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The First RIKEN Quantum International Workshop on Frontiers of Quantum Computing Applications and Quantum-HPC Integration

2026年5月25日(月) - 26日(火)

This two-day workshop will bring together leading experts from academia, industry, and national laboratories to explore the rapidly evolving frontiers of quantum computing applications and their integration with high-performance computing (HPC) platforms. Hosted by RIKEN Quantum, the event will provide a forum for discussing recent advances, practical challenges, and future directions toward achieving utility-scale quantum computations and robust quantum–HPC hybrid workflows. The workshop is primarily an in-person event, but a special session on quantum computing in chemistry and life sciences will also be accessible via Zoom.

会場: 理化学研究所和光キャンパス 本部棟2階大会議室

イベント公式言語: 英語

Positivity constraints for the gravitational path integral

2026年5月21日(木) 10:00 - 11:50

ガブリエル・ディウバルド (理化学研究所 数理創造研究センター (iTHEMS) 国内外連携・人材育成部門 理研バークレーセンター 特別研究員)

For a quantum theory of gravity to have a well-defined Hilbert space, the inner product between different states of open and closed universes must be positive semi-definite. Positivity however is not manifest in the low-energy effective theory and in fact imposes nontrivial constraints on the theory. Working in the Gravitational Path Integral (GPI) approach, we derive the general set of positivity constraints on the closed and open universe Hilbert spaces. In the case of AdS gravity, open universe positivity in principle follows from CFT unitarity, however the holographic description of closed universes remains unclear. Strikingly, we exhibit positivity of closed universes across many theories and prove that open positivity implies closed positivity, showing that the CFT 'knows' about the closed universe hilbert space. We then analyze positivity constraints on gravitational theories coupled to axions. We present a method to compute off-shell axion wormholes in AdS and flat space which we use to show that positivity is violated if the axion shift symmetry is exact. In low-energy EFTs where these wormholes are perturbatively stable, to restore positivity the wormhole must have a non-perturbative instability due to instantons that breaks the shift symmetry. Positivity then leads to a proof of a sharp version of the Axion Weak Gravity Conjecture A-WGC, including precise numerical constants. For the QCD axion this provides a bound on the axion decay constant which has phenomenological and experimental consequences for axion searches. In string theory, positivity gives a bound on the coupling between the axion and the dilaton in the low energy effective action.

会場: via Zoom

イベント公式言語: 英語

Realizing two-dimensional discrete time crystals on a digital quantum computer

2026年5月19日(火) 15:00 - 16:30

新城 一矢 (理化学研究所 創発物性科学研究センター (CEMS) 計算物性物理研究室 研究員)

This work was featured in a RIKEN press release. For details, please see the related link.

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

Introduction to quantum resource theories (3)

2026年5月15日(金) 9:00 - 17:00

高木 隆司 (東京大学 大学院総合文化研究科 准教授)

[Registration Closed] Due to high demand and venue capacity limits, registration for this course is now closed as of April 25. If you wish to be placed on a waiting list in case of cancellations, please contact us via the inquiry form at the bottom of this page. One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 3rd day: May 15 (Fri) 9:00–10:30 Lecture 7 10:30–11:00 Coffee break 11:00–12:30 Lecture 8 12:30-13:30 Lunch time 13:30-15:00 Lecture 9 15:00-15:30 Coffee break 15:30-17:00 Seminar (or Lecture 10) This event is in-person only.

会場: 研究本館 4階 435-437号室

イベント公式言語: 英語

Stochastic Schrödinger Diffusion Models for Pure-State Ensemble Generation

2026年5月14日(木) 14:30 - 15:30

ジアン・シュウ (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 量子数理科学チーム 特別研究員)

