Leeds-Loughborough-Nottingham Non-Equilibrium Seminars

Following the tradition from the previous years,  the Universities of Leeds (Prof Zlatko Papic), Loughborough (Dr Achilleas Lazarides) and Nottingham (Dr Adam Gammon-Smith) will be running a joint hybrid seminar series on non-equilibrium physics during 2024/25. "Hybrid" means that some of the seminars will be delivered in person in one of the Universities and broadcast remotely in others, while some seminars will be fully online.

Seminars will typically take place on Wednesdays at 1pm UK time. The online link for each seminar will be given below.

All recorded talks will be uploaded to our YouTube channel

For a complete list of previous seminars in 2020-2024, please see the archive on the left.

Future seminars (evolving):

• 25/03/2026, 1pm: Nick Jones (University of Oxford)

  Location: Leeds (in-person, and online through Teams)
  Zoom Link: https://teams.microsoft.com/meet/36888923212456?p=XANdbf4EsQ4Ik5cOsa
  Title: Matrix-product state skeletons in Onsager-integrable chains

  Abstract: Matrix-product state (MPS) skeletons are connected networks of Hamiltonians with exact MPS ground states that underlie a phase diagram. I will discuss recent work (arXiv:2511.07212) with Imogen Camp, where we identify such a skeleton in a family of interacting integrable models. I will explain how the Onsager algebra allows us to find multiple exact MPS eigenstates for Hamiltonians on this skeleton. I will also discuss applications to calculating correlation functions in these integrable models.

Previous seminars:

• 16/10/2024, 3pm: Friedrich Huebner(KCL)

  Location: Nottingham (in-person)
  Title: Space-time quadratures’ of the generalized hydrodynamics equation and absence of shocks in the Lieb-Liniger model

  Abstract: I will report on recently introduced tools, called ‘space-time quadratures’ to study the generalized hydrodynamics (GHD) equation, an equation that describes the large scale dynamics of integrable models. They allow to compute the solution directly at an arbitrary space-time point, by solving a fixed-point equation that only depends on the momentum part of the quasi-particle density.

  On the example of the repulsive Lieb-Liniger model, I will explain how these quadratures can be used not only to solve the GHD equation via a new efficient numerical algorithm, but also to gain mathematical insights into its solutions: Specifically, I will show that in this model solutions to the GHD equations for all times exist, are unique and do not form shocks. This implies that, unlike the hydrodynamics of generic 1d models, the hydrodynamic description in this integrable model remains valid for arbitrarily long (Euler scale) times.

• 23/10/2024, 3pm: Chris Hooley (Coventry)

  Location: Nottingham (in-person)
  Title: Describing the transition from a Luttinger liquid to a valence bond solid using the matrix-product-state path integral

  Abstract: In the realm of magnetic insulators, one of the most interesting categories of phase transition is that from a long-range-ordered magnetic state (e.g. a Néel antiferromagnet) to a quantum short-range-ordered one (e.g. a valence bond solid). These are awkward to describe in a conventional spin-coherent-state path integral framework, because one of the phases (the Néel state) is a saddle point of the path integral while the other one (the valence bond solid) isn’t.

  In this talk I shall present our work over the past few years to construct an easier-to-use path-integral framework for such problems, based on matrix product states rather than spin coherent states [1]. Concentrating on the example of the one-dimensional J1-J2 Heisenberg chain, I shall show that our approach obtains the correct equilibrium phases, and also – perhaps more surprisingly – the correct critical theory for the transition between them, via a derivation that (at least in comparison with its spin-coherent-state counterparts) is straightforward.

  1. A. G. Green, CAH, J. Keeling, and S. H. Simon, “Feynman path integrals over entangled states,” arXiv:1607.01778 (2016).
  2. F. Azad, A. J. McRoberts, CAH, and A. G. Green, “A generalised Haldane map from the matrix product state path integral to the critical theory of the J1-J2 chain,” arXiv:2404.16088 (2024).

