We demonstrate a novel approach to obtain a resonance linewidth below the transit limit. The cross correlation between the induced intensity modulation of two lasers coupling the target resonance exhibits a narrow spectrum. $1/30$ of the transit-limited width is achieved in a proof-of-principle experiment where two ground states are the target resonance levels. Attainable linewidth is only limited by laser shot noise in principle. The experimental results qualitatively agree with an intuitive analytical model and numerical calculations. This technique can be easily implemented and should be applicable to many atomic, molecular, and solid state spin systems for spectroscopy, metrology, and resonance-based sensing and imaging.

We report on a study of cold reactive collisions between sympathetically cooled molecular ions and laser-cooled atoms in an ion-atom hybrid trap. Chemical reactions were studied at average collision energies $⟨E_{\mathrm{coll}}⟩/k_{\mathrm{B}}\gtrsim 20\mathrm{mK}$, about 2 orders of magnitude lower than has been achieved in previous experiments with molecular ions. Choosing ${\mathrm{N}}_2^{+}+\mathrm{Rb}$ as a prototypical system, we find that the reaction rate is independent of the collision energy within the range studied, but strongly dependent on the internal state of Rb. Highly efficient charge exchange four times faster than the Langevin rate was observed with Rb in the excited ($5p$) ${}^{2}P_{3/2}$ state. This observation is rationalized by a capture process dominated by the charge-quadrupole interaction and a near resonance between the entrance and exit channels of the system. Our results provide a test of classical models for reactions of molecular ions at the lowest energies reached thus far.

The van der Waals coefficients between quasispherical nanostructures can be modeled accurately and analytically by those of classical solid spheres (for nanoclusters) or spherical shells (for fullerenes) of uniform valence electron density, with the true static dipole polarizability. Here, we derive analytically and confirm numerically from this model the size dependencies of the van der Waals coefficients of all orders, showing, for example, that the asymptotic dependence for $C_6$ is the expected $n^2$ for pairs of nanoclusters $A_n\mathrm{\text{−}}{A}_n$, each containing $n$ atoms, but $n^{2.75}$ for pairs of single-walled fullerenes ${\mathrm{C}}_n\mathrm{\text{−}}{\mathrm{C}}_n$. Large fullerenes are argued to have much larger polarizabilities and dispersion coefficients than those predicted by either the standard atom pair-potential model or widely used nonlocal van der Waals correlation energy functionals.

X-ray lasing is predicted to ensue when molecules are pumped into dissociative core-excited states by a free-electron-laser pulse. The lasing is due to the population inversion created in the neutral dissociation product, and the process features self-trapping of the x-ray pulse at the gain ridge. Simulations performed for the HCl molecule pumped at the $2p_{1/2}\to 6\sigma$ resonance demonstrate that the scheme can be used to create ultrashort coherent x-ray pulses.

Synchronization, the emergence of spontaneous order in coupled systems, is of fundamental importance in both physical and biological systems. We demonstrate the synchronization of two dissimilar silicon nitride micromechanical oscillators, that are spaced apart by a few hundred nanometers and are coupled through an optical cavity radiation field. The tunability of the optical coupling between the oscillators enables one to externally control the dynamics and switch between coupled and individual oscillation states. These results pave a path toward reconfigurable synchronized oscillator networks.

We present a novel concept for x-ray waveguiding based on electromagnetism in photonic crystals, using a waveguide consisting of a pair of claddings sandwiching a core with a periodic structure. By confining the x rays undergoing multiple interference in the core by total reflection, a characteristic waveguide mode whose field distribution matches the periodicity of the core is formed. The distinctively low propagation loss enables the single-mode propagation of x rays. This concept opens broad application possibilities in x-ray physics from coherent imaging to x-ray quantum optics.

The equilibrium theory of the 2D magnetohydrodynamic equations is derived, accounting for the full infinite hierarchies of conserved integrals. An exact description in terms of two coupled elastic membranes emerges, producing long-ranged correlations between the magnetic and velocity fields. This is quite different from the results of previous variational treatments, which relied on a local product ansatz for the thermodynamic Gibbs distribution. The equilibria display the same type of coherent structures, such as compact eddies and zonal jets, previously found in pure fluid equilibria. Possible consequences of this for recent simulations of the solar tachocline are discussed.

The nature of nonlinear interactions in gyrokinetic turbulence, driven by the ion-temperature gradient instability, is investigated using direct numerical simulations in toroidal flux tube geometry. To account for the level of separation existing between scales involved in an energetic interaction, the degree of locality of the free energy scale flux is analyzed employing Kraichnan’s infrared (IR) and ultraviolet locality functions. Because of the nontrivial dissipative nature of gyrokinetic turbulence, an asymptotic level for the locality exponents, indicative of a universal dynamical regime for gyrokinetics, is not recovered and an accentuated nonlocal behavior of the IR interactions is found instead, in spite of the local energy cascade observed.

