Papers

Altermagnets offer a route to spin-polarized electronic states without macroscopic magnetization, because compensated magnetic order can generate momentum-dependent spin splitting through crystal-symmetry-controlled exchange fields. However, experimentally viable altermagnets combining large spin splitting, thermodynamic stability and high magnetic ordering temperatures remain scarce. Here, we develop a machine-learning-accelerated high-throughput framework to explore the tetragonal AB$_2$C$_2$D compounds. Screening 8640 variants identifies 1347 compensated antiferromagnetic candidates satisfying altermagnetic symmetry. An interpretable XGBoost model trained on first-principles spin-splitting data then isolates 34 low-hull-energy candidates,including four previously reported, with giant non-relativistic spin splittings exceeding 1.5 eV near the Fermi level. Detailed first-principles calculations of the representative RbMn$_2$Te$_2$O confirm a maximum spin splitting of $\sim$1.88 eV with dynamical stability and an estimated Néel temperature of $\sim$390 K. The giant splitting originates from symmetry-locked Mn-sublattice exchange fields amplified by directional Mn-d/Te-p hybridization. Furthermore, we uncover a profound soft-mode-driven structural transition associated with an interlayer dimensionality crossover in SrMn$_2$Te$_2$O, yet the unfolded electronic structure demonstrates that the altermagnetic spin splitting remains robust after lattice reconstruction. Hydrostatic pressure provides an additional tuning route, producing non-monotonic modulation of the spin-split Fermi surface governed by local coordination and orbital hybridization. These results establish tetragonal AB$_2$C$_2$D compounds as a tunable materials platform for stray-field-free spintronic devices and provide a general data-driven strategy for discovering robust giant-splitting altermagnets.

Acoustic horizons in Bose–Einstein condensates are usually characterized through long-wavelength Bogoliubov phonons. We study a nonlinear counterpart: whether a one-dimensional dark-soliton branch can sustain upstream laboratory motion in a stationary transonic flow. The mechanism is local at leading order. A regular dark soliton has a bounded fluid-frame velocity, limited by the local sound speed; therefore, in the supersonic region, the background flow exceeds the largest upstream velocity available to the soliton branch. The sonic point is thus the upstream edge of the local dark-soliton branch, rather than a hard wall or a soliton geodesic surface. We construct stationary transonic Gross–Pitaevskii backgrounds and evolve the full order parameter in an open, nonperiodic domain. The simulations show upstream propagation on the subsonic side, finite-depth stalling on the subsonic side, and downstream advection for defects initialized in the supersonic region with upstream velocity relative to the fluid. Convergence, branch-consistency, local-density, phase-jump, and a dense scan of dimensionless upstream attempts support the soliton-like interpretation. The result is a branch-existence constraint, not a rigorous lower bound on arbitrary density minima of the Gross–Pitaevskii field.

Altermagnets are a recently identified class of collinear antiferromagnets that host large spin-split electronic bands, offering a promising platform for efficient spin-current generation. Among proposed candidates, the metallic oxide RuO2 is predicted to exhibit strong altermagnetic spin splitting; however, whether it sustains robust magnetic order beyond the ultrathin thickness limit remains unresolved. Here, we employ optical probes to investigate charge-to-spin conversion in a 12-nm-thick (101)-oriented RuO2 film grown on sapphire. Polarization-resolved second-harmonic generation reveals nonlinear optical responses consistent with the surface symmetry and Néel order of RuO2. Under an applied current, both second-harmonic generation and polar magneto-optical Kerr effect measurements detect a pronounced, directionally anisotropic spin polarization, exhibiting enhanced signals for current along [010] and strongly suppressed responses for current along [-101], in agreement with the symmetry of the altermagnetic spin-splitter effect. Non-magnetic or Rashba-type mechanisms cannot explain this symmetry-selective response. Scanning transmission electron microscopy further reveals that substantial strain persists even in relatively thick films, providing a possible explanation for the observed behavior. Therefore, these results establish RuO2 as an efficient spin source and demonstrate the potential of altermagnets for field-free spintronic devices.

