We show numerically that the “deconfined” quantum critical point between the Néel antiferromagnet and the columnar valence-bond solid, for a square lattice of spin $1/2$, has an emergent SO(5) symmetry. This symmetry allows the Néel vector and the valence-bond solid order parameter to be rotated into each other. It is a remarkable ($2+1$)-dimensional analogue of the $\mathrm{SO}(4)=[\mathrm{SU}(2)\times \mathrm{SU}(2)]/{\mathbb{Z}}_2$ symmetry that appears in the scaling limit for the spin-$1/2$ Heisenberg chain. The emergent SO(5) symmetry is strong evidence that the phase transition in the ($2+1$)-dimensional system is truly continuous, despite the violations of finite-size scaling observed previously in this problem. It also implies surprising relations between correlation functions at the transition. The symmetry enhancement is expected to apply generally to the critical two-component Abelian Higgs model (noncompact ${CP}^1$ model). The result indicates that in three dimensions there is an SO(5)-symmetric conformal field theory that has no relevant singlet operators, so is radically different from conventional Wilson-Fisher-type conformal field theories.

Optical spectroscopy has been combined with computational and theoretical techniques to show how the spin dynamics in the model multiferroic ${\mathrm{BiFeO}}_3$ responds to the application of hydrostatic pressure and its corresponding series of structural phase transitions from $R3c$ to the $Pnma$ phases. As pressure increases, multiple spin excitations associated with noncollinear cycloidal magnetism collapse into two excitations, which show jump discontinuities at some of the ensuing crystal phase transitions. The effective Hamiltonian approach provides information on the electrical polarization and structural changes of the oxygen octahedra through the successive structural phases. The extracted parameters are then used in a Ginzburg-Landau model to reproduce the evolution with pressure of the spin wave excitations observed at low energy, and we demonstrate that the structural phases and the magnetic anisotropy drive and control the spin excitations.

In the three-dimensional Heisenberg spin glass in a random field, we study the properties of the inherent structures that are obtained by an instantaneous cooling from infinite temperature. For a not too large field the density of states $g(\omega )$ develops localized soft plastic modes and reaches zero as ${\omega }^4$ (for large fields a gap appears). When we perturb the system adding a force along the softest mode, one reaches very similar minima of the energy, separated by small barriers, that appear to be good candidates for classical two-level systems.

We study the entanglement spectrum of highly excited eigenstates of two known models that exhibit a many-body localization transition, namely the one-dimensional random-field Heisenberg model and the quantum random energy model. Our results indicate that the entanglement spectrum shows a “two-component” structure: a universal part that is associated with random matrix theory, and a nonuniversal part that is model dependent. The nonuniversal part manifests the deviation of the highly excited eigenstate from a true random state even in the thermalized phase where the eigenstate thermalization hypothesis holds. The fraction of the spectrum containing the universal part decreases as one approaches the critical point and vanishes in the localized phase in the thermodynamic limit. We use the universal part fraction to construct an order parameter for measuring the degree of randomness of a generic highly excited state, which is also a promising candidate for studying the many-body localization transition. Two toy models based on Rokhsar-Kivelson type wave functions are constructed and their entanglement spectra are shown to exhibit the same structure.

The correlation between hierarchical structures and polarization switching in ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene) has been probed by combining transmission electron microscopy studies with piezoresponse force microscopy observations. Differences are demonstrated between homogeneous and anisotropic thin films with well-defined lamellar orientation, with the later exhibiting quadrangular domain shape and double hysteresis. We propose that the polarization switching within lamella is dominated by domain wall flow motion, while the amorphous components between lamellae impede full polarization switching. The coupling between lamellae is controlled by a creep process. These results and interpretations explain well the seemingly contradicting polarization reversal dynamics reported and offer opportunities to change domain reversal speed by making ferroelectric polymer nanostructures.

Electric fields influence many aspects of cell physiology, including various forms of cell migration. Many cells are sensitive to electric fields, and they can migrate toward a cathode or an anode, depending on the cell type. In this Letter, we examine an actomyosin-independent mode of cell migration under electrical fields. Our theory considers a one-dimensional cell with water and ionic fluxes at the cell boundary. Water fluxes through the membrane are governed by the osmotic pressure difference across the cell membrane. Fluxes of cations and anions across the cell membrane are determined by the properties of the ion channels as well as the external electric field. Results show that without actin polymerization and myosin contraction, electric fields can also drive cell migration, even when the cell is not polarized. The direction of migration with respect to the electric field direction is influenced by the properties of ion channels, and are cell-type dependent.

We compare experimental results from a quasi-two-dimensional colloidal hard sphere fluid to a Monte Carlo simulation of hard disks with small particle displacements. The experimental short-time self-diffusion coefficient $D_S$ scaled by the diffusion coefficient at infinite dilution, $D_0$, strongly depends on the area fraction, pointing to significant hydrodynamic interactions at short times in the experiment, which are absent in the simulation. In contrast, the area fraction dependence of the experimental long-time self-diffusion coefficient $D_L/D_0$ is in quantitative agreement with $D_L/D_0$ obtained from the simulation. This indicates that the reduction in the particle mobility at short times due to hydrodynamic interactions does not lead to a proportional reduction in the long-time self-diffusion coefficient. Furthermore, the quantitative agreement between experiment and simulation at long times indicates that hydrodynamic interactions effectively do not affect the dependence of $D_L/D_0$ on the area fraction. In light of this, we discuss the link between structure and long-time self-diffusion in terms of a configurational excess entropy and do not find a simple exponential relation between these quantities for all fluid area fractions.

We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.

