Emergent Gauge Theories: Bridging Quantum Matter, Quantum Information, and Fundamental Interactions

For each poster contribution there will be one poster wall (width: 97 cm, height: 250 cm) available. Please do not feel obliged to fill the whole space. Posters can be put up for the full duration of the event.

Poster sessions take place during each week of the event.

Quantum criticality between topological and symmetry-broken phases in a long-range spin-1 chain

Adira, Mohitha

Quantum systems with long-range interactions enhance the effective connectivity of a system without changing its spatial dimensionality, leading to nontrivial many-body phenomena. Motivated by this, we study a spin-1 chain with unfrustrated RKKY-like longrange exchange interactions $J(r)\sim (-1)^{r-1} r^{-\alpha}$, which naturally arise in several quantum simulation platforms. Using quantum Monte Carlo (QMC) simulations, we find that tuning the interaction exponent (\alpha) drives a transition between the symmetry-protected topological (SPT) Haldane phase and an antiferromagnetically ordered phase exhibiting true long-range order. The transition occurs near $\alpha_c = 1.22$, as identified from crossings of correlation-length ratios. Finite-size scaling collapses of the staggered structure factor and the non-local string order parameter yield a consistent correlation-length exponent $\nu = 1.0(8)$, indicating a continuous quantum critical point separating the two phases. To further probe the universal properties of the transition, we compute the Rényi entanglement entropy using replica quantum Monte Carlo simulations combined with the non-equilibrium work protocol introduced by J. K. De Mídio[1], which allows efficient estimation of entanglement entropies within QMC simulations. This approach will allow us to extract the central charge and characterize the universality class of the critical point. Our results highlight how long-range interactions influence phase transitions between topological and symmetry-broken phases in low-dimensional quantum systems. [1] J. D'Emidio, Phys. Rev. Lett. 124, 110602 (2020).

Dynamical Heterogeneity and fractal subdiffusive transport in spin-ice

Bieringer, Malte

Dynamical heterogeneity, fractality, and topology are central concepts in modern condensed matter physics. Their origin is typically rooted in very different physical settings and microscopic mechanisms, such as glassy dynamics, quenched disorder and the absence of symmetry breaking. We show here that a simple, clean lattice model -- in thermal equilibrium -- hosts all three simultaneously. The dynamical heterogeneity even persists across a thermal phase transition into a long-range ordered nematic phase. Investigating the dynamics of the ordered phase, we find that the motion of its fractionalized quasiparticles is restricted to an emergent fractal network, leading to subdiffusive yet ergodic transport that deviates from conventional hydrodynamic expectations. The fractal exhibits critical scaling from the lattice scale up to long-wavelengths. This fractal structure also shapes the distribution of quasiparticle lifetimes, enhancing short-time dynamics. We discuss how this subdiffusive behavior can be probed experimentally in candidate materials through the power spectral density of the magnetization. Indeed, our results account for recent experimental results on dynamical heterogeneity in the spin ice compound $\mathrm{Dy_2Ti_2O_7}$ [arXiv:2408.00460] by identifying generation recombination noise of its fractionalized quasiparticles as the cause of dynamical heterogeneity. Our results show that dynamical heterogeneity can act as a diagnostic of new cooperative regimes, helping to transcend naive boundaries between equilibrium and non-equilibrium physics and between order and disorder.

