We investigate the behavior of colloidal particles immersed in a binary liquid mixture of water and 2,6-lutidine in the presence of a chemically patterned substrate. Close to the critical point of the mixture, the particles are subjected to critical Casimir interactions with force components normal and parallel to the surface. Because the strength and sign of these interactions can be tuned by variations in the surface properties and the mixtures temperature, critical Casimir forces allow the formation of highly ordered monolayers but also extend the use of colloids as model systems.

Molecular rotors with a fixed off-center rotation axis have been observed for single tetra-tert-butyl zinc phthalocyanine molecules on an Au(111) surface by a scanning tunneling microscope at ${\mathrm{LN}}_2$ temperature. Experiments and first-principles calculations reveal that we introduce gold adatoms at the surface as the stable contact of the molecule to the surface. An off-center rotation axis is formed by a chemical bonding between a nitrogen atom of the molecule and a gold adatom at the surface, which gives them a well-defined contact while the molecules can have rotation-favorable configurations. Furthermore, these single-molecule rotors self-assemble into large scale ordered arrays on Au(111) surfaces. A fixed rotation axis off center is an important step towards the eventual fabrication of molecular motors or generators.

A quantum theory of optical Bloch oscillations and Zener tunneling (ZT) in arrays of coupled waveguides is theoretically presented, and the particlelike behavior of photons undergoing ZT is highlighted. In singly-periodic arrays excited by a photon-number-state input beam, each photon behaves as a classical particle which independently undergoes a coin-toss ZT event with a probability described by classical Zener theory. In binary arrays, excitation with two tilted beams enables us to observe the Hong-Ou-Mandel interference for two photons undergoing Bloch-Zener oscillations.

We present the first observation of an instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strongly perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wave numbers corresponding to wavelengths close to the electron gyroradius.

We prove that the results of a finite set of general quantum measurements on an arbitrary dimensional quantum system can be simulated using a polynomial (in measurements) number of hidden-variable states. In the limit of infinitely many measurements, our method gives models with the minimal number of hidden-variable states, which scales linearly with the number of measurements. These results can find applications in foundations of quantum theory, complexity studies, and classical simulations of quantum systems.

In aggregates of objects moving through a fluid, bodies downstream of a leader generally experience reduced drag force. This conventional drafting holds for objects of fixed shape, but interactions of deformable bodies in a flow are poorly understood, as in schools of fish. In our experiments on “schooling” flapping flags, we find that it is the leader of a group who enjoys a significant drag reduction (of up to 50%), while the downstream flag suffers a drag increase. This counterintuitive inverted drag relationship is rationalized by dissecting the mutual influence of shape and flow in determining drag. Inverted drafting has never been observed with rigid bodies, apparently due to the inability to deform in response to the altered flow field of neighbors.

We measure the response and thermal motion of a high-$Q$ nanomechanical oscillator coupled to a superconducting microwave cavity in the resolved-sideband regime where the oscillator’s resonance frequency exceeds the cavity’s linewidth. The coupling between the microwave field and mechanical motion is strong enough for radiation pressure to overwhelm the intrinsic mechanical damping. This radiation-pressure damping cools the fundamental mechanical mode by a factor of 5 below the thermal equilibrium temperature in a dilution refrigerator to a phonon occupancy of 140 quanta.

We report on the observation of magnetic vortex dynamics in response to rotating magnetic fields in submicron platelets. Unlike linear fields or spin polarized currents, which excite both vortex core polarization states, an in-plane rotating field can selectively excite one of the polarization states. We demonstrate by direct imaging with time-resolved scanning x-ray microscopy that the rotating field only excites the gyrotropic mode if the rotation sense of the field coincides with the vortex gyration sense and that such a field can selectively reverse the vortex polarization.

We propose consistency tests for the cosmological constant which provide a direct observational signal if $\Lambda$ is wrong, regardless of the densities of matter and curvature. As an example of its utility, our flat case test can warn of a small transition of the equation of state $w(z)$ from $w(z)=-1$ of 20% from SNAP (Supernova Acceleration Probe) quality data at 4-$\sigma$, even when direct reconstruction techniques see virtually no evidence for deviation from $\Lambda$. It is shown to successfully rule out a wide range of non-$\Lambda$ dark energy models with no reliance on knowledge of ${\Omega }_m$ using SNAP quality data and a large range for using ${10}^5$ supernovae as forecasted for the Large Synoptic Survey Telescope.

A system consisting of two independently contacted quantum dots with a strong electrostatic interaction shows an interdot Coulomb blockade when the dots are weakly tunnel coupled to their leads. How the blockade can be overcome by correlated tunneling when tunnel coupling to the leads increases is studied experimentally. The experimental results are compared with numerical renormalization group calculations using predefined (measured) parameters. Combining our experimental and theoretical results we identify transport through Kondo correlations due to the electrostatic interaction between the two dots.

