We report, for magnetic fields of 0, 8.8, and 14.8 T, measurements of the temperature dependent ${}^{63}\mathrm{Cu}$ NMR spin lattice relaxation rate for near optimally doped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$, near and above $T_c$. In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required precision and implications of the experiment regarding issues including the spin gap or pseudogap.

We demonstrate a juggling atomic fountain by launching two laser-cooled balls of ${}^{133}\mathrm{Cs}$ atoms in rapid succession. The atoms collide near the top of the fountain and, by varying the delay between launches, we scan the collision energy from 19 to $150\mu \mathrm{K}$. We measure the differential scattering cross section and isolate the contributions from different partial waves including their interferences. We observe the $s$-wave energy dependence and the $p$-wave scattering threshold. We infer a triplet $s$-wave scattering length of ${-400a}_0$ and a $p$ wave of $({-107a}_0{)}^3$ for $|F=4,m=4\mathrm{}〉+|3,3〉$.

Extremely high energy ( $\sim {10}^{22}\mathrm{eV}$) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from the big bang. We perform numerical calculations to show that such cascades could contribute more than 10% to the observed cosmic ray flux above $3\times {10}^{19}\mathrm{eV}$ if neutrinos have $\sim \mathrm{eV}$ masses. The required intensity of primary neutrinos could be consistent with astrophysical models for their production if the maximum neutrino energy reaches to $\sim {10}^{22}\mathrm{eV}$ and the massive neutrino dark matter is locally clustered. Future observations of ultrahigh energy cosmic rays will lead to an indirect but practical search for neutrino dark matter.

Large differences have been observed in the diffraction intensities of normal-hydrogen and pure para-hydrogen scattered from the surface of a LiF(001) single crystal. The observed differences are shown to result from a strong coupling between the quadrupole moment of ${\mathrm{H}}_2$ and the surface electrostatic field, which, in a zeroth order approximation, is averaged out in the case of para-hydrogen. Analogous effects are expected in scattering of all homonuclear diatomic molecules from ionic solids.

We report the first room temperature observation of an emission pattern from a single fluorescent molecule signifying that the emission dipole is aligned along the optic $\left(z\right)$ axis of a microscopic imaging system. This technique takes advantage of the $x$, $y$, and $z$-polarized evanescent fields generated in total internal reflection and the usually nettlesome aberrations commonly encountered when imaging biological samples with high numerical aperture oil-immersion objectives. For both $z$-oriented and transverse-oriented individual molecules of the carbocyanine dye ${\mathrm{DiIC}}_{18}$ embedded in polymethyl-methacrylate (PMMA), calculated images accurately model the main features of observed emission patterns.

We have experimentally discovered a new nonthermal mechanism by which submonolayer and multilayer amorphous ice films, deposited at $T<\mathrm{}100\mathrm{}\mathrm{K}$, crystallize due to UV radiation; the proposed mechanism is that photoexcited charge carriers in the graphite substrate tunnel into defect states in the amorphous film, and induce exothermic relaxation from the metastable amorphous to the stable crystalline phase.

Several approaches to QCD with two massless quarks at finite temperature $T$ and baryon chemical potential $\mu$ suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with massive quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in $T$ and $\mu$ and, simultaneously, enhanced fluctuations in the multiplicity of soft pions.

We have used an atomic force microscope to make precision measurements of the Casimir force between a metallized sphere of diameter 196 μm and flat plate. The force was measured for plate-sphere surface separations from 0.1 to 0.9 μm. The experimental results are consistent with present theoretical calculations including the finite conductivity, roughness, and temperature corrections. The root mean square average deviation of 1.6 pN between theory and experiment corresponds to a $1\%$ deviation at the smallest separation.

Large-scale molecular dynamics simulations were used to study the response of carbon nanotubes to a tensile load. Plastic or brittle behaviors can occur depending upon the external conditions and tube symmetry. All tubes are brittle at high strain and low temperature, while at low strain and high temperature armchair $(n,n)$ nanotubes can be completely or partially ductile. In zigzag $(n,0\mathrm{})$ tubes ductile behavior is expected for tubes with $n<\mathrm{}14\mathrm{}$, while larger tubes are completely brittle. In both cases the curvature determines the mechanical response.

Large grains are well known to rise to the top of granular beds. In this Letter, we report to the contrary on a shaking regime in which large, heavy grains rise, but equally large, light grains sink in a granular bed. This behavior occurs in deep beds with high amplitude vibrations—precisely the regime encountered during transportation of industrial solids mixtures. We examine a simple one-dimensional model that captures some aspects of this effect. The central observation underlying this model is that inertia causes heavy objects to lift off the bed, permitting smaller particles to infiltrate beneath; the motion of light objects, by contrast, can fluctuate wildly, preventing this infiltration.