• 06/11/2024, 3pm: Robert Ott (Innsbruck)

  Location: Online
  Title: Probing topological entanglement entropy on large scales

  Abstract: Topologically ordered quantum matter exhibits intriguing long-range patterns of entanglement, which reveal themselves in subsystem entropies. However, measuring such entropies, which can be used to certify topological order, on large partitions is challenging and becomes practically unfeasible for large systems. We propose a protocol based on local adiabatic deformations of the Hamiltonian which extracts the universal features of long-range topological entanglement from measurements on small subsystems of finite size, trading an exponential number of measurements against a polynomial-time evolution. Our protocol is general and readily applicable to various quantum simulation architectures. We apply our method to various string-net models representing both abelian and non-abelian topologically ordered phases, and illustrate its application to neutral atom tweezer arrays with numerical simulations

• 13/11/2024, 3pm: Carlo Vanoni (Princeton)

  Location: Online
  Title: Renormalization group beta-function for Anderson and many-body localization

  Abstract: This talk aims to provide a different viewpoint on localization transitions induced by disorder based on the renormalization group formalism. I will first discuss, on general grounds, the various types of scaling behaviors a localization critical point can display. I will then move to specific models; firstly, I will discuss Anderson localization in finite dimensional space and how one recovers the Anderson model on expander graphs by taking the limit of infinite dimensions. I will then move to many-body localization and show that, if a many-body localized phase exists, the critical point must be described by a two-parameter scaling theory similar to Anderson localization in infinite dimensions and to the BKT transition.

  References:

  • C. Vanoni, B. L. Altshuler, V. E. Kravtsov and A. Scardicchio, Renormalization group analysis of the Anderson model on random regular graphs, PNAS 121 (29) e2401955121 (2024)
  • B. L. Altshuler, V. E. Kravtsov, A. Scardicchio, P. Sierant, and C. Vanoni, Renormalization group for Anderson localization on high-dimensional lattices, arXiv:2403.01974 (2024)
  • F. Balducci, G. Bracci Testasecca, G. Magnifico, J. Niedda, A. Scardicchio and C. Vanoni, Renormalization Group Analysis of the Many-Body Localization transition in the random field XXZ Chain, to appear

• 20/11/2024, 3pm: Andrew Green (UCL)

  Location: Nottingham (in-person)
  Title: Tensor Networks for Quantum and Classical Simulation

  Abstract: Tensor networks transformed the understanding and simulation of quantum systems. By focussing upon the entanglement structure of quantum states and providing a mathematical structure to capture it, they allow analytical and numerical descriptions of quantum systems to focus on the part Hilbert space where all of the action occurs. This leads to some of the most accurate and efficient classical algorithms - algorithms that have provided the main bar for current quantum computers to surpass.

  Tensor networks can also be translated to run as quantum algorithms and there are many benefits to doing so. I will discuss this application of tensor networks, sharing results obtained on a number of different quantum devices and give a perspective on where this approach is heading.

• 04/12/2024, 3pm: Lakshya Bhardwaj (Oxford)

  Location: Nottingham (in-person)
  Title: Categorical Landau Paradigm

  Abstract: I will discuss extensions of the Landau paradigm for the classification of phases of matter to include so-called "categorical symmetries”, which are characterized by the presence of symmetry transformations that are non-invertible. I will provide a full classification of gapped and gapless phases and transitions between them for categorical symmetries in 1+1 dimensions, and report on the progress towards a classification in 2+1 dimensions.

• 11/12/2024, 3pm: Nat Tantivasadakarn (Caltech)

  Location: Nottingham (in-person)
  Title: Sculpting quantum phases of matter with measurements

  Abstract: Quantum mechanics exhibits a stark dichotomy between unitary time-evolution and measurement. These aspects are further contrasted by the fact that traditional many-body quantum theory is developed solely based on unitary aspects. In this talk, I will explore a fruitful synergy that emerges from the interplay between many-body quantum physics and the non-equilibrium quantum dynamics that arises from measurements. In particular, I will show how measurements can be used to circumvent fundamental constraints imposed by unitary dynamics and efficiently prepare a large class of topological phases of matter. In addition to discovering a new hierarchy of many-body quantum states unseen in the unitary setup and a surprising connection to the unsolvability of the quintic polynomial, our studies also yield practical protocols for quantum processors that led to the first unambiguous observation of non-Abelian anyons.

