Quantum many-body scars and symmetry-associated topological properties

• Chihiro Matsui (The University of Tokyo)

Room: Panasonic Auditorium, Yukawa Hall Recent progress in statistical physics has revealed the emergence of nonthermal phenomena in otherwise ergodic systems. Quantum many-body scars (QMBS) are known to be one of the central ingredients underlying such atypical behaviors. QMBS often appear as special eigenstates of ergodic quantum systems, forming a small but nontrivial invariant subspace. In this talk, we discuss the mathematical structure that stabilizes such subspaces under dynamics. At the same time, we demonstrate that the scar subspace can inherit properties of the underlying ground state, with particular emphasis on symmetry-associated topological properties. This talk is based on recent joint work (arXiv:2512.11216).

Systematic construction of asymptotic quantum many-body scar states and their relation to supersymmetric quantum mechanics

• Masaya Kunimi (Tokyo University of Science)

Room: Panasonic Auditorium, Yukawa Hall Quantum many-body scar (QMBS) states, which are special energy eigenstates that violate the eigenstate thermalization hypothesis in nonintegrable systems, have attracted much attention. Recently, asymptotic quantum many-body scar (AQMBS) states, which are closely related to QMBS states, have been proposed [1]. AQMBS states exhibit nonergodic behavior because their energy variance vanishes in the thermodynamic limit. Moreover, AQMBS states are related to Nambu-Goldstone modes, indicating a connection between thermalization in isolated quantum systems and spontaneous symmetry breaking [2]. However, existing constructions of AQMBS states are heuristic, and a systematic method for constructing them has not yet been established. In this work, we propose a systematic framework for constructing AQMBS states [3]. Within this framework, we assume a restricted spectrum-generating algebra [4,5], a symmetry-based formalism [6], and a specific structure of the Hamiltonian. Under these assumptions, AQMBS states arise as low-energy gapless excitations of a parent Hamiltonian whose ground states are QMBS states. Furthermore, we find that the algebraic relations of N=2 supersymmetric quantum mechanics naturally emerge in systems satisfying these assumptions. In this seminar, I will present the details of the method and its applications to several models. [1]L. Gotta et al, Phys. Rev. Lett. 131, 190401 (2023). [2]J. Ren et al., Phys. Rev. B 110, 245101 (2024). [3]MK, Y. Kato, and H. Katsura, Phys. Rev. Res. 7, 043107 (2025). [4]D. K. Mark et al, Phys. Rev. B 101, 195131 (2020). [5]S. Moudgalya et al, Phys. Rev. B 102, 085140 (2020). [6]N. O'Dea et al, Phys. Rev. Res. 2, 043305 (2020).

Fluctuation-response inequality and gravity

• Shin Nakamura (Chuo University)

Room: Panasonic Auditorium, Yukawa Hall The fluctuation–response inequality (FRI), proposed by Dechant and Sasa, is a general relation between fluctuations and responses in nonequilibrium systems. For instance, the FRI states that the ratio of the effective temperature to the differential mobility of a test particle in a thermal bath is a non-decreasing function of the particle’s velocity. In this work, we compute both the effective temperature and the differential mobility of a probe in a thermal bath using gauge/gravity duality in various gravitational backgrounds. We find that the FRI is satisfied in most setups consistent with superstring theory, with the exception of a few ill-defined cases. We also discuss how the geometry on the gravity side is constrained by the FRI.

Quantum Signatures of Chaos from Free Probability

• Hugo A. Camargo (National Center for Theoretical Sciences, Physics Division)

Room: Panasonic Auditorium, Yukawa Hall Free probability theory provides a rigorous framework for non-commutative random variables with free independence, and is the natural language for operator algebras in quantum mechanics. It has recently been explored as a tool for modeling aspects of quantum chaos, thermalization, and scrambling in regimes where random‑matrix or mean‑field behavior is expected. In this talk, I will provide an introduction to free probability theory and I will motivate and discuss its recent applications to describe quantum mixing in terms of emergent free independence between quantum observables in terms of operator statistics in models such as the mixed-field Ising, the q=2,4 SYK models and the RP model. This talk is based on 2503.20338 and 2506.04520.

