Monday, June 8th, 2026
Workshop: Marcello Dalmonte
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Complexity of the many-body problem beyond entanglement: magic and sampling
Speaker: Marcello Dalmonte
Abstract: Entanglement has revolutionized the way we understand the quantum many-body problem. A key conceptual advance has been the relation between collective phenomena and their computational complexity, rooted in the concept of tensor network states and (lack of) separability. Over the last few years, very remarkable experimental advances have put forward the need to better understand different facets of complexity - in reference to actual cost of quantum computations (in the context of error corrections) and of data structures (in the context of collective measurements of wave functions). In this talk, I will descrive some progress along these two directions. Firstly, I will discuss how magic - the figure of merit of complexity in the context of quantum error correction schemes - relates to the many-body problem. I will discuss examples in the context of gauge theories, symmetry-protected topological phases, and tensor network states, and will show how understanding the magic/entanglement interplay can lead to new classes of variational states with uncharted computational capabilities. Secondly, I will present a new theoretical paradigm to understand snapshots of many-body states, that takes inspiration from the field of classical network theory. Using these tools, I will show how it is possible to reveal universal features in wave functions with no priors, and how one can, with the help of a “snapshot” renormalization group, classify phases of matter in one spatial dimension.
Title: Complexity of the many-body problem beyond entanglement: magic and sampling
Speaker: Marcello Dalmonte
Abstract: Entanglement has revolutionized the way we understand the quantum many-body problem. A key conceptual advance has been the relation between collective phenomena and their computational complexity, rooted in the concept of tensor network states and (lack of) separability. Over the last few years, very remarkable experimental advances have put forward the need to better understand different facets of complexity - in reference to actual cost of quantum computations (in the context of error corrections) and of data structures (in the context of collective measurements of wave functions). In this talk, I will descrive some progress along these two directions. Firstly, I will discuss how magic - the figure of merit of complexity in the context of quantum error correction schemes - relates to the many-body problem. I will discuss examples in the context of gauge theories, symmetry-protected topological phases, and tensor network states, and will show how understanding the magic/entanglement interplay can lead to new classes of variational states with uncharted computational capabilities. Secondly, I will present a new theoretical paradigm to understand snapshots of many-body states, that takes inspiration from the field of classical network theory. Using these tools, I will show how it is possible to reveal universal features in wave functions with no priors, and how one can, with the help of a “snapshot” renormalization group, classify phases of matter in one spatial dimension.
Workshop: Max McGinley
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Universality and complexity in quantum dynamics at early times
Speaker: Max McGinley
Abstract: While many-body quantum systems can be extraordinarily complex, quantitative predictions can often be made by identifying statistical ensembles that capture the universal behaviour of a broad class of systems. For instance, the Haar ensemble is expected to capture the the late-time behaviour of isolated systems without conservation laws. Accordingly, by understanding the key properties of Haar-random states, we can understand the physics of a diverse range of many-body systems in a unified way. In this talk, I will describe new universal statistical theories that capture the dynamics of systems in regimes beyond Haar, focusing in particular on the states generated by early-time dynamics. We argue that the behaviour of these early-time states can be captured by the so-called Scrooge ensemble [PRA 49, 668 (1994)], a more structured generalization of the Haar ensemble. I will first present evidence that the Scrooge ensemble describes the outputs of random constant-depth quantum circuits. This hypothesis has implications for the complexity of simulating shallow circuits: While noiseless simulation is thought to be exponentially hard, we prove that a vanishingly small noise rate ɣ = Ω (log(n) / n) is enough to render these circuits efficiently simulable. I will conclude by illustrating how the Scrooge ensemble could be used to describe other kinds of dynamics with beyond-Haar-random structure, such as the volume-law phase of monitored quantum circuits, and dynamics with conservation laws. Based on work with Thomas Schuster, David Gosset, and Calvin Liu
Title: Universality and complexity in quantum dynamics at early times
Speaker: Max McGinley
Abstract: While many-body quantum systems can be extraordinarily complex, quantitative predictions can often be made by identifying statistical ensembles that capture the universal behaviour of a broad class of systems. For instance, the Haar ensemble is expected to capture the the late-time behaviour of isolated systems without conservation laws. Accordingly, by understanding the key properties of Haar-random states, we can understand the physics of a diverse range of many-body systems in a unified way. In this talk, I will describe new universal statistical theories that capture the dynamics of systems in regimes beyond Haar, focusing in particular on the states generated by early-time dynamics. We argue that the behaviour of these early-time states can be captured by the so-called Scrooge ensemble [PRA 49, 668 (1994)], a more structured generalization of the Haar ensemble. I will first present evidence that the Scrooge ensemble describes the outputs of random constant-depth quantum circuits. This hypothesis has implications for the complexity of simulating shallow circuits: While noiseless simulation is thought to be exponentially hard, we prove that a vanishingly small noise rate ɣ = Ω (log(n) / n) is enough to render these circuits efficiently simulable. I will conclude by illustrating how the Scrooge ensemble could be used to describe other kinds of dynamics with beyond-Haar-random structure, such as the volume-law phase of monitored quantum circuits, and dynamics with conservation laws. Based on work with Thomas Schuster, David Gosset, and Calvin Liu
Workshop: Ben Craps
Time: 1:00 PM - 2:00 PM
Location: SCGP 102
Title: Quantum Chaos, Operator Spreading, and Dynamical Compressed Sensing of Quantum States
Speaker: Ben Craps
Abstract: I will discuss three results related to the distinction between integrable and chaotic quantum dynamics. First, I present a random matrix ensemble that correctly reproduces the level spacing distributions across the integrability-to-chaos transition in a variety of test systems. A key role is played by the statistics of the matrix elements of the nonintegrable perturbation Hamiltonian in the energy eigenbasis of the unperturbed integrable system, which turn out to be dominated by simple power laws. Second, I introduce multiseed Krylov complexity, a generalization of Krylov complexity based on the block-Lanczos algorithm applied simultaneously to all simple operators. It reliably distinguishes chaotic from integrable dynamics by assigning higher complexity saturation values to the former. Third, I propose a method for reconstructing low-rank quantum states from a small number of simple local measurements made at different times. This dynamical compressed sensing protocol succeeds for chaotic systems that sufficiently scramble simple operators.