• 08/01/2025, 3pm: Frederik Moller (Vienna)

  Location: Online
  Title: Characterising transport properties of quantum gases

  Abstract: Drude weights are fundamental transport coefficients of condensed matter physics, which measure the ratio of the density of mobile charge carriers to their mass and are often used for classifying materials according to their conductivity properties. The study of transport properties is however often hindered by the complexity of describing dynamics in interacting condensed matter systems. Recently, a new universality class for the hydrodynamics of one-dimensional integrable systems, known as generalised hydrodynamics (GHD), has been discovered. This breakthrough has led to numerous theoretical advancements in the study of low-dimensional dynamics, including the prediction of transport coefficients (specifically Drude weights). Despite these theoretical developments, experimental validation has remained elusive—until now.

  In our recent experiments, we measure induced currents in a one-dimensional ultracold bosonic gas in response to controlled external perturbations. Using an Atom Chip to confine the gas and a Digital Micromirror Device to create a configurable optical potential, we implement two distinct protocols: probing the response to a constant external force and measuring the charge flow between two subsystems in different equilibrium states. By measuring these induced currents, we extract the Drude weights of the gas. Our findings reveal that Drude weights almost fully describe the large-scale dynamics of the system, confirming the theoretical predictions from GHD and demonstrating nearly dissipationless transport, even at finite temperatures and interactions.

  Our work extends beyond experimental validation, establishing methodologies that can be adapted to a wide range of condensed matter systems. Particularly in analysing the measured dynamics, our use of physics-informed neural networks (PINNs)—a tool that has seen limited use in cold atom systems—represents a powerful approach for future research.

• 15/01/2025, 3pm: Paul Menczel (RIKEN, Japan)

  Location: Nottingham (in-person)
  Title: First Passage Statistics and Full Counting Statistics in Classical and Quantum Markovian Processes

  Abstract: The statistical properties of charge exchanged between an open system and its environment can be analyzed by studying jumps in the system state along dynamical trajectories. Two complementary approaches are Full Counting Statistics, where the distribution of exchanged charge is studied at a fixed time, and First Passage Statistics, which studies the distribution of the time taken to reach a fixed amount of charge. These two approaches are closely related. For both current-like observables and dynamical observables, we discuss the relationship that usually connects both approaches, and then identify situations in which the relationship can be violated. We find that these violations indicate the presence of meta-stable or dark states. We also discuss generalizations of the theory to finite times, to more general counting observables, and beyond Markovian dynamics.

• 22/01/2025, 3pm: Katarzyna Macieszczak (Warwick)

  Location: Nottingham (in-person)
  Title: Ultimate Kinetic Uncertainty Relation and Optimal Performance of Stochastic Clocks

  Abstract: In this talk, I will show how for Markov processes over discrete configurations, an asymptotic bound on the uncertainty of stochastic fluxes can be derived in terms of the harmonic mean of decay rates with respect to the stationary distribution. This new bound is necessarily tighter than the bound in terms of the arithmetic mean, i.e., the activity, known as the kinetic uncertainty relation. What is more, we will see that this bound can always be saturated and therefore the uncertainty relation cannot be further improved upon. As an application of this result, I will obtain exact limits on long-time precision and performance of stochastic clocks. I will also discuss how these results generalise to semi-Markov processes, including quantum reset processes, and consider how coherent driving can improve clock performance.

