The Simons Center for Geometry and Physics is pleased to announce the following talks during the week of Monday, September 21st - Saturday, September 26th

Workshop: Andreas Klümper

Monday, September 21st at 9:45am in SCGP 102

Speaker: Andreas Klümper

Title: Ballistic Transport and Drude Weight

Abstract: Transport phenomena are commonly described in terms of Ohm’s law and its extensions to time-dependent fields and dynamical conductivities. A particularly interesting regime is ballistic transport, in which currents persist without decay and dissipation is absent. Such behavior occurs in a variety of physical systems and is intimately related to conservation laws. For non-relativistic gases, the particle current operator is proportional to the total momentum, implying strictly ballistic particle transport. In this simple setting, the Drude weight admits two natural representations, one of which is expressed in terms of current fluctuations. I will discuss these formulations and explain why they are equivalent in canonical ensembles, while this equivalence need not persist in more general equilibrium states, such as generalized Gibbs ensembles. I will then turn to spin transport in the anisotropic spin-1/2 Heisenberg (XXZ) chain. Here, the notion of ballistic transport raises some subtle questions. In particular, I will discuss the interplay between the thermodynamic and long-time limits and how the resulting Drude weight may depend on the order in which these limits are taken.

Workshop: Frank Göhmann

Monday, September 21st at 11:00am in SCGP 102

Speaker: Frank Göhmann

Title: Asymptotic analysis of form factor series for the Lieb-Liniger Bose gas

Abstract: I will reflect on the problem of extracting the long-time large-distance asymptotic behaviour of integrable models from different form factor series expansions. Over the past years we have pursued two different directions: direct resummation and Riemann-Hilbert analysis. I will present recent results on the Riemann-Hilbert analysis of the Fredhom determinant of a generalized sine-kernel that will allow us to analyse several two-point functions of the Lieb-Liniger Bose gas. As a first concrete result I will present new asymptotic formulae for the field-field correlators of the impenetrable Bose gas in thermal and non-thermal equlibrium and show that they are numerically efficient.

Program Talks: Renzo Ricca

Monday, September 21st at 11:15am in SCGP 313

Speaker: Renzo Ricca

Title: Topological Hydrodynamics

Abstract: With this talk we review some recent developments in topological hydrodynamics and knotted fields. We start with progress on helicity and linking number computations in vortex dynamics. We show how the use of braid theory finds applications in solar physics, and fluid flow mixing in dynamical systems. Then, we review some work on plasma knots and energy lower bounds posed by the knot topology. We discuss the physical implications of the zero-helicity condition on quantum vortex defects in condensates, and show how the use of reconnection number and knot polynomials can be applied to investigate the topological cascade of vortex knots and links in superfluid turbulence.

Workshop: Sarang Gopalakrishnan

Monday, September 21st at 11:45am in SCGP 102

Speaker: Sarang Gopalakrishnan

Title: Hydrodynamic decoupling and recoupling

Abstract: TBD

Workshop: Gábor Takács

Monday, September 21st at 2:00pm in SCGP 102

Speaker: Gábor Takács

Title: From Fractal Drude Weights to Full Counting Statistics: Integrable Transport in the Quantum Sine-Gordon Model

Abstract: Integrable quantum many-body systems are generically characterized by ballistic transport due to their extensive sets of conservation laws. However, their fine-grained transport properties often exhibit subtle anomalous structures driven by the internal symmetries of quasiparticle scattering. In this talk, I will overview our results on the thermodynamic and hydrodynamic description of the quantum sine-Gordon field theory at generic couplings. We show that topological charge transport exhibits singular, fractal-like Drude weights and an interplay with diffusive processes driven by non-diagonal kink–antikink scattering. Finally, we demonstrate that these fractal features carry over to the full counting statistics (FCS) of conserved charges and their currents.