The quantum anomalous Hall (QAH) effect is conventionally understood to exist only in Chern insulators, while a recent study has shown that ferromagnetic metals can also host the QAH effect. Between insulators and metals, we demonstrate that QAH can persist even in a chiral semimetal, where conduction and valence bands touch at zero energy. Transport calculations demonstrate that the Hall conductivity of such a system can be quantized in the presence of dephasing. Interestingly, its longitudinal conductivity remains finite and exhibits semimetallic behavior, in contrast to Chern insulators. This unusual transport behavior originates from the quantization of the Berry curvature integral over occupied states and the semimetallic band structure. This chiral semimetal can transition into a Chern insulator, accompanied by the vanishing of longitudinal conductivity and a reduction of the intrinsic length scale of the Hall response. Our results extend the concept of QAH and uncover the semimetallic QAH transport signatures.

We investigate spin-Hall-like magnon edge transport in a synthetic antiferromagnetic skyrmion lattice composed of two antiferromagnetically coupled skyrmion lattice layers with opposite magnetic textures. Based on a relaxed bilayer texture from micromagnetic simulations, we construct the bosonic Bogoliubov-de Gennes Hamiltonian within linear spin-wave theory and calculate the bulk and strip magnon spectrum. We find counterpropagating in-gap edge modes with opposite layer polarization, whose layer-resolved propagation is further confirmed by dynamical micromagnetic simulations. A symmetry analysis shows that the fully coupled system lacks the pseudo-time-reversal symmetry required for a genuine bosonic Z2 topological phase. Thus, the observed edge modes are not Z2-protected helical magnon edge states, but layer-polarized, spin-Hall-like modes originating from the opposite Hall tendencies of the two skyrmion lattice layers. These results establish synthetic antiferromagnetic skyrmion lattices as a platform for spin-Hall-like magnon transport beyond a strict bosonic Z2 classification.

Chirality, defined by the absence of mirror and inversion symmetries, has attracted considerable attention owing to its unique physical phenomena, including cross-correlated responses such as current-induced magnetization (CIM) and chiral phonons. Recently, it has been established that chirality is characterized by electric toroidal (ET) multipoles: the ET monopole $G_0$ in cubic systems and the ET quadrupole $G_u$ in noncubic systems. In this paper, we investigate achiral-to-chiral (AtC) structural phase transitions driven by atomic displacements and construct $G_{0,u}$ as explicit functions of the displacement order parameter $\eta$ based on a group-theoretical approach. We show that the leading-order dependence of $G_{0,u}(\eta)$ is determined by the symmetry of the parent structure and the character of the displacive mode, providing a symmetry-based classification of AtC transitions beyond a binary distinction between achiral and chiral phases. We also demonstrate that $G_{0,u}(\eta)$ is directly reflected in observable quantities such as CIM and chiral phonon splitting (CPS), both of which scale consistently with $G_{0,u}(\eta)$. We further clarify the microscopic mechanism by which AtC transitions give rise to chiral phonons and CPS through the coupling between $G_{0,u}(\eta)$ and phonon degrees of freedom.

Three lines of second-order phase transitions between the normal phase and two distinct superconducting phases meet at a single point on the phase diagram of UTe$_2$. Although it is commonly believed otherwise, such triple points are not subject to thermodynamic constraints. The phase diagram is interpreted within Landau theory in terms of two superconducting order parameters with different gauge symmetries. Such an interpretation is unique under the assumption of spatial uniformity.

Log-conformation and square-root reconstructions preserve positive definiteness in high-Weissenberg viscoelastic simulations, but positivity alone does not guarantee compatibility with the discrete free-energy balance. We identify three reconstruction-level mechanisms by which strictly positive tensors can still generate nonphysical behavior: Jensen-type entropy bias, exponential amplification of logarithmic perturbations in highly stretched states, and sign-indefinite polymeric-work defects caused by using incompatible tensors in stress work and entropy variables. We formulate an entropy-compatible reconstruction principle and a corrected logarithmic reconstruction selected by a least-damping entropy constraint. The correction is local, positive, computable by bisection, spectrally controlled, and compatible with coupled velocity–pressure–conformation time stepping. We prove existence of the maximal admissible parameter, convexity of the entropy profile along the logarithmic path, a compatible free-energy estimate, a defect-budget estimate for noncompatible reconstructions, asymptotic inactivity on high-order admissible defects, and a conditional high-stretch resolution advantage in log-relative and entropy metrics. Reproducible diagnostics compare logarithmic, square-root, and linear reconstructions and verify the predicted entropy defects, work defects, stress-force errors, and high-Weissenberg accumulation.