• 05/02/2024, 3pm: Simeon Mystakidis (Missouri)

  Location: Online
  Title: Classification of universal dynamics in strongly ferromagnetic spinor superfluids

  Abstract: Scale invariance and self-similarity in physics provide a unified framework to classify phases of matter and dynamical properties of near- and far-from-equilibrium many-body systems. To address universality, we monitor the non-equilibrium dynamics of a two-dimensional ferromagnetic spinor gas subjected to quenches of the quadratic Zeeman coefficient. This allows to dynamically cross the underlying second-order magnetic phase transitions triggering spin-mixing. At early evolution times, we observe the spontaneous nucleation of topological defects (gauge or spin vortices) which annihilate through their interaction giving rise to magnetic domains for longer timescales where the gas enters the universal coarsening regime. This is characterized by the spatiotemporal scaling of the spin correlation functions and structure factor allowing to measure corresponding scaling exponents which depend crucially on the symmetry of the order parameter and belong to distinct universality classes. Our experimental observations are in excellent agreement with the predictions of the truncated Wigner method accounting both for quantum and thermal fluctuations in the initial state. These results represent a prototype for categorizing far-from-equilibrium dynamics in quantum many-body systems and reveal the interplay of topological defects for the emergent universality class.

• 12/02/2025, 3pm: Alioscia Hamma (Napoli)

  Location: Online
  Title: Complexity, Entanglement and Stabilizer entropy

  Abstract: We all know that entanglement is important in quantum mechanics. However, every form of complex behavior, including that which is responsible for quantum advantage, needs a second ingredient, colloquially known as magic. In this talk we will show that quantum advantage and quantum complexity arise from the conspiracy and interplay of two entropic resources, Entanglement Entropy (EE) and Stabilizer Entropy (SE). In particular, quantum complex behavior arises when stabilizer entropy gets scrambled around. We will provide an introduction to the resource theory of SE and applications in quantum many-body systems, quantum metrology, black-hole physics, and foundations of quantum mechanics.

• 19/02/2025, 3pm: Jad Halimeh (Munich)

  Location: Online
  Title: Quantum simulation of far-from-equilibrium dynamics of gauge theories

  Abstract: I will go over our recent research, which bridges quantum many-body physics and quantum simulation through two main pillars. The first focuses on investigating exotic far-from-equilibrium phenomena in lattice gauge theories, uncovering properties of dynamical phase transitions and criticality. The second aims to develop experimentally feasible schemes to probe such dynamics on state-of-the-art quantum hardware, including cold atoms and molecules, superconducting qubits, and trapped ions. We will go over a series of experiments highlighting the interplay between these two pillars.

• 26/02/2025, 11am: Jean-Yves Desaules (ISTA, Vienna)

  Location: Online
  Title: Quantum many-body scars beyond the PXP model in Rydberg simulators

  Abstract: Persistent revivals recently observed in Rydberg atom arrays have challenged our understanding of thermalisation and attracted much interest to the concept of quantum many-body scarring : the presence of coherent dynamics in otherwise chaotic Hamiltonians. They have since been reported in multiple models, including the kinetically-constrained PXP model realised in Rydberg chains. At the same time, questions of how common scarring is and in what systems it can be observed remain open. In particular, decreasing the spacing between Rydberg atoms to make the constraint act beyond nearest-neighbours seemingly destroys scarring.
  In this talk, I will discuss how this breakdown of scarring can be understood through the lens of frustration linked to the constraint. Crucially, this frustration can be lifted by entanglement, making it possible to witness coherent oscillations for an arbitrary constraint range. However, in contrast to the PXP model, their observation requires launching dynamics from weakly entangled initial states rather than from a product state. This key insight allows us to demonstrate that scarring exists in a much broader family of experimentally-realisable models that includes and generalises PXP to longer-range constraints and states with different periodicity. Our approach can also be used in higher dimensions where frustration is more ubiquitous, revealing a plethora of new scarred trajectories.

