II School on Emergent Phenomena in Non-Equilibrium Quantum Many-Body Systems

This two-week school is aimed at Master’s and PhD students interested in the dynamics of quantum many-body systems, with a focus on both foundational concepts and modern theoretical tools. The program will begin with an introduction to many-body statistical mechanics and the equilibrium physics of systems with short- and long-range interactions, setting the stage for an in-depth exploration of non-equilibrium dynamics, thermalization, and ergodicity. The school will provide a hands-on overview of key analytical approaches, including field-theoretical techniques, semiclassical methods, and the physics of disordered systems, including many-body localization, emergent integrability, and driven-dissipative systems. Our program covers also a quick introduction to modern experimental platforms where quantum many body dynamics is nowadays routinely explored, encompassing cavity QED and trapped ions experiments.

A highlight of the program will be two special guest lectures by Subir Sachdev (Harvard University), offering insights into quantum criticality and emergent phenomena in strongly correlated systems. Lectures will be complemented by interactive discussions and problem sessions, creating an environment that fosters both learning and collaboration.

You can find information on the previous School on Emergent Phenomena in Non-Equilibrium Quantum Many-Body Systems here and the Minicourse on open quantum systems: fundamentals, collisional models, and path integrals here.

There is no registration fee and limited funds are available for travel and local expenses.

 

Announcement:

Click HERE for online application

Application deadline: August 03, 2025

Lecturers

1st week

• Nicolo Defenu (ETH Zürich, Switzerland)
• Ana Maria Rey (JILA – University of Colorado, USA)
• Thereza Paiva (UFRJ, Brazil)
• Subir Sachdev (Harvard, USA)
• Mohammad Ali Rajabpour (UFF Niterói, Brazil) – One Critical Story, Three Entropies: Unifying entanglement, Shannon–Rényi, and stabilizer diagnostics

2nd week

• Hossein Hosseinabadi (Johannes Gutenberg University Mainz, Germany)
• Daniel Stariolo (UFF, Brazil)
• Anatoli Polkovnikov (Boston University, USA)
• Martino Stefanini (JGU Mainz, Germany) – Is Lindblad for me?
• Jamir Marino (JGU Mainz, Germany) – Light-matter quantum networks and spin glass dynamics 

Short Talks

• • • • Rivero Jerez, Dalila (IFSC-USP, Brazil): Cold atoms in bad cavities, the perfect playground to study quantum phenomena

    Our research explores the interplay of an ultracold cloud of strontium atoms (Γ/2π = 7.5 kHz) and an optical ‘bad cavity’ (F = 1000, κ/2π = 4 MHz). We prove how collective effects transform “bad” cavities into powerful quantum platforms. By coupling many atoms to the cavity mode, we achieve collective strong coupling and uncover a saturation-driven bistable phase at resonance—a theoretical prediction now experimentally observed(1). Remarkably, the Sr red transition saturates with just 1/11th of a cavity photon in our system, enabling extreme sensitivity to weak fields. This regime harbors unexplored nonlinear quantum optics, including potential squeezing effects. Our work demonstrates that imperfect cavities, when combined with many-body interactions, offer a scalable path to strong coupling phenomena, low-power quantum sensing, and emergent nonlinear dynamics. 1.- D Rivero et al 2023 New J. Phys. 25 093053.

    • • Cazon Tejerina, Diego Matias (IFT-UNESP, Brazil): AdS/CMT thermal and quantum phase transitions and self-duality

    AdS/CMT is a more phenomenological version of the AdS/CFT correspondence, for use in condensed matter systems. The standard thermal phase transition, between superconductor (or superfluid) and normal phases, is described by an AdS black hole, with or without charge, with a scalar field added on, that changes the horizon boundary conditions. A quantum critical phase transition, on the other hand, can be described in an Einstein-Maxwell system with a coupling to the Weyl tensor, from the dual to the ABJM model. We will study the interplay of these two situations, and whether we can put them together, and thus describe the Kosterlitz-Thouless phase transition line. We also consider the self-duality of transport in such an Einstein-Maxwell-scalar system.

    • • Doostani, Reza (University of Cologne, Germany): Dynamical frustration and Propelling domain walls

    I have investigated the dynamics of a ferrimagnet driven out of equilibrium by a weak oscillating magnetic field. This weak external field activates the rotational modes in the system with the direction of rotation chosen by the sign of the out of plane magnetization. This leads to a mechanism called dynamical frustration in presence of ferrimagnetic domain wall. I further studied the effect of dynamical frustration on ordering of such systems with many domain walls.