Parafermions Ex Machina

Bollmann, Steffen

Motivated by recent observations of fractional Chern insulators (FCIs) in the vicinity of superconducting (SC) phases (e.g. $\text{MoTe_2}$), we study fractional quantum (anomalous) Hall-superconductor heterostructures in the presence of U(1) order-parameter fluctuations and particularly focus on the case of $\nu=2/3$ quantum Hall states leading to $Z_3$ parafermions. While the emergence of $Z_3$ parafermions has already been demonstrated in the spin-unpolarized Halperin State, we demonstrate how disorder can also stabilize $ Z_3$ parafermions in the spin-polarized $nu=2/3$ state, which is expected to be present in $\text{MoTe_2}$. Due to a broad phase transition between the FCI and the superconducting state, we further study the effect of phase fluctuations on the $Z_3$ parafermions, using field-theoretical methods as well as the density-matrix renormalization group. We find a rich phase diagram composed of Mott insulating phases and two distinct Luttinger liquids, whose fundamental excitations carry charges 2e and 2e/3, respectively. In agreement with analytical considerations using conformal field theory, we numerically find transitions of Berezinskii-Kosterlitz-Thouless (BKT) type as well as a continuous $Z_3\times\text{U(1)}$ second-order phase transition characterized by central charge c = 9/5.

Order parameter for topological states from conformal geometry

Chakraborty, Nilotpal

Topologically ordered/Long-range entangled phases of matter have been hard to unambiguously detect of due to the lack of a general observable order parameter. As a consequence, most experimental effort is focused either on interferometry of low-lying excitations or simulating the wavefunction on very small lattices and obtaining information theoretic measures from multiple wavefunction snapshots. I will present a different approach which allows one to extract an order parameter from the ground state in toy models of two dimensional topological order with boundaries, based on their quantum loop gas description. Our construction uses a combination of the unique structure of the superposition in the quantum loop gas description and the corresponding connection to the critical classical loop models to extract a universal quantity from the topologically ordered ground state. I shall discuss the extent to which the universal quantity obtained describes the anyon content of the underlying topological order, and its robustness as compared to other information theoretic quantities.

Programmable Kondo Effect Formed by Landau Levels

Chen, Yun

Nanobubbles wield significant influence over the electronic properties of 2D materials, showing diverse applications ranging from flexible devices to strain sensors. Here, we reveal that a strongly-correlated phenomenon, i.e., Kondo resonance, naturally takes place as an intrinsic property of graphene nanobubbles. The localized strain within the nanobubbles engenders pseudo magnetic fields, driving pseudo Landau levels with degenerate Landau orbits. Under the Coulomb repulsion, the Landau orbits form an effective $SU(N)$ pseudospin coupled to the bath via exchange interaction. This results in a new flavor screening mechanism that drives an exotic flavor-frozen Kondo effect, which is absent in conventional Kondo systems. The resonance here also exhibits an unparalleled tunability via strain engineering, establishing a versatile new platform to simulate novel correlated phenomena based on pseudo Landau levels.

Modulated Gauge Theories in 2+1d

Delfino, Guilherme

Modulated gauge theories are gauge theories in which the spatial structure of the symmetry plays a nontrivial role. In this poster, I present a complete classification of such theories in 2+1 dimensions, discuss their key properties, and show how they naturally realize symmetry-enriched topological order.

From wave-function localization to strain induced correlated phases in moire heterostructures

Espinosa Champo, Abdiel de Jesus

Our previous studies on the chiral Hamiltonian of twisted bilayer graphene demonstrated how confinement potentials and non-Abelian interlayer currents explain wave-function localization and the emergence of flat bands at magic angles. Building upon this geometric understanding of single-particle states, we present a self-consistent Hartree-Fock computational workflow to address the many-body interacting problem in twisted double bilayer graphene under realistic uniaxial strain. We explore how non-local Fock exchange interacts with the underlying quantum geometry to drive correlated spatial reconstructions and symmetry breaking. These numerical results extend our confinement models into the strongly correlated regime, offering a practical perspective on how geometric properties dictate the low-energy physics of moire materials. References - L. A. Navarro-Labastida, A. Espinosa-Champo, E. Aguilar-Mendez, and G. G. Naumis, Phys. Rev. B 105, 115434 (2022). - G. G. Naumis, L. A. Navarro-Labastida, E. Aguilar-Mendez, and A. Espinosa-Champo, Phys. Rev. B 103, 245418 (2021).