Title: Quantum Chaos, Operator Spreading, and Dynamical Compressed Sensing of Quantum States
Speaker: Ben Craps
Abstract: I will discuss three results related to the distinction between integrable and chaotic quantum dynamics. First, I present a random matrix ensemble that correctly reproduces the level spacing distributions across the integrability-to-chaos transition in a variety of test systems. A key role is played by the statistics of the matrix elements of the nonintegrable perturbation Hamiltonian in the energy eigenbasis of the unperturbed integrable system, which turn out to be dominated by simple power laws. Second, I introduce multiseed Krylov complexity, a generalization of Krylov complexity based on the block-Lanczos algorithm applied simultaneously to all simple operators. It reliably distinguishes chaotic from integrable dynamics by assigning higher complexity saturation values to the former. Third, I propose a method for reconstructing low-rank quantum states from a small number of simple local measurements made at different times. This dynamical compressed sensing protocol succeeds for chaotic systems that sufficiently scramble simple operators.
Workshop: Monika Aidelsburger
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Out-of-equilibrium dynamics in large-scale neutral-atom quantum simulators
Speaker: Monika Aidelsburger
Abstract: Lattice-based neutral-atom quantum simulators provide highly coherent many-body systems with thousands of atoms, single-site resolution, and microscopic control, enabling new approaches to non-equilibrium dynamics in strongly correlated quantum matter. In this talk, I will highlight recent advances in developing novel state preparation and readout protocols that enable a resource-efficient study of quantum many-body systems. A central example is the subsystem return probability (SRP), a quasi-local and experimentally robust observable whose scaling with subsystem size gives access to thermodynamic-limit properties of a many-body state from small subsystems. Its dependence on subsystem size encodes the correlation structure of the state, while its long-time limit yields the thermodynamic entropy density and the effective dimension of the dynamically accessible Hilbert space. In the second part, I discuss large-scale realizations of (2+1)D U(1) lattice gauge theories (> 3,000 sites) and the non-equilibrium preparation of Rokhsar-Kivelson-type quantum spin liquids in a quantum dimer model with a characteristic size of ~100 lattice sites. We observe real-space correlations and momentum-space pinch points characteristic of an emergent gauge structure, and use interferometric protocols to probe many-body coherence. These results establish non-equilibrium protocols as a powerful route for accessing highly entangled states beyond equilibrium reach. Finally, I will present a new experimental protocol for reversing the time evolution of a Bose-Hubbard system, a key ingredient for measuring out-of-time-order correlators and probing the connection between information scrambling and transport.
Title: Out-of-equilibrium dynamics in large-scale neutral-atom quantum simulators
Speaker: Monika Aidelsburger
Abstract: Lattice-based neutral-atom quantum simulators provide highly coherent many-body systems with thousands of atoms, single-site resolution, and microscopic control, enabling new approaches to non-equilibrium dynamics in strongly correlated quantum matter. In this talk, I will highlight recent advances in developing novel state preparation and readout protocols that enable a resource-efficient study of quantum many-body systems. A central example is the subsystem return probability (SRP), a quasi-local and experimentally robust observable whose scaling with subsystem size gives access to thermodynamic-limit properties of a many-body state from small subsystems. Its dependence on subsystem size encodes the correlation structure of the state, while its long-time limit yields the thermodynamic entropy density and the effective dimension of the dynamically accessible Hilbert space. In the second part, I discuss large-scale realizations of (2+1)D U(1) lattice gauge theories (> 3,000 sites) and the non-equilibrium preparation of Rokhsar-Kivelson-type quantum spin liquids in a quantum dimer model with a characteristic size of ~100 lattice sites. We observe real-space correlations and momentum-space pinch points characteristic of an emergent gauge structure, and use interferometric protocols to probe many-body coherence. These results establish non-equilibrium protocols as a powerful route for accessing highly entangled states beyond equilibrium reach. Finally, I will present a new experimental protocol for reversing the time evolution of a Bose-Hubbard system, a key ingredient for measuring out-of-time-order correlators and probing the connection between information scrambling and transport.
Workshop: Masaki Oshikawa
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Conformal boundary conditions of Z_2 orbifolds and Stabilizer Renyi Entropy
Speaker: Masaki Oshikawa
Abstract: I will discuss conformal boundary conditions of the Z_2 orbifold of free boson conformal field theory in 1+1 dimensions. As applications to statistical mechanics, I will discuss the boundary phase diagram of the critical Ashkin-Teller model including the double-layer critical Ising model and the critical 4-state Potts model. A conformal boundary condition of the Z_2 orbifold of multicomponent free boson conformal field theory is also related to the Stabilizer Renyi Entropy, a measure of "nonstabilizerness" also known as quantum magic which is a resource for quantum computation.
Title: Conformal boundary conditions of Z_2 orbifolds and Stabilizer Renyi Entropy
Speaker: Masaki Oshikawa
Abstract: I will discuss conformal boundary conditions of the Z_2 orbifold of free boson conformal field theory in 1+1 dimensions. As applications to statistical mechanics, I will discuss the boundary phase diagram of the critical Ashkin-Teller model including the double-layer critical Ising model and the critical 4-state Potts model. A conformal boundary condition of the Z_2 orbifold of multicomponent free boson conformal field theory is also related to the Stabilizer Renyi Entropy, a measure of "nonstabilizerness" also known as quantum magic which is a resource for quantum computation.
