One of the important features of non-Hermitian Hamiltonians is the existence of a unique type of singularities, the so-called exceptional points (EPs). When the corresponding systems operate around such singularities, they exhibit ultrasensitive behavior that has no analog in conservative systems. An alternative way to realize such ultra-sensitivity relies on asymmetric couplings. Here we provide a comprehensive analysis based on pseudospectra, that shows the origin of exponential sensitivity, without relying on topological zero modes or the localization of all eigenstates (skin effect), but on the underlying extreme lattice non-normality. In particular, we consider four different types of lattices (Hatano-Nelson, Sylvester-Kac, non-Hermitian Su-Schrieffer-Heeger and a non-Hermitian random lattice) and identify the conditions for exponential sensitivity as a function of the lattice size. Complex and structured pseudospectra reveal the signatures of exponential sensitivity both on the eigenvalue spectra and on the underlying dynamics. Our study, may open new directions on studies related to the exploitation of non-normality for constructing ultra-sensitive systems that do not rely on the existence of EPs.

In this article it is argued that synthetic axions, emergent collective excitations in topological insulators or Weyl semimetals, hybridize with the cosmological axion, a compelling dark matter candidate via a common two-photon decay channel since they both couple to electromagnetic fields via a Chern-Simons term. We point out an analogy to a V-type three-level system with the two upper levels identified with the synthetic and cosmological axions decaying into a two-photon state. The Weisskopf-Wigner theory of spontaneous decay in multilevel atoms is complemented and extended to describe the dynamics of hybridization. The final two-photon state features both kinematic and polarization entanglement and displays quantum beats as a consequence of the interference between the decay paths. An initial population of either axion induces a population of the other via hybridization. Consequently, a dark matter axion condensate induces a condensate of the synthetic axion, albeit with small amplitude. We obtain a momentum- and polarization-resolved Hanbury Brown-Twiss (HBT) second-order coherence describing coincident correlated two-photon detection. It exhibits quantum beats with a frequency given by the difference between the energies of the synthetic and cosmological axion and perhaps may be harnessed to detect either type of axion excitations. The case of synthetic axions individually is obtained in the limit of vanishing coupling of the cosmological axion and features similar two-photon correlations. Hence second-order (HBT) two-photon coherence may provide an alternative detection mechanism for emergent condensed matter axionic collective excitations. Similarities and differences with parametrically down converted photons are discussed.

We investigate the continuous generation of bubbles from a bath of air in viscous liquid in a confined geometry. In our original setup, bubbles are spontaneously generated by virtue of buoyancy and a gate placed in the cell: the gate acts like an inverted funnel trapping air beneath it before continuously generating bubbles at the tip. The dynamics is characterized by the bubble-formation period and the bubble size as a function of the amount of air under the gate. By analyzing the data obtained for various parameters, we clearly identified that the dynamics of the bubble formation is governed by dissipation in the viscous fluid beneath the trapped air balanced by a gravitational energy change due to buoyancy, after examining numerous possibilities of dissipation, which demonstrates the potential of scaling analysis in significantly complex cases. Furthermore, we uncover a general mechanism of pinching-off at low Reynolds numbers, which convincingly explains the bubble size: in the present case viscosity plays a vital role, different from the conventional mechanism of Tate proposed in 1864, in which gravity competes with capillarity. Accordingly, the present study significantly and fundamentally advances our knowledge of the generation and pinch-off of bubbles, with the results relevant for a wide variety of applications in many fields. In particular, the present study demonstrates a promising avenue in microfluidics for understanding physical principles by scaling up the system, without losing the characteristics of the flow at low Reynolds numbers.

The destruction of metallicity due to the mutual Coulomb interaction of quasiparticles gives rise to fascinating phenomena of solid state physics such as the Mott metal-insulator transition and pseudogap. A key observable characterizing their occurrences is the single-particle spectral function, determined by the fermionic self-energy. In this paper, we investigate in detail how real space fluctuations are responsible for a self-energy that drives the Mott-Hubbard metal-insulator transition. To this aim, we first introduce a real space fluctuation diagnostics approach to the Hedin equation, which connects the fermion-boson coupling vertex $\lambda$ to the self-energy $\mathrm{\Sigma }$. Second, by using cellular dynamical mean-field theory calculations, we unambiguously identify nearest-neighbor antiferromagnetic excitations as the leading physical processes responsible for the destruction of metallicity across the transition.

