative scenario has been proposed where multiple collapsing shells prevent the formation of a well-defined event horizon [1]. In this case, radiation is emitted throughout the collapse process, shifting dynamically the Schwarzschild radius inward, and a surface structure is formed just outside. This leads to a distinction between the conventional event horizon and the surface, introducing an intermediate region between the Schwarzschild radius and the surface. Interestingly, this model also suggests that part of the black hole interior effectively belongs to the radiation region, drawing a possible parallel to the island formula. In this talk, we explore spacetimes with multiple energy injections in asymptotically flat two-dimensional black hole backgrounds and analyze the entanglement entropy in such scenarios. Since considering backreaction in gravitational collapse in two dimensions is difficult, we instead construct a spacetime solution with multiple energy injections and analyze EE within this background. The main focus of this talk is to derive the spacetime and examine its properties. Additionally, we perform EE calculations in parallel with previous studies [2], which consider the case of α single injection, and confirm that the behavior of EE depends on the interval between energy injections.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催 (メイン会場) / via Zoom

イベント公式言語: 英語

RIKEN Quantum hands-on workshop on QURI SDK for creating and executing quantum algorithms on various quantum computers and simulators

2025年3月13日(木) 15:00 - 17:30

This workshop will be a hands-on session on QURI SDK, following the RIKEN Quantum seminar by Andreas Thomasen (QunaSys) on January 27. Even if you did not attend the previous seminar, please join us if you would like to learn how to use QURI SDK.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Kyushu IAS-iTHEMS conference: Non-perturbative methods in QFT

2025年3月10日(月) - 14日(金)

The most commonly used approach in the study of QFT is perturbation theory. Indeed, we have succeeded in extracting various physical quantities from perturbative (asymptotic) expansions. However, some physical phenomena cannot be captured through perturbative analyses alone. How can we extract these non-perturbative effects? In QFTs with conformal symmetry (i.e., CFTs), correlation functions can be computed using a method called the conformal bootstrap. This non-perturbative method differs entirely from the usual correlation function analysis methods of QFT, as it does not even assume the existence of a Lagrangian. Through the use of the conformal bootstrap, we have actually made significant progress in the non-perturbative understanding of CFTs. Furthermore, according to the holographic principle, CFTs provide a non-perturbative formulation of QFTs with gravity (i.e., quantum gravity). By applying the holographic principle to various non-perturbative results from CFTs, such as those obtained from the conformal bootstrap, we have made remarkable advances in understanding the non-perturbative aspects of quantum gravity. Conversely, the holographic principle is also used to understand properties of QFTs that are difficult to analyze perturbatively, through gravity.

会場: 九州大学伊都キャンパス稲盛ホール

イベント公式言語: 英語

Quantum-Centric Supercomputing Software

2025年2月26日(水) 13:00 - 14:00

Hanhee Paik (IBM Quantum Head of IBM Quantum Japan)

A quantum-centric supercomputer represents the next generation of computing, combining a quantum computer with a classical supercomputer. It leverages error mitigation and error correction techniques to deliver results within practical timeframes. When fully developed, this system relies on advanced middleware to seamlessly integrate quantum circuits with classical computing resources. In this presentation, we will introduce IBM Quantum’s middleware for quantum-centric supercomputers, highlighting collaborative projects with our research partners.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Asymptotics in astrophysics iTHEMS workshop

2025年2月25日(火) - 28日(金)

This workshop will include overview talks of application of asymptotics and perturbation theory techniques in (wave transport or oscillation related) astrophysics and cosmology eigenvalue problems. In addition, there will be introductory talks about fundamental asymptotics and perturbation theory techniques used in theoretical physics. The purpose of this interdisciplinary workshop is to identify problems in astrophysics and related fields including, but not limited to, stellar structure and evolution, black holes and high-energy physics which can be solved using existing asymptotics and perturbation theory methods in theoretical physics problems (e.g. quantum field theory, gravity), and vice versa.

会場: 融合連携イノベーション推進棟（IIB） 8階

イベント公式言語: 英語

Exploiting hidden low-rank structures in quantum field theories

2025年2月24日(月) 13:00 - 14:30

品岡 寛 (埼玉大学)

Tensor networks are a powerful tool for compressing wave functions and density matrices of quantum systems in physics. Recent developments have shown that tensor network techniques can efficiently compress many functions beyond these traditional objects. Notable examples include the solutions to turbulence in Navier–Stokes equations [1] and the computation of Feynman diagrams [2,3]. These advancements have heralded a new era in the use of tensor networks for expediting the resolution of various complex equations in physics. This talk will provide an overview of our work utilizing tensor networks for computations based on quantum field theories. First, we will introduce the Quantics/quantized Tensor Train (QTT) representation [3,4] for compressing the space-time dependence of correlation functions in quantum systems [5], leveraging inherent length-scale separation for efficient representation. Second, we will present a robust tool named "Quantics Tensor Cross Interpolation" [6], which learns a quantics low-rank representation of a given function. Applications include the computation of Brillouin zone integrals [6] and integration of complex self-energy Feynman diagrams for multiorbital electron-phonon impurity models [7]. Finally, we will introduce new algorithms [8] and open-source libraries [9] for tensor cross interpolation.

会場: via Zoom / Hong Kong University Science and Technology

イベント公式言語: 英語

The Topology, Geometry and Physics of non-Hausdorff manifolds

2025年2月19日(水) 15:00 - 17:00

O'Connell David (沖縄科学技術大学院大学 (OIST) 博士課程)

Non-Hausdorff manifolds are manifolds containing "doubled points" that cannot be separated by disjoint open sets. In this talk we will survey some mathematical and physical results surrounding these unusual spaces. As a theme, we will start with their fundamental description as a topological space, and slowly add in more and more structure of interest until we can meaningfully phrase questions of physics. On the mathematical side, we will see descriptions of non- Hausdorff manifolds as colimits of ordinary manifolds, which allows us to describe their geometric features without appealing to arbitrarily- existent partitions of unity. On the physical side, we will consider the inclusion of non-Hausdorff manifolds in a naïve 2d Lorentzian path integral for gravity, and (time permitting) explain how construct quantum fields on a non-Hausdorff background. Ultimately, we will see that these latter two arguments suggest that non-Hausdorff manifolds may be more appropriate than the standard "Trousers space" for the modelling of topology change in Lorentzian signature.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

New topological quantum order in 2D lattices from non-invertible symmetries

2025年2月18日(火) 15:00 - 16:00

Ayan Mukhopadhyay (Associate Professor, Valparaiso University, Chile)

I will introduce an exactly solvable 2D lattice model which reveals a large number of distinct topological phases with non-invertible (generalized) symmetries. In all these topological phases, which have topological ground state degeneracy, a commutative stabilizer monoid of Hermitian operators leave the ground state invariant and can also distinguish *all* local excitations, (These symmetries are indeed symmetry operations.) There exists novel confined fractonic excitations which change the nature of deconfined excitatons profoundly. The fusion rules form an associative but noncommutative. non-Abelian and non-unital category, and are distinct for each of these phases. A class of these phases are adiabatically connected to a limit which can be described in terms of generalized free field theories. I will describe systematic ways to construct such phases. I will also discuss phases which do not have generalized free field limits. These phases have novel forms of non-local entanglement as many of them share the same topological entanglement entropy. They also violate the entanglement bootstrap axioms. When the phases do not have a generalized free field limit, the violation of the entanglement bootstrap axioms can happen for arbitrary large subregions signifying new forms of long-range entanglement.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語