We study the order statistics of one-dimensional branching Brownian motion in which particles either diffuse (with diffusion constant $D$), die (with rate $d$), or split into two particles (with rate $b$). At the critical point $b=d$, which we focus on, we show that at large time $t$ the particles are collectively bunched together. We find indeed that there are two length scales in the system: (i) the diffusive length scale $\sim \sqrt{Dt}$, which controls the collective fluctuations of the whole bunch, and (ii) the length scale of the gap between the bunched particles $\sim \sqrt{D/b}$. We compute the probability distribution function $\tilde{P}(g_k,t|n)$ of the $k$th gap $g_k=x_k-x_{k+1}$ between the $k$th and ($k+1$)th particles given that the system contains exactly $n>k$ particles at time $t$. We show that at large $t$, it converges to a stationary distribution $\tilde{P}(g_k,t\to \infty |n)=p(g_k|n)$ with an algebraic tail $p(g_k|n)\sim 8(D/b)g_k^{-3}$, for $g_k\gg 1$, independent of $k$ and $n$. We verify our predictions with Monte Carlo simulations.

We search for $CP$ violation in neutral charm meson decays using a data sample with an integrated luminosity of $966{\text{fb}}^{-1}$ collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ asymmetric-energy collider. The asymmetry obtained in the rate of $D^0$ and ${\overline{D}}^0$ decays to the ${\pi }^0{\pi }^0$ final state, $[-0.03\pm 0.64\text{(stat)}\pm 0.10\text{(syst)}]\%$, is consistent with no $CP$ violation. This constitutes an order of magnitude improvement over the existing result. We also present an updated measurement of the $CP$ asymmetry in the $D^0\to K_S^0{\pi }^0$ decay: $A_{CP}(D^0\to K_S^0{\pi }^0)=[-0.21\pm 0.16\text{(stat)}\pm 0.07\text{(syst)}]\%$.

We determine the rate for $D_s^{*}\to D_s\gamma$ for the first time from lattice QCD and include the full effect of $u$, $d$, and $s$ sea quarks. The valence quarks are implemented by using the highly improved staggered quark formalism and we normalize the vector current nonperturbatively. We obtain $M(D_s^{*})-M(D_s)$ of 148(4) MeV, in good agreement with experiment. The value of the decay constant of the $D_s^{*}$ we find to be 274(6) MeV, so that $f_{D_s^{*}}/f_{D_s}=1.10(2)$. For the radiative decay, we find $\mathrm{\Gamma }(D_s^{*}\to D_s\gamma )=0.066(26)\mathrm{keV}$. Given the experimental branching fraction for this decay, we predict a total width for the $D_s^{*}$ of 0.070(28) keV, making this the longest-lived charged vector meson. We also determine the branching fraction for $D_s^{*}$ leptonic decay to be $3.4(1.4)\times 10^{-5}$, putting it within the range of possible detection at next-generation flavor factories.

We report on compact and efficient laser-based THz generation in the terahertz frequency gap (1–10 THz). The radiation is generated by optical rectification of a midinfrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited tabletop THz sources to $\mathrm{GV}/\mathrm{m}$ electric and several tesla magnetic field at millijoule pulse energy. In agreement with simulations, the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded ${\chi }^{(2)}$ process in the organic crystals accompanied by a significant redshift of the pump spectrum. The scheme provides a compact, tabletop THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue toward novel nonlinear THz applications.

We predict the possibility of observing integer and fractional self-imaging (Talbot) phenomena on the discrete angular spectrum of periodic diffraction gratings illuminated by a suitable spherical wave front. Our predictions are experimentally validated, reporting what we believe to be the first observation of self-imaging effects in the far-field diffraction regime.

We experimentally generate speckle patterns with non-Rayleigh statistics using a phase-only spatial light modulator. By introducing high order correlations to the input light fields we redistribute the intensity among the speckle grains, while preserving the granular structure of the pattern. Our method is versatile and allows for generating speckle patterns with enhanced or diminished contrast in a controlled manner.

