Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover, separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window, these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.

We study particle production in ultrarelativistic nuclear collisions at CERN SPS and LHC energies and the conditions of chemical freeze-out. We determine the effect of the inelastic reactions between hadrons occurring after hadronization and before chemical freeze-out employing the ultrarelativistic quantum molecular dynamics hybrid model. The differences between the initial and the final hadronic multiplicities after the rescattering stage resemble the pattern of data deviation from the statistical equilibrium calculations. By taking these differences into account in the statistical model analysis of the data, we are able to reconstruct the original hadrochemical equilibrium points in the ($T$, ${\mu }_B$) plane which significantly differ from chemical freeze-out ones and closely follow the parton-hadron phase boundary recently predicted by lattice quantum chromodynamics.

We present a theoretical study of high-order harmonic generation (HHG) and propagation driven by an infrared field carrying orbital angular momentum (OAM). Our calculations unveil the following relevant phenomena: extreme-ultraviolet harmonic vortices are generated and survive to the propagation effects, vortices transport high-OAM multiples of the corresponding OAM of the driving field and, finally, the different harmonic vortices are emitted with similar divergence. We also show the possibility of combining OAM and HHG phase locking to produce attosecond pulses with helical pulse structure.

Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to $7\times {10}^{14}$, and record fuel areal densities of 0.7 to $1.3\mathrm{g}/{\mathrm{cm}}^2$. These implosions use hohlraums irradiated with shaped laser pulses of 1.5–1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.

Laser-wakefield acceleration constitutes a promising technology for future electron accelerators. A crucial step in such an accelerator is the injection of electrons into the wakefield, which will largely determine the properties of the extracted beam. We present here a new paradigm of colliding-pulse injection, which allows us to generate high-quality electron bunches having both a very low emittance ($0.17\mathrm{mm}·\mathrm{mrad}$) and a low energy spread (2%), while retaining a high charge ($\sim 100\mathrm{pC}$) and a short duration (3 fs). In this paradigm, the pulse collision provokes a transient expansion of the accelerating bubble, which then leads to transverse electron injection. This mechanism contrasts with previously observed optical injection mechanisms, which were essentially longitudinal. We also specify the range of parameters in which this new type of injection occurs and show that it is within reach of existing high-intensity laser facilities.

A semiconductor nanowire quantum dot with strong spin-orbit coupling (SOC) can be used to achieve a spin-orbit qubit. In contrast to a spin qubit, the spin-orbit qubit can respond to an external ac electric field, an effect called electric-dipole spin resonance. Here we develop a theory that can apply in the strong SOC regime. We find that there is an optimal SOC strength ${\eta }_{\mathrm{opt}}=\sqrt{2}/2$, where the Rabi frequency induced by the ac electric field becomes maximal. Also, we show that both the level spacing and the Rabi frequency of the spin-orbit qubit have periodic responses to the direction of the external static magnetic field. These responses can be used to determine the SOC in the nanowire.

Elastic light-by-light scattering ($\gamma \gamma \to \gamma \gamma$) is open to study at the Large Hadron Collider thanks to the large quasireal photon fluxes available in electromagnetic interactions of protons ($p$) and lead (Pb) ions. The $\gamma \gamma \to \gamma \gamma$ cross sections for diphoton masses $m_{\gamma \gamma }>5\mathrm{GeV}$ amount to 12 fb, 26 pb, and 35 nb in $p\mathrm{\text{−}}p$, $p\mathrm{\text{−}}\mathrm{Pb}$, and Pb-Pb collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_{\mathrm{NN}}}=14$, 8.8, and 5.5 TeV, respectively. Such a measurement has no substantial background in Pb-Pb collisions where one expects about 20 signal events per run, after typical detector acceptance and reconstruction efficiency selections.

We demonstrate a planar, tunable superconducting qubit with energy relaxation times up to $44\mu \mathrm{s}$. This is achieved by using a geometry designed to both minimize radiative loss and reduce coupling to materials-related defects. At these levels of coherence, we find a fine structure in the qubit energy lifetime as a function of frequency, indicating the presence of a sparse population of incoherent, weakly coupled two-level defects. We elucidate this defect physics by experimentally varying the geometry and by a model analysis. Our “Xmon” qubit combines facile fabrication, straightforward connectivity, fast control, and long coherence, opening a viable route to constructing a chip-based quantum computer.

We formulate lattice QCD in rotating frames to study the physics of QCD matter under rotation. We construct the lattice QCD action with the rotational metric and apply it to the Monte Carlo simulation. As the first application, we calculate the angular momenta of gluons and quarks in the rotating QCD vacuum. This new framework is useful to analyze various rotation-related phenomena in QCD.

We report on parity-violating asymmetries in the nucleon resonance region measured using inclusive inelastic scattering of 5–6 GeV longitudinally polarized electrons off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the $\Delta (1232)$. They provide a verification of quark-hadron duality—the equivalence of the quark- and hadron-based pictures of the nucleon—at the (10–15)% level in this electroweak observable, which is dominated by contributions from the nucleon electroweak $\gamma Z$ interference structure functions. In addition, the results provide constraints on nucleon resonance models relevant for calculating background corrections to elastic parity-violating electron scattering measurements.