Workshop: Fabian Essler

Monday, September 21st at 2:45pm in SCGP 102

Speaker: Fabian Essler

Title: Dissipative dynamics with decoupled Bogoliubov hierarchies

Abstract: TBD

Workshop: Ruhanshi Barad

Monday, September 21st at 4:00pm in SCGP 102

Speaker: �Ruhanshi Barad

Title: �Universal Suppression of Dissipation across Conformal Interfaces in Open Quantum Critical Systems

Abstract: �Conformal interfaces provide a useful way to probe universal physics in one-dimensional quantum critical systems. In closed systems, they characterize the transmission of energy and information across the interface through universal quantities such as cLR and ceff, respectively. Recent work has shown that conformal interfaces can also control the transmission of dissipation through a relaxation coefficient crelax, extracted from the Liouvillian gap of an open system. In this work, we extend this idea by studying mode-resolved relaxation in non-interacting open quantum critical systems with a conformal interface. In the perfectly reflective limit, the system separates into a dissipative chain and a non-dissipative chain. Modes localized in the non-dissipative chain have zero relaxation rate in this limit and acquire finite relaxation rates only when the interface transmission is increased. These modes therefore provide a direct probe of how dissipation is transmitted across the conformal interface at the level of individual single-particle modes, rather than only through the overall Liouvillian gap. We investigate this behavior analytically and numerically in two critical lattice models: a free-fermion chain and a harmonic chain, each with two choices of boundary conditions. We show that a refined, mode-resolved definition of crelax provides a universal measure of dissipation transmission through the conformal interface. In the weak-dissipation regime, this refined coefficient is independent of the boundary conditions, the dissipation strength, and the location of the local dissipation. For boundary dissipation, the same universal behavior persists even at finite dissipation strength. Our results establish a mode-resolved physical picture of relaxation in open quantum critical systems with conformal interfaces.

Workshop: Marton Lajer

Monday, September 21st at 4:30pm in SCGP 102

Speaker: Marton Lajer

Title: Tail-State RG Improvement for Hamiltonian Truncation in Sine-Gordon and Related Models

Abstract: Numerical precision spectroscopy in perturbed conformal field theories provides an independent route for testing results from integrability. Hamiltonian truncation represents the interacting Hamiltonian in a finite-dimensional space of low-energy states of the unperturbed theory, with the dominant systematic error arising from the omitted high-energy Hilbert space. Existing RG-improvement schemes partially account for these states, but either approximate the resulting nonlocal corrections using a limited number of OPE channels, or become computationally expensive when the full nonlocal contribution is retained. I will present a tail-state RG improvement for the compact boson that uses level-sum recursions to evaluate these finite-cutoff nonlocal corrections directly, without constructing the full high-energy Hilbert space, while preserving a manifestly variational formulation. Applied to sine-Gordon and multifrequency sine-Gordon models, the method substantially improves cutoff convergence over conventional OPE-based RG improvement, with the full cubic correction in some regimes differing significantly from its local approximation. The GPU-adapted algorithm applies to both eigenvalues and matrix elements, including highly excited states.

Workshop: Xie Chen

Tuesday, September 22nd at 9:45am in SCGP 102

Speaker: Xie Chen

Title: Sequential Circuit as Generalized Symmetry on Lattice

Abstract: Generalized symmetry extends the usual notion of symmetry to ones that are of higher form, acting on subsystems, non-invertible, etc. The concept was originally defined in the field theory context using the idea of topological defects. In this talk, we show that on the lattice, generalized symmetries are realized by a special type of quantum circuit called the Sequential Quantum Circuits. We show how to obtain the full, potentially non-invertible symmetry action from the unitary sequential circuit and how the connection to the sequential circuit constrains the properties of the generalized symmetries. Matrix product operator and Tensor product operator representations play an important role in our discussion.