We show theoretically that a directional dipole wave can be perfectly reflected by a single pointlike oscillating dipole. Furthermore, we find that, in the case of a strongly focused plane wave, up to 85% of the incident light can be reflected by the dipole. Our results hold for the full spectrum of the electromagnetic interactions and have immediate implications for achieving strong coupling between a single propagating photon and a single quantum emitter.

We have frozen the coherent evolution of a field in a cavity by repeated measurements of its photon number. We use circular Rydberg atoms dispersively coupled to the cavity mode for an absorption-free photon counting. These measurements inhibit the growth of a field injected in the cavity by a classical source. This manifestation of the quantum Zeno effect illustrates the backaction of the photon number determination onto the field phase. The residual growth of the field can be seen as a random walk of its amplitude in the two-dimensional phase space. This experiment sheds light onto the measurement process and opens perspectives for active quantum feedback.

We present a novel method to realize analog sum computation with a Bose-Einstein condensate in an optical lattice potential subject to controlled phase jumps. We use the method to implement the Gauss sum algorithm for factoring numbers. By exploiting higher order quantum momentum states, we are able to improve the algorithm’s accuracy beyond the limits of the usual classical implementation.

Surface x-ray diffraction has been employed to elucidate the surface structure of the $(011)-(2\times 1)$ termination of rutile ${\mathrm{TiO}}_2$. The data are inconsistent with previously proposed structures. Instead, an entirely unanticipated geometry emerges from the structure determination, which is terminated by zigzag rows of twofold coordinated oxygen atoms asymmetrically bonded to fivefold titanium atoms. The energetic stability of this structure is demonstrated by ab initio total energy calculations.

We construct a supersymmetric model where the left-handed top and bottom quarks are mainly the gauginos of a vector supermultiplet and hence their superpartners are spin 1. The right-handed top quark is unified with the Higgs field; the top Yukawa coupling arises from the gaugino coupling.

Two anomalously weak transitions within the $2{}^{3}S_1-3{}^{3}P_J$ manifolds in ${}^3\mathrm{He}$ have been identified. Their transition strengths are measured to be 1000 times weaker than that of the strongest transition in the same group. This dramatic suppression of transition strengths is due to the dominance of the hyperfine interaction over the fine-structure interaction. An alternative selection rule based on $IS$ coupling (where the nuclear spin is first coupled to the total electron spin) is proposed. This provides qualitative understanding of the transition strengths. It is shown that the small deviations from the $IS$ coupling model are fully accounted for by an exact diagonalization of the strongly interacting states.

By extending traditional particle tracking techniques, we study the dynamics of neutrally buoyant finite-sized particles in a spatiotemporally chaotic flow. We simultaneously measure the flow field and the trajectories of millimeter-scale particles so that the two can be directly compared. While the single-point statistics of the particles are indistinguishable from the flow statistics, the particles often move in directions that are systematically different from the underlying flow. These differences are especially evident when Lagrangian statistics are considered.

The Charney-Hasegawa-Mima equation applies to a broad variety of hydrodynamic systems ranging from the large-scale planetary circulations to small-scale processes in magnetically confined plasma. This equation harbors flow regimes that have not yet been fully understood. One of those is the recently discovered regime of zonostrophic turbulence emerging in the case of small-scale forced, barotropic two-dimensional turbulence on the surface of a rotating sphere or in its $\beta$-plane approximation. The commingling of strong nonlinearity, strong anisotropy and Rossby waves underlying this regime is highlighted by the emergence of stable systems of alternating zonal jets and a new class of nonlinear waves, or zonons. This Letter elucidates the physics of the zonons and their relation to the large-scale coherent structures.

We find that the amplitude of quantum fluctuations of the invariant de Sitter vacuum coincides exactly with that of the vacuum of a comoving observer for a massless scalar (inflaton) field. We propose redefining the actual physical power spectrum as the difference between the amplitudes of the above vacua. An inertial particle detector continues to observe the Gibbons-Hawking temperature. However, although the resulting power spectrum is still scale-free, its amplitude can be drastically reduced since now, instead of the Hubble’s scale at the inflationary period, it is determined by the square of the mass of the inflaton fluctuation field.

Cytoplasmic streaming circulates the contents of large eukaryotic cells, often with complex flow geometries. A largely unanswered question is the significance of these flows for molecular transport and mixing. Motivated by “rotational streaming” in Characean algae, we solve the advection-diffusion dynamics of flow in a cylinder with bidirectional helical forcing at the wall. A circulatory flow transverse to the cylinder’s long axis, akin to Dean vortices at finite Reynolds numbers, arises from the chiral geometry. Strongly enhanced lateral transport and longitudinal homogenization occur if the transverse Péclet number is sufficiently large, with scaling laws arising from boundary layers.