Tuesday, June 9th, 2026
Workshop: Masahito Ueda
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Universal upper bound on ergotropy and no-go theorem by the eigenstate thermalization hypothesis
Speaker: Masahito Ueda
Abstract: We show that the maximum extractable work (ergotropy) from a quantum many-body system is constrained by “local athermality” of an initial state and “local entropy decrease” brought about by quantum operations. The obtained universal upper bound on ergotropy implies that the eigenstate thermalization hypothesis prohibits work extraction from energy eigenstates by means of finite-time unitary operations. This no-go property implies that Planck’s principle, a form of the second law of thermodynamics, holds even for pure quantum states. Our result bridges two independently studied concepts of quantum thermodynamics, the second law and thermalization, via “intrasystem” correlations in many-body systems as a resource for work extraction.
Title: Universal upper bound on ergotropy and no-go theorem by the eigenstate thermalization hypothesis
Speaker: Masahito Ueda
Abstract: We show that the maximum extractable work (ergotropy) from a quantum many-body system is constrained by “local athermality” of an initial state and “local entropy decrease” brought about by quantum operations. The obtained universal upper bound on ergotropy implies that the eigenstate thermalization hypothesis prohibits work extraction from energy eigenstates by means of finite-time unitary operations. This no-go property implies that Planck’s principle, a form of the second law of thermodynamics, holds even for pure quantum states. Our result bridges two independently studied concepts of quantum thermodynamics, the second law and thermalization, via “intrasystem” correlations in many-body systems as a resource for work extraction.
Workshop: Sergej Flach
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Thermalization Universality Classes
Speaker: Sergej Flach
Abstract: Thermalization of closed many body systems is at the heart of fundamental quantum concepts like many body localization, eigenstate thermalization hypothesis, and quantum computers since several decades. More recently it also entered the world of classical many body systems through light propagation in nonlinear photonic multimode waveguides and waveguide networks, relating to such observations as e.g. spatial beam self cleaning. I will introduce concepts of quantifying thermalization, which are tied up to measuring time scales (aka length scales in photonic wave guide applications). The paradoxical upshot is that easy to measure scales are footing on the concept of ergodicity and may quickly lead to ambiguous nonuniversal assessments [1-4]. On the other side stands the universal and unambiguous concept of Lyapunov time scales, which are however much harder to be measured [5-9]. I will present results which show that Lyapunov spectra scale in distinct different ways for different classes of systems, depending on the type of weak coupling network between modes of a decoupled limit (e.g. low intensity light, or weak coupling in wave guide arrays) [5-9]. These results establish the existence of different thermalization universality classes in many body physics. They further allow to numerically determine the type of thermalization class for a variety of systems such as the FPUT chain, the Toda chain, and the BCS model [10-14], and quantum many body systems [15].
Title: Thermalization Universality Classes
Speaker: Sergej Flach
Abstract: Thermalization of closed many body systems is at the heart of fundamental quantum concepts like many body localization, eigenstate thermalization hypothesis, and quantum computers since several decades. More recently it also entered the world of classical many body systems through light propagation in nonlinear photonic multimode waveguides and waveguide networks, relating to such observations as e.g. spatial beam self cleaning. I will introduce concepts of quantifying thermalization, which are tied up to measuring time scales (aka length scales in photonic wave guide applications). The paradoxical upshot is that easy to measure scales are footing on the concept of ergodicity and may quickly lead to ambiguous nonuniversal assessments [1-4]. On the other side stands the universal and unambiguous concept of Lyapunov time scales, which are however much harder to be measured [5-9]. I will present results which show that Lyapunov spectra scale in distinct different ways for different classes of systems, depending on the type of weak coupling network between modes of a decoupled limit (e.g. low intensity light, or weak coupling in wave guide arrays) [5-9]. These results establish the existence of different thermalization universality classes in many body physics. They further allow to numerically determine the type of thermalization class for a variety of systems such as the FPUT chain, the Toda chain, and the BCS model [10-14], and quantum many body systems [15].
Workshop: David Weiss
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Title: Stationary excited many-body states (SEMBSs) and tests of generalized hydrodynamics (GHD) after Bragg scattering in a 1D Bose gas.
Speaker: David Weiss
Abstract: In the Tonks-Girardeau gas limit of a 1D Bose gas, a Bragg pulse puts the central component of the rapidity distribution directly into a stationary excited many body state (SEMBS), which is the globally prethermalized state in the axial trap. While counterintuitive, since one would naively expect that the depleted central component would start to breathe, we understand this phenomenon completely. For finite coupling strengths, it is possible to reach an approximate SEMBS when the axial trap is changed by just the right amount at the time of the pulse. We observe this behavior experimentally, but a complete theoretical explanation is a challenge. In general, the post-pulse evolution of the rapidity distribution in the axial trap is rather feature-rich, and provides opportunities for new tests of GHD.
Title: Title: Stationary excited many-body states (SEMBSs) and tests of generalized hydrodynamics (GHD) after Bragg scattering in a 1D Bose gas.
Speaker: David Weiss
Abstract: In the Tonks-Girardeau gas limit of a 1D Bose gas, a Bragg pulse puts the central component of the rapidity distribution directly into a stationary excited many body state (SEMBS), which is the globally prethermalized state in the axial trap. While counterintuitive, since one would naively expect that the depleted central component would start to breathe, we understand this phenomenon completely. For finite coupling strengths, it is possible to reach an approximate SEMBS when the axial trap is changed by just the right amount at the time of the pulse. We observe this behavior experimentally, but a complete theoretical explanation is a challenge. In general, the post-pulse evolution of the rapidity distribution in the axial trap is rather feature-rich, and provides opportunities for new tests of GHD.
