Coherence times of dressed states of a superconducting qubit under extreme driving

We measure longitudinal dressed states of a superconducting qubit, the single Cooper-pair box, and an intense microwave field. The dressed states represent the hybridization of the qubit and photon degrees of freedom and appear as avoided level crossings in the combined energy diagram. By embedding the circuit in an rf oscillator, we directly probe the dressed states. We measure their dressed gap as a function of photon number and microwave amplitude, finding good agreement with theory. In addition, we extract the relaxation and dephasing rates of these states.     

Adsorption of organic probes on silica through Lewis interactions: a comparison of experimental results and quantum chemical calculations

The adsorption of organic probe molecules on a partly dehydroxylated silica (SiO(2)) surface has been studied in a non-aquatic and non-polar environment. These results were compared to, verified and explained by quantum chemical calculations on the same systems. Since the systems are water free and since the non-polar solvent cyclohexane is used in the experiments, the quantum chemical calculations are well comparable to the experimental results without any additional terms. The characterized surface was found to contain both Lewis acid and Lewis base sites and a good agreement between the experimentally determined and the calculated data was found.     

Molecular dynamics simulations of polyelectrolyte brushes: from single chains to bundles of chains

Using molecular dynamics simulations in combination with scaling analysis, we have studied the effects of the solvent quality and the strength of the electrostatic interactions on the conformations of spherical polyelectrolyte brushes in salt-free solutions. The spherical polyelectrolyte brush could be in one of four conformations: (1) a star-like conformation, (2) a "star of bundles" conformation in which the polyelectrolyte chains self-assemble into pinned cylindrical micelles, (3) a micelle-like conformation with a dense core and charged corona, or (4) a conformation in which there is a thin polymeric layer uniformly covering the particle surface. These different brush conformations appear as a result of the fine interplay between electrostatic and monomer-monomer interactions. The brush thickness depends nonmonotonically on the value of the Bjerrum length. This dependence of the brush thickness is due to counterion condensation inside the brush volume. We have also established that bundle formation in poor solvent conditions for the polymer backbone can also occur in a planar polyelectrolyte brush. In this case, the grafted polyelectrolyte chains form hemispherical aggregates at low polymer grafting densities, cylindrical aggregates at an intermediate range of the grafting densities, and vertically oriented ribbon-like aggregates at high grafting densities.     

Binding affinities in the SAMPL3 trypsin and host–guest blind tests estimated with the MM/PBSA and LIE methods

We have estimated affinities for the binding of 34 ligands to trypsin and nine guest molecules to three different hosts in the SAMPL3 blind challenge, using the MM/PBSA, MM/GBSA, LIE, continuum LIE, and Glide score methods. For the trypsin challenge, none of the methods were able to accurately predict the experimental results. For the MM/GB(PB)SA and LIE methods, the rankings were essentially random and the mean absolute deviations were much worse than a null hypothesis giving the same affinity to all ligand. Glide scoring gave a Kendall's τ index better than random, but the ranking is still only mediocre, τ = 0.2. However, the range of affinities is small and most of the pairs of ligands have an experimental affinity difference that is not statistically significant. Removing those pairs improves the ranking metric to 0.4-1.0 for all methods except CLIE. Half of the trypsin ligands were non-binders according to the binding assay. The LIE methods could not separate the inactive ligands from the active ones better than a random guess, whereas MM/GBSA and MM/PBSA were slightly better than random (area under the receiver-operating-characteristic curve, AUC = 0.65-0.68), and Glide scoring was even better (AUC = 0.79). For the first host, MM/GBSA and MM/PBSA reproduce the experimental ranking fairly good, with τ = 0.6 and 0.5, respectively, whereas the Glide scoring was considerably worse, with a τ = 0.4, highlighting that the success of the methods is system-dependent.     

Vibrational entropy of dislocations in Al

The region nearest to a lattice defect must be described by an atomistic model, while a continuum model suffices further away from the defect. We study such a separation into two regions for an edge dislocation. In particular we focus on the excess defect energy and vibrational entropy, when the dislocation core is described by a cluster of about 500–100?atoms, embedded in a large discrete and relaxed, but static, lattice. The interaction between the atoms is given by a potential of the embedded-atom model type referring to Al. The dynamic matrix of the vibrations in the cluster is fully diagonalized. The excess entropy ΔS near the core has positive and negative contributions, depending on the sign of the local strain. Typically, ΔS/k _B ≈ 2 per atomic repeat length along the dislocation core in fcc Al. In the elastic continuum region far from the dislocation core the excess entropy shows the same logarithmic divergence as the elastic energy. Although the work refers to a specific material and defect type, the results are of a generic nature.     

Charged meson rapidity distributions in central Au+Au collisions at square root(sNN) = 200 GeV

We have measured rapidity densities dN/dy of pi+/- and K+/- over a broad rapidity range (-0.1 < y < 3.5) for central Au + Au collisions at square root(sNN) = 200 GeV. These data have significant implications for the chemistry and dynamics of the dense system that is initially created in the collisions. The full phase-space yields are 1660 +/- 15 +/- 133 (pi+), 1683 +/- 16 +/- 135 (pi-), 286 +/- 5 +/- 23 (K+), and 242 +/- 4 +/- 19 (K-). The systematics of the strange to nonstrange meson ratios are found to track the variation of the baryochemical potential with rapidity and energy. Landau-Carruthers hydrodynamics is found to describe the bulk transport of the pions in the longitudinal direction.     

Centrality dependence of charged-particle pseudorapidity distributions from d + Au collisions at sqrt[sNN] = 200 GeV

Charged-particle pseudorapidity densities are presented for the d + Au reaction at sqrt[s(NN)] = 200 GeV with -4.2 < or = eta < or = 4.2. The results, from the BRAHMS experiment at BNL Relativistic Heavy-Ion Collider, are shown for minimum-bias events and 0%-30%, 30%-60%, and 60%-80% centrality classes. Models incorporating both soft physics and hard, perturbative QCD-based scattering physics agree well with the experimental results. The data do not support predictions based on strong-coupling, semiclassical QCD. In the deuteron-fragmentation region the central 200 GeV data show behavior similar to full-overlap d+Au results at sqrt[s(NN)] = 19.4 GeV.