    • • Saini, Lalit Kumar (S V National Institute of Technology, Surat (Gujarat). India, India): Investigating the Interaction between Cyclo[12]carbon and Graphene Quantum Dot: A First Principles Study

    In this investigation, we explore the interaction between Cyclo[12]carbon (C12) and Coronene Graphene Quantum Dot (C24H12), two zero-dimensional carbon-based nanomaterials characterized by their unique structural and electronic properties. Our study consists of an in-depth analysis of their structural, electronic, and spectroscopic properties to determine the nature of their interaction. The separation between the C12 nanocluster and Coronene GQD is found to be 3.37 Å, indicative of the close proximity. Furthermore, the negative interaction energy and the all-positive frequencies in the IR spectra provide compelling evidence for the stability of the newly formed complex structure. At last, RDG, NCI and QTAIM analysis indicate that the interaction between these two zero dimensional structures is van der Walls interaction.

    • • Garcia, Federico (University of Delaware, United States): Fate of entanglement in quantum spin liquid under Lindbladian or non-Markovian dynamics induced by sudden coupling to dissipative bosonic environment

    We investigate the stability of entanglement in the Kitaev model of quantum spin liquid (QSL) that is suddenly coupled to a dissipative bosonic environment and time-evolved using Markovian (i.e., Lindblad) or non-Markovian (via joint reaction coordinate and polaron transformations or tensor network-based methods) quantum master equation for weak or strong coupling, respectively. Using such a time-evolved density matrix of spins within QSL, we compute spin-spin correlation functions, logarithmic negativity, and Wilson loop expectation values to probe local correlation and flux-sector stability under dissipative dynamics. These quantities reveal dissipation-induced transitions and identify conditions under which QSL features will persist in the long-time limit, as relevant for building QSL-based topological quantum computer operating under realistic conditions and at finite temperature.

    • • Reyes Osorio, Felipe (University of Delaware, Colombia): Nonequilibrium field theory of open spin systems: from semiclassical to nonperturbative quantum dynamics

    Open systems of many interacting spins—as realized by localized magnetic moments in a spintronic device, or qubits in a quantum computer—pose a formidable challenge for presently available theoretical methods, especially when the memory effects induced by the surrounding environment are relevant. Even archetypical examples like the spin-boson model, in which a single spin interacts with a continuum of bosonic modes requires switching between specialized methods for different choice of system-bath parameters. Here, we present a field theory (FT) of open quantum spin systems based on the Schwinger-Keldysh (SK) functional integral, which serves as the starting point for both semiclassical and fully quantum descriptions of the dynamics. In the semiclassical regime, we obtain corrections to the Landau-Lifshitz-Gilbert equations, conventionally employed in spintronics and magnonics, accounting for, e.g., nonlocal magnetic damping. On the other hand, the fully quantum regime is probed by combining SKFT with the two-particle irreducible (2PI) action resumming a class of Feynman diagrams to an infinite order. Remarkably, our SKFT+2PI closely tracks numerically exact benchmarks for the spin-boson and spin-chain-boson models, even in the nonperturbative and non-Markovian regime. The favorable numerical cost of solving integro-differential equations produced by SKFT+2PI framework with increasing number of spins, time steps or spatial dimensionality makes it a promising route for simulation of driven-dissipative systems in quantum computing or quantum spintronics and magnonics in the presence of a single or multiple dissipative environments.

    • • Aupetit-Diallo, Gianni (SISSA, Italy): Accuracy of the time dependant GGE

    Unitary integrable models typically relax to a stationary Generalized Gibbs Ensemble (GGE), but in experimental realizations dissipation often breaks integrability. In this work, we use the recently introduced time-dependent GGE (t-GGE) approach to describe the open dynamics of a gas of bosons subject to atom losses and gains. We employ tensor network methods to provide numerical evidence of the exactness of the t-GGE in the limit of adiabatic dissipation, and of its accuracy in the regime of weak but finite dissipation. That accuracy is tested for two-point functions via the rapidity distribution, and for more complicated correlations through a non-Gaussianity measure. We combine this description with Generalized Hydrodynamics and we show that it correctly captures transport at the Euler scale. Our results demonstrate that the t-GGE approach is robust in both homogeneous and inhomogeneous settings.