A holographic prescription for dissipative hydrodynamical actions and horizon symmetries

• Michael Blake (University of Bristol (UK))

Room: Panasonic Auditorium, Yukawa Hall The last decade has seen significant interest in dissipative hydrodynamical actions in the Schwinger-Keldysh formalism. However there remain very few examples where such actions can be explicitly constructed. I will present a novel prescription that allows, for the first time, one to consistently compute such actions for holographic quantum field theories in general bulk dimension. The explicit construction of such actions allows us to test conjectured relations between hydrodynamical actions and quantum chaos – in particular I will discuss to what extent such actions realise horizon symmetries previously argued for by Knysh, Liu & Pinzani-Fokeeva.

Second law of thermodynamics in closed quantum many-body systems

• Yuuya Chiba (RIKEN)

Room: Panasonic Auditorium, Yukawa Hall The second law of thermodynamics for adiabatic operations --- constraints on state transitions in closed systems under external control --- is one of the fundamental principles of thermodynamics. On the other hand, recent studies of thermalization have established that even pure quantum states can represent thermal equilibrium. However, pure quantum states do not satisfy the second law in that they are not passive, i.e., work can be extracted from them if arbitrary unitary operations are allowed, and that various entropy formulas, such as the von Neumann entropy, deviate from thermodynamic entropy in such states. It therefore remains unresolved how thermal equilibrium represented by a pure quantum state can be reconciled with thermodynamics. Here, based on our key quantum-mechanical notions of thermal equilibrium and adiabatic operations, we address the emergence of the second law of thermodynamics in closed quantum many-body systems. We first introduce infinite-observable macroscopic thermal equilibrium (iMATE); a quantum state, including pure states, is said to represent iMATE if the expectation values of all additive observables, which correspond to additive quantities in thermodynamics, agree with their equilibrium values. We also introduce a macroscopic operation as unitary evolution generated by a time-dependent additive Hamiltonian, which is regarded as corresponding to adiabatic operations. Employing these concepts, we show Planck's principle: no extensive work can be extracted from any quantum state representing iMATE through any macroscopic operations with the operation times independent of the system size. Furthermore, we introduce a quantum-mechanical form of entropy density such that it agrees with thermodynamic entropy density for any quantum state representing iMATE. We then prove the law of increasing entropy: for any initial state representing iMATE, this entropy density cannot be decreased by any macroscopic operations with the operation times independent of the system size, followed by a relaxation process governed by a time-independent Hamiltonian. Our theory thus proves two different forms of the second law, which are quantum mechanically inequivalent to each other, and demonstrates how thermodynamics emerges from quantum mechanics by adopting macroscopically reasonable classes of observables, equilibrium states, and operations. This presentation is based on arXiv:2602.06657.

From Strong-to-Weak Symmetry Breaking to Hydrodynamics in Open Quantum Systems

• Jong Yeon Lee (University of Illinois Urbana-Champaign)

Room: Panasonic Auditorium, Yukawa Hall Hydrodynamics in open quantum systems has recently been proposed to admit a new interpretation: hydrodynamic modes can be viewed as Goldstone modes associated with strong-to-weak spontaneous symmetry breaking (SWSSB) [1]. However, an important conceptual gap remains. SWSSB is defined using nonlinear, information-theoretic diagnostics of mixed states, whereas hydrodynamics is observed through linear response and equal-time correlation functions. In particular, a nontrivial static charge structure factor was identified in Ref. [1] as an additional ingredient linking SWSSB to hydrodynamics, but this point has often been obscured in subsequent discussions. In this talk, I will clarify this connection. I will show how SWSSB constrains the static structure factor, thereby identifying a necessary bridge between nonlinear mixed-state order and physically observable hydrodynamic behavior [2]. I will then present a hydrodynamic Nambu-Goldstone theorem [3] for charge-conserving Lindbladians, showing under what conditions conserved charges in open quantum dynamics necessarily give rise to long-lived hydrodynamic modes. Together, these results provide a sharper framework for understanding when and how hydrodynamics emerges in open quantum systems. [1] O Ogunnaike, J Feldmeier, JY Lee, PRL 131, 220403 (2023) [2] JY Lee, arXiv:2605.05288 [3] JY Lee, ongoing work (2026)

Field Theory in Circuit Dynamics

• Alexander Altland (University of Cologne)