When adiabaticity is not enough to study topological phases in solid-state physics, comparing the Berry and Aharonov-Anandan phases

Espinosa Champo, Abdiel de Jesus

The robust classification of topological phases in driven quantum systems often relies on adiabatic assumptions and the Berry phase. However, these approximations can fail under strong periodic driving or when evaluating responses beyond the adiabatic limit. In this contribution we present an analytical and numerical framework based on the Aharonov-Anandan phase to properly characterize topological properties in non-adiabatic regimes. By applying this formalism to 2D materials, we demonstrate how the breakdown of adiabaticity reveals hidden non-adiabatic features and chiral current vortices that are invisible to conventional Berry phase mapping. We discuss how these geometric diagnostics provide a more rigorous tool to understand chiral dynamics and topological protection in strongly driven quantum matter. Reference - A. de J. Espinosa-Champo, A. Kunold, and G. G. Naumis, J. Phys. Mater. 8, 045013 (2025).

non-invertible higher form symmetries in quantum double model and beyond

Flores Calderon, Rafael Alvaro

We study the relationship between discrete-group topological order, non-Abelian lattice gauge theory, and non-invertible higher-form symmetries in the paradigmatic quantum double model. We analyze how these structures extend away from the fixed-point limit and explore their connection to the confinement of non-Abelian anyons.

Exact stabilizer scars in two-dimensional $U(1)$ lattice gauge theory

Gupta, Sabhyata

The complexity of highly excited eigenstates is a central theme in nonequilibrium many-body physics, underpining questions of thermalization, classical simulability, and quantum information structure. In this work, considering the paradigmatic Rokhsar-Kivelson model, we connect quantum many-body scarring in Abelian lattice gauge theories to an emergent stabilizer structure. We identify a distinct class of scarred eigenstates, termed sublattice scars, originating from gauge-invariant zero modes that form exact stabilizer states. Remarkably, although the underlying Hamiltonian is not a stabilizer Hamiltonian, its eigenspectrum intrinsically hosts exact stabilizer eigenstates. These sublattice scars exhibit vanishing stabilizer R\'enyi entropy together with finite, highly structured entanglement, enabling efficient classical simulation. Exploiting their stabilizer structure, we construct explicit Clifford circuits that prepare these states in a two-dimensional lattice gauge model. Our results demonstrate that the scarred subspace of the Rokhsar-Kivelson spectrum forms an intrinsic stabilizer manifold, revealing a direct connection between stabilizer quantum information, lattice gauge constraints, and quantum many-body scarring.

Quantum simulation of chiral magnetic effect and chirality flipping using one dimensional optical superlattices

Gupta, Sabhyata

The chiral magnetic effect (CME) is a fundamental phenomenon in high-energy physics where an electric current is generated along an external magnetic field in the presence of a chirality imbalance, which is a difference between number of left-handed and right-handed fermions. CME is non-equilibrium phenomena that arises as a consequence of the chiral anomaly, which is the breaking of chiral symmetry that introduces a chiral imbalance. In the presence of a finite chiral chemical potential, this im- balance leads to a macroscopic vector current along the magnetic field, defining the CME. CME plays a crucial role in understanding the behavior of relativistic charged fermions and acts a probe for topological charge fluctuations in quantum chromodynamics (QCD) and has significant implications for heavy-ion collisions and early universe cosmology. Despite its broad significance, understanding the real-time dynamics of the CME poses a significant challenge for classical computation due to the sign problem and the exponential complexity of many-body systems. We propose a scheme to simulate the real-time dynamics of the Chiral Magnetic Effect (CME) and chirality-flipping processes using fermions in one-dimensional optical lattices. Our proposal aims to provide a scalable and controllable route to simulate anomaly-induced transport, establishing optical lattices as a promising platform for the real-time study of CME dynamics.