In quantum machine learning (QML), classical data are often encoded as quantum pure states and processed directly as quantum representations, motivating \emph{representation-level generative modeling} that samples new quantum states from an underlying pure-state ensemble rather than re-preparing them from perturbed classical inputs. However, extending \emph{score-based} diffusion models with well-defined reverse-time samplers to quantum pure-state ensembles remains challenging, due to the non-Euclidean geometry of the complex projective space $\mathbb{CP}^{d-1}$ and the intractability of transition densities. We propose \emph{Stochastic Schr\"odinger Diffusion Models} (SSDMs), an intrinsic score-based generative framework on $\mathbb{CP}^{d-1}$ endowed with the Fubini--Study (FS) metric. SSDMs formulate a forward Riemannian diffusion with a stochastic Schr\"odinger equation (SSE) realization, and derive reverse-time dynamics driven by the Riemannian score $\nabla_{\mathrm{FS}} \log p_t$. To enable training without analytic transition densities, we introduce a local-time objective based on a local Euclidean Ornstein--Uhlenbeck approximation in FS normal coordinates, yielding an analytic teacher score mapped back to the manifold. Experiments show that SSDMs faithfully capture target pure-state ensemble statistics, including observable moments, overlap-kernel MMD, and entanglement measures, and that SSDM-generated quantum representations improve downstream QML generalization via representation-level data augmentation.

会場: セミナー室 (359号室) 3階 359号室 (メイン会場) / via Zoom

イベント公式言語: 英語

From Birkhoff's Polytope to Petz Recovery: Unistochastic Matrices, Quantum Channels, and Approximate Markov Chains

2026年5月13日(水) 13:30 - 15:00

Claude Gravel (Assistant Professor, Department of Computer Science, Toronto Metropolitan University, Canada)

A doubly stochastic matrix is unistochastic if its entries correspond to the squared moduli of a unitary matrix. Determining which n × n doubly stochastic matrices admit such a representation remains an open problem at the intersection of convex geometry, combinatorics, and quantum information. For 3 × 3 matrices, elegant triangle inequalities provide a complete characterization: the unistochastic set occupies approximately 75% of the Birkhoff polytope and exhibits deltoid cross-sections. For n ≥ 4, the characterization problem remains unresolved and is influenced in unexpected ways by the prime factorization of n via the defect of the Fourier matrix. This presentation surveys these results and then establishes a connection to a second, seemingly unrelated question: given a tripartite quantum state with small conditional mutual information, to what extent can one subsystem be recovered from the others? The Petz recovery map and its rotated variants offer a universal solution. These two topics are linked through coherification, which concerns when a classical stochastic process can be elevated to coherent quantum dynamics, and through the conditional mutual information as a continuous measure of non-unistochasticity. The talk concludes with open problems at this interface, including the star-shapedness conjecture for n = 4 and the pursuit of tighter recovery bounds.

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

非平衡量子多体系の普遍則：理解から制御へ

2026年5月12日(火) 15:00 - 16:00

濱崎 立資 (理化学研究所 開拓研究本部 (CPR) 濱崎非平衡量子統計力学理研白眉研究チーム 理研白眉研究チームリーダー)

(この講演は日本語で行われます。またこのセミナーは開拓研究所レクチャーシリーズの一環とも位置付けられています) 近年、量子シミュレータや量子コンピュータの発展により、量子多体系を高精度に実現・操作し、そのダイナミクスを直接観測することが可能になった。これにより、「ミクロな量子力学に基づいてマクロな統計力学を理解する」という、von Neumann以来の基礎的問題が改めて注目を集めている。他方で、こうした系を制御することでその量子性を活用し、古典系を凌駕するデバイスや機能を実現しようとする機運も高まっている。 本講演では、ミクロな量子ダイナミクスから非平衡量子多体系の普遍則を理解し、その制御可能性を理論的に明らかにするという観点から、我々の研究と今後の展望を議論する。特に、開放量子多体系に特有の相の特徴づけ、閉じた量子系における熱統計力学の発現、非平衡ダイナミクスにおける厳密な普遍則の成立といった話題を取り上げる。さらに、これらの知見を踏まえ、制御の統計物理学・多体物理学という未開拓領域をいかに切り開くかを展望する。また、この非平衡統計力学の普遍的枠組みが、量子物性にとどまらず他分野へも適用可能であることについても触れたい。

会場: 理化学研究所和光キャンパス 本部棟2階大会議室

イベント公式言語: 日本語

Introduction to quantum resource theories (2)

2026年5月12日(火) 9:00 - 17:00

高木 隆司 (東京大学 大学院総合文化研究科 准教授)

[Registration Closed] Due to high demand and venue capacity limits, registration for this course is now closed as of April 25. If you wish to be placed on a waiting list in case of cancellations, please contact us via the inquiry form at the bottom of this page. One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 2nd day: May 12 (Tue) 9:00–10:30 Lecture 3 10:30–11:00 Coffee break 11:00–12:30 Lecture 4 12:30-13:30 Lunch time 13:30-15:00 Lecture 5 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 This event is in-person only.