• 05/03/2025, 3pm: Benedikt Placke (Oxford)

  Location: Nottingham (in-person)
  Title: Topological Quantum Spin Glasses and their realization in quantum LDPC codes

  Abstract: Ordered phases of matter have close connections to computation. Two prominent examples are spin glass order, with wide-ranging applications in machine learning and optimization, and topological order, closely related to quantum error correction. Here, we introduce the concept of topological quantum spin glass (TQSG) order which marries these two notions, exhibiting both the complex energy landscapes of spin glasses, and the quantum memory and long-range entanglement characteristic of topologically ordered systems. We use techniques from (quantum) coding theory to show that TQSG order is the low-temperature phase of various quantum LDPC codes on expander graphs, including hypergraph and balanced product codes. En route, we develop a quantum generalization of Gibbs state decompositions and prove a bottleneck theorem for quantum channels, which generalizes its well-known counterpart applying to classical Markov chains. Our techniques are also applicable to classical spin glasses, where we provide a novel proof of the shattering of the Gibbs state in a wide range of spin glass models based on classical error correcting codes.

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• 20/03/2025, 3pm: Thomas Gasenzer (Heidelberg)

  Location: Nottingham (in-person)
  Title: Universal Dynamics and Non-Thermal Fixed Points in Quantum Gases

  Abstract: A quantum many-body system driven far from equilibrium via a parameter quench can show universal dynamics, characterized by self-similar spatio-temporal scaling, associated with the approach to a non-thermal fixed point. Non-linear excitations such as solitons or vortices, rogue waves, and instantons play a key role in the time evolution of such systems. Similar as for universal phenomena close to equilibrium phase transitions, low-energy effective theories are often vital for capturing the relevant mechanisms and symmetries distinguishing different types of (dis)order. The talk will provide a general overview in the context of ultracold quantum gases and highlight the difference between classes of non-thermal fixed points characterized by diffusion-type vs. sub-diffusive scaling.
  

• 02/04/2025, 3pm: Bertrand Lacroix (KCL)

  Location: Nottingham (in-person)
  Title: Fluctuations of the ground-state energy of spherical spin-glasses

  Abstract: Disordered systems, such as a spin glasses, are defined from a set of high-dimensional configurations, the degrees of freedom, and a Hamiltonian, which prescribes a random energy to each configuration, resulting from the complex interactions between these. A natural question for this type of system is to find the ground-state energy (GSE), i.e. the lowest energy accessible by any configuration of the system. In the high-dimensional limit, this GSE is self-averaging and for almost every realisation, the GSE coincides with its average. The latter is expressed as the optimum of a nontrivial functional optimisation problem known as Parisi formula. In the standard physics perspective, the optimal Parisi function can be understood as the cumulative distribution functions of overlaps between replicas. The rare fluctuations of the GSE away from its average have, in comparison, received much less attention.  I will show how replica computations can be used to derive the large deviation function at speed $N$ of the GSE for spherical spin glasses in terms of a functional optimisation problem, extending Parisi’s formula. This large-deviation function generically displays a rich phase diagram. Most interestingly, I will show that the behaviour of the large deviation function in the vicinity of the average and typical GSE is universal and allows to make precise predictions on the non-trivial tails of the distribution of typical fluctuations of the GSE. This talk is based on an article in collaboration with Yan V. Fyodorov and Pierre Le Doussal (J. Stat. Phys. 191 (2), 11 (2024) / arXiv preprint arXiv:2306.11927).

• 03/04/2025, 1pm: Curt Von Keyserlingk (KCL)

  Location: Nottingham (in-person)
  Title: Finite-temperature quantum topological order in three dimensions

  Abstract: We identify a three-dimensional system that exhibits long-range entanglement at sufficiently small but nonzero temperature---it therefore constitutes a quantum topological order at finite temperature. The model of interest is known as the fermionic toric code, a variant of the usual 3D toric code, which admits emergent fermionic point-like excitations. The fermionic toric code, importantly, possesses an anomalous 2-form symmetry, associated with the space-like Wilson loops of the fermionic excitations. We argue that it is this symmetry that imbues low-temperature thermal states with a novel topological order and long-range entanglement. Based on the current classification of three-dimensional topological orders, we expect that the low-temperature thermal states of the fermionic toric code belong to an equilibrium phase of matter that only exists at nonzero temperatures. We conjecture that further examples of topological orders at nonzero temperatures are given by discrete gauge theories with anomalous 2-form symmetries. Our work therefore opens the door to studying quantum topological order at nonzero temperature in physically realistic dimensions.

