Intrinsic toroidal rotation of the deuterium main ions in the core of the DIII-D tokamak is observed to transition from flat to hollow, forming an off-axis peak, above a threshold level of direct electron heating. Nonlinear gyrokinetic simulations show that the residual stress associated with electrostatic ion temperature gradient turbulence possesses the correct radial location and stress structure to cause the observed hollow rotation profile. Residual stress momentum flux in the gyrokinetic simulations is balanced by turbulent momentum diffusion, with negligible contributions from turbulent pinch. The prediction of the velocity profile by integrating the momentum balance equation produces a rotation profile that qualitatively and quantitatively agrees with the measured main-ion profile, demonstrating that fluctuation-induced residual stress can drive the observed intrinsic velocity profile.

We propose an ab initio molecular dynamics method, capable of dramatically reducing the autocorrelation time required for the simulation of classical and quantum particles at finite temperatures. The method is based on an efficient implementation of a first order Langevin dynamics modified by means of a suitable, position dependent acceleration matrix $S$. Here, we apply this technique to both Lennard-Jones models, to demonstrate the accuracy and speeding-up of the sampling, and within a quantum Monte Carlo based wave function approach, for determining the phase diagram of high-pressure hydrogen with simulations much longer than the autocorrelation time. With the proposed method, we are able to equilibrate in a few hundred steps even close to the liquid-liquid phase transition (LLT). Within our approach, we find that the LLT transition is consistent with recent density functionals predicting a much larger transition pressure when the long range dispersive forces are taken into account.

This Letter addresses the dynamical quantum problem of a driven discrete energy level coupled to a semi-infinite continuum whose density of states has a square-root-type singularity, such as states of a free particle in one dimension or quasiparticle states in a BCS superconductor. The system dynamics is strongly affected by the quantum-mechanical repulsion between the discrete level and the singularity, which gives rise to a bound state, suppresses the decay into the continuum, and can produce Stueckelberg oscillations. This quantum coherence effect may limit the performance of mesoscopic superconducting devices, such as the quantum electron turnstile.

We show that femtosecond laser pulse excitation of the orthoferrite ${\mathrm{ErFeO}}_3$ triggers pico- and subpicosecond dynamics of magnetic and electric dipoles associated with the low energy electronic states of the ${\mathrm{Er}}^{3+}$ ions. These dynamics are readily revealed by using polarization sensitive terahertz emission spectroscopy. It is shown that by changing the polarization of the femtosecond laser pulse one can excite either electric dipole-active or magnetic dipole-active transitions between the Kramers doublets of the ${{}^{4}I}_{15/2}$ ground state of the ${\mathrm{Er}}^{3+}$ ($4f^{11}$) ions. These observations serve as a proof of principle of polarization-selective control of both electric and magnetic degrees of freedom at terahertz frequencies, opening up new vistas for optical manipulation of magnetoelectric materials.

Heterogeneous ferroelastic transition that produces hierarchical 90° tetragonal nanodomains via mechanical loading and its effect on facilitating ferroelectric domain switching in relaxor-based ferroelectrics were explored. Combining in situ electron microscopy characterization and phase-field modeling, we reveal the nature of the transition process and discover that the transition lowers by 40% the electrical loading threshold needed for ferroelectric domain switching. Our results advance the fundamental understanding of ferroelectric domain switching behavior.

Glasses exhibit a liquidlike structure but a solidlike rheological response with plastic deformations only occurring beyond yielding. Thus, predicting the rheological behavior from the microscopic structure is difficult, but important for materials science. Here, we consider colloidal suspensions and propose to supplement the static structural information with the local dynamics, namely, the rearrangement and breaking of the cage of neighbors. This is quantified by the mean squared nonaffine displacement and the number of particles that remain nearest neighbors for a long time, i.e., long-lived neighbors, respectively. Both quantities are followed under shear using confocal microscopy and are the basis to calculate the affine and nonaffine contributions to the elastic stress, which is complemented by the viscoelastic stress to give the total stress. During start-up of shear, the model predicts three transient regimes that result from the interplay of affine, nonaffine, and viscoelastic contributions. Our prediction quantitatively agrees with rheological data and their dependencies on volume fraction and shear rate.

The current understanding is that the non-Newtonian rheology of active matter suspensions is governed by fluid-mediated hydrodynamic interactions associated with active self-propulsion. Here we discover an additional contribution to the suspension shear stress that predicts both thickening and thinning behavior, even when there is no nematic ordering of the microswimmers with the imposed flow. A simple micromechanical model of active Brownian particles in homogeneous shear flow reveals the existence of off-diagonal shear components in the swim stress tensor, which are independent of hydrodynamic interactions and fluid disturbances. Theoretical predictions from our model are consistent with existing experimental measurements of the shear viscosity of active suspensions, but also suggest new behavior not predicted by conventional models.

Randomly connected networks of excitatory and inhibitory spiking neurons provide a parsimonious model of neural variability, but are notoriously unreliable for performing computations. We show that this difficulty is overcome by incorporating the well-documented dependence of connection probability on distance. Spatially extended spiking networks exhibit symmetry-breaking bifurcations and generate spatiotemporal patterns that can be trained to perform dynamical computations under a reservoir computing framework.