We study mobility heterogeneity in a two-dimensional Gaussian lattice polymer using dynamic Monte Carlo simulations. The polymer dynamics is generated from a local three-monomer move dictionary, which explicitly enumerates allowed bond-preserving updates on a square lattice. As a homogeneous benchmark, this dictionary reproduces the expected Rouse-like behavior of an ideal chain, including the crossover in monomer mean-squared displacement (MSD) and the center-of-mass diffusion scaling $D_{\rm cm} \sim N^{-1}$. We then introduce a two-block version of the model in which the two halves of the chain are updated with different attempt rates, $\omega_A$ and $\omega_B$, while the local move dictionary remains unchanged. For $\rho=\omega_A/\omega_B>1$, the more frequently updated block shows a larger block-resolved MSD at early and intermediate times, producing a positive normalized MSD asymmetry. However, numerical measurements show that the center-of-mass diffusion coefficient remains consistent with $D_{\rm cm} \sim N^{-1}$ for all rate ratios studied. We invoke a simple coarse-grained Rouse argument to explain this result analytically. In this minimal Gaussian setting, rate-induced mobility heterogeneity modifies internal relaxation without changing the Rouse scaling of center-of-mass transport.

Precision interferometry with atomic wavepackets confined in a one-dimensional optical lattice is an emergent paradigm in quantum sensing of forces and fields, with applications in gravimetry, accelerometry, geophysics, and fundamental physics tests. We report on the realization of a lattice-trapped interferometer where the two arms are sourced from a weakly-interacting ytterbium Bose-Einstein condensate, coherently split and trapped by pulsed optical standing waves before recombination. We directly observe atomic interactions through contrast changes and phase shifts of the interferometer. By changing either the atom number or the sample volume to vary the density, we demonstrate control over interactions and optimize interferometer performance. Our observations are effectively captured by a mean-field theoretical model of the system. This work experimentally probes the boundary where improved performance from source brightening through higher phase space density transitions into a regime beyond single-atom physics in lattice-trapped atom interferometry, and opens a door to incorporating many-body effects for metrological advances in such platforms.

Polymer solutions exhibit anomalous flow thickening – marked by an abrupt increase in the macroscopic flow resistance – above a threshold flow rate in a porous medium, but not in bulk solution. This phenomenon has evaded a mechanistic description for over half a century. Here, we develop a model that quantitatively links pore-scale flow fields and fluid rheology to macroscopic flow thickening, and validate it in experiments in two- and three-dimensional (2D and 3D) porous media. We find that flow thickening in ordered media is governed by polymer extension at stagnation points – in contrast to disordered media, where viscous dissipation by unsteady flow fluctuations also contributes substantially. Our results provide a foundation to predict and control such flows in energy, environmental, industrial, and microfluidic applications.

Hot-exciton relaxation in semiconductor nanocrystals (NCs) is often described using perturbative theories, but their accuracy is difficult to assess for realistic exciton–phonon Hamiltonians. Here, we benchmark the perturbative quantum master equation (QME) and several mixed quantum–classical (MQC) methods against fully quantum mechanical dynamics. Using atomistically parameterized models for CdSe core and CdSe/CdS core–shell NCs, we find that bare CdSe exhibits an ultrafast initial decay followed by slower cooling, whereas the core–shell system is dominated by the slower component. Analysis of reduced models shows that the ultrafast component arises from rapid diabatic state mixing driven by thermal fluctuations of low-frequency phonons, rather than from nuclear-assisted energy relaxation. The QME captures the initial fast decay but can fail for the slower relaxation in the diabatic representation, while the mapping approach to surface hopping (MASH) gives the most consistent agreement with both benchmark dynamics and equilibrium populations. These results establish a benchmark for exciton-cooling dynamics in NCs and clarify the physical regimes in which widely used approximate methods are reliable.

We construct and evaluate group-equivariant neural networks for the prediction of the two-dimensional $Q$-tensor order parameter of nematic liquid crystals from synthetically generated microscopic textures. Seven architectures, equivariant to cyclic groups $C_k$ of order $k$ for $k=4,\,8,\,16,\,32,\,64,\,128,\, 256$, are built using a combination of weight-sharing constraints, equivariant activations and regularization techniques. To do this, we construct rotation-like permutation matrix groups with elements $\varrho_{C_k}(g)$ that act on row-wise vectorized images, thereby approximating a $\frac{2\pi}{k}$ rotation of the circular subdomain on square images. We show that all seven equivariant models satisfy the $Q$-tensor equivariance constraint to within single-precision floating point accuracy. Comparing against approximate parameter-matched non-equivariant benchmarks, with and without data augmentation, we find that the equivariant models consistently achieve lower errors and generalize more robustly to unseen defect configurations. Performance increases with group order, suggesting that the incorporation of finer rotational symmetry leads to lower errors.