Workshop: Kareljan Schoutens

Tuesday, September 22nd at 11:00am in SCGP 102

Speaker: Kareljan Schoutens

Title: Strong Zero Modes in Supersymmetry-Inspired Quantum Circuits

Abstract: We investigate discrete dynamics in quantum circuits with 2-qubit gates corresponding to the S-matrix of an integrable supersymmetric 1+1D quantum field theory. For a brick-wall configuration such circuits support both localized and delocalized dynamically conserved operators known as strong zero modes (SZM), the number of which depends on the parameter regime. While some of the SZM remain localized at boundaries, other SZM can be guided to propagate across the circuit, inspiring protocols for quantum information transport.

Program Mini Course: Alexei Mailybaev

Tuesday, September 22nd at 11:15am in SCGP 313

Speaker: Alexei Mailybaev

Title: Hidden Symmetry

Workshop: Ho Tat Lam

Tuesday, September 22nd at 11:45am in SCGP 102

Speaker: Ho Tat Lam

Title: Symmetry Enforced Entanglement From Projective Generalized Symmetries

Abstract: The celebrated Lieb-Schultz-Mattis theorem dictates that projective symmetry forces a many-body system to possess long-range entanglement. In this talk, we will discuss the consequence of projective generalized symmetries on many-body entanglement. Surprisingly, unlike ordinary projective symmetries, projective generalized symmetries do not always enforce long-range entanglement. Nevertheless, when long-range entanglement is not required, the symmetries can still enforce non-trivial short-range entanglement and a nontrivial symmetry protected topological order.

Workshop: Ananda Roy

Tuesday, September 22nd at 2:00pm in zoom

Speaker: Ananda Roy

Title: Signatures of Topological Symmetries on a Noisy Quantum Simulator

Abstract: Topological symmetries, invertible and otherwise, play a fundamental role in the investigation of quantum field theories. Despite their ubiquitous importance across a multitude of disciplines ranging from string theory to condensed matter physics, controlled realizations of models exhibiting these symmetries in physical systems are rare. Quantum simulators based on engineered solid-state devices provide a novel alternative to conventional condensed matter systems for realizing these models. In this work, eigenstates of impurity Hamiltonians and loop operators associated with the topological symmetries for the Ising conformal field theory in two space-time dimensions are realized on IBM's Kingston simulator. The relevant states are created on the quantum device using a hybrid quantum-classical algorithm. The latter is based on a variation of the quantum approximate optimization algorithm ansatz combined with the quantum natural gradient optimization method. Signatures of the topological symmetry are captured by measuring correlation functions of different qubit operators with results obtained from the quantum device in reasonable agreement with those obtained from classical computations. The current work demonstrates the viability of noisy quantum simulators as platforms for investigating low-dimensional quantum field theories with direct access to observables that are often difficult to probe in conventional condensed matter experiments.

Workshop: German Sierra

Tuesday, September 22nd at 2:45pm in SCGP 102

Speaker: German Sierra

Title: The c-d conjecture

Abstract: We propose the c-d conjecture, which relates the long-distance degrees of freedom of a critical quantum chain to its microscopic local Hilbert space. For a unitary, local, nearest-neighbour Hamiltonian with local dimension d, whose low-energy limit is described by a conformal field theory of central charge c, the conjecture states that c <= d-1. We discuss its physical interpretation in terms of short- and long-range entanglement and examine its consistency with a variety of integrable spin chains, fermionic systems and anyonic models, as well as its extension to random critical chains. Finally, we introduce finite-size lattice c-functions constructed from lattice realizations of the Virasoro generators and test them in several critical and non-critical models.

Workshop: Dirk Schuricht

Tuesday, September 22nd at 4:00pm in SCGP 102

Speaker: Dirk Schuricht

Title: Parastatistics in Interacting Periodic Chains Revealed by Peierls Phase Twists and Shifted Conformal Towers

Abstract: We consider interacting paraparticle chains with a constant R matrix where the Hamiltonian sums over the internal degrees (flavors) of the paraparticles. For such flavor-blind Hamiltonians, we show a general factorization of the Hilbert space into occupation and flavor parts with the Hamiltonian acting nontrivially only on the former. For open boundaries, the spectrum therefore coincides with that of the occupation Hamiltonian with the flavor part merely adding degeneracies. For periodic boundaries, a cyclic reordering of the flavors leads to a separation of the occupation Hamiltonian into flux sectors at fixed particle number, thus making the parastatistics directly observable in the energy spectrum. For important exemplary cases, the occupation Hamiltonian reduces to the XXZ chain with flux, allowing for an exact solution. In the gapless regime, this solution shows flux-shifted conformal towers in the low-energy spectrum and a temperature-dependent chemical potential in the bulk thermodynamics.

Workshop: Andrei Katsevich

Tuesday, September 22nd at 4:45pm in SCGP 102

Speaker: Andrei Katsevich

Title: Quintic Ginzburg-Landau description of M(2,7) minimal model

Abstract: My talk will be devoted to Ginzburg-Landau descriptions of non-unitary minimal models. I will discuss dimensional continuation of the massless scalar field theory with the iφ^5 interaction term. It preserves the so-called PT symmetry, which acts by φ → −φ accompanied by i → −i. Below its upper critical dimension 10/3, this theory has interacting infrared fixed points. I will argue that the fixed point in d = 2 describes the non-unitary minimal conformal model M(2,7). I identify the operators φ and φ^2 with the Virasoro primaries φ_{1,2} and φ_{1,3}, respectively, and iφ^3 with a quasi-primary operator, which is a Virasoro descendant of φ_{1,3}. These identifications appear to be consistent with the operator product expansions and with considerations based on integrability. Using constrained Pade extrapolations, it can be obtained estimates of the critical exponents in d = 3. I will also comment on possible lattice descriptions of M(2,7) and discuss RG flows to and from this CFT. Finally, I will conjecture that the minimal models M(2,2n+1) are described by the massless scalar field theories with the iφ^{2n−1} interaction terms.

Workshop: Masaki Oshikawa

Wednesday, September 23rd at 9:45am in SCGP 102

Speaker: Masaki Oshikawa

Title: Charge gap in quantum many-body systems

Abstract: TBD

Workshop: Joe Bhaseen

Wednesday, September 23rd at 11:00am in SCGP 102

Speaker: Joe Bhaseen

Title: Quantum Algorithms for Classical Fluid Dynamics

Abstract: Recent advances have shown the potential for quantum algorithms in the numerical simulation of classical fluid dynamics. The use of tensor networks allows for the compression of classical data and the possibility of efficient simulation. Here we discuss recent work on the solution of the discretised Navier-Stokes equation. We discuss the potential for practical applications.

Workshop: Andrea Trombettoni

Wednesday, September 23rd at 11:45am in SCGP 102

Speaker: Andrea Trombettoni

Title: Thermodynamics of the quantum Nagle-Kardar model

Abstract: We study the thermodynamic phase diagram of a one-dimensional quantum spin chain subjected to both mean-field and nearest-neighbor interactions, and to a transverse magnetic field . The purpose is to determine the effect of the quantum fluctuations, due to the transverse field, on the phase diagram, in particular with respect to the occurrence of ensemble inequivalence. We denote our model as a quantum Nagle-Kardar model. To perform the calculation of the canonical partition function, we show that, due to the presence of the mean-field term, in the thermodynamic limit one can use the Hubbard-Stratonovich transformation in spite of the non-commutativity of the different operators appearing in the Hamiltonian, and we adopt a procedure of successive approximations that lead to the determination of the phase diagram thanks to a scaling property of the phase transition lines. The results show that the ensemble inequivalence, present in the classical Nagle-Kardar model, is removed above a threshold value hc for the transverse field. For h larger than hc the phase diagram exhibits only second-order phase transition lines, implying therefore restoration of ensemble equivalence.