• 02/05/2025, 3pm: Mircea Bejan (Cambridge)

  Location: Leeds (in-person, and online through Zoom)
  Zoom Link: https://universityofleeds.zoom.us/j/9561865908?pwd=YlFZUFl0V2Fsdmt4T3lVZzNJdEVqZz09
  Title: Dynamics of magic: measurement-induced transitions and spreading

  Abstract: Magic and entanglement are two key quantum resources for quantum advantage. Recently discovered measurement-induced transitions (MIPTs) in entanglement are phase transitions in classical simulability. However, some highly-entangling dynamics (e.g., integrable systems or Clifford circuits) are easy to simulate classically. Here, we study simulability transitions beyond entanglement by asking how the dynamics of magic competes with measurements. We find distinct MIPTs in magic, simulability, and entanglement. We identify dynamical “stabilizer-purification” as the mechanism driving the magic transition. En route, we use Pauli-based computation to distil the quantum essence of the dynamics to a set of measurements. We link stabilizer-purification to “magic fragmentation”, wherein these measurements separate into disjoint, O(1)-weight blocks and relate this to the spread of magic in the original circuit becoming arrested. Finally, we quantify the speed at which magic spreads in certain quantum circuits by focusing on quantum error-correcting codes dynamically generated by T gates.

• 24/09/2025, 1pm: Martin Schnee (Institut Quantique, Sherbrooke)

  Location: Leeds (in-person, and online through Zoom)
  Title: Concentration-Free Quantum Kernel Learning in the Rydberg Blockade

  Abstract: Quantum kernel methods (QKMs) offer an appealing framework for machine learning data on near-term quantum computers. By projecting data points to the high-dimensional Hilbert space of an ensemble of qubits, they allow for constructing kernel-based models capable of recognizing otherwise intractable complex patterns with guaranteed convergence towards optimal training. However, QKMs generically suffer from exponential concentration, requiring an exponential number of measurements to obtain the kernel values from the quantum hardware. Here we propose a QKM that is free of exponential concentration yet remains hard to simulate classically. Our QKM utilizes the weak ergodicity-breaking many-body dynamics arising in Rydberg-blockaded neutral-atom arrays. We demonstrate the fundamental properties of our QKM by analytically solving an approximate toy model of its underpinning quantum dynamics, as well as by extensive numerical simulations on randomly generated datasets. We further show that the proposed kernel exhibits effective learning on real data. The proposed QKM can be implemented in current neutral atom quantum computers.

• 22/10/2025, 1pm: Daniel Kious (Department of Mathematics, University of Bath)

  Location: Nottingham (in-person, and online through Teams)
  Title: On the speed and fluctuations of random walks on the exclusion process

  Abstract: In this talk, I will overview mathematical results and questions around random walks in dynamical random environments. I will start by introducing the model in a friendly manner, giving some background on random walks in random environments and the type of questions this brings for random walks in dynamical environments. I will discuss mathematical results I obtained in collaboration with Hilario and Teixeira and with Conchon--Kerjan and Rodriguez, as well as questions from the Physics literature that still remain open. I will keep the exposition technically light and aimed at non-specialists. I will attempt to give the intuition of the proof for my work with Conchon--Kerjan and Rodriguez and explain how this can be seen as a « sharpness » result and that the general strategy is indeed inspired by techniques developed for studying the sharpness of strongly-correlated percolation models. I expect no background on probability from the audience, except perhaps very basic concepts (undergrad level).

• 05/11/2025, 3pm: Steven Thomson (University of Edinburgh)

  Location: Leeds (in-person, and online through Teams)
  Title: Breaking the Entanglement Barrier

  Abstract: The study of low-dimensional many-body quantum systems is extremely challenging, particularly in two dimensions. Exact numerical methods can simulate only a few tens of particles, and many approximate methods work only for weakly entangled systems, a situation known as the 'entanglement barrier'. Here, I'll present a new numerical technique known as the Tensor Flow Equation method which is able to overcome this obstacle not only in one dimension, but also allows us to simulate two and three dimensional many-body quantum systems, including driven and dissipative models. With rigorous guarantees on its accuracy, this method allows us to make reliable calculations in a parameter regime that has previously been almost inaccessible. I will show how the method has allowed us to discover surprising properties of quasiperiodic systems, and shed light on the ongoing debate regarding the fate of many-body localisation in two dimensions.

