When: Monday, 24th Nov, 2025
Where: SISSA, room 5.
Program
| 10.00–10:30 | Welcome coffee break | |
|---|---|---|
| 10:30–11:00 | Andrea Stampiggi (SISSA) | |
| 11:00–11:30 | Antonio Štrkalj (IRB) | |
| 11:30–12:00 | Konstantinos Chalas (SISSA) | |
| 12:00–14:00 | Lunch break | |
| 14:00–14:30 | Devendra Bhakuni & Lenart Zadnik (ICTP & FMF) | |
| 14:30–15:00 | Vanja Marić (FMF) | |
| 15:00–15:30 | Iris Ulčakar (IJS) | |
| 15:30–16:00 | Coffee break | |
| 16:00–16:30 | Adam McRoberts (ICTP) | |
| 16:30–18:00 | Free discussion | |
| 20:00 | Dinner in Trieste | |
| FMF | = | Faculty of Mathematics and Physics (Ljubljana) |
| IJS | = | Jožef Stefan Institute (Ljubljana) |
| IRB | = | Ruđer Bošković Institute (Zagreb) |
| SISSA | = | International School for Advanced Studies (Trieste) |
| ICTP | = | International Centre for Theoretical Physics (Trieste) |
Abstracts
| Exact Results on the Hydrodynamics of certain Kinetically-Constrained Hopping Processes | |
| Speaker | Adam McRoberts (ICTP) |
| Abstract |
We consider a model of interacting random walkers on a triangular chain and triangular lattice, where a particle can move only if the other two sites of the triangle are unoccupied — a kinetically-constrained hopping process (KCHP) recently introduced in the context of non-linear diffusion cascades. Using a classical-to-quantum mapping — where the rate matrix of the stochastic KCHP corresponds to a spin Hamiltonian, and the equilibrium probability distribution to the quantum ground state — we develop a systematic perturbation theory to calculate the diffusion constant; the hydrodynamics of the KCHPs is determined by the low-energy properties of the spin Hamiltonian, which we analyse with the standard Holstein-Primakoff spin-wave expansion.
For the triangular hopping we consider, we show that \textit{non-interacting} spin-wave theory predicts the \textit{exact} diffusion constant. We conjecture this holds for all KCHPs with (i) hard-core occupancy, (ii) parity-symmetry, and (iii) where the hopping processes are given by three-site gates — that is, where hopping between two sites is conditioned on the occupancy of a third. We further show that there are corrections to the diffusion constant when the KCHP is described by \textit{four}-site gates, which we calculate at leading order in the semi-classical $1/S$ expansion. We support all these conclusions with numerical simulations. |
| Statistical Signatures of Integrable and Non-Integrable Quantum Hamiltonians | |
| Speaker | Andrea Stampiggi (SISSA) |
| Abstract |
Integrability bears crucial physical implications for quantum many-body dynamics, both in and out of equilibrium, influencing correlation functions, thermalization behavior, and spectral statistics. Because the Hilbert space scales exponentially with system size, spectral correlations provide a powerful probe of the statistical signatures of integrable and non-integrable dynamics. In this framework, quantum Hamiltonians are treated as matrices from which spectra can be numerically obtained and analyzed. In this seminar, I will describe tools from statistical spectroscopy that identify features of integrability and non-integrability not only in conventional settings but also in more subtle cases where non-integrable dynamics may lie at the core of systems that appear integrable by standard diagnostics. These tools are computationally efficient and help guide intuition in the study of both new and established models. This approach complements methods of exact solvability as well as more established numerical techniques. |
| Quench dynamics of entanglement from crosscap states | |
| Speaker | Konstantinos Chalas (SISSA) |
| Abstract |
The linear growth of entanglement after a quench from a state with short-range correlations is a universal feature of many body dynamics.It has been shown to occur in integrable and chaotic systems undergoing either Hamiltonian, Floquet or circuit dynamics and has also been observed in experiments. The entanglement dynamics emerging from long-range correlated states is far less studied, although no less viable using modern quantum simulation experiments. In this talk, I will present the dynamics of the bipartite entanglement entropy and mutual information in quenches starting from Crosscap States, also knows as Entangled Antipodal Pair States, which are volume law states, constructed by entangling antipodal points of a finite and periodic system. I will focus on the evolution of a crosscap initial state, in a free fermionic quench and probe the dynamics of bipartite entanglement entropy and mutual information.In particular, I will show how one can derive an effective description of the entanglement dynamics, that matches the exact results. The quench dynamics is captured by an emergent quasiparticle picture description, which differs from the one that characterizes quenches from lowly entangled states, due to the long-range correlations of the initial state. The main phenomenology for the entanglement entropy, is that after an initial time delay where entanglement remains to the initial volume law value, there is a linear in time decrease, followed by a series of oscillatory revivals which happen around a constant value. This behavior, as well as the characteristic times of the revivals and the constant time averaged value can be explained in terms of the emergent quasiparticle picture that we derive.I will also briefly comment on what changes for the cases of interacting integrable quenches, as well as chaotic random unitary and generic dual unitary circuit dynamics of these states. |