Spontaneous symmetry breaking is a well-understood mechanism for generating distinct phases of matter. Recently, the notion of symmetry has been broadened to include operations without inverses, leading to the concept of non-invertible symmetries. How do symmetry-breaking phases associated with non-invertible symmetries differ from those arising from conventional invertible symmetries? We address this question using concrete lattice models of the gapped phases with non-invertible Rep($H_8$) symmetry as an example. We find that, despite the symmetry being non-invertible, the symmetry-breaking phases can still be characterized by the long-range correlation of local order parameters, which obey a more general algebraic structure than in the invertible setting. Furthermore, via generalized gauging, certain non-invertible symmetry-breaking transitions can be mapped to deconfined quantum critical points of invertible symmetries, and vice versa. We establish precise conditions under which this duality holds and illustrate them with several families of examples, providing a systematic route to studying beyond-Landau phase transitions.

We investigate the charge and spin transport properties of a Weyl semimetal under an external magnetic field using a low-energy effective theory. By performing a chiral transformation, we remove the axial term from the fermionic Lagrangian, while its physical effects are retained through the system's electromagnetic response. This response, derived from integrating out the fermionic degrees of freedom, takes the form of axionic electrodynamics and enters the Dirac equation via minimal coupling. The resulting dynamics separate naturally into magnetic and electric components: the magnetic sector admits a supersymmetric factorization, while the electric part exhibits a PT-supersymmetric structure. Robin boundary conditions are applied to the spinor, setting the energy spectrum and defining exact spinor solutions. We obtain the chiral projections of probability and current densities, exhibiting a chiral imbalance in the material. We show that in the x-direction, only one chirality contributes to the chiral current ($j^x_l = 0$). Spin density and currents where also computed. Our results demonstrate how the interplay between axionic response and supersymmetry governs transport phenomena in our specific setup, offering novel insights into the effective field theory description of Weyl semimetals.

The entropy production rate is central to the study of non-equilibrium systems. This parameter is closely connected to violation of time-reversal symmetry, energy consumption, efficiency, and other properties of interest; in short, it quantifies how far a system is from thermodynamic equilibrium. Standard formulas for the entropy production require knowledge of the system's underlying dynamics, but this knowledge may be hard to acquire in practice. Here, I present a method for inferring the entropy production rate of a Markovian system from the sequence of states that the system occupies on a single long trajectory or many shorter trajectories, and the total time of the trajectory or trajectories. The method does not require knowledge of the dwell times in the various states, the times at which transitions occur, or of the transition rates characterizing the Markov process.

We show that the local gauge-invariance of the quantum geometric tensor (QGT) defined in the two-dimensional Block-momentum (BM) space of a generic $N$-band (arising out of sub-lattice degrees of freedom) insulator represented by a tight-binding hamiltonian, leads to the existence of zero modes of non-abelian Dirac operator in such BM space. These zero modes in the two-dimensional Brillouin zone torus $T^{2}$, determines the probability amplitudes associated with the $N$-component ground state wave-function under adiabatic approximation. We analytically derive the expansion coefficients of maximally localized Wannier function in one-dimension from the solutions of these zero mode equations, and obtain momentum-space generalization of celebrated Laughlin gauge condition as a by-product.The commutator of these non-abelian Dirac operators define the algebra of the guiding center co-ordinates which provide a more general frame-work to study such systems than one based on the Landau-level analogues. In the ideal quantum geometric limit, these zero-mode solutions become self-dual momentum-space instantons, and can be linked to the non-abelian generalization of the vortexability criterion of Chern bands in momentum-space. We derive some exact solutions of such zero-mode on the complex torus geometry, and discuss implications of this framework for realistic systems such as two-dimensional topological insulators, rhombohedral $N_{L}$-layer graphene.