Physics Seminar: Gauri Batra

Wednesday, September 23rd at 2:00pm in 313

Title: A backreacted bouncing geodesic in 2D    

Abstract: In holography, analytically continued finite temperature correlation functions exhibit a “t_c singularity” whose bulk origin is a null geodesic “bouncing off” the black hole singularity. In this talk, I will describe how certain quantum corrections modify the t_c singularity in two-dimensional dilaton gravity. In particular, the backreaction of this bouncing geodesic on the geometry smooths out the t_c singularity. However, this does not mean that the black hole singularity itself is resolved. By following the backreacted geodesic saddle in a steepest descent analysis, I will show that the black hole singularity physics instead gets encoded in a subtle way near the coincident point singularities. I will conclude by discussing how such a signature is consistent with the structure of the OPE in higher-dimensional CFTs. Based on work to appear soon with Adam Levine and Steve Shenker.

Workshop: Jerome Dubail

Wednesday, September 23rd at 2:00pm in SCGP 102

Speaker: Jerome Dubail

Title: Limit shapes in measured many-particle quantum states in the large deviation regime

Abstract: TBD

Workshop: Alexei Tsvelik

Wednesday, September 23rd at 2:45pm in SCGP 102

Speaker: Alexei Tsvelik

Title: Tractable model for a fractionalized Fermi liquid (FL$^*$) on a square lattice

Abstract: Motivated by the continued interest in Fermi-surface reconstruction without symmetry breaking, we present an analytically tractable microscopic model of a fractionalized Fermi liquid (FL$^*$) on a square lattice and discuss its potential relevance to the cuprates. As in ancilla-qubit constructions, the model is related to Kondo lattice systems, but in this case, the conduction electrons interact with a $\mathbb{Z}_2$ spin liquid of the Yao--Lee type, with a Majorana Fermi surface. The associated $\mathbb Z_2$ gauge theory is static so that the model can be analytically solved to leading-logarithic accuracy. There are two phases: one in which the fractionalized fermions of the spin liquid hybridize with conduction electrons to form a common Fermi surface violating the naive Luttinger count, and one in which they remain decoupled. We discuss the salient features of the small Fermi-surface phase, including analytically derived momentum dependent coherence factors responsible for the appearance of Fermi arcs \`{a} la Yang-Rice-Zhang. We further discuss the impact of quantum and thermal fluctuations, including a strong diamagnetic response and a logarithmically divergent Sommerfeld coefficient at the onset of the pseudogap.

Workshop: Fei Yan

Wednesday, September 23rd at 4:00pm in SCGP 102

Speaker: Fei Yan

Title: Symmetry-enhanced entanglement detection

Abstract: Entanglement depth, measuring the size of the largest entangled cluster in a quantum state, serves as a critical benchmark for validating quantum resources and has important applications in quantum metrology and quantum computing. While quantum Fisher information (QFI) has been shown to provide bounds on entanglement depth, existing criterion is often modest in certifying entanglement in real materials. In this talk, I will introduce sharpened QFI bounds which can certify entanglement depth more efficiently, utilizing symmetries that are already present in the underlying quantum system. I will also describe the application of such improved QFI bounds in neutron scattering experiments of quantum magnets.

Workshop: Zihan Zhou

Wednesday, September 23rd at 4:30pm

Speaker: Zihan Zhou

Title: Bootstrapping Weak Symmetries of Open Quantum Dynamics from Cross Spectral Form Factors

Abstract: Symmetries of open quantum dynamics can be realized in distinct strong and weak forms. A weak symmetry need not be respected by each individual quantum trajectory or jump operator, but acts as a symmetry of the full Lindblad evolution. Building on our recent work introducing the cross spectral form factor as a probe of hidden finite-group symmetries in quantum many-body Hamiltonians, I will discuss its extension to weak symmetries of open quantum systems. Starting from a known subgroup, cross spectral correlations between symmetry-resolved sectors constrain the branching and fusion data of a larger hidden symmetry. This provides a route toward reconstructing the representation-theoretic structure of weak symmetries directly from the complex spectrum of the Lindbladian.