| Superdiffusion and non-KPZ fluctuations in chiral SU(2) systems | |
| Speakers | Devendra Bhakuni & Lenart Zadnik (ICTP & FMF) |
| Abstract | Symmetries play crucial role in shaping transport in quantum many-body systems, often leading to departures from conventional diffusion. In this talk, we will discuss transport at infinite temperature in chiral integrable systems with global SU(2) symmetry. We study both Hamiltonian and Floquet (circuit) realizations, finding that the dynamics exhibit a dynamical critical exponent z=3/2, consistent with superdiffusion in the Kardar–Parisi–Zhang (KPZ) universality class. However, as in the isotropic XXX model, the analysis of higher-order fluctuations of net charge transfer reveals clear deviations from the KPZ scaling, signalling anomalous behavior beyond this universality. Moreover, the charge current fluctuations obey fluctuation symmetry despite broken time- and space-reversal, suggesting that the role of fundamental space-time symmetries in transport phenomena remains to be fully understood. |
| Slow dynamics from a nested hierarchy of frozen states | |
| Speaker | Vanja Marić (FMF) |
| Abstract | We identify the mechanism of slow heterogeneous relaxation in quantum kinetically constrained models (KCMs) in which the potential energy strength is controlled by a coupling parameter. The regime of slow relaxation includes the large-coupling limit. By expanding around that limit, we reveal a nested hierarchy of states that remain frozen on time scales determined by powers of the coupling. The classification of such states, together with the evolution of their Krylov complexity, reveal that these time scales are related to the distance 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. We compute the plateau heights of correlations across all frozen states up to second-order corrections in the inverse coupling. Our results explain slow relaxation in quantum KCMs and elucidate dynamical heterogeneity by relating the relaxation times to the spatial separations between the active regions. |
| Conserved quantities enable the quantum Mpemba effect in weakly open systems |
|
| Speaker | Iris Ulčakar (IJS) |
| Abstract | Observation of the quantum Mpemba effect has spurred much interest in its enabling conditions and its relation to the classical counterpart. Here, we consider weakly open many-body quantum systems initialized in different thermal states and examine when the initially farther state relaxes to the (non-equilibrium) steady state faster. We claim that the number of conserved quantities in the unitary part plays a crucial role: the Mpemba effect is possible only when the Hamiltonian commutes with other extensive operators or is integrable. The reason lies in the dynamical evolution happening in spaces of different dimensions. When energy is the only approximately conserved quantity, dissipation pushes the dynamics within a single-parameter manifold of different thermal states. In contrast, for Hamiltonians with several conserved quantities, the dynamics drift in the multi-dimensional space of generalized Gibbs ensembles, whose distance to the steady state is less trivial. We provide numerical results for large system sizes using tensor networks and free-fermion techniques, thereby supporting our claim. |
| Title Reentrant localisation and anomalous many-body dynamics in quasiperiodic chains | |
| Speaker | Antonio Štrkalj (IRB) |
| Abstract |
Transport properties of quantum systems crucially depend on their degree of structural order. Periodic order favours extended Bloch waves and metallic bands, whereas disorder localises the motion of particles, especially in lower dimensions. Quasiperiodic systems, lying between these extremes, exhibit exotic transport properties, self-similar wavefunctions, and critical phenomena. In this talk, I will present a theoretical study of localisation in a particular one-dimensional quasiperiodic model, known as the interpolating Aubry-André-Fibonacci (IAAF) model. This model interpolates between two paradigmatic quasiperiodic examples: the Aubry-André model, known for a metal-to-insulator transition under diagonal modulation, and the Fibonacci model, which is always critical. In the single-particle case, contrary to what one might naively expect, we find that both diagonal and off-diagonal realisations of the IAAF model exhibit non-monotonic, non-uniform behaviour of the spectrum. More precisely, we discover that by evolving the Aubry-André model into the Fibonacci model, a cascade of localisation-delocalisation transitions occurs before the spectrum becomes critical. In a many-body IAAF model, we find that this cascade of reentrant localisation transitions is destroyed even for weak interactions between particles. Moreover, in the region of the parameter space where the single-particle spectrum contains a non-trivial mobility edge, we observe an anomalous effect with varying the interaction strength; namely, weak interactions localise the system, whereas stronger interactions enhance ergodicity. These results provide new insights into the criticality of quasiperiodic chains and establish the IAAF model as a versatile platform for studying the interplay between many-body interactions and tunable potentials. |
