We address the formation of topological states in twisted circular waveguide arrays and find that twisting leads to important differences of the fundamental properties of new vortex solitons with opposite topological charges that arise in the nonlinear regime. We find that such system features the rare property that clockwise and counterclockwise vortex states are nonequivalent. Focusing on arrays with ${\mathcal{C}}_{6v}$ discrete rotation symmetry, we find that a longitudinal twist stabilizes the vortex solitons with the lowest topological charges $m=\pm 1$, which are always unstable in untwisted arrays with the same symmetry. Twisting also leads to the appearance of instability domains for otherwise stable solitons with $m=\pm 2$ and generates vortex modes with topological charges $m=\pm 3$ that are forbidden in untwisted arrays. By and large, we establish a rigorous relation between the discrete rotation symmetry of the array, its twist direction, and the possible soliton topological charges.

We report measurements of the Brillouin frequencies of acoustically driven metastable states of superfluid ${}^4\mathrm{He}$ at $T\sim 1\mathrm{K}$. This is done using a stimulated Brillouin gain spectrometer operating on a confined spatiotemporal domain ($\sim 40\mu \mathrm{m}$, 200 ns). Our work questions previous experimental results regarding the metastable states of liquid ${}^4\mathrm{He}$ and suggests that thermal effects or vortices can play a significant role in the cavitation process. Thanks to our time-resolved measurements, we also find that it is possible to probe metastable superfluid ${}^4\mathrm{He}$ beyond the commonly defined cavitation threshold.

${\mathrm{CrBr}}_3$ is an excellent realization of the two-dimensional honeycomb ferromagnet, which offers a bosonic equivalent of graphene with Dirac magnons and topological character. We perform inelastic neutron scattering measurements using state-of-the-art instrumentation to update 50-year-old data, thereby enabling a definitive comparison both with recent experimental claims of a significant gap at the Dirac point and with theoretical predictions for thermal magnon renormalization. We demonstrate that ${\mathrm{CrBr}}_3$ has next-neighbor $J_2$ and $J_3$ interactions approximately 5% of $J_1$, an ideal Dirac magnon dispersion at the $K$ point, and the associated signature of isospin winding. The magnon lifetime and the thermal band renormalization show the universal $T^2$ evolution expected from an interacting spin-wave treatment, but the measured dispersion lacks the predicted van Hove features, pointing to the need for more sophisticated theoretical analysis.

Dynamically encircling exceptional points (EPs) have unveiled intriguing chiral dynamics in photonics. However, the traditional approach based on an open manifold of Hamiltonian parameter space fails to explore trajectories that pass through an infinite boundary. Here, by mapping the full parameter space onto a closed manifold of the Riemann sphere, we introduce a framework to describe encircling-EP loops. We demonstrate that an encircling trajectory crossing the north vertex can realize near-unity asymmetric transmission. An efficient gain-free, broadband asymmetric polarization-locked device is realized by mapping the encircling path onto $L$-shaped silicon waveguides.

Semiflexible polymer glasses (SPGs), including those formed by the recently synthesized semiflexible conjugated polymers, are expected to be brittle because classical formulas for their craze extension ratio ${\lambda }_{\text{craze}}$ and fracture stretch ${\lambda }_{\mathrm{frac}}$ predict that systems with $N_e=C_{\infty }$ have ${\lambda }_{\text{craze}}={\lambda }_{\mathrm{frac}}=1$ and hence cannot be deformed to large strains. Using molecular dynamics simulations, we show that in fact such glasses can form stable crazes with ${\lambda }_{\text{craze}}\simeq N_e^{1/4}\simeq C_{\infty }^{1/4}$, and that they fracture at ${\lambda }_{\mathrm{frac}}=(3N_e^{1/2}-2{)}^{1/2}\simeq (3C_{\infty }^{1/2}-2{)}^{1/2}$. We argue that the classical formulas for ${\lambda }_{\text{craze}}$ and ${\lambda }_{\mathrm{frac}}$ fail to describe SPGs’ mechanical response because they do not account for Kuhn segments’ ability to stretch during deformation.

Fractures are a critical process in how materials wear, weaken, and fail, whose unpredictable behavior can have dire consequences. While the behavior of smooth cracks in ideal materials is well understood, it is assumed that for real, heterogeneous systems, fracture propagation is complex, generating rough fracture surfaces that are highly sensitive to specific details of the medium. Here we show how fracture roughness and material heterogeneity are inextricably connected via a simple framework. Studying hydraulic fractures in brittle hydrogels that have been supplemented with microbeads or glycerol to create controlled material heterogeneity, we show that the morphology of the crack surface depends solely on one parameter: the probability to perturb the front above a critical size to produce a steplike instability. This probability scales linearly with the number density, and with heterogeneity size to the $5/2$ power. The ensuing behavior is universal and is captured by the 1D ballistic propagation and annihilation of steps along the singular fracture front.