会場: 研究本館 4階 435-437号室

イベント公式言語: 英語

Introduction to quantum resource theories (1)

2026年5月11日(月) 13:30 - 17:00

高木 隆司 (東京大学 大学院総合文化研究科 准教授)

[Registration Closed] Due to high demand and venue capacity limits, registration for this course is now closed as of April 25. If you wish to be placed on a waiting list in case of cancellations, please contact us via the inquiry form at the bottom of this page. One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 1st day: May 11 (Mon) 13:30-15:00 Lecture 1 15:00-15:30 Coffee break 15:30-17:00 Lecture 2 This event is in-person only.

会場: 研究本館 4階 435-437号室

イベント公式言語: 英語

Building autonomous AI physicists for frontier physics research

2026年4月30日(木) 15:00 - 16:00

Tingjia Miao (Ph.D. Student, School of Artificial Intelligence, Shanghai Jiao Tong University, China)

Advances in LLMs have led to agents with knowledge and operational capabilities comparable to human scientists, suggesting potential to assist, accelerate, and automate research. Physics, especially theoretical and computational physics, which requires integrating analytical reasoning, code-based computation, and profound domain expertise, is well suited for verifying the end-to-end research capabilities of AI scientists. Accordingly, we construct a general-purpose AI physicist PhysMaster, equipped with a layered academic knowledge base, adapted to the agent skill ecosystem, and adopting an adaptive exploration strategy that balances efficiency and exploration, enabling robust performance in ultra-long-horizon tasks; PhysMaster has been open-sourced. Meanwhile, we introduce PRL-Bench (Physics Research by LLMs), a benchmark with 100 tasks adapted from recent Physical Review Letters papers, covering astrophysics, condensed matter physics, high-energy physics, quantum information, and statistical physics. Evaluation across frontier models shows that failures are dominated by conceptual and formulaic errors, and that exploration and derivations remain unstable over long horizons. In addition, we develop domain-specialized AI scientists, including LQCD Master, which integrates Lattice QCD workflows and expert skills, enabling automated generation and submission of lattice computation scripts from concise physics goals.

会場: via Zoom

イベント公式言語: 英語

Uniform Matrix Product States for Hamiltonian Lattice Gauge Theories: Methods and Applications

2026年4月28日(火) 16:00 - 17:30

藤倉 浩平 (京都大学 基礎物理学研究所 基研特任助教)

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

Seeing Photons, from Einstein to Bohr to Hanbury Brown-Twiss and related Hong-Ou-Mandel Interference Phenomena

2026年4月22日(水) 15:00 - 16:30

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

Why do we believe that the electromagnetic field is quantized, and photons exist? This talk will focus on two ways that the quantization of the electromagnetic field manifests itself in interference experiments. Bohr, who initially doubted photons after Einstein's initial proposal of the photon to explain the photoeffect, eventually proposed a thought experiment showing that the consistency of elementary quantum mechanics at the level of two slit diffraction requires the quantization of the electromagnetic field. In addition, as I will argue, both Hanbury Brown-Twiss interferometry and the closely related Hong-Ou-Mandel effect provide yet another way to see that the electromagnetic field must be quantized.

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

Quantum Computing of Molecular Properties for Fundamental Physics

2026年4月21日(火) 16:30 - 18:00

プラディヨット・プリタム・サフー (東京大学 大学院理学系研究科 大学院外国人研究生)

This is the self-introduction talk by Pradyot Pritam Sahoo. Pradyot is a Student Trainee in iTHEMS.