Spatial clustering of identical particles falling through a turbulent flow enhances the collision rate between the falling particles, an important problem in aerosol science. We analyze this problem using perturbation theory in a dimensionless parameter, the so-called Kubo number. This allows us to derive an analytical theory quantifying the spatial clustering. We find that clustering of small particles in incompressible random velocity fields may be reduced or enhanced by the effect of gravity (depending on the Stokes number of the particles) and may be strongly anisotropic.

A statistical relationship between magnetic reconnection, current sheets, and intermittent turbulence in the solar wind is reported for the first time using in situ measurements from the Wind spacecraft at 1 AU. We identify intermittency as non-Gaussian fluctuations in increments of the magnetic field vector $\mathbf{B}$ that are spatially and temporally nonuniform. The reconnection events and current sheets are found to be concentrated in intervals of intermittent turbulence, identified using the partial variance of increments method: within the most non-Gaussian 1% of fluctuations in $\mathbf{B}$, we find 87%–92% of reconnection exhausts and $\sim 9\%$ of current sheets. Also, the likelihood that an identified current sheet will also correspond to a reconnection exhaust increases dramatically as the least intermittent fluctuations are removed from the data set. Hence, the turbulent solar wind contains a hierarchy of intermittent magnetic field structures that are increasingly linked to current sheets, which in turn are progressively more likely to correspond to sites of magnetic reconnection. These results could have far reaching implications for laboratory and astrophysical plasmas where turbulence and magnetic reconnection are ubiquitous.

It is demonstrated experimentally and by numerical simulations that the presence of a long-pulse-laser-created back plasma on the target backside can focus the relativistic electrons produced by short-pulse laser interaction with the front of a solid target. Comparing this to that without the back plasma, the number density of the fast electrons is increased by one order of magnitude, and their divergence angle is reduced fivefold. The effect is attributed to the absence of the backside sheath electric field and the collimation effect of the megagauss self-generated baroclinic magnetic field there. Such an acceleration scheme can be useful to applications requiring high-energy and charge-density electron bunches, such as fast ignition in inertial fusion.

We compute the zero-point renormalization (ZPR) of the optical band gap of diamond from many-body perturbation theory using the perturbative $G_0{W}_0$ approximation as well as quasiparticle self-consistent $GW$. The electron-phonon coupling energies are found to be more than 40% higher than standard density functional theory when many-body effects are included with the frozen-phonon calculations. A similar increase is observed for the zero-point renormalization in GaAs when $G_0{W}_0$ corrections are applied. We show that these many-body corrections are necessary to accurately predict the temperature dependence of the band gap. The frozen-phonon method also allows us to validate the rigid-ion approximation which is always present in density functional perturbation theory.

Superhydrophobic coatings repel liquids by trapping air inside microscopic surface textures. However, the resulting composite interface is prone to collapse under external pressure. Nanometer-size textures should facilitate more resilient coatings owing to geometry and confinement effects at the nanoscale. Here, we use in situ x-ray diffraction to study the collapse of the superhydrophobic state in arrays of $\approx 20\mathrm{nm}$-wide silicon textures with cylindrical, conical, and linear features defined by block-copolymer self-assembly and plasma etching. We reveal that the superhydrophobic state vanishes above critical pressures which depend on texture shape and size. This phenomenon is irreversible for all but the conical surface textures which exhibit a spontaneous, partial reappearance of the trapped gas phase upon liquid depressurization. This process is influenced by the kinetics of gas-liquid exchange.

We investigate the energy transfer between counterpropagating quantum Hall edge channels (ECs) in a two-dimensional electron system at a filling factor of $\nu =1$. The ECs are separated by a thin impenetrable potential barrier and Coulomb coupled, thereby constituting a quasi-one-dimensional analogue of a spinless Luttinger liquid (LL). We drive one, say hot, EC far from thermal equilibrium and measure the energy transfer rate $P$ into the second, cold, EC using a quantum point contact as a bolometer. The dependence of $P$ on the drive bias indicates a breakdown of the momentum conservation, whereas $P$ is almost independent of the length of the region where the ECs interact. Interpreting our results in terms of plasmons (collective density excitations), we find that the energy transfer between the ECs occurs via plasmon backscattering at the boundaries of the LL. The backscattering probability is determined by the LL interaction parameter and can be tuned by changing the width of the electrostatic potential barrier between the ECs.