    • • Tapia De La Rosa, Alondra Jazmin (Universidad Nacional Autónoma de México, Mexico): Moiré–Floquet engineering of nonequilibrium topological bands in 2D semiconductor heterostructures

    Transition-metal dichalcogenide (TMD) heterobilayers provide a versatile platform where strong spin–orbit coupling and long-wavelength moiré superlattices intertwine. Theory predicts that specific atomic registries can drive band inversion and topological transitions in type-II TMD stacks, but accessing these phases is challenged by the large (~1 eV) interlayer gap typical of WSe2/MoSe2 bilayers. We propose and analyze a route to overcome this limitation using Floquet band engineering in rotated moiré WSe2/MoSe2 heterobilayers. Combining a k·p description with a realistic moiré potential for finite twist angle, we compute the Floquet–moiré minibands under off-resonant periodic driving and map the emergence of nonequilibrium topological phases characterized by drive-tunable gaps and non-trivial Chern indices. Our results show that the interplay of drive frequency/intensity, and interlayer alignment enables controllable topological mosaics domains of distinct topology on mesoscopic moiré scales. Overall, our work demonstrates that Moiré–Floquet engineering offers a practical pathway to induce and manipulate topological bands in 2D semiconductors, expanding the nonequilibrium toolkit to realize designer phases beyond the static band-inversion constraints.

    • • Machado, Joao Paulo Neves Azevedo (Universidade Federal Fluminense, Brazil): From Quantum to Classical: Unraveling the Origin of Counterintuitive Phenomenology in Heat Engines

    Counterintuitive thermodynamic phenomena, such as bidirectional operation and efficiency gains, have recently been demonstrated in quantum Otto engines [1]. These effects have been attributed to the presence of energy levels that do not interact with the outer parameter of the Hamiltonian. However the role of quantum adiabatic that takes the systems out of equilibrium is still open. In this work, we investigate whether analogs to these phenomena can emerge in classical Otto Cycle operating with a thermodynamic adiabatic. We demonstrate that, under specific conditions, the classical cycle also exhibits operation in the reverse direction of the usual cycle and other thermodynamic anomalies. We seek to determine the origin of quantum effects using classical cycles. References: 1. de Oliveira, Thiago R. and Jonathan, Daniel – Efficiency gain and bidirectional operation of quantum engines with decoupled internal levels

    • • Rabelo, Lucas Gabriel (Instituto de Física da Universidade de São Paulo, Brazil): Kondo screening and random singlet formation in highly disordered systems

    In this work, we introduce the two-impurity Kondo problem as a minimal model to capture the anomalous low-temperature thermodynamics of doped semiconductors, such as Si:P, across the metal-insulator transition (MIT). In particular, we consider pairs of local magnetic moments coupled to a highly disordered, non-interacting electronic bath that undergoes a MIT as a function of doping. Using a large-N variational mean-field approach, we capture both the inhomogeneous local Fermi-liquid and the insulating random-singlet phase and find that the local moment susceptibility exhibits a robust power-law behavior, χ(T) ∝ T^(-α), where the exponent $\alpha$ evolves smoothly with doping and saturates in the metallic regime, in close agreement with experimental observations. Our results highlight the competition between Kondo screening and random singlet formation as the minimal ingredients required for a microscopic description of the anomalous low-temperature behavior of strongly disordered, interacting systems.

    • • Manya Suni, Marco Antonio (Universidad Federal Fluminense, Brazil): Quantum Fisher Information and the Method of Moments in Discrete Time Crystals for Sensing Applications

    We investigate the quantum metrological properties of a star-topology spin system subjected to periodic driving in the linear response regime. The system is initialized in a product state and evolves under resonant sinusoidal modulation of a global magnetic field. We analyze the dynamics of the central spin magnetization and the Quantum Fisher Information (QFI) associated with the estimation of a weak field parameter \( h \). Our results reveal a size-dependent preservation of magnetization over long times, followed by fluctuations linked to the buildup of many-body correlations. The QFI exhibits quadratic growth at early times, plateaus during an intermediate regime, and increases again at later times, exceeding the standard quantum limit. The method of moments, used as an alternative estimator, identifies optimal measurement times that scale with system size, though it captures less information overall.