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

Quantum generative learning via diffusion

2026年4月21日(火) 10:00 - 11:00

Zhang Bingzhi (PostDoc, University of Southern California, USA)

Deep generative models are key-enabling technology to computer vision, text generation, and large language models. Generative models for quantum data offer a promising route toward learning and preparing complex quantum-state ensembles. In this talk, I will introduce the quantum denoising diffusion probabilistic model (QuDDPM) [1], which adapts the diffusion-model idea to quantum systems through a forward randomization process and a trainable backward denoising dynamics. I will discuss how this framework enables stepwise learning of target quantum state ensembles and demonstrate its capabilities in various learning tasks. I will then present its extension to mixed states to eliminate the need for scrambling [2]. I will conclude with a brief discussion of recent results on scaling laws of quantum information lifetime in monitored quantum dynamics, emphasizing how mid-circuit measurements can maintain information and provide useful intuition for measurement-assisted quantum machine learning.

会場: via Zoom

イベント公式言語: 英語

Analytical parametrization of the primordial power spectrum in effective Loop Quantum Cosmology

2026年4月20日(月) 13:00 - 14:00

Almudena Sánchez Guillén (Ph.D. Student, Institute of Structure of Matter (IEM-CSIC), Spain)

We investigate the imprints on the angular power spectra of cosmological perturbations of a pre-inflationary bounce phase, as described by the hybrid and dressed metric approaches to loop quantum cosmology. For this purpose, we derive a new parametrization of the primordial power spectrum at the end of the inflationary regime. Apart from slow-roll coefficients and cosmological parameters that are present in the standard cosmological scenario without quantum modifications, this parametrization additionally depends only on pre-inflationary physics. More specifically, we find a dependence on the number of e-folds during the bounce epoch and on a characteristic suppression scale which, given the e-folds accumulated during cosmic evolution, is determined by the energy density at the bounce.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

RIKEN Seminar: Formulation of Life Phenomena from Quantum Theory

2026年4月16日(木) 14:00 - 16:05

13:45 Opening 14:00-14:05 Introduction Atsushi Iriki (Teikyo University Advanced Comprehensive Research Organization Division of Artificial Intelligence, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) 14:05-14:35 "Interpretation of Life Phenomena Using Quantum Wave Functions and Field Theory" Kazuhiro Sakurada (Keio University Medical School and RIKEN Center for Integrative Medical Sciences (IMS), Predictive Medicine Special Project (PMSP)) 14:35-14:45 Q&A 14:45-15:30 "Bridging neurophysiology and quantum-like cognition" Andrei Khrennikov (Center for Mathematical Modeling in Physics and Cognitive Sciences Linnaeus University) 15:30-15:45 Q&A 15:45-16:00 "Quantum-Like Measurement" Masanao Ozawa (RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN TRIP FQSP, and Nagoya University) 16:00-16:05 Closing Remarks Satoshi Iso (Director, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) Host Laboratory: Predictive Medicine Special Project, RIKEN Center for Integrative Medical Sciences (IMS) / RIKEN Center for Interdisciplinary Theoretical and Mathematical Science (iTHEMS) *Registration is required by April 14 via the registration form. Contact: Predictive Medicine Special Project (pmsp-web@ml.riken.jp)

会場: 理化学研究所 和光キャンパス 脳科学池の端研究棟（建物番号C56）3階305

イベント公式言語: 英語

From Classical Definiteness to Geometric Predictability: Complementarity, Coherence, and Thermodynamic Triality

2026年4月10日(金) 15:30 - 17:00

Ezra Acalapati Madani (Ph.D. Student, Laboratoire de Physique de l'École Normale Supérieure, France)