When an ideal insulator is cooled, four regimes of thermal conductivity are expected to emerge one after another. Two of these, the Ziman and the Poiseuille, are hydrodynamic regimes in which collision among phonons are mostly normal. It has been difficult to observe them, save for a few insulators with high levels of isotopic and chemical purity. Our thermal transport measurements, covering four decades of temperatures between 0.1 K and 900 K, reveal that sapphire displays all four regimes, despite its isotopic impurity. In the Ziman regime, the thermal conductivity exponentially increases, attaining an amplitude as large as 35 000 W/Km. We show that the peak thermal conductivity of ultrapure, simple insulators, including diamond, silicon, and solid helium, is set by a universal scaling depending on isotopic purity. The thermal conductivity of sapphire is an order of magnitude higher than what is expected by this scaling. We argue that this may be caused by the proximity of optical and acoustic phonon modes, as a consequence of the large number of atoms in the primitive cell.

The supersolid is a long-sought phase in condensed matter physics, characterized by the coexistence of density wave and superfluid orders. This phase is counterintuitive, as different symmetry-breaking orders typically compete with one another. A deeper understanding of how such a state forms in condensed matter systems remains an open question, especially in quasi-one-dimensional correlated systems. In this work, we investigate the emergence of supersolids in Luttinger-Emery liquids using a variational method. As the system consists of coupled Luttinger-Emery liquid chains, we refer to this phase as a quasi-one-dimensional supersolid. Notably, we demonstrate that the quasi-one-dimensional supersolid phase is energetically favorable in chains with finite size or short-range order. Furthermore, we investigate the collective dynamics of these coexisting charge density waves and superconducting states, identifying a quasi-Goldstone mode. Our theory provides valuable insights into both the ground state and the dynamic properties of supersolids in strongly correlated systems.

From self-assembly and protein folding to combinatorial metamaterials, a key challenge in material design is finding the right combination of interacting building blocks that yield targeted properties. Such structures are fiendishly difficult to find—not only are they rare, but often the design space is so rough that gradients are useless and direct optimization is hopeless. Here, we design ultrarare combinatorial metamaterials, capable of multiple desired deformations, by introducing a twofold strategy that avoids the drawbacks of direct optimization. We first combine convolutional neural networks with genetic algorithms to prospect for metamaterial designs with a potential for high performance; in our case, these metamaterials have a high number of spatially extended modes—they are pluripotent. Second, we exploit this library of pluripotent designs to generate metamaterials with multiple target deformations, which we finally refine by strategically placing defects. Our multishape metamaterials would be impossible to design through trial-and-error or standard optimization. Instead, our data-driven approach is systematic and ideally suited to tackling the large and intractable combinatorial problems that are pervasive in material science.

We present a combined experimental and theoretical investigation of the formation and decay kinetics of vortices in two-dimensional, compressible quantum turbulence. We follow the temporal evolution of a quantum fluid of exciton polaritons, hybrid light-matter quasiparticles, and measure both phase and modulus of the order parameter in the turbulent regime. Fundamental topological conservation laws require that the formation and annihilation of vortices also involve critical points of the velocity field, namely nodes and saddles. Identifying the simplest mechanisms underlying these processes enables us to develop an effective kinetic model that closely aligns with the experimental observations, and shows that different processes are responsible for vortex number growth and decay. These findings underscore the crucial role played by topological constraints in shaping nonlinear, turbulent evolution of two-dimensional quantum fluids.