    • • Seifi Mirjafarlou, Miradel (Federal University of Fluminense, Brazil): Explicit Pfaffian Formula for Amplitudes of Fermionic Gaussian Pure States in Arbitrary Pauli Bases

    The explicit computation of amplitudes for fermionic Gaussian pure states in arbitrary Pauli bases is a long-standing challenge in quantum many-body physics, with significant implications for quantum tomography, experimental studies, and quantum dynamics. These calculations are essential for analyzing complex properties beyond traditional measures, such as formation probabilities, global entanglement, and entropy in non-standard bases, where exact and computationally efficient methods remain underdeveloped. % In addition to these physical applications, having explicit formulas is crucial for optimizing negative log-likelihood functions in quantum tomography, a key task in the NISQ era. % In this work, we present an explicit Pfaffian formula (Theorem \ref{theorem1}) for determining these amplitudes in arbitrary Pauli bases, utilizing a matrix whose structure reflects the qubit parity. Additionally, we introduce a recursive relation (Theorem \ref{theorem2recursiveformula}) that connects amplitudes for systems with varying qubit numbers, enabling scalable computations for large systems. % Together, these results provide a versatile framework for studying global entanglement, Shannon-Rényi entropies, formation probabilities, and performing efficient quantum tomography, thereby significantly expanding the computational toolkit for analyzing complex quantum systems. % Finally, we utilize our formalism to determine the post-measurement entanglement entropy, reflecting how local measurements alter entanglement, and compare the outcomes with conformal field theory predictions.

    • • Heinsdorf, Niclas (Max Planck Institute for Solid State Research, Stuttgart, Canada): Nature of the current-induced insulator-to-metal transition in calcium ruthenate

    The Mott insulator Ca2RuO4 exhibits a rare insulator-to-metal transition (IMT) induced by DC current. While structural changes associated with this transition have been tracked by neutron diffraction, Raman scattering, and x-ray spectroscopy, work on elucidating the response of the electronic degrees of freedom is still in progress. Our experimental results obtained by transport angle-resolved photoemission spectroscopy (ARPES) show a clear reduction of the Mott gap and a modification in the dispersion of the Ru-bands. We present a free energy analysis in terms of the (correlated) electronic degrees of freedom and model the electric field by a disproportion in occupation of electronic orbitals. While the Landau theory predicts the field- and temperature-induced metallic phases to be thermodynamically equivalent, varying values of the order parameter over a range of temperatures and electric field strengths reveal that they are electronically distinct.

    • • Villanueva Filho, Orion De Macedo Xavier (Institute of Physics of São Carlos at the University of São Paulo (IFSC/USP), Brazil): Approximations for the quantum work extracted from a correlated fermionic system

    The present project is inspired by the idea of approximating the work extracted in a quantum interacting system using Density Functional Theory (DFT). One of the key elements in DFT is the Kohn-Sham formulation, which converts the many-body problem in an effective non-interacting one by means of the so-called exchange-correlation functional. It has been shown that dealing with systems at finite temperature by means of DFT approximations built at previous works could produce accurate results up to a characteristic temperature. While in the previous studies for the quantum thermodynamics of the Hubbard model aforementioned the DFT approximations considered the exchange-correlation potential static and as that for the ground-state, an interesting route to improve their accuracy would be employing approximations constructed in the thermal DFT and Time-Dependent (TDDFT) framework. In this project, we propose to study the extracted quantum work in the driven Hubbard model using density functional approximations. Our goal is to identify strategies for designing reliable approximations for quantities of interest of Quantum Thermodynamics in various correlation regimes and thermal ranges.

    • • Farinas, Pedro Sanchez (IFSC, USP, Brazil): Effects of dissipation and disorder in systems with two order parameters and continuous symmetry

    The effects of disorder in phase transitions are often studied in closed systems, where it leads to different and unexpected behavior of matter, such as Griffiths singularities, infinite-randomness criticality, and glassy behavior, to name a few. Because real materials are seldom closed systems, it is important to understand how the phase diagram of a system changes when coupled with other degrees of freedom. The combined effects of quenched disorder and Ohmic dissipation have been investigated for systems with continuous O(N) symmetry by Hoyos et al. (1,2). Their findings reveal that the phase transition is governed by an infinite-randomness fixed point, belonging to the same universality class as the random transverse-field Ising model. We aim to extend this framework to phase transitions involving multiple order-parameter fields, as the combined effects of dissipation and disorder remain largely unexplored in such cases. The study of systems with multiple order-parameter fields is particularly relevant in the context of iron-based superconductors, where phase transitions involve both s-wave and d-wave superconducting order parameters. Understanding how disorder and dissipation affect these transitions can provide valuable insights into the critical behavior of these materials, which remain an active area of research.