We propose a method to create a nontrivial Haldane phase in an atomic two-component Fermi gas loaded on a one-dimensional optical lattice with trap potential. The Haldane phase is naturally formed on a $p$-band Mott core in a wide range of the strong on-site repulsive interaction. The present proposal is composed of two steps, one of which is theoretical derivation of an effective 1D $S=1$ interacting-chain model from the original tight-binding Hamiltonian handling the two $p$ orbitals, and the other of which is a numerical demonstration employing the density-matrix renormalization group for the formation of the Haldane phase on a $p$-band Mott core and its associated features in the original tight-binding model with the harmonic trap potential.

We consider fermions on a 2D square lattice with a finite-range pairing interaction, and obtain signatures for unconventional pair-symmetry states, $d_{x^2\mathrm{\text{−}}{y}^2}$ and extended-s ($s^{*}$), in the Bardeen-Cooper-Schrieffer–Bose-Einstein Condensation crossover region. We find that the fermion momentum distribution function, $v_k^2$, the ratio of the Bogoliubov coefficients, $v_k/u_k$, and the Fourier transform of $v_k^2$ are strikingly different for $d$ and $s^{*}$ symmetries in the crossover region. The chemical potential and the gap functions for both pairing symmetries show several interesting features as a function of interaction. Fermionic atoms in 2D optical lattices may provide a way to test these signatures. We discuss current generation cold atom experiments that may be utilized.

The ground state of a one-dimensional (1D) quantum gas of dipoles oriented perpendicular to the longitudinal axis, with a strong $1/x^3$ repulsive potential, is studied at low 1D densities $n$. Near contact the dependence of the many-body wave function on the separation $x_{j\ell }$ of two particles reduces to a two-body wave function ${\Psi }_{\mathrm{rel}}(x_{j\ell })$. Immediately after a sudden rotation of the dipoles so that they are parallel to the longitudinal axis, this wave function will still be that of the repulsive potential, but since the potential is now that of the attractive potential, it will not be stationary. It is shown that as $n{d}^2\to 0$ the rate of change of this wave function approaches zero. It follows that for small values of $n{d}^2$, this state is metastable and is an analog of the super Tonks-Girardeau state of bosons with a strong zero-range attraction. The dipolar system is equivalent to a spinor Fermi gas with spin $z$ components ${\sigma }_{\uparrow }=\perp$ (perpendicular to the longitudinal axis) and ${\sigma }_{\downarrow }=\parallel$ (parallel to the longitudinal axis). A Fermi-Fermi mapping from spinor to spinless Fermi gas followed by the standard 1960 Fermi-Bose mapping reduces the Fermi system to a Bose gas. Potential experiments realizing the sudden spin rotation with ultracold dipolar gases are discussed, and a few salient properties of these states are accurately evaluated by a Monte Carlo method.

We present calculations of the ground state and excitations of an anisotropic dipolar Bose gas in two dimensions, realized by a nonperpendicular polarization with respect to the system plane. For sufficiently high density, an increase of the polarization angle leads to a density instability of the gas phase in the direction where the anisotropic interaction is strongest. Using a dynamic many-body theory, we calculate the dynamic structure function in the gas phase which shows the anisotropic dispersion of the excitations. We find that the energy of roton excitations in the strongly interacting direction decreases with increasing polarization angle and almost vanishes close to the instability. Exact path integral ground state Monte Carlo simulations show that this instability is indeed a quantum phase transition to a stripe phase, characterized by long-range order in the strongly interacting direction.

Motivated by the recent experimental success in realizing synthetic spin-orbit coupling in ultracold atomic systems, we consider $N$-component atoms coupled to a non-Abelian $\mathrm{SU}(N)$ gauge field. More specifically, we focus on the case, referred to here as “SU(3) spin-orbit-coupling,” where the internal states of three-component atoms are coupled to their momenta via a matrix structure that involves the Gell-Mann matrices (in contrast to the Pauli matrices in conventional SU(2) spin-orbit-coupled systems). It is shown that the SU(3) spin-orbit-coupling gives rise to qualitatively different phenomena and in particular we find that even a homogeneous SU(3) field on a simple square lattice enables a topologically nontrivial state to exist, while such SU(2) systems always have trivial topology. In deriving this result, we first establish an equivalence between the Hofstadter model with a $1/N$ Abelian flux per plaquette and a homogeneous $\mathrm{SU}(N)$ non-Abelian model. The former is known to have a topological spectrum for $N>2$, which is thus inherited by the latter. It is explicitly verified by an exact calculation for $N=3$, where we develop and use a new algebraic method to calculate topological indices in the SU(3) case. Finally, we consider a strip geometry and establish the existence of three gapless edge states—the hallmark feature of such an SU(3) topological insulator.

The structure of the fragile glass-forming material ${\mathrm{CaAl}}_2{\mathrm{O}}_4$ was measured by applying the method of neutron diffraction with Ca isotope substitution to the laser-heated aerodynamically levitated liquid at 1973(30) K and to the glass at 300(1) K. The results, interpreted with the aid of molecular dynamics simulations, reveal key structural modifications on multiple length scales. Specifically, there is a reorganization on quenching that leads to an almost complete breakdown of the ${\mathrm{AlO}}_5$ polyhedra and threefold coordinated oxygen atoms present in the liquid, and to their replacement by a predominantly corner-sharing network of ${\mathrm{AlO}}_4$ tetrahedra in the glass. This process is accompanied by the formation of branched chains of edge and face-sharing Ca-centered polyhedra that give cationic ordering on an intermediate length scale, where the measured coordination number for O around Ca is 6.0(2) for the liquid and 6.4(2) for the glass.

Using in situ atomic-resolution electron microscopy observations, we report observations of the oxide growth during the oxidation of stepped Cu surfaces. Oxidation occurs via direct growth of ${\mathrm{Cu}}_2\mathrm{O}$ on flat terraces with Cu adatoms detaching from steps and diffusing across the terraces. This process involves neither reconstructive oxygen adsorption nor oxygen subsurface incorporation and is rather different from the mechanism of solid-solid transformation of bulk oxidation that is most commonly postulated. These results demonstrate that the presence of surface steps can promote the development of a flat metal-oxide interface by kinetically suppressing subsurface oxide formation at the metal-oxide interface.

The contact angle that a liquid drop makes on a soft substrate does not obey the classical Young’s relation, since the solid is deformed elastically by the action of the capillary forces. The finite elasticity of the solid also renders the contact angles differently from those predicted by Neumann’s law, which applies when the drop is floating on another liquid. Here, we derive an elastocapillary model for contact angles on a soft solid by coupling a mean-field model for the molecular interactions to elasticity. We demonstrate that the limit of a vanishing elastic modulus yields Neumann’s law or a variation thereof, depending on the force transmission in the solid surface layer. The change in contact angle from the rigid limit to the soft limit appears when the length scale defined by the ratio of surface tension to elastic modulus $\gamma /E$ reaches the range of molecular interactions.

The wetting properties of solid substrates with mesoscale (between van der Waals tails and the capillary length) random roughness are considered as a function of the microscopic contact angle of the wetting liquid and its partial pressure in the surrounding gas phase. It is shown that the well-known transition occurring at Wenzel’s angle is accompanied by a transition line at which a jump in the adsorbed liquid volume occurs. This should be present generally on surfaces bearing homogeneous, isotropic random roughness. While a similar abrupt filling transition has been reported before for certain idealized groove or trough geometries, it is identified here as a universal phenomenon. Its location can be analytically calculated under certain mild conditions.

Keeping the full quantum nature of the problem, we compute the relaxation time of the Holstein polaron in one dimension after it was driven far from the equilibrium by a strong oscillatory pulse. Just after the pulse, the polaron’s kinetic energy increases and subsequently exhibits a relaxation-type decrease with simultaneous emission of phonons. In the weak coupling regime, partial tunneling of the electron from the polaron self-potential is observed. The inverse relaxation time is for small values of electron-phonon coupling $\lambda$ linear with $\lambda$, while it deviates downwards from the linear regime at $\lambda \gtrsim 0.1/{\omega }_0$. The imaginary part of the equilibrium self-energy shows good agreement with the inverse relaxation time obtained from nonequilibrium simulations.

We perform charge self-consistent density functional theory combined with dynamical mean field theory calculations to study correlation effects on the Fermi surfaces of the iron pnictide superconductors LaFePO and LiFeP. We find a distinctive change in the topology of the Fermi surface in both compounds where a hole pocket with Fe $d_{z^2}$ orbital character changes its geometry from a closed shape in the local-density approximation to an open shape upon inclusion of correlations. The opening of the pocket occurs in the vicinity of the $\Gamma$ ($Z$) point in LaFePO (LiFeP). We discuss the relevance of these findings for the low superconducting transition temperature and the nodal gap observed in these materials.

We characterize the Mott-insulator and Luther-Emery phases of the 1D Hubbard model through correlators that measure the parity of spin and charge strings along the chain. These nonlocal quantities order in the corresponding gapped phases and vanish at the critical point $U_c=0$, thus configuring as hidden order parameters. The Mott insulator consists of bound doublon-holon pairs, which in the Luther-Emery phase turn into electron pairs with opposite spins, both unbinding at $U_c$. The behavior of the parity correlators is captured by an effective free spinless fermion model.