We study the steady states of translation-invariant open quantum many-body systems governed by Lindblad master equations, where the Hamiltonian is quadratic in the ladder operators, and the Lindblad operators are either linear or quadratic and Hermitian. These systems are called quasifree and quadratic, respectively. We find that steady states of one-dimensional systems with finite-range interactions necessarily have exponentially decaying Green’s functions. For the quasifree case without quadratic Lindblad operators, we show that fermionic systems with finite-range interactions are noncritical for any number of spatial dimensions and provide bounds on the correlation lengths. Quasifree bosonic systems can be critical in $D>1$ dimensions. Last, we address the question of phase transitions in quadratic systems and find that, without symmetry constraints beyond invariance under single-particle basis and particle-hole transformations, all gapped Liouvillians belong to the same phase.

We study the nonequilibrium evolution of coexisting ferromagnetic domains in the two-dimensional quantum Ising model—a setup relevant in several contexts, from quantum nucleation dynamics and false-vacuum decay scenarios to recent experiments with Rydberg-atom arrays. We demonstrate that the quantum-fluctuating interface delimiting a large bubble can be studied as an effective one-dimensional system through a “holographic” mapping. For the considered model, the emergent interface excitations map to an integrable chain of fermionic particles. We discuss how this integrability is broken by geometric features of the bubbles and by corrections in inverse powers of the ferromagnetic coupling, and provide a lower bound to the timescale after which the bubble is ultimately expected to melt. Remarkably, we demonstrate that a symmetry-breaking longitudinal field gives rise to a robust ergodicity breaking in two dimensions, a phenomenon underpinned by Stark many-body localization of the emergent fermionic excitations of the interface.

We present a new formula for the angular momentum $J^{\mu \nu }$ carried away by gravitational radiation in classical scattering. This formula, combined with the known expression for the radiated linear momentum $P^{\mu }$, completes the set of radiated Poincaré charges due to scattering. We parametrize $P^{\mu }$ and $J^{\mu \nu }$ by nonperturbative form factors and derive exact relations using the Poincaré algebra. There is a contribution to $J^{\mu \nu }$ due to static (zero-frequency) modes, which can be derived from Weinberg’s soft theorem. Using tools from scattering amplitudes and effective field theory, we calculate the radiated $J^{\mu \nu }$ due to the scattering of two spinless particles to third order in Newton’s constant $G$, but to all orders in velocity. Our form-factor analysis elucidates a novel relation found by Bini, Damour, and Geralico between energy and angular momentum loss at $\mathcal{O}(G^3)$. Our new results have several nontrivial implications for binary scattering at $\mathcal{O}(G^4)$. We give a procedure to bootstrap an effective radiation reaction force from the loss of Poincaré charges due to scattering.

We compute the electromagnetic corrections to neutron $\beta$ decay using a low-energy hadronic effective field theory. We identify new radiative corrections arising from virtual pions that were missed in previous studies. The largest correction is a percent-level shift in the axial charge of the nucleon proportional to the electromagnetic part of the pion-mass splitting. Smaller corrections, comparable to anticipated experimental precision, impact the $\beta \text{−}\nu$ angular correlations and the $\beta$ asymmetry. We comment on implications of our results for the comparison of the experimentally measured nucleon axial charge with first-principles computations using lattice QCD and on the potential of $\beta$ decay experiments to constrain beyond-the-standard-model interactions.

We study the direct production of the $J^{PC}=1^{++}$ charmonium state ${\chi }_{c1}(1P)$ in electron-positron annihilation by carrying out an energy scan around the mass of the ${\chi }_{c1}(1P)$. The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process $e^{+}{e}^{-}\to {\chi }_{c1}(1P)\to \gamma J/\psi \to \gamma {\mu }^{+}{\mu }^{-}$ and the background processes $e^{+}{e}^{-}\to {\gamma }_{\mathrm{ISR}}J/\psi \to {\gamma }_{\mathrm{ISR}}{\mu }^{+}{\mu }^{-}$ and $e^{+}{e}^{-}\to {\gamma }_{\mathrm{ISR}}{\mu }^{+}{\mu }^{-}$ is observed by combining all the data samples. The ${\chi }_{c1}(1P)$ signal is observed with a significance of $5.1\sigma$. This is the first observation of a $C$-even state directly produced in $e^{+}{e}^{-}$ annihilation. The electronic width of the ${\chi }_{c1}(1P)$ resonance is determined to be ${\mathrm{\Gamma }}_{ee}=(0.12_{-0.08}^{+0.13})\mathrm{eV}$, which is of the same order of magnitude as theoretical calculations.

We study collective processes for an electron beam propagating through a background plasma using simulations and analytical theory. A new regime where the instability of a Langmuir wave packet can grow locally much faster than ion frequency is clearly identified. The key feature of this new regime is an electron modulational instability that rapidly creates a local Langmuir wave packet, which in its turn produces local charge separation and strong ion density perturbations because of the action of the ponderomotive force, such that the beam-plasma wave interaction stops being resonant. Three evolution stages of the process and observed periodic burst features are discussed. Different physical regimes in the plasma and beam parameter space are demonstrated for the first time.