Magic-angle twisted bilayer graphene Josephson junctions (MATBG-JJ) with a gate-tunable valley-polarized weak link exhibit an intrinsic Josephson diode effect originating from broken symmetries associated with valley polarization and band-structure anisotropy. Exploiting this nonreciprocal superconducting platform, we construct quantum Stirling (QSC), Otto (QOC), and Carnot (QCC) thermodynamic cycles, where the valley-polarization potential $\Delta_v$ acts as the principal control parameter, in contrast to conventional Josephson thermal machines driven by superconducting phase bias. We systematically compare the performance of MATBG-based Josephson diode thermal machines (MATBG-JDTM) with MATBG-based Josephson junction thermal machines (MATBG-JJTM) and AA-stacked bilayer graphene Josephson junction thermal machines (AABLG-JJTM). Owing to the flat-band-enhanced density of states and electrically tunable nonreciprocal transport in MATBG, both MATBG-JDTM and MATBG-JJTM exhibit significantly enhanced work output and efficiency over a broad operating regime compared to AABLG-JJTM. In particular, the gate-controlled MATBG-JDTM provides a flux-free alternative to conventional phase-driven architectures, mitigating limitations associated with magnetic-flux control and flux-noise effects. Our results establish MATBG Josephson diode platforms as a promising route toward electrically tunable quantum thermal machines and nonreciprocal superconducting caloritronics.

Spatial control of topology is highly desirable for realizing tunable quantum functionalities in materials. Moiré superlattices formed by twisting van der Waals heterostructures provide a natural platform for spatially modulated electronic phases, yet the emergence of tunable topological domains in these systems remains largely unexplored. Here we show that structural relaxation in twisted bilayer BiSb drives the formation of a distinct moiré topological phase, characterized by coexisting topologically nontrivial (Z$_2$ = 1) and trivial (Z$_2$ = 0) domains within a single moiré unit cell. As the twist angle is reduced, relaxation-induced modulation of the interlayer separation stabilizes an expanding network of topological regions embedded within trivial backgrounds of the moiré unit cell. The resulting internal domain boundaries host topologically-protected gapless 1D edge states that are directly visible in our simulated scanning-tunnelling microscopy maps.Furthermore, we demonstrate that the real-space topological domain structure and associated gapless edge states can be reversibly tuned by an out-of-plane electric field. Together, these results establish twisted BiSb as a promising platform for programmable topological domain patterning, where intrinsic networks of edge channels can be continuously tuned and electrically reconfigured in moiré materials.

The recent discovery of altermagnetism has sparked growing interest in compensated magnetic systems as promising platforms for highly scalable spintronics. Altermagnetism is a distinct magnetic order where opposite spin sublattices are connected by rotation, yielding zero net magnetization but momentum-dependent spin splitting. To date, experimental verification of altermagnetic order has been achieved predominantly through bulk-sensitive techniques, including spin-dependent electronic spectra and transport responses. However, direct atomic-scale evidence that explicitly correlates crystal symmetry, local structural distortions, and magnetic ordering has remained unexplored. Here, we report the direct atomic-scale observation of coexisting polar distortions and altermagnetic order in MnTe, combining atomic resolution scanning transmission electron microscopy (STEM) imaging with electron magnetic chiral dichroism (EMCD) measurements. We reveal that MnTe is not an ideal uniform P63/mmc g-wave altermagnet at the atomic scale. Instead, it hosts ubiquitous inversion-symmetry-breaking distortions that lower the spin-space-group (SSG) symmetry, admits d-wave altermagnetic components, and in lower-symmetry regimes, even allow s-wave spin splitting (net magnetization). The coexistence of ferroelectric signatures and altermagnetic order establishes local lattice symmetry in MnTe as a control knob for altermagnetic spin splitting, spin current generation, and multiferroic memory applications.

Multimode cavity optomechanical systems allow light to couple otherwise non-interacting mechanical resonators, enabling non-Hermitian phenomena such as exceptional points, where eigenfrequencies and eigenvectors of coupled modes coalesce. Accessing an exceptional point and its nearby parameter space is a first step towards chiral mode dynamics and topological state transfer. Diamond optomechanical devices support strong coherent optomechanical coupling required to tune resonances to an exceptional point, as well as strain-coupling to spin-defects for hybrid quantum technologies, but have not yet been used for multimode non-Hermitian physics. Here we tune to an exceptional point in a diamond optomechanical crystal, which uses structural symmetry breaking to produce two high-frequency mechanical resonances coupled to an optical cavity. The exceptional point is reached within a stable operating window below the phonon-lasing threshold, and we observe asymmetric redistribution of optomechanical damping and anti-damping between hybridized modes. These results establish diamond optomechanical crystals as a platform for non-Hermitian optomechanics, opening routes to topological mechanical dynamics in hybrid spin-phonon interfaces.