• 12/11/2025, 1pm: Tanja Schilling (Albert-Ludwigs-Universität Freiburg)

  Location: Nottingham (in-person, and online through Teams)
  Title: The trouble with free energy landscapes

  Abstract: In Kramers’ theory of chemical reaction rates, classical nucleation theory, phase field modeling, and the modeling of biomolecular kinetics, the dynamics of coarse-grained variables is treated as a stochastic process driven by the gradient of a thermodynamic potential. We will discuss how these models can be motivated based on the physics of the underlying microscopic processes. We will show which (often uncontrolled) assumptions need to be made to arrive at stochastic dynamics in a free energy landscape and we will discuss common misperceptions regarding the fluctuation dissipation theorem.

• 13/03/2025, 1pm: Fabian Coupette (University of Leeds)

  Location: Nottingham (in-person, and online through Teams)
  Title: Physics of Fixational Eye Movements

  Abstract: Fixational Eye Movements (FEMs) are small scale seemingly random eye motions unconsciously performed when fixating on a stationary stimulus. As the photoreceptors on the retina adapt toconstant illumination, FEMs provide a transient image and thus ensure that the stimulus does not fade from view entirely. Yet, individual receptors are subject to neural noise and distributing a signal across many receptors also limits the amount of physically available information at the retina. Thus emerges an optimisation problem promising insight into the impact of FEMs on visual perception. We model the retina as a continuous receptor array with a memory kernel governing the local response to stimulation. Within a Bayesian framework, we analytically determine the distribution of available information across different ensembles of stochastic trajectories for arbitrary stimuli thus discerning optimal motion for various psychophysical task such as detection,localisation, or differentiation between different stimuli.We use our findings to quantify the trial-to-trial variability with eye movements on performance in a detection task and directly observe the impact of FEMs in a correspondingly designed psychophysical experiment.

• 08/12/2025, 3pm: Frank Schindler (Imperial)

  Location: Leeds (in-person, and online through Teams)
  Title: Is non-equilibrium band topology a feature or a bug?

  Abstract: There has been a great deal of work in generalising the notion of band topology to the non-equilibrium setting. Much of this work has focused on non-Hermitian Hamiltonians that are thought of as describing quantum systems with loss and gain. In the first part of my talk, I will pedagogically explain one of the central results of this field — the winding number and associated skin effect. I will then argue, however, that the non-Hermitian framework is fundamentally inadequate to properly describe quantum many-body systems — even non-interacting ones — calling into question the physical relevance of non-Hermitian topological invariants. I will end my talk by working out to what extent such invariants, in particular the winding number, can be saved in the more general Lindblad description of open quantum systems.

• 10/12/2025, 1pm: Fabian Essler (Oxford)

  Location: Nottingham (in-person, and online through Teams)
  Title: Lindblad dynamics with decoupled Bogoliubov hierarchies

  Abstract: I consider a class of spinless-fermion Lindblad equations that exhibit decoupled BBGKY [Bogoliubov–Born–Green–Kirkwood–Yvon] hierarchies. In the cases where particle number is conserved, their late time behaviour is characterized by diffusive dynamics, leading to an infinite temperature steady state. Some of these models are Yang-Baxter integrable, others are not. The simple structure of the BBGKY hierarchy makes it possible to map the dynamics of Heisenberg-picture operators on few-body imaginary-time Schrödinger equations with non-Hermitian Hamiltonians. We use this formulation to obtain exact hydrodynamic projections of operators quadratic in fermions, and to determine linear response functions in Lindbladian non-equilibrium dynamics. 