A common scenario in a variety of biological systems is that multiple particles are searching in parallel for an immobile target located in a bounded domain, and the fastest among them that arrives to the target first triggers a given desirable or detrimental process. The statistics of such extreme events—the fastest first-passage to the target—is well-understood by now through a series of theoretical analyses, but exclusively under the assumption that all $N$ particles start simultaneously, i.e., all are introduced into the domain instantly, by $\delta$-function-like pulses. However, in many practically important situations this is not the case: to start their search, the particles often have to enter first into a bounded domain, e.g., a cell or its nucleus, penetrating through gated channels or nuclear pores. This entrance process has a random duration so that the particles appear in the domain sequentially and with a time delay. Here we focus on the effect of such an extended-in-time injection of multiple particles on the fastest first-passage time (fFPT) and its statistics. We derive the full probability density function $H_N\left(t\right)$ of the fFPT with an arbitrary time-dependent injection intensity of $N$ particles. Under rather general assumptions on the survival probability of a single particle and on the injection intensity, we derive the large-$N$ asymptotic formula for the mean fFPT, which is quite different from that obtained for the instantaneous $\delta$-pulse injection. The extended injection is also shown to considerably slow down the convergence of $H_N\left(t\right)$ to its large-$N$ limit—the Gumbel distribution—so that the latter may be inapplicable in the most relevant settings with few tens to few thousands of particles.

The string landscape accommodates a broad range of possible effective field theories. This poses a challenge for extracting verifiable predictions as well as falsifiable signatures of string theory. Motivated by these considerations, in this work we observe that all known stringy standard models support only low-dimensional representations of the gauge group. While it is in principle possible to produce contrived models with higher-dimensional representations, these generically appear in a tower of states with lighter ones in lower-dimensional representations, i.e., not in isolation. With this in mind, we consider the phenomenologically well-motivated scenario given by adding a single Majorana field in a real, $n$-dimensional representation of $SU{\left(2\right)}_L$ with $n\ge 5$ and nothing else. This scenario is not realized in any known string construction, and we conjecture that this is true of string theory in general. Detection of this scenario would thus amount to falsifying the (known) string landscape. We recast existing LHC searches for new electroweak states to extract updated bounds on this class of scenarios. Improved limits from future colliders and dark matter detection experiments provide additional routes to potentially falsifying string theory.

We present a scheme to realize a topological superconducting system supporting Majorana zero modes, within a number-conserving framework suitable for optical-lattice experiments. Our approach builds on the engineering of pair-hopping processes on a ladder geometry, using a sequence of pulses that activate single-particle hopping in a time-periodic manner. We demonstrate that this dynamic setting is well captured by an effective Hamiltonian that preserves the parity symmetry, a key requirement for the stabilization of Majorana zero modes. The phase diagram of our system is determined using a bosonization theory, which is then validated by a numerical study of the topological bulk gap and entanglement spectrum using matrix product states. Our results indicate that Majorana zero modes can be stabilized in a large parameter space, accessible in optical-lattice experiments.

The control of wave scattering in complex non-Hermitian settings is an exciting subject—often challenging the creativity of researchers and stimulating the imagination of the public. Successful outcomes include invisibility cloaks, wavefront shaping protocols, active metasurface development, and more. At their core, these achievements rely on our ability to engineer the resonant spectrum of the underlying physical structures, which is conventionally accomplished by carefully imposing geometrical and/or dynamical symmetries. In contrast, by taking active control over the boundary conditions in complex scattering environments that lack artificially imposed geometric symmetries, we demonstrate via microwave experiments the ability to manipulate the spectrum of the scattering operator. This active control empowers the creation, destruction, and repositioning of exceptional point degeneracies (EPDs) in a two-dimensional parameter space. The presence of EPDs signifies a coalescence of the scattering eigenmodes, which dramatically affects transport. The scattering EPDs are partitioned in domains characterized by a binary charge, as well as an integer winding number, they are topologically stable in the two-dimensional parameter space, and they obey winding number-conservation laws upon interactions with each other, even in cases in which Lorentz reciprocity is violated; in this case, the topological domains are destroyed. The ramifications of this understanding are the proposition for a unique input-magnitude and phase-insensitive 50:50 in-phase/quadrature (I/Q) power splitter. Our study establishes an important step towards complete control of scattering processes in complex non-Hermitian settings.