    • • Boehly, Simon (Heidelberg University, Germany): Probing universal relaxation speed in a Bose-Einstein condensate far from equilibrium

    The dynamics of a Bose-Einstein condensate initialized in a far-from-equilibrium state can exhibit behavior that is reminiscent of fixed points in phase transitions—namely, self-similar scaling and universality. This phenomenon is referred to as a “non-thermal fixed point”. The properties of non-thermal fixed points enable predictions about the system’s relaxation dynamics, particularly the speed at which relaxation occurs. Dimensional analysis suggests that the relaxation speed exhibits universality—that is, counterintuitively, it does not depend on microscopic details such as the condensate’s density or interaction strength or on the exact initial state. Recent experimental results support this prediction (arXiv:2410.08204 [cond-mat.quant-gas]). In this talk, I will introduce the concept of non-thermal fixed points and their connection to relaxation dynamics. I will present experimental findings on the universality of the relaxation speed and discuss my own results based on numerical simulations and analytical approaches, addressing the question: “To what extent is the relaxation speed in a far-from-equilibrium Bose-Einstein condensate universal?”

    • • Velasco Roland Da Silva, Victor (International School for Advanced Studies (SISSA), Italy): Finite-temperature quasiparticle properties of an impurity immersed in a two-dimensional bosonic superfluid

      We investigate the finite-temperature properties of a single impurity immersed in a two-dimensional (2D) Bose gas, the Bose polaron, using an extended non-self-consistent T-matrix approach. This framework incorporates the interaction between the impurity and thermally excited bosons, accounting for the depletion of the 2D superfluid. To accurately describe the 2D Bose gas at finite temperature, we employ a leading-order-auxiliary-field (LOAF) theory of interacting bosons, together with a renormalization group (RG) analysis to determine the superfluid density and the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature, T_BKT, marking the onset of superfluidity. We explore how the polaron’s energy, quasiparticle residue, and damping evolve with temperature, identifying a discontinuous change in these properties at the BKT transition. This jump, caused by the superfluid density abrupt vanishing at T_BKT, highlights the sensitivity of the Bose polaron to the BKT transition. We suggest that this sensitivity could allow the Bose polaron to serve as an experimental probe for detecting the BKT transition temperature in 2D confined ultracold quantum Bose gases. Finally, we analyze the dynamical formation of the Bose polaron and highlight the interplay between the exponentially large binding energy, inherent of the 2D two-body problem, and thermal decoherence, which plays a substantial role in determining the lifetime of the quasiparticle.