Entanglement in Free-Fermion Systems: Unitary Dynamics and Measurement-Induced Transitions

Haller, Lukas

Measurement-induced entanglement transitions (MIETs) represent a new paradigm of nonequilibrium phase transitions, but their existence and universality in some free-fermion systems remain debated. In this thesis, we study both unitary and monitored free-fermion dynamics using analytical and numerical techniques. We analyze the Braid and Gaussian random brickwork circuits. In the Braid circuit, a mapping to a classical model yields an intuitive picture of the entanglement dynamics and allows analytical predictions for the steady-state averages of the entanglement entropy, subsystem purity, and mutual information. In the Gaussian circuit, we adapt methods developed for Haar random circuits to compute the steady-state subsystem purity and numerically show that the annealed average second R´enyi entropy approximates the true R´enyi entropy well in large systems. Including measurements qualitatively changes the dynamics and can lead to entanglement transitions. We map the monitored Braid circuit to a classical model and provide numer- ical evidence that a genuine MIET occurs, and is described by the universality class of the completely packed loop model with crossings. For monitored Hamiltonian models, particle number conservation and a bipartite structure of the model are important for the existence of MIETs. When both symmetries are broken — in our case through adding pairing terms and onsite disorder to a fermionic hopping Hamiltonian — a genuine MIET between a phase with $log(L)^2$ entanglement and an area law phase exists. A numerical analysis of universal quantities supports a description in terms of the $SO(N)$ nonlinear sigma model (NL$\sigma$M) in the replica limit $N \rightarrow 1$. When the particle number is conserved or the bipartite structure is not broken, we find evidence that only finite-size crossovers occur, and the model is in the area law phase for all measurement rates. Finally, we speculate on a classification framework of generic free-fermion models: moni- tored systems are governed by the same NLσMs as their nonunitary circuit counterparts but in the replica limit $N \rightarrow 1$. We discuss how our results and previous literature fit into the framework and begin numerically testing its predictions. A striking conjecture is the existence of exactly one additional generic free-fermion MIET universality class in one dimension.

The BF Theory of non-Abelian dihedral topological order

Liu, Chunxiao

Non-Abelian topological orders, which support anyonic excitations, are central to quantum computing but remain difficult to realize. We show that the twisted quantum double of the dihedral group—a key family of non-Abelian topological orders—can emerge via Higgsing from a parent O(2) gauge theory. This correspondence is established by matching anyon statistics with Wilson loop observables in a BF theory framework. We further construct lattice models realizing these phases and, through renormalization group analysis, propose that they can undergo a direct transition to a U(1) Coulomb or chiral topological phase at a multicritical point with emergent O(3) symmetry.

Fracton-elasticity duality for a Wigner crystal and the anti-Higgs mechanism

Matus, Paweł

I will present an effective gauge field theory of Wigner crystal elasticity, which considers the presence of elastic defects: interstitials/vacancies and dislocations. Using this theory, we calculate defect-defect interaction energies, and study the effects of defect proliferation on the long-wavelength physics of the charged crystal. Unexpectedly, we find that upon a condensation of vacancies or interstitials the corresponding gauge field does not become massive – on the contrary, the number of massless modes in the system increases. We dub this mechanism the anti-Higgs mechanism. [1] P. Matus, "Defects in Wigner crystals: Fracton-elasticity duality and vacancy proliferation", Phys. Rev. B 113 (7), 075138 [2] A. Głódkowski, P. Matus, F. Peña-Benítez, and L. Tsaloukidis, "Quadrupole gauge theory: Anti-Higgs mechanism and elastic dual", Phys. Rev. D 112 (12), L121702