Quantum simulations are traditionally confined to exploring dynamics starting from unentangled or low-entanglement states due to severe bottlenecks in protocol design, hardware performance, and classical verification. Here, we report the first quantum simulation of non-equilibrium dynamics initiated directly from a many-body critical ground state. Using a fully-connected trapped-ion processor, we prepare the critical ground state of a transverse-field Ising model via a hardware-tailored, logarithmic-depth quantum circuit based on multi-scale entanglement renormalization. Following this initialization, we apply a deep Floquet drive that maintains emergent conformal symmetry, enabling us to benchmark lattice dynamics against analytical results from continuum theory. In the resulting conformal heating phase, we extract a central charge consistent with the Ising universality class ($c=1/2$) from the universal decay of the Loschmidt echo and observe spatial energy localization predicted by field theory. Conversely, the non-heating phase exhibits global finite-time revivals. This work establishes a scalable and versatile framework for exploring critical quantum dynamics.

We examine the emergence of topological Anderson insulating phases in the spinful Haldane model with Hubbard and next-neighbor density-density interactions, subject to Anderson disorder. Using finite-size exact diagonalization, we characterize the phases that arise from the interplay between topology, interactions, and disorder. In addition to standard $C=2$ topological Anderson phases, we observe an antiferromagnetic $C=1$ topological Anderson phase, consistent with the antiferromagnetic quantum anomalous Hall insulator previously identified in the clean model at finite staggered mass. We further analyze these phases using a neural network trained on the exact diagonalization data. Our results support the hypothesis that an explicit charge imbalance is required to induce the $C=1$ phase, generated by Anderson disorder rather than by a staggered mass.

Cobalt-based quantum magnets forming layered honeycomb arrangements have attracted much attention recently, as they are considered as a potential platform for materials with exotic Kitaev spin exchange. Amongst the discussed candidate materials are Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$, both possessing a low-temperature ground state with some form of antiferromagnetic ordering (zigzag or triple-$Q$), similar to Na$_2$IrO$_3$ and $\alpha$-RuCl$_3$. Here we report inelastic neutron scattering experiments on the quantum magnet Li$_3$Co$_2$SbO$_6$, which features ferromagnetic honeycomb planes with opposite magnetizations in neighboring planes. By comparing with linear spin wave theory, we show that the magnetic properties of Li$_3$Co$_2$SbO$_6$ can be well-modelled by an extended Kitaev–Heisenberg model, establishing it as a Kitaev-ferromagnet, or more specifically, as a Kitaev A-type antiferromagnet. Our analysis is complemented by magnetic field measurements and simulations.

Designing superconducting quantum hardware requires simulation tools that can account for various deviations from ideal scenarios. This, in turn, requires approaches that automatically detect certain structures and leverage them to make the computation affordable. Here, we develop a tensor network based technique to simulate the Lindblad dynamics of a few interacting bosonic modes with a focus on superconducting quantum circuits. The technique detects and takes advantage of two very common situations: (i) the density matrix being pure or not far from pure and (ii) the entanglement between different modes being moderate (typically qubit-like). However, (iii) the occupation of the modes can be arbitrarily high (making naïve truncations inefficient). To leverage these features, we use three different nested levels of tensor network compression: (i) we work with a global purification of the density matrix, (ii) we compress the connection between different modes to account for the moderate entanglement and (iii) we use a quantics representation of the Fock occupation number. We showcase the technique for the simulation of large cat qubits as well as for the ionization of transmon qubits, demonstrating orders-of-magnitude speed-up with respect to brute force approaches. In the latter example, it brings the simulation, previously reported on a large supercomputing infrastructure, to laptop level. The favorable scaling with system size should bring genuine computer assisted design of these systems within scope.

