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 3pm 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):

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

  Location: Nottingham (in-person)
  Title: TBC

  Abstract: TBC

• 03/04/2025, 3pm: Curt Von Keyserlingk (KCL)

  Location: Nottingham (in-person)
  Title: TBC

  Abstract: TBC

• 25/04/2025, 3pm: Mircea Bejan (Cambridge)

  Location: Leeds (in-person)
  Title: TBC

  Abstract: TBC

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.