Non-Hermiticity driven ground state entanglement in Heisenberg spin chains

Midya, Bikashkali

Theoretical analysis of an effective non-Hermitian systems characterized by asymmetric Heisenberg XY interactions in the absence of external magnetic fields demonstrates that maximal bipartite entanglement and quantum phase transitions can be induced exclusively through non-Hermiticity. At thermal equilibrium as $T \rightarrow 0$, the system attains maximal entanglement $C= 1$ for values of the non-Hermiticity parameter greater than a critical value $\gamma > \gamma_c = J(1−\delta^2)^{1/2}$, where $J$ denotes the exchange interaction and $\delta$ represents the anisotropy of the system; conversely, for $$\gamma < \gamma_c $, entanglement is nonmaximal and given by $C= \sqrt{1−(\gamma/J)^2}$. The entanglement undergoes a discontinuous transition to zero precisely at $\gamma =\gamma_c$. This phase transition originates from non-Hermiticity driven ground state degeneracy, which differs fundamentally from an exceptional point. Reference: B . Midya, Non-Hermiticity induced thermal entanglement phase transition, J. Appl. Phys. (2026) (to appear).

Towards quantum simulation of fingering instabilities

Muzzi, Cristiano

Systems of charged particles in a nonuniform magnetic field can show growth processes similar to those observed in viscous flows. In particular, a quantum hall droplet under the influence of a nonuniform magnetic field can develop fingering pattern (cusp formation) instabilities which arise due to purely quantum mechanical effects. Such fingering pattens are analogous to those observed in the presence of interfaces between two immiscible phases of incompressible fluids with different viscosity, a phenomenon which is known as Laplacian growth. In this poster, I present results and progress toward realizing and observing Laplacian growth–like behavior in cold atomic systems. In this poster, I will present results and progress toward realizing and observing Laplacian growth–like behavior in cold atomic systems.

2D-THz spectroscopy for the detection of collective modes in superconductors

Neri, Silvia

An intriguing question in superconductivity is how to efficiently detect signature of the collective excitations associated to the superconducting order parameter. The feature associated to collective mode can indeed provide insight on the pairing symmetry of the order parameter and to other features of the superconducting state. We address this question by we theoretically model a 2D THz pump-probe spectroscopy experiment for a two-band superconductor. Two-dimensional spectroscopy has proven to be an important method with wide applications ranging from rovibronic excitations in bio-molecular systems, excitons in semiconductors, to magnons in antiferromagnets and has been recently applied to superconducting collective modes. To numerically compute the non linear dyanamics we adopt a pseudospin model and we chose realistic parameter to model the pulses and as well for the superconducting state, reflective of MgB2. The numerically evaluated 2d spectrum shows, in addition to the first and third harmonic signals, the presence of sidebands along ω= ωΔt ± Ω, where Ω is associated to the Leggett mode frequency of the system. We proceed by analytically deriving an expression for the non linear current. Our results show that the extension of 2d techniques to the superconducting realm may therefore provide an important new avenue to investigate the physics of superconductors.

Effective Field Theory for Quantum Skyrmion Hall Effect

Patil, Vinay Rajendra

We derive an effective field theory (EFT) description for the quantum skyrmion Hall effect (QSkHE) and related topologically non-trivial phases of matter. An almost point-like Landau level with small orbital degeneracy can host an intrinsically 2+1 D topological many-body state, meaning internal degrees of freedom can encode a finite number of spatial dimensions. This almost point-like 2+1 D many-body state plays the role, in the quantum skyrmion Hall effect (QSkHE), that a charged particle plays in the quantum Hall effect. We also present a Matrix formalism for QSkHE, to account for the non-commutative character of gauge theories hosted in LLLs. 1. V. Patil, R. Flores-Calderón, and A. M. Cook, Effective field theory of the quantum skyrmion hall effect (2024), arXiv:2412.19565 [hep-th] 2. V. Patil, A. Banerjee, and A. M. Cook, Microscopic field theories of the quantum skyrmion hall effect (2025), arXiv:2508.16547 [hep-th].

