We report on Bose-Einstein condensation in a gas of strontium atoms, using laser cooling as the only cooling mechanism. The condensate is formed within a sample that is continuously Doppler cooled to below $1\mu \mathrm{K}$ on a narrow-linewidth transition. The critical phase-space density for condensation is reached in a central region of the sample, in which atoms are rendered transparent for laser cooling photons. The density in this region is enhanced by an additional dipole trap potential. Thermal equilibrium between the gas in this central region and the surrounding laser cooled part of the cloud is established by elastic collisions. Condensates of up to ${10}^5$ atoms can be repeatedly formed on a time scale of 100 ms, with prospects for the generation of a continuous atom laser.

We study matter-wave bright solitons in spin-orbit coupled Bose-Einstein condensates with attractive interactions. We use a multiscale expansion method to identify solution families for chemical potentials in the semi-infinite gap of the linear energy spectrum. Depending on the linear and spin-orbit coupling strengths, the solitons may present either a ${\mathrm{sech}}^2$-shaped or a modulated density profile reminiscent of the stripe phase of spin-orbit coupled repulsive Bose-Einstein condensates. Our numerical results are in excellent agreement with our analytical findings and demonstrate the potential robustness of solitons for experimentally relevant conditions.

The dynamic features of the low-intermediate–high-(L-I-H) confinement transitions on HL-2A tokamak are presented. Here we report the discovery of two types of limit cycles (dubbed type-$Y$ and type-$J$), which show opposite temporal ordering between the radial electric field and turbulence intensity. In type-$Y$, which appears first after an L-I transition, the turbulence grows first, followed by the localized electric field. In contrast, the electric field leads type-$J$. The turbulence-induced zonal flow and pressure-gradient-induced drift play essential roles in the two types of limit cycles, respectively. The condition of transition between types-$Y$ and -$J$ is studied in terms of the normalized radial electric field. An I-H transition is demonstrated to occur only from type-$J$.

Three-dimensional kinetic simulations of magnetic reconnection reveal that the electron diffusion region is composed of two or more current sheets in regimes with weak magnetic shear angles $\varphi \lesssim 80°$. This new morphology is explained by oblique tearing modes which produce flux ropes while simultaneously driving enhanced current at multiple resonance surfaces. This physics persists into the nonlinear regime leading to multiple electron layers embedded within a larger Alfvénic inflow and outflow. Surprisingly, the thickness of these layers and the reconnection rate both remain comparable to two-dimensional models. The parallel electric fields are supported predominantly by the electron pressure tensor and electron inertia, while turbulent dissipation remains small.

By a novel reciprocal space analysis of the measurement, we report a calibrated in situ observation of the bunching effect in a 3D ultracold gas. The calibrated measurement with no free parameters confirms the role of the exchange symmetry and the Hanbury Brown–Twiss effect in the bunching. Also, the enhanced fluctuations of the bunching effect give a quantitative measure of the increased isothermal compressibility. We use 2D images to probe the 3D gas, using the same principle by which computerized tomography reconstructs a 3D image of a body. The powerful reciprocal space technique presented is applicable to systems with one, two, or three dimensions.

High resolution resonant inelastic x-ray scattering has been performed to reveal the role of lattice coupling in a family of quasi-1D insulating cuprates, ${\mathrm{Ca}}_{2+5x}{\mathrm{Y}}_{2-5x}{\mathrm{Cu}}_5{\mathrm{O}}_{10}$. Site-dependent low-energy excitations arising from progressive emissions of a 70 meV lattice vibrational mode are resolved for the first time, providing a direct measurement of electron-lattice coupling strength. We show that such electron-lattice coupling causes doping-dependent distortions of the Cu-O-Cu bond angle, which sets the intrachain spin exchange interactions. Our results indicate that the lattice degrees of freedom are fully integrated into the electronic behavior in low-dimensional systems.

The rate of curvature-driven grain growth in polycrystalline materials is well known to be limited by interface dissipation. We show analytically and by simulations that, for systems forming modulated phases or nonequilibrium patterns with crystal ordering, growth is limited by bulk dissipation associated with lattice translation, which dramatically slows down grain coarsening. We also show that bulk dissipation is reduced by thermal noise and that this reduction leads to faster coarsening behavior dominated by interface dissipation for a high Peierls-Nabarro barrier to dislocation motion and high noise. Those results provide a unified theoretical framework for understanding and modeling polycrystalline pattern evolution in diverse systems over a broad range of length and time scales.