    Posters

    • Pinto, Emmanuel Maurício Silveira (Instituto de Física de São Carlos (IFSC/USP), Brazil): Signatures of the Unruh effect in condensed-matter systems
    • The Unruh Effect, a fundamental result of Quantum Field Theory in Curved Spacetime (QFTCS), states that a uniformly accelerating observer in vacuum experiences a thermal bath with temperature proportional to its acceleration. This effect sheds light on the relative nature of particles, and shows that the fundamental entities of the universe are the fields, of which particles are only excitations. However, there is still debate within academia over whether this effect is capable of having observable physical consequences. Several articles have already been published in this regard, and it remains being an active research topic. With this in mind, this project aims to verify the physical nature of the Unruh effect through its effect in accelerated condensed matter systems.
    • Buda, Gabriel Alves (Unicamp, IMECC, Brazil): On quaternionic perturbation theory
    • Recent studies comparing complex and quaternionic formulations of quantum mechanics have demonstrated the significance of quaternionic potentials as natural extensions of conventional models. A fundamental result shows that asymptotic dynamics in quaternionic Hilbert spaces can always be described by a purely complex scattering matrix ($S$-matrix), as quaternionic components cancel out in observable physical processes. This reduction effectively collapses the quaternionic description into an equivalent complex theory at experimentally accessible energy scales, suggesting that quaternionic structures may underlie conventional physics as a unifying framework. Building on the approach of De Leo et al., which examines how quaternionic perturbations modulate energy eigenvalues in quantum systems, we address a key challenge: computing quaternionic potential-induced energy corrections without solving the full quaternionic equation, instead developing an adapted perturbation theory.
    • Zapana Choquehuanca, John Milton (Universidade Federal Fluminense, Brazil): Ergotropy-Based Quantum Thermodynamics
    • We introduce an ergotropy-based formulation of quantum thermodynamics, which provides a strong connection between average heat and von Neumann entropy. By adopting this formulation, we can reinterpret the infinitesimal average heat in terms of the infinitesimal change of the passive state associated with the density operator behind the quantum dynamics. Such as entropy, this leads to a heat concept that is invariant under passive state transformations. As an application, the average heat can be used as a general non-Markovinity measure for unital maps. Moreover, a positive-semidefinite temperature naturally emerges in an out-of-equilibrium ergotropy-based scenario. Concerning the infinitesimal average work, it arises as the infinitesimal variation of ergotropy, as well as an extra passive work contribution in the case of a time-dependent Hamiltonian. As illustrations, we consider the thermodynamics of a single-qubit open system in the cases of generalized amplitude-damping and phase-damping channels.
    • Ibañez, Jorge (Facultad de Ciencias, Universidad de la República, Uruguay): Conformal invariance constraints in the framework of the gradient expansion of the non-perturbative renormalization group
    • In the critical regime of statistical-mechanical systems, thermodynamic quantities follow power laws in some control parameter due to the effective interaction of the system at all scales, partially losing memory of the microscopic physics and becoming scale invariant. In general, this invariance is accompanied by invariance under the most general group of transformations that preserve angles, called conformal invariance. The non-perturbative renormalization group, a modern version of Wilson’s renormalization group, is a theoretical framework developed to study this phenomenology. In this framework, a prominent approximation scheme is the gradient expansion, which has proven to be very accurate in the calculation of critical properties. Despite this, the non-perturbative renormalization group and its approximation schemes are relatively new, and conformal invariance has not yet been thoroughly studied within this framework. In this work, the critical regime of the scalar phi^4 theory, which models the critical behavior of pure substances, was studied within the framework of the non-perturbative renormalization group. To this end, a set of constraints arising from conformal invariance that are violated when the gradient expansion is implemented were analyzed. In particular, how the violation of these constraints varies with the order of the approximation scheme was studied.
    • Gomes Alvarinho Squillante, Lucas Cesar (São Paulo State University (Unesp) – Rio Claro, SP, Brazil): Grüneisen parameter as an entanglement compass and the breakdown of the Hellmann-Feynman theorem
    • The Grüneisen ratio Γ, i.e., the singular part of the ratio of thermal expansion to the specific heat, has been broadly employed to explore both finite T and quantum critical points (QCPs). For a genuine quantum phase transition (QPT), thermal fluctuations are absent and thus the thermodynamic Γ cannot be employed. We propose a quantum analog to Γ that computes entanglement as a function of a tuning parameter λ and show that QPTs take place only for systems in which the ground-state energy depends on λ nonlinearly. Furthermore, we demonstrate the breakdown of the Hellmann-Feynman theorem in the thermodynamic limit at any QCP. We showcase our approach using the quantum one-dimensional Ising model with a transverse field and Kane’s quantum computer. The slowing down of the dynamics and thus the “creation of mass” close to any QCP/QPT is also discussed.
    • Alpino Da Silva, Marcos Gabriel (Federal University of Minas Gerais, Brazil): A Complexity-Based Approach to Quantum Observable Equilibration
    • We investigate the role of a statistical complexity measure to assign equilibration in isolated quantum systems. While unitary dynamics preserve global purity, expectation values of observables often exhibit equilibration-like behavior, raising the question of whether complexity can track this process. In addition to examining observable equilibration, we extend our analysis to study how the complexity of the quantum states evolves, providing insight into the transition from initial coherence to equilibrium. We define a classical statistical complexity measure based on observable entropy and deviation from equilibrium, which captures the dynamical progression towards equilibration and effectively distinguishes between complex and non-complex trajectories. In particular, our measure is sensitive to non-complex dynamics, such as the quasi-periodic behavior exhibited by low effective dimension initial states, where the systems explore a limited region of the Hilbert space as they oscillate in an informational coherence-preserving manner.
    • Jafari, Mohammad (Universidade Federal Fluminense, Brazil): Entanglement Entropy in the open quantum systems
    • I will show dynamics of open quantum systems in specific configurations and specially behavior of entanglement entropy
    • Santos Bento, Pedro Henrique (Universidade Federal de Goiás, Brazil): Krylov complexity and dynamical criticality in infinite-range interacting quantum many-body systems
    • I present recent results on the role of Krylov complexity as a probe of dynamical criticality in quantum many-body systems with infinite-range interactions. In the LMG model, we show that Krylov complexity acts as an order parameter for DQPTs and admits a physical interpretation via collective magnetization. Preliminary results also indicate sensitivity to ESQPTs, suggesting that Krylov complexity captures both dynamical and equilibrium-like transitions in a unified framework.