Bose-Einstein condensation and superfluidity on a fuzzy sphere

Shyta, Vira

We study the behavior of superfluids defined over a non-commutative (fuzzy) compact space. In particular, we investigate the Bose--Einstein condensation (BEC) and thermal fluctuations of the superfluid density on the surface of a fuzzy sphere. A central feature of these systems is the truncation of the spectrum due to an angular momentum cutoff set by the non-commutativity scale. In ideal and weakly interacting Bose gases, we derive the critical temperature for condensation $T_{BEC}$ and show that, while the compactness of the system facilitates BEC in $d=2$, increasing non-commutativity lowers the critical temperature $T_{BEC}$, ultimately leading to a complete suppression of condensation for high enough degree of non-commutativity. Since superfluidity can occur even in the absence of a condensate, we further investigate superfluid behavior on the fuzzy sphere by deriving the superfluid density from the response to a phase twist (analogous to a Galilei boost) as a function of both the sphere radius and the space non-commutativity parameter.

S-matrix approach and Harris criterion in the Integer quantum Hall effect

Topchyan, Hrant

We propose an S-matrix approach to numerical simulations of network models, applying it to random networks (GKNS networks) previously introduced for the Integer quantum Hall effect (IQHE) plateau transitions, which capture the physics of electrons moving in a strong magnetic field and smooth disorder potential more accurately. The S-matrix method offers significant advantages over the transfer matrix approach, allowing for a high precision calculation of the a localization length critical exponent, $\nu \approx 2.37$. This value aligns closely with the experimental result $\nu_{exp} \approx 2.38$ observed at the IQH transition, while differing notably from the CC model’s value of $\nu_{CC}\approx 2.6$. Additionally, we analyze the applicability of the Harris criterion to the GKNS network disorder and demonstrate that the fluctuations in the geometry are relevant despite the condition $d\nu > 2$, suggesting a need for modification of Harris criterion. Specifically, we find that the fluctuations of the critical point in different quenched configurations of disordered network blocks are of order $L^0$, rather than decreasing as $L^{-d/2}$ as implied by the Harris criterion. This behavior suggests that the GKNS network disorder is never irrelevant, with the critical indices of the system being subject to change. Moreover, we show that the GKNS disordered network differs fundamentally from the usually studied Voronoi-Delaunay and dynamically triangulated random lattices, as the probability of higher connectivity in the GKNS network decaying as a power law rather than exponentially, indicating that the network is "scale-free", which are almost not studied in the context of matter physics.

$Z_2$ quantum spin liquid in the $J_1-J_2$ Heisenberg model on the square lattice

Walther, Luis

The spin-$1/2$ $J_1-J_2$-Heisenberg antiferromagnet on the square lattice is a paradigmatic system in quantum magnetism. While a Néel-ordered phase at small $J_2/J_1$ and a stripe-ordered phase at large $J_2/J_1$ are well established, the nature of the intermediate phase remains under debate. Numerical studies have reported conflicting results, proposing either a valence-bond solid phase or a possible $Z_2$ quantum spin liquid. In this work, we study the stability of a candidate $Z_2$ quantum spin liquid phase in this model using a fully self-consistent analytic approach. We first determine the mean-field parametrization of the system self-consistently and then incorporate fluctuation effects beyond mean field theory through an infinite resummation of interaction diagrams within the random phase approximation (RPA). Within the RPA, a collective low energy excitation emerges that allows us to assess the stability of the spin liquid state. At transitions toward magnetically ordered phases, this mode condenses at the corresponding ordering wavevector, whereas it remains gapped within the spin liquid regime. This approach further enables the calculation of the full finite-frequency spectral function, allowing for direct comparison with numerical methods such as variational Monte Carlo and density matrix renormalization group calculations, as well as experimental probes including inelastic neutron scattering.