Room: Panasonic Auditorium, Yukawa Hall Recent years have witnessed major advances in the understanding of quantum circuit dynamics — progress essential to the success of the field as quantum hardware increasingly moves beyond the reach of classical simulation. The emerging “theory” of quantum devices is largely discrete in character, with prevalent concepts drawn from statistical mechanics, tensor networks, or the combinatorics of random matrices. At the same time, quantum field theory — physics’ established lingua franca for the understanding of complex many-body systems — remains strangely underrepresented, raising the question of why this is so. In this talk we discuss two paradigmatic aspects of circuit dynamics, thermalization toward ergodic late-time regimes and entanglement generation, to suggest some answers. We argue that quantum field theory provides both access to system classes that may be difficult to approach otherwise and insight into non-perturbative aspects of irreversible circuit evolution. We further argue that these aspects can be relevant to the understanding of realistic hardware, substantiating this claim through comparison with exact diagonalization results for small-system prototypes.

Holographic Krylov complexity　(ONLINE)

• Anatoly Dymarsky (University of Kentucky)

Room: Panasonic Auditorium, Yukawa Hall I will discuss how the Krylov space method can be formulated for holographic theories, and how it can help to define a dual holographic description for non-holographic systems.

Level Rank Duality in Quantum Mechanics

• Shiraz Minwalla (Tata Institute of Fundamental Research)

Room: Panasonic Auditorium, Yukawa Hall We study Chern Simons theories coupled to massive matter fields in an energy regime in which the kinetic energy of all particles is small compared to their rest masses. In this limit, the dynamics is described by a non relativistic Schrodinger equation. We present an explicit formulation of this Schrodinger equation. In situations in which the two Chern Simons theories are related by conjectured Bose Fermi dualities, we find an explicit linear transformation of wave functions, that turns one Schrodinger equation into another, `proving' the duality in the limit under study.

Quantum Mpemba effect in holography

• Shuta Ishigaki (Shanghai University)

Room: Panasonic Auditorium, Yukawa Hall The Mpemba effect is a counterintuitive phenomenon in which hotter substances cool down faster. This phenomenon can be observed under limited conditions. On the other hand, the quantum Mpemba effect (QME) is quantum analogue of it by replacing the temperature with other quantities. The QME may have various origins but it is helpful if we can understand its common mechanism. To shed light on it, we investigate the emergence of the QME by analyzing time evolution in the bottom-up holographic superfluid model. Our results indicate that the QME widely occurs in the holographic superfluid model under the probe limit.

Active Matter, KPZ, and (possibly) Gravity

• Kazuaki Takasan (The University of Tokyo)

Room: Panasonic Auditorium, Yukawa Hall In this talk, I will discuss two recent developments in nonequilibrium phenomena in condensed matter physics and then touch on possible connections to quantum gravity. The first topic is quantum active matter. Active matter consists of self-propelled constituents that consume energy locally and exhibit collective behavior far from equilibrium [1]. Although active matter has mostly been studied in classical soft-matter systems, recent work has begun to extend its concepts to quantum many-body systems. I will introduce our results on non-Hermitian quantum many-body systems that share key features with active matter [2,3]. The second topic is the emergence of the Kardar-Parisi-Zhang (KPZ) universality class in quantum spin chains. KPZ universality was originally found in stochastic classical nonequilibrium dynamics, such as interface growth. It is therefore striking that KPZ scaling can appear in the deterministic time evolution of isolated quantum systems [4]. I will present our numerical study showing that KPZ universality appears in certain two-point correlation functions, rather than in all aspects of the dynamics [5]. In this sense, it may be viewed as a partial, yet definite, emergence of KPZ physics. I will conclude the talk by briefly commenting on possible connections to quantum gravity. In these comments, I will touch on links between non-Hermitian systems and curved-space physics [6], as well as a proposed JT/KPZ correspondence involving double-scaled SYK, open ASEP, and KPZ correlations [7]. References: [1] e.g., M. C. Marchetti, J. F. Joanny, S. Ramaswamy, T. B. Liverpool, J. Prost, M. Rao, and R. A. Simha, Rev. Mod. Phys. 85, 1143 (2013). [2] K. Adachi, KT, and K. Kawaguchi, Phys. Rev. Research 4, 013194 (2022). [3] KT, K. Adachi, and K. Kawaguchi, Phys. Rev. Research 6, 023096 (2024). [4] M. Ljubotina, M. Znidaric, and T. Prosen, Phys. Rev. Lett. 122, 210602 (2019). [5] K. A. Takeuchi, KT, O. Busani, P. L. Ferrari, R. Vasseur, and J. De Nardis, Phys. Rev. Lett. 134, 097104 (2025). [6] C. Lv, R. Zhang, Z. Zhai, and Q. Zhou, Nat. Commun. 13, 2184 (2022). [7] M. Watanabe, arXiv:2511.02529 (2025).