Charge symmetry for parton distributions can be tested by comparing structure functions from neutrino and charged lepton deep inelastic scattering. New experiments provide rather tight upper limits on parton charge symmetry violation (CSV) for intermediate $x$, but suggest CSV effects at small $x$. Careful study of several corrections fails to remove this low- $x$ discrepancy. We are thus forced to consider surprisingly large CSV effects in nucleon sea distributions.

It is quantitatively explained why incoherent transmission electron microscope imaging is extremely robust to the effects of chromatic aberration, which usually limits the resolution in the conventional coherent mode of imaging. Combining this robustness with using underfocus to counter the effects of spherical aberration, we demonstrate subangstrom lattice resolution and information transfer to 0.078 nm.

We report observation of Bose-Einstein condensation (BEC) of a trapped, dilute gas of atomic hydrogen. The condensate and normal gas are studied by two-photon spectroscopy of the $1S$- $2S$ transition. Interactions among the atoms produce a shift of the resonance frequency proportional to density. The condensate is clearly distinguished by its large frequency shift. The peak condensate density is $4.8\pm 1.1\times {10}^{15}{\mathrm{cm}}^{-3\mathrm{}}$, corresponding to a condensate population of ${10}^9$ atoms. The BEC transition occurs at about $T=50\mathrm{}\mu \mathrm{K}$ and $n=1.8\mathrm{}\times {10}^{14}{\mathrm{cm}}^{-3\mathrm{}}$.

A thin solid, burning against an oxidizing wind, develops a fingering instability. The effect is observed in a narrow gap geometry, where free convection is suppressed. Focusing on the developed nonlinear state, we find that two length scales coexist. The spacing between fingers is determined by the Péclet number, and the finger width is determined by heat losses. Dense fingers develop by tip splitting. A phenomenological model accurately predicts the fingers' spacing, and is generally applicable to diffusion limited systems. We suggest that the effect is a new, accurately controllable, version of the thermal-diffusive instability.

Through use of quantum coherence in an atomic system, we demonstrate that an optical field can be used to completely control the polarization state of another field. Theoretical and experimental results show that by applying a field with a frequency tuned near one transition, an initially isotropic atomic vapor can be made to behave as a linearly or circularly birefringent material for fields tuned near an adjoining transition.

The conductance of carbon-atom chains is found from first-principles calculations to vary in an oscillatory manner as the number of carbon atoms is increased, with odd-numbered chains having a lower resistance than even-numbered chains. This finding is explained in terms of the electronic structure of the free chains and its modification by interaction with the metal electrodes: the critical factor is the density of states at the Fermi level of the combined electrode–atomic-wire system. Stronger electrode–atomic-wire coupling, i.e., shorter metal-carbon distance, does not necessarily imply a higher conductance.

A working free-space quantum key distribution system has been developed and tested over an outdoor optical path of $\sim 1\mathrm{km}$ at Los Alamos National Laboratory under nighttime conditions. Results show that free-space quantum key distribution can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite quantum key distribution.

We have combined electron heating experiments and noise thermometry to perform quantitative measurements of the thermopower in mesoscopic samples. This new measuring technique allows us to detect finite size effects in the thermopower of narrow AuFe wires with an Fe concentration ranging from 50 to 3000 ppm. The size effects emerge when reducing the width of the wires below $\simeq 300\mathrm{nm}$ and may be related to a spin-orbit induced magnetic anisotropy close to the wire surface.

In this paper we present results of experimental and theoretical studies of both elastic and inelastic scattering of fast electrons on the fullerene ${\mathrm{C}}_{60}$ in the gas phase. We report the first experimental observation of the electron diffraction on ${\mathrm{C}}_{60}$, manifesting itself in both elastic and inelastic scattering processes. Diffraction patterns of the cross sections carry important information about the characteristics of the target fullerene, such as its size, distribution of the charge density near the cluster surface, frequencies of plasmon resonance excitations, etc.

$(2+1)$-dimensional anti–de Sitter (AdS) gravity is quantized in the presence of an external scalar field. We find that the coupling between the scalar field and gravity is equivalently described by a perturbed conformal field theory at the boundary of ${\mathrm{AdS}}_3$. This allows us to perform a microscopic computation of the transition rates between black hole states due to absorption and induced emission of the scalar field. Detailed thermodynamic balance then yields Hawking radiation as spontaneous emission, and we find agreement with the semiclassical result, including greybody factors. This result also has application to four and five-dimensional black holes in supergravity.