Workshop: Boris Fine
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Classical periodic trajectories and quantum scars in many-spin systems
Speaker: Boris Fine
Abstract: We numerically investigate the stability of exceptional periodic classical trajectories in chaotic many-spin systems and explore a possible connection between these trajectories and quantum many-body scars. The systems considered are chaotic spin chains with short-range interactions, both classical and quantum. On the classical side, the chosen periodic trajectories are such that all spins instantaneously point in the same direction, which evolves as a function of time. We find that the largest Lyapunov exponents characterizing the stability of these trajectories have surprisingly strong and nontrivial dependencies on the interaction constants and chain lengths. In particular, we identify rather long spin chains, where the above periodic trajectories are Lyapunov stable on many-body energy shells overwhelmingly dominated by chaotic motion. The above phenomenology can be quantitatively described by connecting the Lyapunov instabilities to irreducible representations of the translational symmetry group with well-defined wave vectors. We also find that instabilities around periodic trajectories in modestly large spin chains develop into a transient nearly quasiperiodic nonergodic regime. In some cases, the lifetime of this regime is extremely long, which we interpret as a manifestation of Arnold diffusion in the vicinity of integrable dynamics. On the quantum side, we numerically investigate the dynamics of quantum counterparts of the above classical trajectories, where all quantum spins initially point in the same direction. Our investigation reveals the existence of quantum many-body scars for numerically accessible finite chains of spins-3/2 and higher. No evidence of quantum scars was observed for spin-1/2 chains, while spin-1 chains were found to be transitional in this respect. The dynamic thermalization process dominated by quantum scars is shown to exhibit a slowdown in comparison with generic thermalization at the same energy. Finally, we identify quantum signatures of the proximity to a classical separatrix of the periodic motion. Reference: I. Ermakov, O. Lychkovskiy and B. V. Fine, Phys. Rev. E 112, 064109 (2025), DOI: 10.1103/zcgw-q34x
Title: Classical periodic trajectories and quantum scars in many-spin systems
Speaker: Boris Fine
Abstract: We numerically investigate the stability of exceptional periodic classical trajectories in chaotic many-spin systems and explore a possible connection between these trajectories and quantum many-body scars. The systems considered are chaotic spin chains with short-range interactions, both classical and quantum. On the classical side, the chosen periodic trajectories are such that all spins instantaneously point in the same direction, which evolves as a function of time. We find that the largest Lyapunov exponents characterizing the stability of these trajectories have surprisingly strong and nontrivial dependencies on the interaction constants and chain lengths. In particular, we identify rather long spin chains, where the above periodic trajectories are Lyapunov stable on many-body energy shells overwhelmingly dominated by chaotic motion. The above phenomenology can be quantitatively described by connecting the Lyapunov instabilities to irreducible representations of the translational symmetry group with well-defined wave vectors. We also find that instabilities around periodic trajectories in modestly large spin chains develop into a transient nearly quasiperiodic nonergodic regime. In some cases, the lifetime of this regime is extremely long, which we interpret as a manifestation of Arnold diffusion in the vicinity of integrable dynamics. On the quantum side, we numerically investigate the dynamics of quantum counterparts of the above classical trajectories, where all quantum spins initially point in the same direction. Our investigation reveals the existence of quantum many-body scars for numerically accessible finite chains of spins-3/2 and higher. No evidence of quantum scars was observed for spin-1/2 chains, while spin-1 chains were found to be transitional in this respect. The dynamic thermalization process dominated by quantum scars is shown to exhibit a slowdown in comparison with generic thermalization at the same energy. Finally, we identify quantum signatures of the proximity to a classical separatrix of the periodic motion. Reference: I. Ermakov, O. Lychkovskiy and B. V. Fine, Phys. Rev. E 112, 064109 (2025), DOI: 10.1103/zcgw-q34x
Wednesday, June 10th, 2026
Workshop: Pavel Kos
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Mixed state deep thermalization
Speaker: Pavel Kos
Abstract: We introduce the notion of the mixed state projected ensemble (MSPE), a collection of mixed states describing a local region of a quantum many-body system, conditioned upon incomplete measurements of the complementary region. This constitutes a generalization of the pure state projected ensemble in which measurements are assumed ideal and complete, and which has been shown to tend towards limiting pure state distributions depending only on symmetries of the system, thus representing a new kind of universality in quantum equilibration dubbed deep thermalization. We study the MSPE generated by solvable (1+1)d dual-unitary quantum circuit evolution, and identify the limiting mixed state distributions which emerge at late times depending on the size of the incomplete measurement, which we assume to be lossy, finding that they correspond to certain random density matrix ensembles known in the literature. We also derive the rate of the emergence of such universality. Furthermore, we uncover a sharp transition in the ensemble's capacity to teleport quantum information: the fidelity switches from zero to maximal when the number of lost measurement outcomes matches the number of teleported degrees of freedom. These results provide a framework for observing deep thermalization and sampling random matrix ensembles in realistic, lossy quantum simulators. Based on PRL 135, 260402 (2025) (arXiv:2505.07795), done together with Xie-Hang Yu, Wen Wei Ho.
Title: Mixed state deep thermalization
Speaker: Pavel Kos
Abstract: We introduce the notion of the mixed state projected ensemble (MSPE), a collection of mixed states describing a local region of a quantum many-body system, conditioned upon incomplete measurements of the complementary region. This constitutes a generalization of the pure state projected ensemble in which measurements are assumed ideal and complete, and which has been shown to tend towards limiting pure state distributions depending only on symmetries of the system, thus representing a new kind of universality in quantum equilibration dubbed deep thermalization. We study the MSPE generated by solvable (1+1)d dual-unitary quantum circuit evolution, and identify the limiting mixed state distributions which emerge at late times depending on the size of the incomplete measurement, which we assume to be lossy, finding that they correspond to certain random density matrix ensembles known in the literature. We also derive the rate of the emergence of such universality. Furthermore, we uncover a sharp transition in the ensemble's capacity to teleport quantum information: the fidelity switches from zero to maximal when the number of lost measurement outcomes matches the number of teleported degrees of freedom. These results provide a framework for observing deep thermalization and sampling random matrix ensembles in realistic, lossy quantum simulators. Based on PRL 135, 260402 (2025) (arXiv:2505.07795), done together with Xie-Hang Yu, Wen Wei Ho.