Different instabilities have been speculated for a three-dimensional electron gas confined to its lowest Landau level. The phase transition induced in graphite by a strong magnetic field, and believed to be a charge density wave, is the only experimentally established case of such instabilities. Studying the magnetoresistance in graphite for the first time up to 80 T, we find that the magnetic field induces two successive phase transitions, consisting of two distinct ordered states each restricted to a finite field window. In both states, an energy gap opens up in the out-of-plane conductivity and coexists with an unexpected in-plane metallicity for a fully gap bulk system. Such peculiar metallicity may arise as a consequence of edge-state transport expected to develop in the presence of a bulk gap.

We demonstrate one and two photoelectron trapping and the subsequent dynamics associated with interdot transfer in double quantum dots over a time scale much shorter than the typical spin lifetime. Identification of photoelectron trapping is achieved via resonant interdot tunneling of the photoelectrons in the excited states. The interdot transfer enables detection of single photoelectrons in a nondestructive manner. When two photoelectrons are trapped at almost the same time we observed that the interdot resonant tunneling is strongly affected by the Coulomb interaction between the electrons. Finally the influence of the two-electron singlet-triplet state hybridization has been detected using the interdot tunneling of a photoelectron.

Our ab initio studies show clear evidence that magnetic anisotropy (MA) and the direction of magnetization in metallic magnetic multilayers can be tailored at once by surface charging. By taking Fe-Pt multilayers as a representative example, we demonstrate that surface charging has a deep effect on the magnitude of the MA, which is composition dependent, achieving remarkably large values for systems featuring a single Fe layer capped with Pt. More intriguing is the behavior of the multilayers capped with iron bilayers, for which surface charging not only affects the value of the anisotropy but an easy-axis switching is also revealed. By analyzing the electronic structure of the magnetic layers and relating the MA to the orbital moment anisotropy, some insights about the origin of the MA from a local perspective can be inferred.

Hole and electron doped ${\mathrm{LaCoO}}_3$ is studied using dynamical mean-field theory. The one-particle spectra are analyzed and compared to the available experimental data, in particular the x-ray absorption spectra. Analyzing the temporal spin-spin correlation functions we find the atomic intermediate spin state is not important for the observed Curie-Weiss susceptibility. Contrary to the commonly held view about the roles played by the $t_{2g}$ and $e_g$ electrons we find narrow quasiparticle bands of $t_{2g}$ character crossing the Fermi level accompanied by strongly damped $e_g$ excitations.

We studied gas-exposure effects on pentacene (Pn) films on ${\mathrm{SiO}}_2$ and Au(111) substrates by ultrahigh sensitivity photoelectron spectroscopy, which can detect the density of states of $\sim {10}^{16}$ states ${\mathrm{eV}}^{-1}{\mathrm{cm}}^{-3}$ comparable to electrical measurements. The results show the striking effects for $\mathrm{Pn}/{\mathrm{SiO}}_2$: exposure to inert gas (${\mathrm{N}}_2$ and Ar) produces a sharp rise in gap states from $\sim {10}^{16}$ to $\sim {10}^{18}$ states ${\mathrm{eV}}^{-1}{\mathrm{cm}}^{-3}$ and pushes the Fermi level closer to the valence band (0.15–0.17 eV), as does exposure to ${\mathrm{O}}_2$ (0.20 eV), while no such gas-exposure effect is observed for $\mathrm{Pn}/\mathrm{Au}(111)$. The results demonstrate that these gap states originate from small imperfections in the Pn packing structure, which are induced by gas penetration into the film through the crystal grain boundaries.

For scattering by potentials with attractive inverse-cube ($-C_3/r^3$) tails, the threshold law for elastic collisions is presented. The expansion of the scattering phase shift contains all terms up to and including $O(k^2)$ and only relies on the value of the threshold quantum number’s remainder $\Delta \in [0,1)$, which accounts for short-range deviations of the full potential from the pure $-C_3/r^3$ form. In contrast to previous approaches, the threshold law presented provides a connection to the regular solution at zero energy as well as to the position of a weakly bound $s$-wave state.

We show that optically encoded two-qubit Bell states can be unambiguously discriminated with a success probability of more than 50% in both single-rail and dual-rail encodings by using active linear-optical resources that include Gaussian squeezing operations. These results are in contrast to the well-known upper bound of 50% for unambiguous discrimination of dual-rail Bell states using passive, static linear optics and arbitrarily many vacuum modes. We present experimentally feasible schemes that improve the success probability to 64.3% in dual-rail and to 62.5% in single-rail for a uniform random distribution of Bell states. Conceptually, this demonstrates that neither interactions that induce nonlinear mode transformations (such as Kerr interactions) nor auxiliary entangled photons are required to go beyond the one-half limit. We discuss the optimality of our single-rail scheme and talk about an application of our dual-rail scheme in quantum communication.