Growing axons are one-dimensional active structures that are important for wiring the brain and repairing nerves. However, the biophysical mechanisms underlying the complex kinetics of growing axons remain elusive. Here, we develop a theoretical framework to recapitulate force-regulated states and their transitions in growing axons. We demonstrate a unique negative feedback mechanism that defines four distinct kinetic states in a growing axon, whose transitional boundaries depend on the interplay between cytoskeletal dynamics and axon-substrate adhesion. A phase diagram for axonal growth is formulated based on two dimensionless numbers.

Recent theoretical and experimental works have explored universal dynamics related to surface growth physics in isolated quantum systems. In this Letter, we theoretically elucidate that dissipation drastically alters universal particle-number-fluctuation dynamics associated with surface-roughness growth in one-dimensional free fermions and bosons. In a system under dephasing that causes loss of spatial coherence, we numerically find that a universality class of surface-roughness dynamics changes from the ballistic class to a class with the Edwards-Wilkinson scaling exponents and an unconventional scaling function. We provide the analytical derivation of the diffusion equation from the dephasing Lindblad equation via a renormalization-group technique and succeed in explaining the drastic change. Furthermore, we numerically find the same change of the universality class under a more nontrivial dissipation, i.e., symmetric incoherent hopping.

Qubits are physical, a quantum gate thus not only acts on the information carried by the qubit but also on its energy. What is then the corresponding flow of energy between the qubit and the controller that implements the gate? Here we exploit a superconducting platform to answer this question in the case of a quantum gate realized by a resonant drive field. During the gate, the superconducting qubit becomes entangled with the microwave drive pulse so that there is a quantum superposition between energy flows. We measure the energy change in the drive field conditioned on the outcome of a projective qubit measurement. We demonstrate that the drive’s energy change associated with the measurement backaction can exceed by far the energy that can be extracted by the qubit. This can be understood by considering the qubit as a weak measurement apparatus of the driving field.

Dark matter (DM) annihilation in our Galaxy may produce a linearly polarized synchrotron signal. We use, for the first time, synchrotron polarization to constrain the DM annihilation cross section by comparing theoretical predictions with the latest polarization maps obtained by the Planck satellite collaboration. We find that synchrotron polarization is typically more constraining than synchrotron intensity by about 1 order of magnitude, independently of uncertainties in the modeling of electron and positron propagation, or of the Galactic magnetic field. Our bounds compete with cosmic microwave background limits in the case of leptophilic DM.

One of the primary reasons behind the difficulty in observing the Unruh effect is that for achievable acceleration scales the finite temperature effects are significant only for the low frequency modes of the field. Since the density of field modes falls for small frequencies in free space, the field modes which are relevant for the thermal effects would be less in number to make an observably significant effect. In this Letter, we investigate the response of an Unruh-DeWitt detector coupled to a massless scalar field which is confined in a long cylindrical cavity. The density of field modes inside such a cavity shows a resonance structure, i.e., it rises abruptly for some specific cavity configurations. We show that an accelerating detector inside the cavity exhibits a nontrivial excitation and de-excitation rates for small accelerations around such resonance points. If the cavity parameters are adjusted to lie in a neighborhood of such resonance points, the (small) acceleration-induced emission rate can be made much larger than the already observable inertial emission rate. We comment on the possibilities of employing this detector-field-cavity system in the experimental realization of the Unruh effect, and argue that the necessity of extremely high acceleration can be traded off in favor of precision in cavity manufacturing for realizing noninertial field theoretic effects in laboratory settings.

We study the processes $e^{+}{e}^{-}\to K_{\mathit{S}}^0{D}_s^{+}{D}^{*-}$ and $e^{+}{e}^{-}\to K_{\mathit{S}}^0{D}_s^{*+}{D}^{-}$, as well as their charge conjugated processes, at five center-of-mass energies between 4.628 and 4.699 GeV, using data samples corresponding to an integrated luminosity of $3.8{\mathrm{fb}}^{-1}$ collected by the BESIII detector at the BEPCII storage ring. Based on a partial reconstruction technique, we find evidence of a structure near the thresholds for $D_s^{+}{D}^{*-}$ and $D_s^{*+}{D}^{-}$ production in the $K_{\mathit{S}}^0$ recoil-mass spectrum, which we refer to as the $Z_{cs}(3985{)}^0$. Fitting with a Breit-Wigner line shape, we find the mass of the structure to be $(3992.2\pm 1.7\pm 1.6)\mathrm{MeV}/c^2$ and the width to be $(7.7_{-3.8}^{+4.1}\pm 4.3)\mathrm{MeV}$, where the first uncertainties are statistical and the second are systematic. The significance of the $Z_{cs}(3985{)}^0$ signal is found to be $4.6\sigma$ including both the statistical and systematic uncertainty. We report the Born cross section multiplied by the branching fraction at different energy points. The mass of the $Z_{cs}(3985{)}^0$ is close to that of the $Z_{cs}(3985{)}^{+}$. Assuming SU(3) symmetry, the cross section of the neutral channel is consistent with that of the charged one. Hence, we conclude that the $Z_{cs}(3985{)}^0$ is the isospin partner of the $Z_{cs}(3985{)}^{+}$.