When in close contact, plasmonic resonances interact and become strongly correlated. In this work we develop a quantum mechanical model for an array of coupled particle plasmons. This model predicts that when the coupling strength between plasmons approaches or surpasses the local dissipation, a sizable amount of entanglement is stored in the collective modes of the array. We also prove that entanglement manifests itself in far-field images of the plasmonic modes, through the statistics of the quadratures of the field, in what constitutes a novel family of entanglement witnesses. Finally, we estimate the amount of entanglement, the coupling strength and the correlation properties for a system that consists of two or more coupled nanospheres of silver, showing evidence that our predictions could be tested using present-day state-of-the-art technology.

The distribution of Coulomb blockade peak heights as a function of magnetic field is investigated experimentally in a Ge/Si nanowire quantum dot. Strong spin-orbit coupling in this hole-gas system leads to antilocalization of Coulomb blockade peaks, consistent with theory. In particular, the peak height distribution has its maximum away from zero at zero magnetic field, with an average that decreases with increasing field. Magnetoconductance in the open-wire regime places a bound on the spin-orbit length ($l_{\mathrm{so}}<20\mathrm{nm}$), consistent with values extracted in the Coulomb blockade regime ($l_{\mathrm{so}}<25\mathrm{nm}$).

Ultrashort, coherent x-ray pulses of a free-electron laser are used to holographically image the magnetization dynamics within a magnetic domain pattern after creation of a localized excitation via an optical standing wave. We observe a spatially confined reduction of the magnetization within a couple of hundred femtoseconds followed by its slower recovery. Additionally, the experimental results show evidence of a spatial evolution of magnetization, which we attribute to ultrafast transport of nonequilibrium spin-polarized electrons for early times and to a fluence-dependent remagnetization rate for later times.

Using a renormalization group approach, we solve the time evolution of random Ising spin chains with generic interactions starting from initial states of arbitrary energy. As a function of the Hamiltonian parameters, the system is tuned through a dynamical transition, similar to the ground-state critical point, at which the local spin correlations establish true long-range temporal order. In the state with a dominant transverse field, a spin that starts in an up state loses its orientation with time, while in the “ordered” state it never does. As in ground-state quantum phase transitions, the dynamical transition has unique signatures in the entanglement properties of the system. When the system is initialized in a product state, the entanglement entropy grows as $\log (t)$ in the two “phases,” while at the critical point it grows as ${\log }^{\alpha }(t)$, with $\alpha$ a universal number. This universal entanglement growth requires generic (“integrability breaking”) interactions to be added to the pure transverse field Ising model.

Electrically induced reorientation of liquid crystals (LCs) is a fundamental phenomenon widely used in modern technologies. We observe experimentally an electrooptic effect in a cholesteric LC with a distinct oblique-helicoidal director deformation. The oblique helicoid, predicted in late 1960s, is made possible by recently developed dimer materials with an anomalously small bend elastic constant. Theoretical, numerical, and experimental analysis establishes that both the pitch and the cone angle of the oblique helicoid increase as the electric field decreases. At low fields, the oblique helicoid with the axis parallel to the field transforms into a right-angle helicoid (the ground state of field-free cholesteric) with the axis perpendicular to the field.

The kinetic separation of repulsive active Brownian particles into a dense and a dilute phase is analyzed using a systematic coarse-graining strategy. We derive an effective Cahn-Hilliard equation on large length and time scales, which implies that the separation process can be mapped onto that of passive particles. A lower density threshold for clustering is found, and using our approach we demonstrate that clustering first proceeds via a hysteretic nucleation scenario and above a higher threshold changes into a spinodal-like instability. Our results are in agreement with particle-resolved computer simulations and can be verified in experiments of artificial or biological microswimmers.