We present the design, fabrication, and performance analysis for a class of two-dimensional acoustic cloaking coatings in air. Our approach takes advantage of transformation acoustics and linear coordinate transformations that result in shells which are homogeneous, broadband, and compact. The required material parameters are highly anisotropic; however, we show that they are easily achievable in practice in metamaterials made of perforated plastic plates. The good performance of the fabricated design is assessed from measurements of the sound field produced around the cloak by a broadband source. The remarkably low complexity of the device made of perforated plastic plates shows that sound in air can be fully and effectively manipulated using realizable transformation acoustics devices.

Radio-frequency induced spin transitions of one individual proton are observed. The spin quantum jumps are detected via the continuous Stern-Gerlach effect, which is used in an experiment with a single proton stored in a cryogenic Penning trap. This is an important milestone towards a direct high-precision measurement of the magnetic moment of the proton and a new test of the matter-antimatter symmetry in the baryon sector.

We show that the superconformal index (the partition function on the three-sphere times a circle) of a certain class of 4D supersymmetric field theories is exactly equal to a partition function of $q$-deformed nonsupersymmetric 2D Yang-Mills theory.

We report the direct observation of optical precursors of heralded single photons with step- and square-modulated wave packets passing through cold atoms. Using electromagnetically induced transparency and the slow-light effect, we separate the single-photon precursor, which always travels at the speed of light in vacuum, from its delayed main wave packet. In the two-level superluminal medium, our result suggests that the causality holds for a single photon.

We report that double-stranded DNA collapses in the presence of ac electric fields at frequencies of a few hundred Hertz, and does not stretch as commonly assumed. In particular, we show that confinement-stretched DNA can collapse to about one quarter of its equilibrium length. We propose that this effect is based on finite relaxation times of the counterion cloud, and the subsequent partitioning of the molecule into mutually attractive units. We discuss alternative models of those attractive units.

Scanning-tunneling microscopy and density-functional theory have been employed to identify the spatial correlation between an oxygen vacancy and the associated ${\mathrm{Ce}}^{3+}$ ion pair in a defective ${\mathrm{CeO}}_2(111)$ film. The two ${\mathrm{Ce}}^{3+}$ ions can occupy different cationic shells around the vacancy. The resulting variation in the chemical environment leads to a splitting of the filled ${\mathrm{Ce}}^{3+}$ $f$ levels, which is detected with STM spectroscopy. The position of the ${\mathrm{Ce}}^{3+}$ ion pair is reflected in characteristic defect patterns observed in empty-state STM images, which arise from the bright appearance of ${\mathrm{Ce}}^{4+}$ ions next to the defect while the ${\mathrm{Ce}}^{3+}$ remain dark. Both findings demonstrate that at least one excess electron localizes in a Ce ion that is not adjacent to the O vacancy.

We observe a large excess of power in the statistical clustering of luminous red galaxies in the photometric SDSS galaxy sample called MegaZ DR7. This is seen over the lowest multipoles in the angular power spectra $C_{\ell }$ in four equally spaced redshift bins between $0.45\le z\le 0.65$. However, it is most prominent in the highest redshift band at $\sim 4\sigma$ and it emerges at an effective scale $k\lesssim 0.01\mathrm{h}{\mathrm{Mpc}}^{-1}$. Given that MegaZ DR7 is the largest cosmic volume galaxy survey to date ($3.3({\mathrm{Gpch}}^{-1}{)}^3$) this implies an anomaly on the largest physical scales probed by galaxies. Alternatively, this signature could be a consequence of it appearing at the most systematically susceptible redshift. There are several explanations for this excess power that range from systematics to new physics. We test the survey, data, and excess power, as well as possible origins.

We use phase-resolved transient grating spectroscopy to measure the drift and diffusion of electron-hole density waves in a semiconductor quantum well. The unique aspects of this optical probe allow us to determine the frictional force between a two-dimensional Fermi liquid of electrons and a dilute gas of holes. Knowledge of electron-hole friction enables prediction of ambipolar dynamics in high-mobility electron systems.

Small particles transported by a fluid medium do not necessarily have to follow the flow. We show that for a wide class of time-periodic incompressible flows inertial particles have a tendency to spontaneously align in one-dimensional dynamic coherent structures. This effect may take place for particles so small that often they would be expected to behave as passive tracers and be used in PIV measurement technique. We link the particle tendency to form one-dimensional structures to the nonlinear phenomenon of phase locking. We propose that this general mechanism is, in particular, responsible for the enigmatic formation of the “particle accumulation structures” discovered experimentally in thermocapillary flows more than a decade ago and unexplained until now.

Three oriented bosonic dipoles are treated by using the hyperspherical adiabatic representation, providing numerical evidence that the Efimov effect persists near a two-dipole resonance and in a system where angular momentum is not conserved. Our results further show that the Efimov features in scattering observables become universal, with a known three-body parameter; i.e., the resonance energies depend only on the two-body physics, which also has implications for the universal spectrum of the four-dipole problem. Moreover, the Efimov states should be long-lived, which is favorable for their creation and manipulation in ultracold dipolar gases. Finally, deeply bound two-dipole states are shown to be relatively stable against collisions with a third dipole, owing to the emergence of a repulsive interaction originating in the angular momentum nonconservation for this system.