Pseudo-first-order transition and deconfined criticality from competing Dirac masses in 1D

Weber, Manuel

Emergent symmetries and slow crossover phenomena are central topics in quantum criticality and prominently manifest in the pseudocritical scaling discussed in the context of deconfined criticality. Here we identify its conceptual counterpart: a symmetry-enhanced pseudo-first-order transition. It emerges from a one-dimensional realization of deconfined criticality between charge- and bond-ordered states driven by competing Holstein and Su-Schrieffer-Heeger electron-phonon couplings. In this setup, quantum fluctuations and thereby the nature of the transition can be tuned systematically via the phonon frequency. In the classical phonon limit, a low-energy Dirac theory predicts a direct first-order transition with emergent U(1) symmetry. Exact quantum Monte Carlo simulations provide strong evidence for symmetry enhancement and even finite-size scaling on intermediate length scales. However, in the thermodynamic limit a narrow intermediate phase emerges in which both order parameters are finite, as chiral U(1) symmetry is weakly broken on the lattice. Including quantum lattice fluctuations narrows the intermediate phase, gradually restores the U(1) symmetry, and ultimately tunes the system to a deconfined quantum critical point.

Probing the Quantum Merger of Holographic Spacetimes with Entanglement Imagitivity

Wei, Chenan

The merger of two highly entangled systems offers a holographic perspective on the unification of black hole spacetimes. In this ongoing work, we investigate the time evolution of two complex Sachdev-Ye-Kitaev (SYK) models coupled through random four-body interactions. By treating the inter-system coupling as a probabilistic network, we explore the transition from decoupled systems to a single merged entity. Our preliminary analysis reveals a multi-stage thermalization process. We observe that standard spatial entanglement metrics, such as logarithmic negativity and mutual information, saturate rapidly, suggesting an early formation of a geometric bridge. To capture the subsequent scrambling within the newly formed interior, we utilize Entanglement Imagitivity, a measure of timelike correlations. Our early results suggest that Imagitivity continues to grow and exhibits non-monotonic behavior long after spatial metrics plateau, highlighting a prolonged period of internal complexity growth. This study aims to clarify the distinction between the establishment of a geometric connection and the full dynamical unification of quantum spacetimes.

Suppression of Thermalization in Systems with Competing Integrable Structures

Wei, Chenan

The Eigenstate Thermalization Hypothesis typically governs the relaxation of generic quantum many-body systems. However, systems constructed from competing integrable structures may exhibit anomalous thermalization dynamics. We are currently investigating a one-dimensional spin-1/2 model where an anisotropic Heisenberg interaction competes with a chiral three-spin interaction. By tuning the relative strength between these non-commuting integrable terms, the system undergoes a crossover into an intermediate chaotic regime. While initial spectral analyses show strong level repulsion characteristic of quantum chaos, we observe that the average eigenstate entanglement entropy remains significantly suppressed compared to the ergodic prediction for random pure states. Our ongoing research explores the Liouvillian spectrum of this system to identify the mechanism behind this suppressed thermalization. Current data points to the presence of quasi-conserved operators that create a dynamical bottleneck, effectively fragmenting the phase space and decoupling spectral chaos from full eigenstate ergodicity. These preliminary findings highlight the complex landscape of intermediate dynamical regimes between integrability and chaos.

Topological mixed states: Axiomatic approaches and phases of matter and emergent symmetries