Workshop: Jesko Sirker
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Length-resolved Operator Growth and Path-Entropy Obstructions to Many-Body Localization
Speaker: Jesko Sirker
Abstract: The status of many-body localization (MBL) in disordered spin chains has remained controversial for years, with much of the debate focussing on resonance effects, avalanche instabilities, and the interpretation of finite-size numerics. In this talk I take a different angle and approach MBL through the lens of operator growth. Starting from the rigorous result that the iterated commutator [H, …,[H,sigma^z]] grows at the maximal almost factorially rate with the commutator order k, I will discuss what this growth implies for spatial locality and for the various formulations of MBL. The picture that emerges places significant restrictions on the surviving physical content of MBL and suggests a structural obstruction to the perturbative construction of local integrals of motion that is independent of resonance physics.
Title: Length-resolved Operator Growth and Path-Entropy Obstructions to Many-Body Localization
Speaker: Jesko Sirker
Abstract: The status of many-body localization (MBL) in disordered spin chains has remained controversial for years, with much of the debate focussing on resonance effects, avalanche instabilities, and the interpretation of finite-size numerics. In this talk I take a different angle and approach MBL through the lens of operator growth. Starting from the rigorous result that the iterated commutator [H, …,[H,sigma^z]] grows at the maximal almost factorially rate with the commutator order k, I will discuss what this growth implies for spatial locality and for the various formulations of MBL. The picture that emerges places significant restrictions on the surviving physical content of MBL and suggests a structural obstruction to the perturbative construction of local integrals of motion that is independent of resonance physics.
Workshop: Anushya Chandra
Time: 1:00 PM - 2:00 PM
Location: SCGP 102
Title: Stabilizing Floquet orders to infinite time
Speaker: Anushya Chandra
Abstract: Floquet engineering, in which the properties of a quantum system are modified through the application of strong periodic drives, is an indispensable tool in atomic and condensed matter systems. It enables quantum simulation, the dynamic stabilization of unstable states, and the realization of exotic topological order and time crystals. However, it is inevitably limited by intrinsic heating processes, so that the engineered states are, at best, pre-thermal. I will describe a general-purpose dissipative scheme that autonomously cools a strongly driven system to close to a desired Floquet engineered state. I will present experimental evidence that few-level systems cool to quasi-energy states, and theoretical evidence that many-body systems instead cool to ground states of effective Hamiltonians. These ground state can support non-trivial Floquet orders in the steady state. I will give a concrete example of such an order in a driven and dissipative spin chain that exhibits discrete time-crystalline order in the steady state.
Title: Stabilizing Floquet orders to infinite time
Speaker: Anushya Chandra
Abstract: Floquet engineering, in which the properties of a quantum system are modified through the application of strong periodic drives, is an indispensable tool in atomic and condensed matter systems. It enables quantum simulation, the dynamic stabilization of unstable states, and the realization of exotic topological order and time crystals. However, it is inevitably limited by intrinsic heating processes, so that the engineered states are, at best, pre-thermal. I will describe a general-purpose dissipative scheme that autonomously cools a strongly driven system to close to a desired Floquet engineered state. I will present experimental evidence that few-level systems cool to quasi-energy states, and theoretical evidence that many-body systems instead cool to ground states of effective Hamiltonians. These ground state can support non-trivial Floquet orders in the steady state. I will give a concrete example of such an order in a driven and dissipative spin chain that exhibits discrete time-crystalline order in the steady state.
Workshop: Katja Klobas
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Quantum dynamics and chaos in permutation circuits
Speaker: Katja Klobas
Abstract: I will talk about a series of recent works [1-4], studying many-body dynamics generated by circuits where each unitary gate acts as a randomly-chosen permutation in the computational basis, and comparing their behaviour to that of random unitary circuits, a standard toy model for generic quantum dynamics. Random permutation circuits permit the analytical computation of several key quantities such as out-of-time order correlators, or entanglement entropies. Remarkably, despite the fundamental differences between unitary and permutation dynamics, they exhibit qualitatively similar behaviours, though there are important differences coming from the classical nature of the underlying dynamics.
Title: Quantum dynamics and chaos in permutation circuits
Speaker: Katja Klobas
Abstract: I will talk about a series of recent works [1-4], studying many-body dynamics generated by circuits where each unitary gate acts as a randomly-chosen permutation in the computational basis, and comparing their behaviour to that of random unitary circuits, a standard toy model for generic quantum dynamics. Random permutation circuits permit the analytical computation of several key quantities such as out-of-time order correlators, or entanglement entropies. Remarkably, despite the fundamental differences between unitary and permutation dynamics, they exhibit qualitatively similar behaviours, though there are important differences coming from the classical nature of the underlying dynamics.
Workshop: Lev Vidmar
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Mechanism of eigenstate thermalization breakdown
Speaker: Lev Vidmar
Abstract: The mechanism of thermalization is today understood via the eigenstate thermalization hypothesis, which states that all eigenstates of a Hamiltonian are already thermal. I will also discuss counterexamples to thermalization. In particular, I will comment on our recent proposal of the regime of ”fading ergodicity”, which acts as a precursor of the ergodicity breaking phase transition and provides a possible mechanism of eigenstate thermalization breakdown.