Wave–particle complementarity is one of the central principles of quantum mechanics, traditionally quantified through the Englert–Greenberger–Yasin relation between which-way information and interference visibility. In higher-dimensional and resource-theoretic settings, however, visibility is no longer unique, and it becomes natural to reformulate complementarity in terms of basis-dependent predictability, coherence, and mixedness. In this talk, I present two related works along this line. First, I discuss an exact complementarity relation between classical definiteness and quantumness, where definiteness is defined operationally through the resilience of a quantum state under nonselective dichotomic yes/no measurements, while the complementary quantum contribution is quantified using a Kirkwood–Dirac-based notion of coherence/interference motivated by recent KD-based coherence measures. Second, I introduce a geometric predictability defined by the Bures distance between the dephased state and the maximally mixed state. This predictability depends only on the observed measurement statistics and admits a closed form in terms of the Bhattacharyya overlap. For pure states, it satisfies an exact complementarity relation with nonclassical Kirkwood–Dirac coherence; for mixed states, this motivates a convex-roof extension whose operational meaning is the classically irreducible part of measurement randomness, with implications for guessing probability and min-entropy. Finally, motivated by the decomposition of entropy production into population and coherence contributions in quantum thermodynamics, and by standard wave–particle–mixedness triality relations, I show how the usual predictability–coherence duality can be promoted into a triality relation involving predictability, coherence, and mixedness. Altogether, the talk connects wave–particle duality, coherence resource theories, operational guessing tasks, and thermodynamic balance relations within a unified framework.

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

非可換ゲージ理論の量子シミュレーション

2026年4月7日(火) 18:00 - 19:30

花田 政範 (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Kogut-Susskingハミルトニアンを用いればゲージ理論の量子シミュレーションができ、高エネルギー物理学の様々な問題を解けるはずであると言われて久しいのですが、実際にどのような研究がなされたのかを調べてみると、非可換ゲージ理論に関する論文が極端に少ないことに気が付きます。これは、Kogut-Susskingハミルトニアンは非可換ゲージ理論の場合にはとても複雑で、量子回路を構成する（ = プログラムをコンパイルする）以前に、そもそもハミルトニアンをqubitの言葉に書き直すための一般論すら存在しないからです。具体的には、無限次元のヒルベルト空間を正則化して有限自由度で近似する際に、SU(N)のような非自明な群多様体をどう扱えば良いのかが分かっていません。 この問題は、Kogut-Susskingハミルトニアンではなくてもっと筋の良いハミルトニアンを用いることで容易に回避できます。具体的には、Kaplan, Katz, Unsalによって構成されたorbifold lattice Hamiltonianを用いるのが便利です。Orbifold lattice Hamiltonianはゲージ場とスカラー場が相互作用する系を記述しますが、スカラー場は連続極限には寄与しません。（大きな質量を手で与えてUVの物理にすら寄与しなくすることも可能です。）しかし、ゲージ場とスカラー場をまとめて複素行列として記述するので、リンク変数がSU(N)ではなく\mathbb{C}^{N^2} = \mathbb{R}^{2N^2}に値をとります。たったこれだけの違いで、無限次元のヒルベルト空間の正則化が劇的に簡単になり、任意のSU(N)について効率的な量子回路を解析的に書き下すことが可能になります。 本講義では、量子シミュレーションの基礎から出発し、QCDを含む一般的な非可換ゲージ理論の時間発展を記述する量子回路を構成してシミュレーションコストを見積もるところまで解説したいと思います。 (3/24, 3/31, 4/7 の3回シリーズ)

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: 日本語

Quantum Computation SG seminar 2026

2026年4月7日(火) 15:00 - 17:00

Self-introductions (name + research interests) and discussion about study group activities in FY2026.

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

Tensor networks for QCD in the strong-coupling expansion

2026年4月2日(木) 15:30 - 17:00

Tilo Wettig (Professor, Universität Regensburg, Germany)

We present the order-separated Grassmann higher-order tensor renormalization group (OS-GHOTRG) method for QCD with staggered quarks in the strong-coupling expansion. Themethod allows us to determine the expansion coefficients of the partition function, from which we can obtain the strong-coupling expansions of thermodynamical observables. We use the method in two dimensions to compute the free energy, the particle-number density, and the chiral condensate as a function of the chemical potential up to third order in the inverse coupling 𝛽. Although the expansion itself is only a good approximation to the full theory at small 𝛽, we show that in the vicinity of the phase transition the range of applicability can be greatly extended by fits to judiciously chosen transition functions. These fits also yield a valuable expansion of the critical chemical potential in 𝛽. https://www.uni-regensburg.de/physics/hep/people/professors/wettig/index.html

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