The physics of quantum mechanics is the inspiration for, and underlies, quantum computation. As such, one expects physical intuition to be highly influential in the understanding and design of many quantum algorithms, particularly simulation of physical systems. Surprisingly, this has been challenging, with current Hamiltonian simulation algorithms remaining abstract and often the result of sophisticated but unintuitive constructions. We contend that physical intuition can lead to optimal simulation methods by showing that a focus on simple single-qubit rotations elegantly furnishes an optimal algorithm for Hamiltonian simulation, a universal problem that encapsulates all the power of quantum computation. Specifically, we show that the query complexity of implementing time evolution by a $d$-sparse Hamiltonian $\widehat{H}$ for time-interval $t$ with error $\epsilon$ is $\mathcal{O}[td\parallel \widehat{H}{\parallel }_{\max }+\log (1/\epsilon )/\log \log (1/\epsilon )]$, which matches lower bounds in all parameters. This connection is made through general three-step “quantum signal processing” methodology, comprised of (i) transducing eigenvalues of $\widehat{H}$ into a single ancilla qubit, (ii) transforming these eigenvalues through an optimal-length sequence of single-qubit rotations, and (iii) projecting this ancilla with near unity success probability.

We discuss quantum field theories with global $SU(N)$ and $O(N)$ symmetries for which temporal direction is compactified on a circle of size $L$ with periodicity of fields up to a global symmetry transformation, i.e., twisted boundary conditions. Such boundary conditions correspond to an insertion of the global symmetry operator in the partition function. We argue in general and prove in particular for $CP(N-1)$ and $O(N)$ nonlinear sigma models that large-$N$ volume independence holds. Further we show that the $CP(N-1)$ theory is free from the Affleck phase transition confirming the Ünsal-Dunne continuity conjecture.

We report on a direct search for sub-GeV dark photons ($A^{\prime }$), which might be produced in the reaction $e^{-}Z\to e^{-}Z{A}^{\prime }$ via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The dark photons would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with $2.75\times 10^9$ electrons on target. We set new limits on the $\gamma -A^{\prime }$ mixing strength and exclude the invisible $A^{\prime }$ with a mass $\lesssim 100\mathrm{MeV}$ as an explanation of the muon $g_{\mu }-2$ anomaly.

$W$ boson pair production processes at $e^{+}{e}^{-}$ and $pp$ colliders have been conventionally interpreted as measurements of $WWZ$ and $WW\gamma$ triple gauge couplings (TGCs). Such an interpretation is based on the assumption that new physics effects other than anomalous TGCs are negligible. While this “TGC dominance assumption” was well motivated and useful at LEP2 thanks to precision electroweak constraints, it is already challenged by recent LHC data. In fact, contributions from anomalous $Z$ boson couplings that are allowed by electroweak precision data but neglected in LHC analyses, which are enhanced at high energy, can even dominate over those from the anomalous TGCs considered. This limits the generality of the anomalous TGC constraints derived in current analyses and necessitates extension of the analysis framework and a change of physics interpretation. The issue will persist as we continue to explore the high-energy frontier. We clarify and analyze the situation in the effective field theory framework, which provides a useful organizing principle for understanding standard model deviations in the high-energy regime.

Based on a sample of $1.31\times 10^{9}J/\psi$ events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\pi }^0$ and ${\eta }^{\prime }\to {\pi }^0{\pi }^0{\pi }^0$ is performed. A significant $P$-wave contribution from ${\eta }^{\prime }\to {\rho }^{\pm }{\pi }^{\mp }$ is observed for the first time in ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\pi }^0$. The branching fraction is determined to be $\mathcal{B}({\eta }^{\prime }\to {\rho }^{\pm }{\pi }^{\mp })=(7.44\pm 0.60\pm 1.26\pm 1.84)\times {10}^{-4}$, where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant $S$-wave component, there is a significant $\sigma$ meson component. The branching fractions of the combined $S$-wave components are determined to be $\mathcal{B}({\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\pi }^0{)}_S=(37.63\pm 0.77\pm 2.22\pm 4.48)\times {10}^{-4}$ and $\mathcal{B}({\eta }^{\prime }\to {\pi }^0{\pi }^0{\pi }^0)=(35.22\pm 0.82\pm 2.54)\times {10}^{-4}$, respectively. The latter one is consistent with previous BESIII measurements.

We present the first measurement of charge-dependent directed flow in $\mathrm{Cu}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The results are presented as a function of the particle transverse momentum and pseudorapidity for different centralities. A finite difference between the directed flow of positive and negative charged particles is observed that qualitatively agrees with the expectations from the effects of the initial strong electric field between two colliding ions with different nuclear charges. The measured difference in directed flow is much smaller than that obtained from the parton-hadron-string-dynamics model, which suggests that most of the electric charges, i.e., quarks and antiquarks, have not yet been created during the lifetime of the strong electric field, which is of the order of, or less than, $1\mathrm{fm}/c$.

Intense, circularly polarized extreme-ultraviolet and near-infrared (NIR) laser pulses are combined to double ionize atomic helium via the oriented intermediate ${\mathrm{He}}^{+}(3p)$ resonance state. Applying angle-resolved electron spectroscopy, we find a large photon helicity dependence of the spectrum and the angular distribution of the electrons ejected from the resonance by NIR multiphoton absorption. The measured circular dichroism is unexpectedly found to vary strongly as a function of the NIR intensity. The experimental data are well described by theoretical modeling and possible mechanisms are discussed.

Although individual spins in quantum dots have been studied extensively as qubits, their investigation under strong resonant driving in the scope of accessing Mollow physics is still an open question. Here, we have grown high quality positively charged quantum dots embedded in a planar microcavity that enable enhanced light-matter interactions. Under a strong magnetic field in the Voigt configuration, individual positively charged quantum dots provide a double lambda level structure. Using a combination of above-band and resonant excitation, we observe the formation of Mollow triplets on all optical transitions. We find that when the strong resonant drive power is used to tune the Mollow-triplet lines through each other, we observe anticrossings. We also demonstrate that the interaction that gives rise to the anticrossings can be controlled in strength by tuning the polarization of the resonant laser drive. Quantum-optical modeling of our system fully captures the experimentally observed spectra and provides insight on the complicated level structure that results from the strong driving of the double lambda system.