Yang, Tai Hsuan

For closed quantum systems, topological orders are understood through the equivalence classes of ground states of gapped local Hamiltonians. The generalization of this conceptual paradigm to open quantum systems, however, remains elusive, often relying on operational definitions without fundamental principles. Here, we fill this gap by proposing an approach based on three axioms: (i) local recoverability, (ii) absence of long-range correlations, and (iii) spatial uniformity. States that satisfy these axioms are fixed points; requiring the axioms only after coarse-graining promotes each fixed point to an equivalence class, i.e. a phase, presenting the first step towards the axiomatic classification of mixed-state phases of matter: mixed-state bootstrap program. From these axioms, a rich set of topological data naturally emerges; importantly, these data are robust under relaxation of axioms. For example, each topological mixed state supports locally indistinguishable classical and/or quantum logical memories with distinct responses to topological operations. These data label distinct mixed-state phases, allowing one to distinguish them. We further uncover a hierarchy of secret-sharing constraints: in non-Abelian phases, reliable recovery— even of information that looks purely classical—demands a specific coordination among spatial subregions, a requirement different across non-Abelian classes. This originates from non-Abelian fusion rules that can stay robust under decoherence. Finally, we performed large-scale numerical simulations to corroborate stability: weakly decohered fixed points respect the axioms once coarse- grained. Surprisingly, the axiom violations at different length scales exhibit an exact crossing at the critical point, enabling its identification without any rescaling or data-collapse ambiguities. These results lay the foundation for a systematic classification of topological states in open quantum systems.

Non-Hermiticity Induced Universal Anomalies in Kondo Conductance

Yi, Wei-Zhu

Strong correlation, when combined with dissipation in open systems, can lead to a variety of exotic quantum phenomena. Here, we study nontrivial interplays between non-Fermi liquid behaviors emerging from strong correlation and non-Hermiticity arising from open systems. We propose a practical physical setup that realizes a non-Hermitian multichannel Kondo model. We identify a weak-coupling local moment fixed point and a strong-coupling non-Fermi liquid fixed point under PT symmetry, both are enriched by the non-Hermitian effect. Remarkably, universal unconventional Kondo conductance behaviors are found for both cases, which are distinct from all previously studied Kondo systems. Particularly, we show that an anomalous upturn of conductance could take place with increasing the temperature, originating from the interplay between non-Fermi liquid and non-Hermiticity. Our results identify a novel class of transport phenomena unrecognized before, driven by intertwined effects of correlation and dissipation

Incompressible quantum liquid on the four-dimensional sphere

Zhao, Junwen

The study of quantum Hall effect (QHE) is a foundation of topological physics, inspiring extensive explorations of its high-dimensional generalizations. Notably, the four dimensional (4D) QHE has been experimentally realized in synthetic quantum systems, including cold atoms, photonic lattices, and metamaterials. However, the many-body effect in the 4D QHE system remains poorly understood. In this study, we explore this problem by formulating the microscopic wavefunctions inspired by Laughlin's seminal work. Employing a generalized pseudo-potential framework, we derive an exact microscopic Hamiltonian consisting of two-body projectors that annihilate the microscopic wavefunctions. Diagonalizations on a small size system show that the quasi-hole states remain zero energy while the quasi-particle states exhibit a finite gap, in consistency with an incompressible state. Furthermore, the pairing distribution is calculated to substantiate the liquid-like nature of the wavefunction. Our work provides a preliminary understanding to the fractional topological states in high dimension.

Ergotropy of quantum many-body scars

Zhi, Zhaohui

Quantum many-body scars break ergodicity and evade thermalization, resulting in area law entanglement entropy even with high energy density. While their quantum correlations and entanglement have been elaborated previously, their capacity in storing extractable energy, quantified by the notion ergotropy, remains an open question. Here we focus on the representative PXP model, and unveil the extensive ergotropy scaling of a family of states interpolating between quantum many-body scars and thermal states, the latter of which are known to be passive with vanishing ergotropy. A phenomenological relation between ergotropy and entanglement is uncovered, which generalizes the existing free fermion integrable results to an interacting scenario. The ergotropy in a dynamical protocol shows that a reset with a global uniform coherent rotation can inject extractable energy, as a proof of principle way to charge a quantum "battery". Our protocol is tailored for near term Rydberg neutral atoms array, while also being feasible for other quantum processors. Our results establish that quantum many-body scars, despite the tiny fraction of the Hilbert space they occupy, can be efficiently exploited for storing extractable energy, and "scarring" a many-body system as a promising route for engineering quantum many-body battery.