We present the first experimental evidence for the morphological transition from twisted to helical ribbons in amphiphile aggregates. This transition, from structures possessing negative Gaussian curvature to helically curved structures, is shown to be directly linked to ribbon width. Time-resolved cryotransmission electron microscopy images of a peptidomimetic amphiphile further capture the dynamic transformation between the two geometries along a single ribbon unit. Quantitative analysis indicates that both ribbon width and pitch grow with ribbon maturation, maintaining a constant ratio.

We describe a simple method for certifying that an experimental device prepares a desired quantum state $\rho$. Our method is applicable to any pure state $\rho$, and it provides an estimate of the fidelity between $\rho$ and the actual (arbitrary) state in the lab, up to a constant additive error. The method requires measuring only a constant number of Pauli expectation values, selected at random according to an importance-weighting rule. Our method is faster than full tomography by a factor of $d$, the dimension of the state space, and extends easily and naturally to quantum channels.

A search for neutral minimal supersymmetric standard model (MSSM) Higgs bosons in $pp$ collisions at the LHC at a center-of-mass energy of 7 TeV is presented. The results are based on a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$ recorded by the CMS experiment. The search uses decays of the Higgs bosons to tau pairs. No excess is observed in the tau-pair invariant-mass spectrum. The resulting upper limits on the Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, yield stringent new bounds in the MSSM parameter space.

We scrutinize the concept of saturation of the thermal component in a partially condensed trapped Bose gas. Using a ${}^{39}\mathrm{K}$ gas with tunable interactions, we demonstrate strong deviation from Einstein’s textbook concept of a saturated vapor. However, the saturation picture can be recovered by extrapolation to the strictly noninteracting limit. We provide evidence for the universality of our observations through additional measurements with a different atomic species, ${}^{87}\mathrm{Rb}$.

We show theoretically that the sudden application of an appropriate ac field to correlated lattice fermions flips the band structure and effectively switches the interaction from repulsive to attractive. The nonadiabatically driven system is characterized by a negative temperature with a population inversion. We numerically demonstrate the converted interaction in an ac-driven Hubbard model with the nonequilibrium dynamical mean-field theory solved by the continuous-time quantum Monte Carlo method. Based on this, we propose an efficient ramp-up protocol for ac fields that can suppress heating, which leads to an effectively attractive Hubbard model with a temperature below the superconducting transition temperature of the equilibrium system.

We show that a suitable combination of geometric frustration, ferromagnetism, and spin-orbit interactions can give rise to nearly flatbands with a large band gap and nonzero Chern number. Partial filling of the flatband can give rise to fractional quantum Hall states at high temperatures (maybe even room temperature). While the identification of material candidates with suitable parameters remains open, our work indicates intriguing directions for exploration and synthesis.

We report the theoretical discovery of a class of 2D tight-binding models containing nearly flatbands with nonzero Chern numbers. In contrast with previous studies, where nonlocal hoppings are usually required, the Hamiltonians of our models only require short-range hopping and have the potential to be realized in cold atomic gases. Because of the similarity with 2D continuum Landau levels, these topologically nontrivial nearly flatbands may lead to the realization of fractional anomalous quantum Hall states and fractional topological insulators in real materials. Among the models we discover, the most interesting and practical one is a square-lattice three-band model which has only nearest-neighbor hopping. To understand better the physics underlying the topological flatband aspects, we also present the studies of a minimal two-band model on the checkerboard lattice.

We present a simple prescription to flatten isolated Bloch bands with a nonzero Chern number. We first show that approximate flattening of bands with a nonzero Chern number is possible by tuning ratios of nearest-neighbor and next-nearest-neighbor hoppings in the Haldane model and, similarly, in the chiral-$\pi$-flux square lattice model. Then we show that perfect flattening can be attained with further range hoppings that decrease exponentially with distance. Finally, we add interactions to the model and present exact diagonalization results for a small system at $1/3$ filling that support (i) the existence of a spectral gap, (ii) that the ground state is a topological state, and (iii) that the Hall conductance is quantized.

We construct a gravitational dual of a Josephson junction. Calculations on the gravity side reproduce the standard relation between the current across the junction and the phase difference of the condensate. We also study the dependence of the maximum current on the temperature and size of the junction and reproduce familiar results.

We report an in-depth study on how spin information propagates at supramolecular scale through a family of heteroaromatic linkers. By density-functional theory calculations, we rationalize the behavior of a series of ${\mathrm{Cr}}_7\mathrm{Ni}$ dimers for which we are able to systematically change the aromatic linker thus tuning the strength of the magnetic interaction, as experimentally shown by low temperature micro-SQUID and specific heat measurements. We also predict a ${cos}^2$ dependence of the magnetic coupling on the twisting angle between the aromatic cycles in bicyclic linkers, a mechanism parallel to charge transport on similar systems [L. Venkataraman et al., Nature (London) 442, 904 (2006)].