The configuration space of causal sets is vast. It is a critical goal to map out this space. Here, we take a practical step towards this goal. We investigate nine classes of causal sets, most of them not studied before. These include manifoldlike causal sets with inhomogeneous Ricci curvature, both topologically trivial and nontrivial. We also study classes of non-manifoldlike causal sets, including lattices, layered orders as well as Lorentzian quasicrystals. Finally, we study classes of causal sets that are not manifoldlike, but are expected to become manifoldlike under a suitable coarse-graining process. We use this broad range of distinct classes of causal sets as a testbed for observables. Rather than focusing on continuum-geometry inspired observables, such as curvature invariants, which often exhibit large fluctuations and are computationally very expensive, we focus on graph observables, including some observables that constitute subgraph statistics and some that are global. We find that three observables, namely the link degree distribution, the eigenvalues of the graph Laplacian of the symmetrized Hasse diagram and the recently proposed abundance of causal intervals, can distinguish between the distinct classes of causal sets. This is made possible by the small fluctuations that these observables have in most classes.

We describe the dynamics of many-body quantum chaotic systems at all time scales by studying the Green's and out-of-time order correlation (OTOC) functions of the four-body, $N$-Majorana Sachdev-Ye-Kitaev model. By combining the scramblon formalism and random-matrix-theory techniques, we obtain analytical expressions for these functions at all times. The early exponential growth of the OTOC is followed by an exponential decay at a rate governed by that of the Green's function (the real part of the leading complex Ruelle-Pollicott resonances). For late times that scale exponentially with $N$, both functions have a dip-ramp-plateau pattern for $N \mathrm{mod}8 = 2, 6$ that deviates substantially from the ergodic prediction due to local-in-energy correlations of matrix elements and eigenvalues, even after the Heisenberg time.

We describe the quantum phase transitions in the ferromagnetic Dicke-Ising model using a Landau theory approach. The theory quantitatively captures the change from a second- to a first-order transition between the normal and superradiant phases through a tricritical point. We identify virtual nearest-neighbor double spin-flip processes as the crucial mechanism responsible for this behavior. The tricritical point constitutes a quantum phase transition above the upper critical dimension. We discuss the modifications to finite-size scaling required for the correct interpretation of numerical data at the tricritical point. Our results emphasize the need for adapted finite-size scaling forms in all-to-all interacting quantum systems and establish the ferromagnetic Dicke-Ising model as a paradigmatic platform for quantum phase transitions above the upper critical dimension, encompassing both standard $\phi^4$ criticality and beyond.

We theoretically investigate the Aharonov-Bohm effect in a thick-walled Weyl semimetal (WSM) cylinder subject to an external axial magnetic field. By employing a low-energy effective Hamiltonian, we analytically solve the eigenvalue problem for both infinite and finite-length cylindrical geometries. We apply infinite-mass boundary conditions at the radial walls and MIT bag boundary conditions at the cylinder caps to properly account for intra-node confinement and inter-valley scattering, respectively. Our numerical results demonstrate that the spatial separation of the Weyl nodes acts as an internal chiral gauge field. This geometric field intrinsically breaks time-reversal (TR) symmetry, lifting the chiral degeneracy even at zero external flux. This symmetry breaking manifests as spontaneous persistent currents and the unfolding of conductance channels. Furthermore, longitudinal confinement induces propagation-direction-dependent energy splitting, altering the partial density of states and causing spatio-chiral current imbalances.

Resistance in standard conductors decreases with increasing cross-section. Yet, in low-dimensional superconductors and superfluids residual resistance arises from topological fluctuations of the order parameter manifesting as phase slips in one-dimensional (1D) and vortices in two-dimensional (2D) systems. How resistance and dissipation evolve as geometry interpolates between these regimes remains an open question. This evolution is masked in solid-state experiments by disorder, impurities, and geometric imperfections, and poses theoretical challenges due to competing dissipative processes and pronounced finite-size effects. Here, we use a defect-free unitary Fermi gas in a digitally programmable transport geometry to isolate geometric effects on superfluid dissipation and discover a paradox: in the crossover from 1D to 2D, the resistance reaches a minimum. There, widening a channel increases its resistance. Narrower, quasi-1D channels show dissipation described by Langer-Ambegaokar-McCumber-Halperin theory of phase slips. In this regime, varying the channel width yields the predicted exponential scaling of the activation factor over more than ten orders of magnitude. Wider, quasi-2D channels show dissipation consistent with a finite-size vortex model. The minimal dissipation in the dimensional crossover reflects a transition in the dominant dissipative mechanism, with both phase slips and vortices simultaneously suppressed. Our measurements suggest a route to minimizing dissipation in superconducting devices and provide a benchmark for theoretical efforts aimed at describing the dimensional crossover.