Workshop: Yuto Ashida

Thursday, September 24th at 9:45am in SCGP 102

Speaker: Yuto Ashida

Title: Quantum computational resources in integrable models: non-Gaussianity, CFT, and noninvertible symmetry

Abstract: ‘Correlatedness’ plays a key role in many disciplines of condensed matter physics, but it remains largely unexplored how one can precisely quantify the degree of correlation in a given many-body state. In this talk, I will approach this question from both quantum information and condensed matter perspectives. Specifically, we provide an information-theoretic measure to quantify the non-Gaussianity of a fermionic/bosonic many-body state and reveal its universal aspects for a 1D critical state through the lens of CFT. We then give a unified perspective for non-Gaussianity and nonstabilizerness, which allows us to provide analytical predictions of their universal behaviors. I will present tensor network calculations of the prototypical integrable models (fermionic XXZ and Ising models) that validate these predictions. Time permitting, I will also talk about how nonstabilizerness measure can encode fusion rules of conformal defects, which might be useful to probe noninvertible symmetries.

Workshop: Tzu-Chieh Wei

Thursday, September 24th at 11:00am in SCGP 102

Speaker: Tzu-Chieh Wei

Title: Universal energy-space localization and stable quantum phases against time-dependent perturbations

Abstract: Stability against perturbations is a defining property of quantum many-body phases of matter. However, most rigorous stabilities are only established for static perturbations; whether any system can remain stable against generic time-dependent perturbations is largely elusive. Here, we identify a universal phenomenon, where the evolving state driven by time-dependent q-local Hamiltonians can be exponentially localized in an energy window of instantaneous spectrum, and prove its survival under generic time-dependent perturbations. Applying such energy-space localization to classical and quantum LDPC codes whose codewords are separated by extensive energy barriers, we show that the system remains localized near the original codeword for an exponentially long time under generic time-dependent perturbations. For classical optimization problems with clustered solution spaces, the stability becomes an obstacle for quantum Hamiltonian-based algorithms to escape local minima. Our work provides a new lens for analyzing quantum non-equilibrium dynamics and tools for establishing stability and designing quantum algorithms.

Program Mini Course : Theodore Drivas

Thursday, September 24th at 11:15am in SCGP 313

Speaker: �Theodore Drivas


Title: �Mathematics of turbulence - Part 1

Workshop: Frank Verstraete

Thursday, September 24th at 11:45am in SCGP 102

Speaker: Frank Verstraete

Title: DMRG in the generalized Landau paradigm

Abstract: TBD

Workshop: Vincenzo Alba

Thursday, September 24th at 2:00pm in SCGP 102

Speaker: Vincenzo Alba

Title: A toy model for entanglement spreading in diffusive systems

Abstract: TBD

Workshop: Nathanan Tantivasadakarn

Thursday, September 24th at 2:45pm in SCGP 102

Speaker: Nathanan Tantivasadakarn

Title: Quantum multicritical point with non-invertible symmetries in a simple spin chain

Abstract: I will construct a simple qubit spin chain with Rep(D₈) symmetry and discuss exact and numerical results of the phase diagram, including evidence that it hosts a multicritical point connecting all gapped phases with this symmetry.

Workshop: Arkya Chatterjee

Thursday, September 24th at 4:00pm in SCGP 102

Speaker: Arkya Chatterjee

Title: Proliferation of non-invertible symmetries in the Q-state Potts model

Abstract: The 1+1d Q-state Potts model is a family of Z_Q clock models distinguished by an enhanced S_Q global symmetry. We show that for Q = 4 and above, the Potts model with periodic boundary conditions in fact enjoys a larger non-invertible symmetry for arbitrary couplings, thus providing new conserved quantities beyond those known from integrability. For Q = 4, they form an SO(3)-parameterized continuous family, which contains S_4 as an invertible sub-symmetry. For Q > 4, the algebraic closure of their matrix product operator representations, computed numerically, contains an infinite number of irreducible non-invertible symmetries.