    • Mittal, Rohan (University of Cologne, Germany): Fermion quantum criticality far from equilibrium
    • Driving a quantum system out of equilibrium while preserving its subtle quantum mechanical correlations on large scales presents a major challenge, both fundamentally and for technological applications. At its core, this challenge is pinpointed by the question of how quantum effects can persist at asymptotic scales, analogous to quantum critical points in equilibrium. In this work, we construct such a scenario using fermions as building blocks. These fermions undergo an absorbing-to-absorbing state transition between two topologically distinct and quantum-correlated dark states. Starting from a microscopic, interacting Lindbladian, we derive an effective Lindblad-Keldysh field theory in which critical fermions couple to a bosonic bath with hydrodynamic fluctuations associated with particle number conservation. A key feature of this field theory is an emergent symmetry that protects the purity of the fermions’ state even in the presence of the thermal bath. We quantitatively characterize the critical point using a leading-order expansion around the upper critical dimension, thereby establishing the first non-equilibrium universality class of fermions. The symmetry protection mechanism, which exhibits parallels to the problem of directed percolation, suggests a pathway toward a broader class of robust, universal quantum phenomena in fermionic systems.
    • Pintar, Rok (Jozef Stefan Institute, Slovenia): Scaling of Chaotic Dynamics in the Mixed-Field Ising Model
    • The study of chaotic dynamics in closed many-body quantum systems remains an active area of research. Due to the exponential growth of Hilbert space with system size, we are limited to relatively small systems where exact diagonalization is feasible. This restricts the direct computation of chaos indicators such as level repulsion, entanglement entropy, and others. In this work, we investigate the scaling behavior of such indicators across the many-body localization transition using an improved polynomially filtered exact diagonalization method. This approach allows access to larger system sizes beyond the reach of conventional exact diagonalization techniques. Our results reveal sublinear scaling of the critical point with system size.
    • Jiricek, Simon (1. University of Ljubljana 2. Jožef Stefan Institute, Slovenia): Universal Relation between Spectral and Wavefunction Properties at Criticality
    • Quantum-chaotic systems exhibit several universal properties, ranging from level repulsion in the energy spectrum to wavefunction delocalization. On the other hand, if wavefunctions are localized, the levels exhibit no level repulsion and their statistics is Poisson. At the boundary between quantum chaos and localization, however, one observes critical behavior, not complying with any of those characteristics. An outstanding open question is whether there exist yet another type of universality, which is genuine for the critical point. Previous work suggested that there may exist a relation between the global characteristics of energy spectrum, such as spectral compressibility χ, and the degree of wavefunction delocalization, expressed via the fractal dimension D1 of the Shannon–von Neumann entropy in a preferred (e.g., real-space) basis. Here we study physical systems subject to local and non-local hopping, both with and without time-reversal symmetry, with the Anderson models in dimensions three to five being representatives of the first class, and the banded random matrices as representatives of the second class. Our thorough numerical analysis supports validity of the simple relation χ+ D1 = 1 in all systems under investigation. Hence we conjecture that it represents a universal property of a broad class of critical models. Moreover, we test and confirm the accuracy of our surmise for a closed-form expression of the spectral compressibility in the one-parameter critical manifold of random banded matrices. Based on these findings we derive a universal function D1(r), where ris the averaged level spacing ratio, which is valid for a broad class of critical systems.
    • De Souza, Vitória Freitas (Universidade Federal Fluminense, Brazil): Scrambling of Information and Complexity in Floquet time crystals: An Analysis through the Lipkin-Meshkov-Glick model
    • We investigate the interplay between information scrambling, complexity, and time-translation symmetry breaking in out-of-equilibrium quantum many-body systems. Using the Lipkin-Meshkov-Glick (LMG) model under periodic driving as a platform, we analyze the emergence of discrete time-crystalline phases and their associated dynamical properties. Numerical simulations are performed using the Dicke basis to efficiently diagonalize the Floquet operator and compute key observables such as spin expectation values, Loschmidt echoes, and out-of-time-ordered correlators (OTOCs). These quantities allow us to probe how quantum information spreads and how complexity builds up in the system, offering insights into ergodicity breaking and the persistence of long-range coherence. Our study contributes to a deeper understanding of collective quantum dynamics and emergent phenomena far from equilibrium.
    • Moledo, Matheus Fibger Lopes Brugger (UFF, Brazil): Semi-analytical solution for quantum many-body scars as effective quantum sensors.
    • In this work, we analyze the Fisher information for a quantum many-body scar system. We derive a semi-analytical solution for the Fisher information under two types of perturbations to be measured by the sensor. Using the analytical expression, we identify the optimal frequency for each type of perturbation and explain why it is the most efficient, showing that a quantity we call the “connection” is responsible for this behavior.
    • Tsypilnikov, Andrei (Instituto de Fisica, Universidade Federal Fluminense, Brazil): Optimal observables for AC sensors based on Floquet time crystals
    • We investigate optimal observables for AC quantum sensors based on Floquet Time Crystals (FTCs). The Quantum Fisher Information (QFI) dynamics in such systems display a characteristic step-like structure, originating from dephasing processes within the cat-state subspaces. We discuss the behavior of the system for various initial preparations, including ground, weakly correlated, and highly correlated states. This mechanism enables a robust Heisenberg-scaling precision, sustained for long times depending on the system size. We analyze how Symmetric Logarithmic Derivative (SLD) operators can be used to achieve the best possible precision in a closed system in FTC phase. We provide an analytical treatment of QFI dynamics in connection with SLD operators which allows construction of optimal observables with precision that saturate, or come very close to, the Cramér–Rao bound. We expect that our analysis will provide guidance for future experimental implementations of AC sensors using a FTC system.
    • Islam, Tanbir (Universidade Federal Fluminense (UFF), Brazil): Tuning Quantum Jumps to Preserve Entanglement Under Continuous Measurement
    • We investigate entanglement dynamics in continuously monitored quantum many-body systems using quantum-jump trajectory simulations in the symmetric-spin subspace. By analyzing entanglement entropy and waiting-time statistics, we reveal how measurement back-action drives a transition from stationary to active regimes of quantum dynamics. These results establish the ideal, perfectly resolved limit against which realistic detection must be compared. Incorporating the coarse-grained measurement model of Fazio et al. (2024), we show that finite detector resolution can mix classical uncertainty with quantum correlations, while systems tuned to produce periodic or controlled jumps remain largely unaffected. Our findings outline practical conditions under which experimental observations of entropy growth faithfully reflect genuine quantum entanglement.