Accurate interaction potentials between microscopic components such as colloidal particles or cells are crucial to understanding a range of processes, including colloidal crystallization, bacterial colony formation, and cancer metastasis. Even in systems where the precise interaction mechanisms are unknown, effective interactions can be measured to inform simulation and design. However, these measurements are difficult and time-intensive, and often require conditions that are drastically different from in situ conditions of the system of interest. Moreover, existing methods of measuring interparticle potentials rely on constraining a small number of particles at equilibrium, placing limits on which interactions can be measured. We introduce a method for inferring interaction potentials directly from trajectory data of interacting particles. We explicitly solve the equations of motion to find a form of the potential that maximizes the probability of observing a known trajectory. Our method is valid for systems both in and out of equilibrium, is well-suited to large numbers of particles interacting in typical system conditions, and does not assume a functional form of the interaction potential. We apply our method to infer the interactions of colloidal spheres from experimental data, successfully extracting the range and strength of a depletion interaction from the motion of the particles.

We have investigated the low temperature $\left(T\right)$ transport properties of fractional quantum Hall (FQH) states in a high-mobility two-dimensional hole gas. According to the composite fermion (CF) model, FQH states stemming from a half-filled Landau level, specifically at fillinsg factors $\nu =p/\left(2p+1\right)$ ($p=\pm 1,\pm 2,\pm 3,...$), can be associated with two-flux-attached CFs at the corresponding Lambda filling factor $p$. The zero-resistance minima and Hall plateaus of these states exhibit unusual temperature dependencies, characterized by rapid increases in width below a threshold temperature around $100\mathrm{mK}$. Differential conductivity measurements from Corbino samples reveal that the regimes surrounding the CF liquid display clear nonlinear transport characteristics. This nonlinearity implies that each CF liquid is surrounded by CF solid phase composed of dilute CF excitations. Quantitatively, the applied electric field $E$ influences the motion of CF solid in a way analogous to $T$, which is dubbed the “$E-T$ duality.” Our analysis indicates that this $E-T$ duality is consistent with the Berezinskii-Kosterlitz-Thouless theory in two-dimensional phase transitions.

Understanding single photon emission from defects in hexagonal boron nitride (h-BN) is an essential yet challenging step towards further utilizing the material as a room-temperature quantum device. Here, we systematically examine potential luminescence candidates in h-BN using the full configuration interaction quantum Monte Carlo approach. With such a high-level treatment of electron correlation, we can finally determine the electronic states of all the defects studied, revealing high-spin ground states for quantum manipulation and correcting previous misunderstandings. Furthermore, by computing the low-lying electronic states and analyzing the corresponding many-body wave functions, we identify two potential sources for the mysterious luminescence band in the visible region, including a doublet-doublet transition. Our calculations shed light on the intricate correlated electronic states of single photon emitters in h-BN, and establish a reliable theoretical foundation for addressing other challenges beyond the electronic structure.

We investigate the transient and steady-state dynamics of the Bennati-Dragulescu-Yakovenko money game in the presence of probabilistic cheaters, who can misrepresent their financial status by claiming to have no money. We derive the steady-state wealth distribution per player analytically, and we show how the presence of hidden cheaters can be inferred from the relative variance of wealth per player. In scenarios with a finite number of cheaters amidst an infinite pool of honest players, we identify a critical probability of cheating at which the total wealth owned by the cheaters experiences a second-order discontinuity. Below this point, the transition probability to lose money is larger than the probability to gain; conversely, above this point, the direction is reversed. We further establish a threshold cheating probability at which cheaters collectively possess half of the total wealth in the game. Lastly, we provide bounds on the rate at which both cheaters and honest players can gain or lose wealth, contributing to a deeper understanding of deception in asset-exchange models.

