Microwave transport experiments have been performed in a quasi-two-dimensional resonator with randomly distributed conical scatterers. At high frequencies, the flow shows branching structures similar to those observed in stationary imaging of electron flow. Semiclassical simulations confirm that caustics in the ray dynamics are responsible for these structures. At lower frequencies, large deviations from Rayleigh’s law for the wave height distribution are observed, which can only partially be described by existing multiple-scattering theories. In particular, there are “hot spots” with intensities far beyond those expected in a random wave field. The results are analogous to flow patterns observed in the ocean in the presence of spatially varying currents or depth variations in the sea floor, where branches and hot spots lead to an enhanced frequency of freak or rogue wave formation.

We report single-shot measurements of resistance versus time for thermally assisted spin-torque switching in magnetic tunnel junctions. We achieve the sensitivity to resolve the magnetic dynamics prior to as well as during switching, yielding detailed views of switching modes and variations between events. Analyses of individual traces allow measurements of coherence times, nonequilibrium excitation spectra, and variations in magnetization precession amplitude. We find that with a small in-plane hard-axis magnetic field the switching dynamics are more spatially coherent than for a zero field.

A comprehensive investigation of the frequency-noise spectral density of a free-running midinfrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white-noise plateau, corresponding to an intrinsic linewidth of a few hundred hertz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.

We report the demonstration of nuclear forward scattering of synchrotron radiation from ${}^{57}\mathrm{Fe}$ in ferromagnetic $\alpha$ iron in pulsed high magnetic fields up to 30 T. The observed magnetic hyperfine field follows the calculated high field bulk magnetization within 1%, establishing the technique as a precise tool for the study of magnetic solids in very high magnetic fields. To perform these experiments in pulsed fields, we have developed a detection scheme for fully time resolved nuclear forward scattering applicable to other pump probe experiments.

We observe experimentally a novel type of nonlinear diffraction in the process of two-wave mixing on a nonlinear quadratic grating. We demonstrate that when the nonlinear grating is illuminated simultaneously by two noncollinear beams, a second-harmonic diffraction pattern is generated by a virtual beam propagating along the bisector of the two pump beams. The observed diffraction phenomena is a purely nonlinear effect that has no analogue in linear diffraction.

We present nuclear magnetic resonance (NMR) measurements on the three distinct In sites of ${\mathrm{CeCoIn}}_5$ with a magnetic field applied in the [100] direction. We identify the microscopic nature of the long range magnetic order (LRO) stabilized at low temperatures in fields above 10.2 T while still in the superconducting (SC) state. We infer that the ordered moment is oriented along the $\widehat{c}$ axis and map its field evolution. The study of the field dependence of the NMR shift for the different In sites indicates that the LRO likely coexists with a modulated SC phase, possibly that predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. Furthermore, we discern a field region dominated by strong spin fluctuations where static LRO is absent and propose a revised phase diagram.

The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around $7\mu \mathrm{W}$. The device features a continuously tunable gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.

The bias voltage applied to a weakly coupled $n$-doped GaAs/AlAs superlattice increases the amplitude of the coherent hypersound oscillations generated by a femtosecond optical pulse. This bias-induced amplitude increase and experimentally observed spectral narrowing of the superlattice phonon mode with a frequency 441 GHz provides the evidence for hypersound amplification by stimulated emission of phonons in a system where the inversion of the electron populations for phonon-assisted transitions exists.

Recent studies in nonlinear electrokinetics reveal the standard theory to generally overpredict measured velocities, sometimes dramatically. Contamination of the driving surface provides a natural mechanism for electrokinetic suppression. We measure induced charge electro-osmosis over gold electrodes “contaminated” with silica layers of controlled thickness for nearly a thousand distinct conditions, in a system that enables direct comparisons between theoretical predictions and experimental measurements. Both the magnitude and frequency dependence of the measured slip velocity are captured quantitatively over the entire range of experiments by accounting for the physical capacitance and surface chemistry of the dielectric layer. More generally, the quantitative characterization enabled by our apparatus will prove invaluable for the rational design and prediction of electrokinetic systems.

We have investigated the hyperfine structure of the transition between the $5d^{7}6s^2$ ${}^{4}F_{9/2}^e$ ground state and the $5d^{6}6s^{2}6p$ ${}^{6}D_J^o$ excited state in the negative osmium ion by high-resolution collinear laser spectroscopy. This transition is unique because it is the only known electric-dipole transition in atomic anions and might be amenable to laser cooling. From the observed hyperfine structure in ${}^{187}\mathrm{Os}^{-}$ and ${}^{189}\mathrm{Os}^{-}$ the yet unknown total angular momentum of the bound excited state was found to be $J=9/2$. The hyperfine structure constants of the ${}^{4}F_{9/2}^e$ ground state and the ${}^{6}D_{9/2}^o$ excited state were determined experimentally and compared to multiconfiguration Dirac-Fock calculations. Using the knowledge of the ground and excited state angular momenta, the full energy level diagram of ${}^{192}\mathrm{Os}^{-}$ in an external magnetic field was calculated, revealing possible laser cooling transitions.