     

Announcement:

Click HERE for online application

Application deadline: August 03, 2025

i

Participants of this event are welcome to attend the open lecture by Subir Sachdev: “100 years of many-particle quantum mechanics: from Bose and Fermi to quantum materials and black holes”.

Date and time: October 31, 2025, 19h00

Venue: Auditorium of IFT-UNESP

More information

 

• •  The schedule might be changed.

Attention! Some participants in ICTP-SAIFR activities have received email from fake travel agencies asking for credit card information. All communication with participants will be made by ICTP-SAIFR staff using an e-mail “@ictp-saifr.org”. We will not send any mailings about accommodation that require a credit card number or any sort of deposit. Also, if you are staying at Hotel Intercity the Universe Paulista, please confirm with the Uber/Taxi driver that the hotel is located at Rua Pamplona 83 in Bela Vista (and not in Jardim Etelvina).

BOARDING PASS: All participants, whose travel has been provided or will be reimbursed by ICTP-SAIFR, should bring the boarding pass  upon registration. The return boarding pass (PDF, if online check-in, scan or picture, if physical) should be sent to secretary@ictp-saifr.org by e-mail.

Visa information: Nationals from several countries in Latin America and Europe are exempt from tourist visa. Nationals from Australia, Canada and USA will be required to obtain a tourist e-visa for visits after April 10, 2025. Please check here which nationals need a tourist visa to enter Brazil.

Accommodation: Participants whose accommodations are provided by ICTP-SAIFR will stay at Hotel Intercity the Universe Paulista. Other hotel recommendations are available here.

Poster presentation: Participants who are presenting a poster MUST BRING A PRINTED BANNER . The banner size should be at most 1 m (width) x 1,5 m (length). We do not accept A4 or A3 paper.