Title: Mechanism of eigenstate thermalization breakdown
Speaker: Lev Vidmar
Abstract: The mechanism of thermalization is today understood via the eigenstate thermalization hypothesis, which states that all eigenstates of a Hamiltonian are already thermal. I will also discuss counterexamples to thermalization. In particular, I will comment on our recent proposal of the regime of ”fading ergodicity”, which acts as a precursor of the ergodicity breaking phase transition and provides a possible mechanism of eigenstate thermalization breakdown.
Thursday, June 11th, 2026
Workshop: Olexei Motrunich
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Charge Transport Capacity as a Probe of Resonances in Models of Many-Body Localization
Speaker: Olexei Motrunich
Abstract: I will present our recent study [J.K. Jiang, F.M. Surace, and O.I. Motrunich, arXiv:2604.18710] of charge transport capacity (CTC) in an interacting Anderson model on the 1d open chain. The CTC bounds the maximal charge that can move across a given link under any dynamical process and can thus serve as a worst-case measure of the localization in the system. For ergodic systems, the CTC grows linearly with the system size, while we expect it to be finite for localized models, which we prove for non-interacting fermions. In the interacting model, we find that unlike the quick saturation in the Anderson insulator, the disorder-averaged CTC grows with the system size even deep in the MBL regime. We trace this behavior to particular many-body resonances (MBR) whose probability is still growing on available system sizes because of their large collars (regions of sensitivity of the resonances to background charge configurations). On the other hand, we also quantify the MBR importance for charge transport in typical-case quenches and find that they are not important for strong enough disorder where typical product states can transport only finite charge, providing strong evidence for non-ergodic localizing behavior in this regime.
Title: Charge Transport Capacity as a Probe of Resonances in Models of Many-Body Localization
Speaker: Olexei Motrunich
Abstract: I will present our recent study [J.K. Jiang, F.M. Surace, and O.I. Motrunich, arXiv:2604.18710] of charge transport capacity (CTC) in an interacting Anderson model on the 1d open chain. The CTC bounds the maximal charge that can move across a given link under any dynamical process and can thus serve as a worst-case measure of the localization in the system. For ergodic systems, the CTC grows linearly with the system size, while we expect it to be finite for localized models, which we prove for non-interacting fermions. In the interacting model, we find that unlike the quick saturation in the Anderson insulator, the disorder-averaged CTC grows with the system size even deep in the MBL regime. We trace this behavior to particular many-body resonances (MBR) whose probability is still growing on available system sizes because of their large collars (regions of sensitivity of the resonances to background charge configurations). On the other hand, we also quantify the MBR importance for charge transport in typical-case quenches and find that they are not important for strong enough disorder where typical product states can transport only finite charge, providing strong evidence for non-ergodic localizing behavior in this regime.
Workshop: Marine De Clerck
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Bounds on quantum evolution complexity via lattice cryptography
Speaker: Marine De Clerck
Abstract: In this talk, I will address some of the difference between integrable and chaotic motion in quantum theories as manifested by the complexity of the corresponding evolution operators. The notion of complexity of interest to us will be Nielsen’s complexity applied to the time-dependent evolution operator of the quantum systems. I will review Nielsen’s complexity, discuss the difficulties associated with this definition and introduce a simplified approach that produces an upper bound on the complexity while retaining essential information about the integrable properties of the dynamical systems.
Title: Bounds on quantum evolution complexity via lattice cryptography
Speaker: Marine De Clerck
Abstract: In this talk, I will address some of the difference between integrable and chaotic motion in quantum theories as manifested by the complexity of the corresponding evolution operators. The notion of complexity of interest to us will be Nielsen’s complexity applied to the time-dependent evolution operator of the quantum systems. I will review Nielsen’s complexity, discuss the difficulties associated with this definition and introduce a simplified approach that produces an upper bound on the complexity while retaining essential information about the integrable properties of the dynamical systems.
Workshop: Sam Garratt
Time: 1:00 PM - 2:00 PM
Location: SCGP 102
Title: Entanglement transitions and non-unitary quantum chaos in translation-invariant tensor networks
Speaker: Sam Garratt
Abstract: I will discuss the complexity of contracting translation-invariant tensor networks. The computational cost of row-by-row tensor network contraction, which defines a discrete time evolution governed by a fixed transfer matrix, is associated with the entanglement of the state of a row. Analyzing a family of two-dimensional tensor networks whose transfer matrices interpolate between chaotic Floquet and strongly non-unitary limits, I will show that there is a transition between volume- and area-law entanglement in states evolved under the transfer matrix 2605.04026. Deep in the volume-law phase the spectrum of the transfer matrix in the complex plane consists of a dense ring with a sharp outer edge, and I will introduce a non-unitary random matrix model that describes this feature (which can be understood as arising from a kind of level attraction) 2512.02934. The existence of the volume-law entangled phase suggests a barrier to the computation of quantum state amplitudes from tensor-network descriptions of translation-invariant many-body states. Wang, Altman, SG 2512.02934, Wang, SG, Altman 2605.04026
Title: Entanglement transitions and non-unitary quantum chaos in translation-invariant tensor networks
Speaker: Sam Garratt
Abstract: I will discuss the complexity of contracting translation-invariant tensor networks. The computational cost of row-by-row tensor network contraction, which defines a discrete time evolution governed by a fixed transfer matrix, is associated with the entanglement of the state of a row. Analyzing a family of two-dimensional tensor networks whose transfer matrices interpolate between chaotic Floquet and strongly non-unitary limits, I will show that there is a transition between volume- and area-law entanglement in states evolved under the transfer matrix 2605.04026. Deep in the volume-law phase the spectrum of the transfer matrix in the complex plane consists of a dense ring with a sharp outer edge, and I will introduce a non-unitary random matrix model that describes this feature (which can be understood as arising from a kind of level attraction) 2512.02934. The existence of the volume-law entangled phase suggests a barrier to the computation of quantum state amplitudes from tensor-network descriptions of translation-invariant many-body states. Wang, Altman, SG 2512.02934, Wang, SG, Altman 2605.04026