We put AdS/CFT dualities involving probe branes to a precision test. On the holographic side we use a new class of supersymmetric $D7$-brane embeddings into ${\mathrm{AdS}}_5\times S^5$, which allow us to describe $\mathcal{N}=4$ super Yang-Mills theory coupled to massive $\mathcal{N}=2$ supersymmetric flavors on $S^4$. With these embeddings we can compare holographic results to a field theory analysis of the free energy using supersymmetric localization. Localization allows us to get results at strong coupling, and hence to compare in detail to AdS/CFT. We find analytically matching results: a phase transition at the same critical mass in both calculations and matching free energies up to a scheme-dependent constant in both phases.

We study a quantum information metric (or fidelity susceptibility) in conformal field theories with respect to a small perturbation by a primary operator. We argue that its gravity dual is approximately given by a volume of maximal time slice in an anti–de Sitter spacetime when the perturbation is exactly marginal. We confirm our claim in several examples.

We studied the effect of crystallization on the embrittlement of bulk metallic glasses. Specifically, we measured fracture toughness for ${\mathrm{Zr}}_{44}{\mathrm{Ti}}_{11}{\mathrm{Cu}}_{10}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{25}$ and ${\mathrm{Pd}}_{43}{\mathrm{Cu}}_{27}{\mathrm{Ni}}_{10}{\mathrm{P}}_{20}$ after annealing at various times to introduce controlled volume fraction of crystallization. We found that crystallization of up to $\sim 6\%$ by volume does not measurably affect fracture toughness. When exceeding $\sim 6\%$, a dramatic drop in fracture toughness occurs; an additional 1% of crystallization reduces fracture toughness by 50%. Such a dramatic transition can be explained by the interaction among the crystals’ stress fields in the amorphous matrix that becomes effective at $\sim 7\%$ crystallinity. Our findings of a critical crystallization for embrittlement of metallic glasses help in designing tough metallic glasses and their composites, as well as defining processing protocols for the unique thermoplastic forming of metallic glasses to avoid embrittlement.

Dielectric relaxation studies for model glass-forming liquids confined to nanoporous alumina matrices were examined together with high-pressure results. For confined liquids which show the deviation from bulk dynamics upon approaching the glass transition (the change from the Vogel-Fulcher-Tammann to the Arrhenius law), we have observed a striking agreement between the temperature dependence of the $\alpha$-relaxation time in the Arrhenius-like region and the isochoric relaxation times extrapolated from the positive range of pressure to the negative pressure domain. Our finding provides strong evidence that glass-forming liquid confined to native nanopores enters the isochoric conditions once the mobility of the interfacial layer becomes frozen in. This results in the negative pressure effects on cooling. We also demonstrate that differences in the sensitivity of various glass-forming liquids to the “confinement effects” can be rationalized by considering the relative importance of thermal energy and density contributions in controlling the $\alpha$-relaxation dynamics (the $E_v/E_p$ ratio).

We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.

We demonstrate a new approach to precision NMR with hyperpolarized gases designed to mitigate NMR shifts due to the alkali spin-exchange field. The NMR bias field is implemented as a sequence of alkali (Rb) $2\pi$ pulses, allowing the Rb polarization to be optically pumped transverse to the bias field. When the Rb polarization is modulated at the noble-gas (Xe) NMR resonance, spin-exchange collisions buildup a precessing transverse Xe polarization. We study and mitigate novel NMR broadening effects due to the oscillating spin-exchange field. Spin-exchange frequency shifts are suppressed $2500\times$, and Rb magnetometer gain measurements project photon shot-noise limited NMR frequency uncertainties below $10\mathrm{nHz}/\sqrt{\mathrm{Hz}}$.

We show, experimentally and numerically, that a mode-locked fiber laser can operate in a regime where two dissipative soliton solutions coexist and the laser will periodically switch between the solutions. The two dissipative solitons differ in their pulse energy and spectrum. The switching can be controlled by an external perturbation and triggered even when switching does not occur spontaneously. Numerical simulations unveil the importance of the double-minima loss spectrum and nonlinear gain to the switching dynamics.

Linear gravity water waves are highly dispersive; therefore, the spreading of initially short wave trains characterizes water surface waves, and is a universal property of a dispersive medium. Only if there is sufficient nonlinearity does this envelope admit solitary solutions which do not spread and remain in fixed forms. Here, in contrast to the nonlinear localized wave packets, we present both theoretically and experimentally a new type of linearly nondispersive water wave, having a cosine-Gauss envelope, as well as its higher-order Hermite cosine-Gauss variations. We show that these waves preserve their width despite the inherent dispersion while propagating in an 18-m wave tank, accompanied by a slowly varying carrier-envelope phase. These wave packets exhibit self-healing; i.e., they are restored after bypassing an obstacle. We further demonstrate that these nondispersive waves are robust to weakly nonlinear perturbations. In the strong nonlinear regime, symmetry breaking of these waves is observed, but their cosine-Gauss shapes are still approximately preserved during propagation.

Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy, and density functional theory we find that a simple necklacelike chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modeling the electronic and magnetic properties of Mn atom chains on Si(001).

Separating between the ordinary Hall effect and anomalous Hall effect in the paramagnetic phase of ${\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Si}$ reveals an ordinary Hall effect sign inversion associated with the hidden quantum critical (QC) point $x^{*}\sim 0.11$. The effective hole doping at intermediate Fe content leads to verifiable predictions in the field of fermiology, magnetic interactions, and QC phenomena in ${\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Si}$. The change of electron and hole concentrations is considered as a “driving force” for tuning the QC regime in ${\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Si}$ via modifying the Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism.