We perform a theoretical and experimental study of a system of two ultracold atoms with tunable interaction in an elongated trapping potential. We show that the coupling of center-of-mass and relative motion due to an anharmonicity of the trapping potential leads to a coherent coupling of a state of an unbound atom pair and a molecule with a center of mass excitation. By performing the experiment with exactly two particles we exclude three-body losses and can therefore directly observe coherent molecule formation. We find quantitative agreement between our theory of inelastic confinement-induced resonances and the experimental results. This shows that the effects of center-of-mass to relative-motion coupling can have a significant impact on the physics of quantum systems near center-of-mass to relative-motion coupling resonances.

We perform bimodal atomic force microscopy measurements on a Br-doped NaCl (001) surface to investigate the mechanisms behind frequency shift and energy dissipation contrasts. The peculiar pattern of the dissipated energy in the torsional channel, related to frictional processes, is increased at the positions of Br impurities, otherwise indistinguishable from Cl ions in the other measured channels. Our simulations reveal how the energy dissipates by the rearrangement of the tip apex and how the process is ultimately governed by lateral forces. Even the slightest change in lateral forces, induced by the presence of a Br impurity, is enough to trigger the apex reconstruction more often, thus increasing the dissipation contrast; the predicted dissipation pattern and magnitude are in good quantitative agreement with the measurements.

We demonstrate orbital angular momentum (OAM) transfer by chiral plasmonic nanostructures designed on both sides of a thin suspended metallic membrane. We show how far-field vortex beams with tunable OAM indices can be tailored through nanostructure designs. We reveal the crucial role played by the central aperture that connects the two sides of the membrane from which OAM selection rules are derived in perfect agreement with experimental data.

Recent step strain experiments in well-entangled polymeric liquids demonstrated a bulk fracturelike phenomenon. We study this instability by using a modern version of the Doi-Edwards theory for entangled polymers, and we find close quantitative agreement with the experiments. The phenomenon occurs because the viscoelastic liquid is sheared into a rubbery state that possesses an elastic constitutive instability [G. Marrucci and N. Grizzuti, J. Rheol. 27, 433 (1983)]. The fracture is a transient manifestation of this instability, which relies on the amplification of spatially inhomogeneous fluctuations. This mechanism differs from the fracture in glassy materials and dense suspensions.

The elementary excitations of vibration in solids are phonons. But in liquids phonons are extremely short lived and marginalized. In this Letter through classical and ab initio molecular dynamics simulations of the liquid state of various metallic systems we show that different excitations, the local configurational excitations in the atomic connectivity network, are the elementary excitations in high temperature metallic liquids. We also demonstrate that the competition between the configurational excitations and phonons determines the so-called crossover phenomenon in liquids. These discoveries open the way to the explanation of various complex phenomena in liquids, such as fragility and the rapid increase in viscosity toward the glass transition, in terms of these excitations.

The vanadium oxyfluoride $[{\mathrm{NH}}_4{]}_2[{\mathrm{C}}_7{\mathrm{H}}_{14}\mathrm{N}][{\mathrm{V}}_7{\mathrm{O}}_6{\mathrm{F}}_{18}]$ (DQVOF) is a geometrically frustrated magnetic bilayer material. The structure consists of $S=1/2$ kagome planes of ${\mathrm{V}}^{4+}$ $d^1$ ions with $S=1$ ${\mathrm{V}}^{3+}$ $d^2$ ions located between the kagome layers. Muon spin relaxation measurements demonstrate the absence of spin freezing down to 40 mK despite an energy scale of 60 K for antiferromagnetic exchange interactions. From magnetization and heat capacity measurements we conclude that the $S=1$ spins of the interplane ${\mathrm{V}}^{3+}$ ions are weakly coupled to the kagome layers, such that DQVOF can be viewed as an experimental model for $S=1/2$ kagome physics, and that it displays a gapless spin liquid ground state.

A first-principles-based effective Hamiltonian is used to investigate low-temperature properties of $\mathrm{Ba}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_3$ relaxor ferroelectrics under an increasing dc electric field. This system progressively develops an electric polarization that is highly nonlinear with the dc field. This development leads to a maximum of the static dielectric response at a critical field, $E_{\mathrm{th}}$, and involves four different field regimes. Each of these regimes is associated with its own behavior of polar nanoregions, such as shrinking, flipping, and elongation of dipoles or change in morphology. The clusters propagating inside the whole sample, with dipoles being parallel to the field direction, begin to form at precisely the $E_{\mathrm{th}}$ critical field. Such a result, and further analysis we perform, therefore, reveal that field-induced percolation of polar nanoregions is the driving mechanism for the transition from the relaxor to ferroelectric state.

Enzymes within biochemical pathways are often colocalized, yet the consequences of specific spatial enzyme arrangements remain poorly understood. We study the impact of enzyme arrangement on reaction efficiency within a reaction-diffusion model. The optimal arrangement transitions from a cluster to a distributed profile as a single parameter, which controls the probability of reaction versus diffusive loss of pathway intermediates, is varied. We introduce the concept of enzyme exposure to explain how this transition arises from the stochastic nature of molecular reactions and diffusion.

The relatively small fraction of the spin of the proton carried by its quarks presents a major challenge to our understanding of the strong interaction. Traditional efforts to explore this problem have involved new and imaginative experiments and QCD based studies of the nucleon. We propose a new approach to the problem that exploits recent advances in lattice QCD. In particular, we extract values for the spin carried by the quarks in other members of the baryon octet in order to see whether the suppression observed for the proton is a general property or depends significantly on the baryon structure. We compare these results with the values for the spin fractions calculated within a model that includes the effects of confinement, relativity, gluon exchange currents, and the meson cloud required by chiral symmetry, finding a very satisfactory level of agreement given the precision currently attainable.

We argue that the domain structure of deconfined QCD matter, which can be inferred from the properties of the Polyakov loop, can simultaneously explain the two most prominent experimentally verified features of the quark-gluon plasma, namely its large opacity as well as its near ideal fluid properties.

We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of $2\times {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$. Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45° from the laser wave vector $k_{\mathrm{laser}}$ for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields.

We report the experimental observation and a theoretical explanation of collective suppression of linewidths for multiple superconducting qubits coupled to a good cavity. This demonstrates how strong qubit-cavity coupling can significantly modify the dephasing and dissipation processes that might be expected for individual qubits, and can potentially improve coherence times in many-body circuit QED.

Recent fully nonlinear, kinetic three-dimensional simulations of magnetic reconnection [W. Daughton et al., Nat. Phys. 7, 539 (2011)] evolve structures and exhibit dynamics on multiple scales, in a manner reminiscent of turbulence. These simulations of reconnection are among the first to be performed at sufficient spatiotemporal resolution to allow formal quantitative analysis of statistical scaling, which we present here. We find that the magnetic field fluctuations generated by reconnection are anisotropic, have nontrivial spatial correlation, and exhibit the hallmarks of finite range fluid turbulence: they have non-Gaussian distributions, exhibit extended self-similarity in their scaling, and are spatially multifractal. Furthermore, we find that the rate at which the fields do work on the particles, $\mathbf{J}·\mathbf{E}$, is also multifractal, so that magnetic energy is converted to plasma kinetic energy in a manner that is spatially intermittent. This suggests that dissipation in this sense in collisionless reconnection on kinetic scales has an analogue in fluidlike turbulent phenomenology, in that it proceeds via multifractal structures generated by an intermittent cascade.

Despite a renewed interest in Ge as a competitor with Si for a broad range of electronic applications, the microstructure and the electronic properties of the dangling bonds that, in analogy with Si, are expected at the Ge/oxide interface have escaped a firm spectroscopy observation and characterization. Clear evidence based on contactless electrically detected magnetic resonance spectroscopy of a dangling bond at the $\mathrm{Ge}(111)/{\mathrm{GeO}}_2$ interface is reported in this Letter. This result supports the similarity between dangling bonds at the Si(111)/oxide and Ge(111)/oxide interfaces, both showing ${\mathrm{C}}_{3v}$ trigonal point symmetry with the main axis oriented along the $⟨111⟩$ direction. In contrast, at the Ge(001)/oxide interface the absence of the trigonal center in favor of a lower symmetry dangling bond marks the difference with the Si(001)/oxide interface, where both centers are present and the one having higher point symmetry prevails. This fact is rationalized in terms of suboxide interface rearrangement and oxide viscoelasticity, which promote the generation of the nonaxial centers at distorted dimers. The unambiguous identification of the centers at the Ge/oxide interfaces yields a deeper insight into the physical properties of the suboxide interface structure and offers a valid indicator for the evaluation of different surface capping and passivation techniques, with the potential to boost the Ge-related technology.

Inversionless ultralow threshold coherent emission, or polariton lasing, can be obtained by spontaneous radiative recombination from a degenerate polariton condensate with nonresonant excitation. Such excitation has, hitherto, been provided by an optical source. Coherent emission from a GaAs-based quantum well microcavity diode with electrical injection is observed here. This is achieved by a combination of modulation doping of the wells, to invoke polariton-electron scattering, and an applied magnetic field in the Faraday geometry to enhance the exciton-polariton saturation density. These measures help to overcome the relaxation bottleneck and to form a macroscopic and degenerate condensate as evidenced by angle-resolved luminescence, light-current characteristics, spatial coherence, and output polarization. The experiments were performed at 30 K with an applied field of 7 T.

The role of gravity in gelation of adhesive hard spheres is studied and a critical criterion developed for homogeneous gelation within the gas-liquid binodal. We hypothesize that gelation by Brownian diffusion competes with phase separation enhanced by gravitational settling. This competition is characterized by the gravitational Péclet number ${\mathrm{Pe}}_g$, which is a function of particle size, volume fraction, and gravitational acceleration. Through a systematic variation of the parameters, we observe the critical ${\mathrm{Pe}}_g$ of $\sim 0.01$ can predict the stability of gels composed of adhesive hard spheres.

We propose a general framework to solve tight binding models in $D$ dimensional lattices driven by ac electric fields. Our method is valid for arbitrary driving regimes and allows us to obtain effective Hamiltonians for different external field configurations. We establish an equivalence with time-independent lattices in $D+1$ dimensions and analyze their topological properties. Furthermore, we demonstrate that nonadiabaticity drives a transition from topological invariants defined in $D+1$ to $D$ dimensions. Our results have potential applications in topological states of matter and nonadiabatic topological quantum computation, predicting novel outcomes for future experiments.

We show that a one-dimensional discrete time quantum walk can be used to implement a generalized measurement in terms of a positive operator value measure (POVM) on a single qubit. More precisely, we show that for a single qubit any set of rank 1 and rank 2 POVM elements can be generated by a properly engineered quantum walk. In such a scenario the measurement of a particle at a position $x=i$ corresponds to a measurement of a POVM element $E_i$ on a qubit. Since the idea of quantum walks originates from the von Neumann model of measurement, in which the change of the position of the pointer depends on the state of the system that is being measured, we argue that von Neumann measurements can be naturally extended to POVMs if one includes the internal evolution of the system in the model.

A virial expansion of fluid pressure in powers of the density can be used to calculate a wealth of thermodynamic information, but the $N$th virial coefficient, which multiplies the $N$th power of the density in the expansion, becomes rapidly more complicated with increasing $N$. This Letter shows that the $N$th virial coefficient can be calculated using a method that scales exponentially with $N$ in computer time and memory. This is orders of magnitude more efficient than any existing method for large $N$, and the method is simple and general. New results are presented for $N=11$ and 12 for hard spheres, and $N=9$ and 10 for soft spheres.

We study a subsystem of an isolated one-dimensional correlated metal when it is driven by a steady electric field or when it relaxes after driving. We obtain numerically exact reduced density matrix $\rho$ for subsystems which are sufficiently large to give significant eigenvalue statistics and spectra of $\log (\rho )$. We show that both for generic as well as for the integrable model, the statistics follows the universality of Gaussian unitary and orthogonal ensembles for driven and equilibrium systems, respectively. Moreover, the spectra of modestly driven subsystems are well described by the Gibbs thermal distribution with the entropy determined by the time-dependent energy only.