Complex-CFT governed pseudocriticality in quantum spin chains

• Sumiran Pujari (Indian Institute of Technology Bombay)

Room: Panasonic Auditorium, Yukawa Hall Weak first-order pseudocriticality with approximate scale invariance has been observed in a variety of settings, including the intriguing case of deconfined criticality in 2+1 dimensions. Recently, this has been interpreted as extremely slow flows ("walking behavior") for real-valued couplings in proximity to a bona fide critical point with complex-valued couplings, described by a complex conformal field theory (CFT). Here we study an SU(N) generalization of the the Heisenberg antiferromagnet, which is a familiar model for deconfined criticality in 2+1 dimensions. We show that in 1+1 dimensions the model is located near a complex CFT, whose proximity can be tuned as a function of N. We employ state-of-the-art quantum Monte Carlo simulations for continuous N along with an improved loop estimator for the Rényi entanglement entropy based on a nonequilibrium work protocol. These techniques allow us to track the central charge of this model in detail as a function of N, where we observe excellent agreement with CFT predictions. Notably, this includes the region N>2, where the CFT moves into the complex plane and pseudocritical drifts enable us to recover the real part of the complex central charge with remarkable accuracy. Since the present model with N=3 is also equivalent to the spin-1 biquadratic model, our work sheds new light on the dimerized phase of the spin-1 chain, demonstrating that it is pseudocritical and proximate to a complex CFT.

Resonance-Suppression Principle for Prethermalization beyond Periodic Driving (https://arxiv.org/abs/2603.21540)

• Jian Xian Sim (Center for Quantum Technologies Singapore)

Room: Panasonic Auditorium, Yukawa Hall Non-equilibrium dynamics of strongly and rapidly driven quantum many-body systems is poorly understood beyond periodic driving, where heating is exponentially slow in the drive frequency (Floquet Prethermalization). In contrast, non-periodic drives were found to exhibit widely different heating scalings with no unifying principle. This work identifies a resonance-suppression principle governing slow heating up to a prethermal lifetime τ∗: When the drive's spectral arithmetic structure restricts multiphoton resonances, τ∗ is controlled by low-frequency spectral suppression. The principle distinguishes (i) Single-photon suppression, quantified by a low-frequency suppression law f(Ω) for the drive's Fourier Transform weight near Ω=0, from (ii) Multi-photon suppression, where nested commutators remain controlled if exceptional arithmetic structure satisfies a subadditive property. Remarkably, if multi-photon suppression holds, τ∗ scaling with drive speed λ is governed by f(Ω). This law of τ∗ is found through a small-divisor mechanism in this work's iterative rotating frame scheme. Multi-photon suppression breakdown separates λ-scaling of τ∗ in linear response and non-perturbative theory, shown by a case study of Quasi-Floquet driving. The principle is applied to (i) Resolve inconsistencies in literature on non-periodic driving, and (ii) Provide design principles for engineering prethermal phases of matter in programmable quantum simulators, exemplified by new non-periodic `Factorial' drives with tunable τ∗.

Modern field-theoretical approaches to hydrodynamics

• Masaru Hongo (Niigata Universiity)

Room: Panasonic Auditorium, Yukawa Hall Hydrodynamics is a universal low-energy effective field theory describing the macroscopic real-time dynamics of many-body systems. Over the past decade, remarkable progress has been made in reformulating hydrodynamics from the viewpoint of quantum field theory. In this talk, I will review these developments, focusing on both the imaginary-time and real-time formalisms of hydrodynamics and their connections to modern effective field theory.