The plasma astrophysical $S$ factor for the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with ${}^3\mathrm{He}$ atoms. Different proportions of ${\mathrm{D}}_2$ and ${}^3\mathrm{He}$ or ${\mathrm{CD}}_4$ and ${}^3\mathrm{He}$ were mixed in the gas target in order to allow the measurement of the cross section for the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ reaction. The yield of 14.7 MeV protons from the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ reaction was measured in order to extract the astrophysical $S$ factor at low energies. Our result is in agreement with other $S$ factor parametrizations found in the literature.

We present spatially resolved measurements characterizing the stagnation layer between two obliquely merging supersonic plasma jets. Intrajet collisionality is very high, but the interjet ion-ion mean free path is of the order of the stagnation layer thickness of a few centimeters. Fast-framing camera images show a double-peaked emission profile transverse to the stagnation layer, with the central emission dip consistent with a density dip in the interferometer data. We demonstrate that our observations are consistent with collisional oblique shocks.

The vibrational spectrum of a thiolate-based self-assembled monolayer fabricated by the adsorption of benzylmercaptan on a Au(111) substrate is studied using a combined experimental and theoretical approach employing infrared reflection absorption spectroscopy and density functional theory. The vibrational spectra are derived both using a finite differences approach and from ab initio molecular dynamics simulations at various temperatures. In addition, the possibility of adsorbate-induced reconstructions of the Au(111) substrate is taken into account. It turns out that the measured spectra can only be understood by taking finite temperatures into account.

We study the “hybrid” heterostructure formed by one sheet of single-layer graphene (SLG) and one sheet of bilayer graphene (BLG) separated by a thin film of dielectric material. In general, it is expected that interlayer interactions can drive the system to a spontaneously broken-symmetry state characterized by interlayer phase coherence. The peculiarity of the SLG-BLG heterostructure is that the electrons in the two layers have different chiralities. We find that this difference causes the spontaneously broken-symmetry state to be $N$-fold degenerate. Moreover, we find that some of the degenerate states are chiral superfluid states, topologically distinct from the usual layer ferromagnetism. The chiral nature of the ground state opens the possibility to realize protected midgap states. The $N$-fold degeneracy of the ground state makes the physics of SLG-BLG hybrid systems analogous to the physics of ${}^3\mathrm{He}$, in particular given the recent discovery of chiral superfluid states in this system.

Despite intense studies the exact nature of the order parameter in superconducting ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ remains unresolved. We have used small-angle neutron scattering to study the vortex lattice in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ with the field applied close to the basal plane, taking advantage of the transverse magnetization. We measured the intrinsic superconducting anisotropy between the $c$ axis and the Ru-O basal plane ($\sim 60$), which greatly exceeds the upper critical field anisotropy ($\sim 20$). Our result imposes significant constraints on possible models of triplet pairing in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and raises questions concerning the direction of the zero spin projection axis.

Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between ${\mathrm{SrTiO}}_3$ and two insulating polar oxides, ${\mathrm{BiMnO}}_3$ and ${\mathrm{LaAlO}}_3$. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic ${\mathrm{Ti}}^{3+}$ ions at the interface itself for ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ and to ${\mathrm{Mn}}^{3+}$ ions in the overlayer for ${\mathrm{BiMnO}}_3/{\mathrm{SrTiO}}_3$. In ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.

The irreversible thermodynamics of a continuous medium with magnetic dipoles predicts that a temperature gradient in the presence of magnetization waves induces a magnetic induction field, which is the magnetic analog of the Seebeck effect. This thermal gradient modulates the precession and relaxation. The magnetic Seebeck effect implies that magnetization waves propagating in the direction of the temperature gradient and the external magnetic induction field are less attenuated, while magnetization waves propagating in the opposite direction are more attenuated.

Stochastic dynamics of spin torque oscillators can be described in terms of magnetization drift and diffusion over a current-dependent effective energy surface given by the Fokker-Planck equation. Here we present a method that directly probes this effective energy surface via time-resolved measurements of the microwave voltage generated by a spin torque oscillator. We show that the effective energy approach provides a simple recipe for predicting spectral linewidths and line shapes near the generation threshold. Our time domain technique also accurately measures the fieldlike component of spin torque in a wide range of the voltage bias values.

The intensively studied Si(111)-($5\times 2$)-Au surface is reexamined using reflectance anisotropy spectroscopy and density functional theory simulations. We identify distinctive spectral features relating directly to local structural motifs such as Si honeycomb chains and atomic gold wires that are commonly found on Au-reconstructed vicinal Si(111) surfaces. Optical signatures of chain dimerization, responsible for the observed ($\times 2$) periodicity, are identified. The optical response, together with STM simulations and first-principles total-energy calculations, exclude the new structure proposed very recently based on the reflection high-energy electron diffraction technique analysis of Abukawa and Nishigaya [Phys. Rev. Lett. 110, 036102 (2013)] and provide strong support for the Si honeycomb chain with the triple Au chain model of Erwin et al. [Phys. Rev. B 80, 155409 (2009)]. This is a promising approach for screening possible models of complex anisotropic surface structures.

We develop a path-based approach to continuous-time random walks on networks with arbitrarily weighted edges. We describe an efficient numerical algorithm for calculating statistical properties of the stochastic path ensemble. After demonstrating our approach on two reaction rate problems, we present a biophysical model that describes how proteins evolve new functions while maintaining thermodynamic stability. We use our methodology to characterize dynamics of evolutionary adaptation, reproducing several key features observed in directed evolution experiments. We find that proteins generally fall into two qualitatively different regimes of adaptation depending on their binding and folding energetics.