Workshop: Thomas Barthel
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Tensor network simulation of quantum scattering in D>1 spatial dimensions
Speaker: Thomas Barthel
Abstract: Tensor network states are an indispensable tool for the simulation of strongly correlated quantum many-body systems. In recent years, tree tensor network states (TTNS) have been successfully used for two-dimensional systems and to benchmark quantum simulation approaches for condensed matter, nuclear, and particle physics. In comparison to the more traditional approach based on matrix product states (MPS), the graph distance of physical degrees of freedom can be drastically reduced in TTNS. In extension of corresponding results for MPS [Verstraete and Cirac, PRB 73, 094423 (2006); Schuch et al., PRL 100, 030504 (2008)], I will show how to bound TTNS approximation errors using Renyi entanglement entropies. Conversely, one obtains bounds on tensor-network bond dimensions needed to achieve a specific approximation accuracy. Surprisingly, it turns out that, for large systems in D>1 spatial dimensions, MPS simulations of low-energy states are more efficient than TTNS simulations. We will discuss the scaling of computational costs for different boundary conditions under the assumption that the system obeys an entanglement (log-)area law, implying that bond dimensions scale exponentially in the surface area of the associated subsystems. The ultimate goal of this project is the investigation of quantum scattering events, and I will comment on the use of helical boundary conditions and a novel gauge-fixing scheme for the tensor-network excitation ansatz. [arXiv:2512.20215, arXiv:2601.08132]
Title: Tensor network simulation of quantum scattering in D>1 spatial dimensions
Speaker: Thomas Barthel
Abstract: Tensor network states are an indispensable tool for the simulation of strongly correlated quantum many-body systems. In recent years, tree tensor network states (TTNS) have been successfully used for two-dimensional systems and to benchmark quantum simulation approaches for condensed matter, nuclear, and particle physics. In comparison to the more traditional approach based on matrix product states (MPS), the graph distance of physical degrees of freedom can be drastically reduced in TTNS. In extension of corresponding results for MPS [Verstraete and Cirac, PRB 73, 094423 (2006); Schuch et al., PRL 100, 030504 (2008)], I will show how to bound TTNS approximation errors using Renyi entanglement entropies. Conversely, one obtains bounds on tensor-network bond dimensions needed to achieve a specific approximation accuracy. Surprisingly, it turns out that, for large systems in D>1 spatial dimensions, MPS simulations of low-energy states are more efficient than TTNS simulations. We will discuss the scaling of computational costs for different boundary conditions under the assumption that the system obeys an entanglement (log-)area law, implying that bond dimensions scale exponentially in the surface area of the associated subsystems. The ultimate goal of this project is the investigation of quantum scattering events, and I will comment on the use of helical boundary conditions and a novel gauge-fixing scheme for the tensor-network excitation ansatz. [arXiv:2512.20215, arXiv:2601.08132]
Workshop: Marko Znidaric
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Truncated propagator -- a tool for many-body physics
Speaker: Marko Znidaric
Abstract: I will address the question of how to describe and study relaxation in unitary quantum or classical systems. The momentum resolved truncated operator propagator turns out to be a rather handy tool to that end. While the spectrum of a unitary propagator has no direct relation to dynamic, that of the truncated propagator does. The leading eigenvalue and the associated eigenvector (the so-called Ruelle-Pollicott resonance) can be used to find conserved operators, including new integrable systems, numerically efficiently study diffusion, or calculate the long timescales present under weak conservation-law breakdown. Via a many-body operator Kolmogorov cascade it also offers a quantum many-body analog of classical chaotic structures responsible for chaos. On mathematical level it exposes subtle issues arising in the thermodynamic limit and shows the usefulness of rigged Hilbert space formalism.
Title: Truncated propagator -- a tool for many-body physics
Speaker: Marko Znidaric
Abstract: I will address the question of how to describe and study relaxation in unitary quantum or classical systems. The momentum resolved truncated operator propagator turns out to be a rather handy tool to that end. While the spectrum of a unitary propagator has no direct relation to dynamic, that of the truncated propagator does. The leading eigenvalue and the associated eigenvector (the so-called Ruelle-Pollicott resonance) can be used to find conserved operators, including new integrable systems, numerically efficiently study diffusion, or calculate the long timescales present under weak conservation-law breakdown. Via a many-body operator Kolmogorov cascade it also offers a quantum many-body analog of classical chaotic structures responsible for chaos. On mathematical level it exposes subtle issues arising in the thermodynamic limit and shows the usefulness of rigged Hilbert space formalism.
Friday, June 12th, 2026
Workshop: Wen Wei Ho
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Phase transitions in deep thermalization: resource localizability and deep ergodicity-breaking
Speaker: Wen Wei Ho
Abstract: In this talk, I will explain how phase transitions can arise in deep thermalization --- the limiting behavior of the ensemble of local post-measurement quantum states conditioned on knowledge of the environment, obtained in late-time quantum many-body dynamics. Specifically, I will show how distinct phases of wavefunction distributions emerge, tuned by the amount of quantum resource (e.g. coherence, magic, purity) present in the system. These phases are distinguished by having sharply different accessible information content --- the maximal amount of classical information extractable from the ensemble of states, and can also be understood as the ability or inability of the system to concentrate the given quantum resource on a small subsystem, a quantum information concept called "resource localizability". Since these transitions are undetectable at the level of local observables, they constitute a more refined form of ergodicity-breaking in quantum systems going beyond conventional ones like Anderson or many-body localization. Time-permitting, I will also explain how our work informs quantum state certification protocols and recent discoveries of magic phase transitions in encoding-decoding dynamics.