We derive a relativistic chiral kinetic equation with manifest Lorentz covariance from Wigner functions of spin-$1/2$ massless fermions in a constant background electromagnetic field. It contains vorticity terms and a four-dimensional Euclidean Berry monopole which gives an axial anomaly. By integrating out the zeroth component of the 4-momentum $p$, we reproduce the previous three-dimensional results derived from the Hamiltonian approach, together with the newly derived vorticity terms. The phase space continuity equation has an anomalous source term proportional to the product of electric and magnetic fields ($F_{\sigma \rho }{\tilde{F}}^{\sigma \rho }\sim E_{\sigma }{B}^{\sigma }$). This provides a unified interpretation of the chiral magnetic and vortical effects, chiral anomaly, Berry curvature, and the Berry monopole in the framework of Wigner functions.

We investigate the $\alpha +{}^{16}\mathrm{O}$ cluster structure in the inversion-doublet band ($K^{\pi }=0_1^{\pm }$) states of ${}^{20}\mathrm{Ne}$ with an angular-momentum-projected version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function, which was successful “in its original form” for the description of, e.g., the famous Hoyle state. In contrast with the traditional view on clusters as localized objects, especially in inversion doublets, we find that these single THSR wave functions, which are based on the concept of nonlocalized clustering, can well describe the $K^{\pi }=0_1^{-}$ band and the $K^{\pi }=0_1^{+}$ band. For instance, they have 99.98% and 99.87% squared overlaps for $1^{-}$ and $3^{-}$ states (99.29%, 98.79%, and 97.75% for $0^{+}$, $2^{+}$, and $4^{+}$ states), respectively, with the corresponding exact solution of the $\alpha +{}^{16}\mathrm{O}$ resonating group method. These astounding results shed a completely new light on the physics of low energy nuclear cluster states in nuclei: The clusters are nonlocalized and move around in the whole nuclear volume, only avoiding mutual overlap due to the Pauli blocking effect.

We report the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. Working in a regime where the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction, we observe partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. Quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and observe its characteristic $C_6/R^6$ dependence. The measured $C_6$ coefficients agree well with ab initio calculations, and we observe their dramatic increase with the principal quantum number $n$ of the Rydberg state.

Experiments are performed at the Enormous Toroidal Plasma Device at UCLA to study the neutral boundary layer (NBL) between a magnetized plasma and a neutral gas along the direction of a confining magnetic field. This is the first experiment to measure plasma termination within a neutral gas without the presence of a wall or obstacle. A magnetized, current-free helium plasma created by a lanthanum hexaboride (${\mathrm{LaB}}_6$) cathode terminates entirely within a neutral helium gas. The plasma is weakly ionized ($n_e/n_n\sim 1\%$) and collisional ${\lambda }_n\ll L_{\mathrm{plasma}}$. The NBL occurs where the plasma pressure equilibrates with the neutral gas pressure, consistent with a pressure balance model. It is characterized by a field-aligned ambipolar electric field, developing self-consistently to maintain a current-free termination of the plasma on the neutral gas. Probes are inserted into the plasma to measure the plasma density, flow, temperature, current, and potential. These measurements confirm the presence of the ambipolar field and the pressure equilibration model of the NBL.

We report results from high pressure and temperature experiments that provide evidence for the reactivity of xenon with water ice at pressures above 50 GPa and a temperature of 1500 K—conditions that are found in the interiors of Uranus and Neptune. The x-ray data are sufficient to determine a hexagonal lattice with four Xe atoms per unit cell and several possible distributions of O atoms. The measurements are supplemented with ab initio calculations, on the basis of which a crystallographic structure with a ${\mathrm{Xe}}_4{\mathrm{O}}_{12}{\mathrm{H}}_{12}$ primitive cell is proposed. The newly discovered compound is formed in the stability fields of superionic ice and $\eta$-${\mathrm{O}}_2$, and has the same oxygen subnetwork as the latter. Furthermore, it has a weakly metallic character and likely undergoes sublattice melting of the H subsystem. Our findings indicate that Xe is expected to be depleted in the atmospheres of the giant planets as a result of sequestration at depth.

The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent ($\beta =3/7$) follows a theoretical prediction made by Phillips for homogeneous glasses.