The full counting statistics for the charge transport through an undoped graphene sheet in the presence of strong potential impurities is studied. Treating the scattering off the impurity in the $s$-wave approximation, we calculate the impurity correction to the cumulant generating function. This correction is universal provided the impurity strength is tuned to a resonant value. In particular, the conductance of the sample acquires a correction of $16e^2/({\pi }^{2}h)$ per resonant impurity.

The dilemma of identifying the correct form for the momentum of light in a medium has run for a century and has been informed by many distinguished contributions, both theoretical and experimental. We show that both the Abraham and Minkowski forms of the momentum density are correct, with the former being the kinetic momentum and the latter the canonical momentum. This identification allows us to explain why the experiments supporting each of the rival momenta gave the results that they did. The inclusion of dispersion and absorption provides an interesting subtlety, but does not change our conclusion.

We have constructed an optical clock with a fractional frequency inaccuracy of , based on quantum logic spectroscopy of an ion. A simultaneously trapped ion serves to sympathetically laser cool the ion and detect its quantum state. The frequency of the clock transition is compared to that of a previously constructed optical clock with a statistical measurement uncertainty of . The two clocks exhibit a relative stability of , and a fractional frequency difference of , consistent with the accuracy limit of the older clock.

We squeeze unconditionally the collective spin of a dilute ensemble of laser-cooled ${}^{87}\mathrm{Rb}$ atoms using their interaction with a driven optical resonator. The shape and size of the resulting spin uncertainty region are well described by a simple analytical model [M. H. Schleier-Smith, I. D. Leroux, and V. Vuletić, arXiv:0911.3936 [Phys. Rev. A (to be published)]] through 2 orders of magnitude in the effective interaction strength, without free parameters. We deterministically generate states with up to 5.6(6) dB of metrologically relevant spin squeezing on the canonical ${}^{87}\mathrm{Rb}$ hyperfine clock transition.

In a recent experiment Paoletti et al. [Phys. Rev. Lett. 101, 154501 (2008)] monitored the motion of tracer particles in turbulent superfluid helium and inferred that the velocity components do not obey the Gaussian statistics observed in ordinary turbulence. Motivated by their experiment, we create a small 3D turbulent state in an atomic Bose-Einstein condensate, compute directly the velocity field, and find similar nonclassical power-law tails. We obtain similar results in 2D trapped and 3D homogeneous condensates, and in classical 2D vortex points systems. This suggests that non-Gaussian turbulent velocity statistics describe a fundamental property of quantum turbulence. We also track the decay of the vortex tangle in the presence of the thermal cloud.

We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to $W^{+}{W}^{-}$. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) ${\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162–166 GeV at the 95% C.L.

We present a search for standard model (SM) Higgs boson production using $p\overline{p}$ collision data at $\sqrt{s}=1.96\mathrm{TeV}$, collected with the CDF II detector and corresponding to an integrated luminosity of $4.8{\mathrm{fb}}^{-1}$. We search for Higgs bosons produced in all processes with a significant production rate and decaying to two $W$ bosons. We find no evidence for SM Higgs boson production and place upper limits at the 95% confidence level on the SM production cross section (${\sigma }_H$) for values of the Higgs boson mass ($m_H$) in the range from 110 to 200 GeV. These limits are the most stringent for $m_H>130\mathrm{GeV}$ and are 1.29 above the predicted value of ${\sigma }_H$ for $m_H=165\mathrm{GeV}$.

A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from $5.4{\mathrm{fb}}^{-1}$ of integrated luminosity in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected with the D0 detector at the Fermilab Tevatron collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at $m_H=165\mathrm{GeV}$.

We have mapped the molecular-atomic transition in liquid hydrogen using first principles molecular dynamics. We predict that a molecular phase with short-range orientational order exists at pressures above 100 GPa. The presence of this ordering and the structure emerging near the dissociation transition provide an explanation for the sharpness of the molecular-atomic crossover and the concurrent pressure drop at high pressures. Our findings have nontrivial implications for simulations of hydrogen; previous equation of state data for the molecular liquid may require revision. Arguments for the possibility of a first order liquid-liquid transition are discussed.

We use a mesoscopic simulation technique to study the effect of short-ranged interparticle attractions on the steady-state sedimentation of colloidal suspensions. Attractions increase the average sedimentation velocity $v_s$ compared to the pure hard-sphere case, and for strong enough attractions, a nonmonotonic dependence on the packing fraction $\varphi$ with a maximum velocity at intermediate $\varphi$ is observed. Attractions also strongly enhance hydrodynamic velocity fluctuations, which show a pronounced maximum size as a function of $\varphi$. These phenomena arise from a complex interplay between nonequilibrium hydrodynamic effects and the thermodynamics of transient cluster formation.