Title: Phase transitions in deep thermalization: resource localizability and deep ergodicity-breaking
Speaker: Wen Wei Ho
Abstract: In this talk, I will explain how phase transitions can arise in deep thermalization --- the limiting behavior of the ensemble of local post-measurement quantum states conditioned on knowledge of the environment, obtained in late-time quantum many-body dynamics. Specifically, I will show how distinct phases of wavefunction distributions emerge, tuned by the amount of quantum resource (e.g. coherence, magic, purity) present in the system. These phases are distinguished by having sharply different accessible information content --- the maximal amount of classical information extractable from the ensemble of states, and can also be understood as the ability or inability of the system to concentrate the given quantum resource on a small subsystem, a quantum information concept called "resource localizability". Since these transitions are undetectable at the level of local observables, they constitute a more refined form of ergodicity-breaking in quantum systems going beyond conventional ones like Anderson or many-body localization. Time-permitting, I will also explain how our work informs quantum state certification protocols and recent discoveries of magic phase transitions in encoding-decoding dynamics.
Workshop: Tarun Grover
Time: 1:00 PM - 2:00 PM
Location: SCGP 102
Title: Hidden area-law sectors and hierarchical entanglement structure in quantum many-body dynamics
Speaker: Tarun Grover
Abstract: Chaotic many-body dynamics is usually associated with rapid growth of entanglement, suggesting that generic long-time dynamics should not admit a simple low-entanglement description. In this talk I will describe a more structured picture that partly challenges this viewpoint. Although the full time-evolved state can contain volume-law entanglement, I will show that the linear-response signal is carried by a surprisingly small dominant Schmidt sector with area-law entanglement. Due to this dichotomy, the full state exhibits a Renyi-index-tuned transition at a critical Renyi index alpha_c = 1. More strikingly, the Schmidt states encoding the linear response exhibit their own area-to-volume-law transitions at critical indices α_c < 1, consistent with the existence of polynomial bond-dimension representations in one dimension. This hierarchy persists recursively: upon bipartitioning the dominant Schmidt states, their leading Schmidt sectors exhibit analogous structure. I will explain this mechanism in a simple circuit model and then show how it appears in locally quenched Gibbs states of chaotic spin chains. Based on arXiv: 2605.04540.
Title: Hidden area-law sectors and hierarchical entanglement structure in quantum many-body dynamics
Speaker: Tarun Grover
Abstract: Chaotic many-body dynamics is usually associated with rapid growth of entanglement, suggesting that generic long-time dynamics should not admit a simple low-entanglement description. In this talk I will describe a more structured picture that partly challenges this viewpoint. Although the full time-evolved state can contain volume-law entanglement, I will show that the linear-response signal is carried by a surprisingly small dominant Schmidt sector with area-law entanglement. Due to this dichotomy, the full state exhibits a Renyi-index-tuned transition at a critical Renyi index alpha_c = 1. More strikingly, the Schmidt states encoding the linear response exhibit their own area-to-volume-law transitions at critical indices α_c < 1, consistent with the existence of polynomial bond-dimension representations in one dimension. This hierarchy persists recursively: upon bipartitioning the dominant Schmidt states, their leading Schmidt sectors exhibit analogous structure. I will explain this mechanism in a simple circuit model and then show how it appears in locally quenched Gibbs states of chaotic spin chains. Based on arXiv: 2605.04540.
Workshop: Lenart Zadnik
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Elusive hierarchy of relaxation times in quantum kinetically constrained models
Speaker: Lenart Zadnik
Abstract: I will discuss the mechanism of slow heterogeneous relaxation in quantum kinetically constrained models (KCMs) in which the strength of the potential energy is controlled by a coupling parameter. I will focus on the regime of slow dynamics which includes the large-coupling limit. By performing a large coupling expansion around that limit we find a nested hierarchy of states that remain frozen on time scales determined by powers of the coupling. Classification of such states, together with the evolution of their Krylov complexity, reveal that these time scales are related to the distances between the sites where facilitated dynamics is allowed by the kinetic constraint. While correlations within frozen states relax slowly and exhibit metastable plateaus that persist on time scales set by powers of the coupling parameter, the correlations in the rest of the states decay rapidly. I will describe how to compute the plateau heights in correlation functions and discuss the elusive nature of the time-scale hierarchy in thermodynamically large systems. The results presented in this talk explain the observed slow relaxation in quantum KCMs and elucidate dynamical heterogeneity in such models by relating the relaxation times to the spatial separations between the active regions. If time permits, I will also discuss how the large coupling expansion and its nested hierarchy of frozen states can be used to access the low-temperature glassy dynamics in the classical stochastic KCMs.
Title: Elusive hierarchy of relaxation times in quantum kinetically constrained models
Speaker: Lenart Zadnik
Abstract: I will discuss the mechanism of slow heterogeneous relaxation in quantum kinetically constrained models (KCMs) in which the strength of the potential energy is controlled by a coupling parameter. I will focus on the regime of slow dynamics which includes the large-coupling limit. By performing a large coupling expansion around that limit we find a nested hierarchy of states that remain frozen on time scales determined by powers of the coupling. Classification of such states, together with the evolution of their Krylov complexity, reveal that these time scales are related to the distances between the sites where facilitated dynamics is allowed by the kinetic constraint. While correlations within frozen states relax slowly and exhibit metastable plateaus that persist on time scales set by powers of the coupling parameter, the correlations in the rest of the states decay rapidly. I will describe how to compute the plateau heights in correlation functions and discuss the elusive nature of the time-scale hierarchy in thermodynamically large systems. The results presented in this talk explain the observed slow relaxation in quantum KCMs and elucidate dynamical heterogeneity in such models by relating the relaxation times to the spatial separations between the active regions. If time permits, I will also discuss how the large coupling expansion and its nested hierarchy of frozen states can be used to access the low-temperature glassy dynamics in the classical stochastic KCMs.