Hydrodynamic attractor in ultracold atoms

• Keisuke Fujii (Institute of Science Tokyo)

Room: Panasonic Auditorium, Yukawa Hall The hydrodynamic attractor is a concept that describes universal equilibration behavior in which systems lose microscopic details before hydrodynamics becomes applicable. We propose a setup to observe hydrodynamic attractors in ultracold atomic gases, taking advantage of the fact that driving the two-body s-wave scattering length causes phenomena equivalent to isotropic fluid expansions. We specifically consider two-component fermions with contact interactions in three dimensions and discuss their dynamics under a power-law drive of the scattering length in a uniform system. By explicit computation, we derive a hydrodynamic relaxation model. We analytically solve their dynamics and find the hydrodynamic attractor solution. Our proposed method using the scattering length drive is applicable to a wide range of ultracold atomic systems, and our results establish these as a new platform for exploring hydrodynamic attractors.

Exact many-body dynamics in quantum circuits via space-time duality

• Bruno Bertini (University of Birmingham)

Room: Panasonic Auditorium, Yukawa Hall In recent years, quantum circuits have emerged as useful effective models to understand generic quantum many-body dynamics, and as concrete platforms for quantum simulation. The most appealing feature of these systems is that, contrary to generic many-body systems in continuous time, the dynamics of quantum circuits are sometimes amenable to analytical treatment. In the talk I will present a fruitful route to achieve this goal based on imposing a duality symmetry between space and time. I will review how this symmetry allows to fully characterise interesting features of quantum many-body dynamics, such as entanglement spreading and operator growth, and examine its implications. I will then discuss how to systematically weaken this symmetry while retaining (some) solvability, and how an exchange of space and time can help characterising general aspects of quantum many-body dynamics.

Mixed-State Entanglement in a Minimal Model of Quantum Chaos

• Tanay Pathak (Kyoto University)

Room: Panasonic Auditorium, Yukawa Hall We study the dynamics of mixed-state entanglement in a minimal model of quantum chaos, the kicked field Ising model, using a class of solvable initial states. By combining the replica trick with the space-time duality of the model, we show that the exact spectrum of the partially transposed reduced density matrix is flat at early times. This leads to exact relations between entanglement negativity, odd entropy and R´enyi mutual information. Extensive numerical simulations also demonstrate that this relation remains quantitatively valid for generic initial states and at late times, motivating the conjecture that it holds in general. Our results indicate that this relation extends beyond the present minimal model to more general Ising-type quantum spin chains.

An Observer-Based Approach to Thermalization

• Teruaki Nagasawa (Kanazawa University)

Room: Panasonic Auditorium, Yukawa Hall Thermalization and gravity have one thing in common: they do not align well with quantum mechanics. One possible explanation for this is that these phenomena are macroscopic rather than microscopic. So, what does it mean to be 'macro'? Furthermore, these phenomena may be characterized by the fact that they are described as relative to each observer. In order to address these questions, we will discuss a mathematical framework based on the concept of observer-dependent entropy. In particular, we will discuss how the increase in entropy occurs.

Tunable many-body burst in isolated quantum systems

• Shozo Yamada (The University of Tokyo)

Room: Panasonic Auditorium, Yukawa Hall While thermalization in isolated quantum many-body systems can be explained by the eigenstate thermalization hypothesis, its process can be nonmonotonic depending on an initial state. In this talk, we propose a numerical method to construct a low-entangled initial state that creates a “burst”——a transient deviation of an expectation value of an observable from its thermal equilibrium value——at a designated time. Our method utilizes the density matrix renormalization group algorithm to find such a state within the matrix product state manifold. We apply this method to demonstrate that a burst of magnetization can be realized for a nonintegrable mixed-field Ising chain on a timescale comparable to the onset of quantum scrambling. Contrary to the typical spreading of information in this regime, the created burst is accompanied by a slow or even negative entanglement growth. Analytically, we employ a local random quantum circuit to show that a burst becomes probabilistically rare after a long time. Our results suggest that a nonequilibrium state is maintained for an appropriately chosen initial state until scrambling becomes dominant. Due to the low-entangled nature of the initial state, our predictions can be tested with programmable quantum simulators. Ref: S. Yamada, A. Hokkyo, and M. Ueda, arXiv:2602.09665 [quant-ph] (2026).