Workshop: Zhijun Qiao

Thursday, September 24th at 4:30pm in SCGP 102

Speaker: Zhijun Qiao

Title: Peaked Solitons in Integrable Systems

Abstract: In this talk, I will introduce some integrable scalar models which possess peaked solitons (peakons), including the well-known Camassa-Holm (CH), the Degasperis-Procesi (DP), and other new peakon equations developed in recent years. I will take the CH case as a typical example to explain the details and show that the Camassa-Holm spectral problem yields two different integrable hierarchies of nonlinear evolution equations. In particular, the CH peakon equation is able to be extended to the DP, the b-family, the FORQ, the Novikov, the modified CH (MoCH), and other higher order models with peakons or pseudo-peakons. Open problems will also be addressed for discussion in the end. Part of work is joint with Dr. Baoqiang Xia and Dr. Enrique Reyes.

Workshop: Marton Kormos

Friday, September 25th at 9:45am in SCGP 102

Speaker: Marton Kormos

Title: Observing quantum criticality at finite temperature through nonanalytic correlation times

Abstract: I will report recent results on the finite-temperature dynamical correlation function of the magnetization operator in the quantum Ising spin chain. Using methods based on hydrodynamic fluctuations, I will show that the decay rate exhibits non-analytic behavior as the magnetic field, space-time direction, and temperature are varied. As a function of the magnetic field, the non-analyticity occurs at a value that continuously approaches the zero-temperature quantum critical point as the velocity is decreased. Inside the light cone, it reaches the critical point itself, where we find a new, temperature-independent logarithmic divergence. I will argue that the same phenomenon also occurs in the interacting sine-Gordon field theory. These results demonstrate that collective effects induced by quantum fluctuations can persist in the dynamics of local observables even at finite temperature.

Workshop: Miłosz Panfil

Friday, September 25th at 11:00am in SCGP 102

Speaker: Miłosz Panfil

Title: Quantum hard rods: a minimal model for complex quantum gases

Abstract: The classical gas of hard rods has long served as a simple and exactly solvable model in the statistical physics of interacting particles. In contrast, its quantum counterpart has attracted relatively little attention. In this talk, I will argue that, while computationally simpler, the quantum hard-rod model exhibits a level of complexity comparable to the Lieb–Liniger model, which has been a fundamental exactly solvable quantum gas for over 60 years. I will support this claim by presenting our recent results on the exact dynamic correlation functions, non-equilibrium dynamics and Fermi-Bose hard rods mixtures.

Workshop: Juan Pablo Bayona Pena

Friday, September 25th at 11:45am in SCGP 102

Speaker: Juan Pablo Bayona Pena

Title: Correlation and entanglement dynamics of free fermions in disguise

Abstract: We study the nonequilibrium dynamics following a quantum quench in spin chains that can be solved via a mapping to free fermions in disguise. These models feature an exponential degeneracy of all energy eigenvalues, raising the question of the validity of the established framework describing the properties of integrable systems out of equilibrium. We present two main results. First, we develop an analytic method to compute the quasi-momentum distribution function characterizing the generalized Gibbs ensemble, and derive an analytic formula to compute the corresponding expectation values for special observables. Second, we adapt the standard formula for the entanglement growth based on the quasi-particle picture, discussing how our constructions do not explicitly make use of the zero-energy auxiliary free fermions responsible of the exponential degeneracies. We test our theoretical predictions against numerical tensor-network computations for different initial states and Hamiltonian parameters. For the local observables, we find excellent agreement. For the entanglement dynamics, we find small deviations suggesting that the standard quasi-particle picture is only approximately correct for the initial state considered. Our results represent a first step towards the extension of the established framework of integrable systems out of equilibrium to models hosting free fermions in disguise.