• 04/02/2025, 1pm: Debasish Banerjee (University of Southampton)

  Location: Leeds (in-person, and online through Teams)
  Title: Ergodicity-breaking scenarios in quantum link lattice gauge theories

  Abstract: While the widespread applicability of statistical mechanics indicates the ubiquitous occurrence of thermalization, guided by the Eigenstate Thermalization Hypothesis (ETH), there are increasing examples of violations of the ETH paradigm; both for translational invariant and disordered systems. In this talk, we will discuss various such examples occurring in pure U(1) quantum link gauge theories in two and three spatial dimensions involving exotic phenomena such as scarring and fragmentation.

• 25/02/2025, 1pm: Gabriel Matos (Quantinuum)
  

  Location: Leeds (in-person, and online through Teams)
  Title: Lindblad engineering for quantum Gibbs state preparation under the eigenstate thermalization hypothesis

  Abstract: In this talk, I will present a simplified approach to quantum Gibbs state preparation based on recent advances in Lindblad engineering. By leveraging the eigenstate thermalization hypothesis (ETH), we show that the Lindblad simulation protocol can be made more efficient, with reduced circuit overhead and fast convergence to the target Gibbs state. A key feature of the resulting dynamics is its intrinsic robustness to stochastic noise, which makes the protocol particularly well suited for near-term quantum hardware.

  I will support these claims with numerical studies in the mixed-field Ising model, where we observe polynomial scaling of the mixing time with system size whenever the ETH holds. In addition, I will discuss the impact of both algorithmic imperfections and hardware-induced errors, based on quantum circuit simulations incorporating local depolarizing noise. Overall, this work helps bridge the gap between recent theoretical proposals for dissipative Gibbs state preparation and their practical realization on quantum computers.

• 10/03/2025, 3pm: Weibin Li (Nottingham)
  

  Location: Leeds (in-person, and online through Teams)
  Title: Hilbert space fragmentation in a driven-dephasing Rydberg atom array

  Abstract: We investigate the onset and mechanism of Hilbert space fragmentation (HSF) in a chain of strongly interacting Rydberg atoms subjected to local dephasing. It is found that the emergence of multiple long-lived metastable states is fundamentally tied to the HSF of the driven-dephasing Rydberg atom system. We demonstrate that the manifesting HSF is captured by a dephasing PXP model that supports multiple degenerate zero modes. These modes form disconnected block- diagonal subspaces of maximally mixed states, which consist of many-body spin states sharing the same symmetry. A key result is the identification of the underlying symmetry in the HSF, where the conserved quantities in each subspace are defined by the consecutive double excitation addressing operator. Moreover, we show explicitly that the number of fragmented Hilbert spaces grows exponentially with the chain length, following a modified Fibonacci sequence. Our work provides insights into many-body dynamics under dynamical constraints and opens avenues for controlling and manipulating HSF in Rydberg atom systems.

• 18/03/2026, 3pm: Pablo Poggi (University of Strathclyde)

  Location: Leeds (in-person, and online through Teams)
  Title: Crossover between collective dynamics and scrambling in sparse spin models

  Abstract: Long-range interactions in many-body quantum systems give rise to a rich variety of dynamical phenomena, with both fundamental and practical implications. On one hand, highly symmetric all-to-all couplings display collective dynamics that aligns closely with integrable mean-field models. Conversely, disordered long-range interactions are essential for fast quantum information scrambling, which is classically intractable to simulate. In this work we show that a continuous interpolation between both regimes can be seen in a single, parameter-free, deterministic model — the powers-of-two Hamiltonian, a sparse coupling scheme where each spin interacts with a logarithmic number of neighbours. By changing the initial state, we show that the dynamics changes from collective to scrambling and characterize this crossover by analysing entanglement dynamics (both bipartite and multipartite), and semiclassical Lyapunov exponents. We further propose a systematic graph-theoretical framework that explains the observed dynamical regimes. Our results offer a unified framework for exploring the crossover between collective and scrambling dynamics in a setup with direct relevance to near-term quantum simulation experiments.