The vertex model for epithelia models the apical surface of a tissue by a tiling, with polygons representing cells and edges representing cell-cell junctions. The mechanics are described by an energy governed by deviations from a target area and target perimeter for each cell. It has been shown that the target perimeter $p_0$ governs a solid-to-fluid phase transition: when the target perimeter is low, there is an energy barrier to rearrangement, and when it is high, cells may rearrange for free and the tissue can flow like a liquid. One simplification often made is modeling junctions using straight edges. However, the Young-Laplace equation states that interfaces should be circular arcs, with the curvature being equal to the pressure difference between the neighboring cells divided by the interfacial tension. Here, we investigate how including curved edges alters the mechanical properties of the vertex model and the equilibrium shape of individual cells. Importantly, we show how curved edges shift the solid-to-fluid transition point, from $p_0=3.81$ to $p_0=3.73$, allowing tissues to fluidize sooner than in the traditional model with straight edges.

We report on numerical simulations of the two-dimensional spin-1 Blume-Capel ferromagnet embedded in a triangular lattice. Utilizing a range of Monte Carlo and finite-size scaling techniques, we explore several critical aspects along the crystal field–temperature $(\mathrm{\Delta },T)$ transition line. Wang-Landau simulations measuring the joint density of states in combination with the method of field mixing allow us to probe the phase coexistence curve in high resolution, determining the tricritical point $({\mathrm{\Delta }}_{\mathrm{t}},T_{\mathrm{t}})$ with improved accuracy and verifying the tricritical exponents. Extensive multicanonical simulations identifying transition points across the phase diagram characterize the Ising universality class for $\mathrm{\Delta }<{\mathrm{\Delta }}_{\mathrm{t}}$ with precise determination of thermal and magnetic critical exponents expected in the second-order regime. On the other hand, for $\mathrm{\Delta }>{\mathrm{\Delta }}_{\mathrm{t}}$, a finite-size scaling analysis is dedicated to revealing the first-order signature in the surface tension that linearly increases upon lowering the temperature deeper into the first-order transition regime. Finally, a comprehensive picture of the phase diagram for the model is presented, collecting transition points obtained from the combined numerical approach in this study and previous estimates in the literature.

Single-mode fibers are used in fiber-optic gyroscopes to measure the Sagnac effect and are planned to be used in forthcoming experiments on the gravitationally induced phase shift in single photons. However, current theoretical models of such experiments are limited to ray-optics approximations or, if based on wave optics, to a restricted class of fiber alignments. To overcome these shortcomings, this paper develops a comprehensive perturbative scheme to solve for electromagnetic modes, i.e., monochromatic solutions to Maxwell's equations, of arbitrarily bent step-index fibers in general stationary space-times. This leads to transport equations for the electromagnetic phase and polarization that include the gravitational redshift, the Sagnac effect, a generalization of Rytov's law to curved space, a gravitational Faraday effect in the form of shift-induced gyrotropy, as well as inverse spin Hall effects caused by fiber bending, gravitational acceleration, and space-time curvature.

Convolutional neural networks (CNNs) have been employed along with variational Monte Carlo methods for finding the ground state of quantum many-body spin systems with great success. However, it remains uncertain how CNNs, with a model complexity that scales at most linearly with the number of particles, solve the “curse of dimensionality” and efficiently represent wavefunctions in exponentially large Hilbert spaces. In this work, we use methodologies from information theory, group theory and machine learning, to elucidate how CNN captures relevant physics of quantum systems. We connect CNNs to a class of restricted maximum entropy (MaxEnt) and entangled plaquette correlator product state (EP-CPS) models that approximate symmetry constrained classical correlations between subsystems. For the final part of the puzzle, inspired by similar analyses for matrix product states and tensor networks, we show that the CNNs rely on the spectrum of each subsystem's entanglement Hamiltonians as captured by the size of the convolutional filter. All put together, these allow CNNs to simulate exponential quantum wave functions using a model that scales at most linear in system size as well as provide clues into when CNNs might fail to simulate Hamiltonians. We incorporate our insights into a new training algorithm and demonstrate its improved efficiency, accuracy, and robustness. Finally, we use regression analysis to show how the CNNs solutions can be used to identify salient physical features of the system that are the most relevant to an efficient approximation. Our integrated approach can be extended to similarly analyzing other neural network architectures and quantum spin systems.