A novel mechanism of asymmetric frequency conversion is investigated in nonlinear dispersive devices driven parametrically with a biharmonic pump. When the relative phase between the first and second harmonics combined in a two-tone pump is appropriately tuned, nonreciprocal frequency conversion, either upward or downward, can occur. Full directionality and efficiency of the conversion process is possible, provided that the distribution of pump power over the harmonics is set correctly. While this asymmetric conversion effect is generic, we describe its practical realization in a model system consisting of a current-biased, resistively shunted Josephson junction. Here, the multiharmonic Josephson oscillations, generated internally from the static current bias, provide the pump drive.

In a coupled system of one classical and one quantum mechanical degree of freedom, the quantum degree of freedom can facilitate the escape of the whole system. Such unusual escape characteristics have been theoretically predicted as the “Münchhausen effect.” We implement such a system by shunting one of the two junctions of a dc SQUID with an additional capacitance. In our experiments, we detect a crossover between quantum and classical escape processes related to the direction of escape. We find that, under varying external magnetic flux, macroscopic quantum tunneling periodically alternates with thermally activated escape, a hallmark of the “Münchhausen effect.”

We report spontaneous motion in a fully biocompatible system consisting of pure water droplets in an oil-surfactant medium of squalane and monoolein. Water from the droplet is solubilized by the reverse micellar solution, creating a concentration gradient of swollen reverse micelles around each droplet. The strong advection and weak diffusion conditions allow for the first experimental realization of spontaneous motion in a system of isotropic particles at sufficiently large Péclet number according to a straightforward generalization of a recently proposed mechanism [S. Michelin, E. Lauga, and D. Bartolo, Phys. Fluids 25, 061701 (2013); S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)]. Experiments with a highly concentrated solution of salt instead of water, and tetradecane instead of squalane, confirm the above mechanism. The present swimming droplets are able to carry external bodies such as large colloids, salt crystals, and even cells.

Globalization is one of the central concepts of our age. The common perception of the process is that, due to declining communication and transport costs, distance becomes less and less important. However, the distance coefficient in the gravity model of trade, which grows in time, indicates that the role of distance increases rather than decreases. This, in essence, captures the notion of the globalization puzzle. Here, we show that the fractality of the international trade system (ITS) provides a simple solution for the puzzle. We argue that the distance coefficient corresponds to the fractal dimension of ITS. We provide two independent methods, the box counting method and spatial choice model, which confirm this statement. Our results allow us to conclude that the previous approaches to solving the puzzle misinterpreted the meaning of the distance coefficient in the gravity model of trade.

The superfluid-crystal quantum phase transition of a system of purely repulsive dipolar bosons in two dimensions is studied by quantum Monte Carlo simulations at zero temperature. We determine freezing and melting densities and estimate the energy per unit length of a macroscopic interface separating the two phases. The results rule out the microemulsion scenario for any physical realization of this system, given the exceedingly large predicted size of the bubbles.

We propose a novel island nucleation and growth model explicitly including transient (ballistic) mobility of the monomers deposited at rate $F$, assumed to be in a hot precursor state before thermalizing. In limiting regimes, corresponding to fast (diffusive) and slow (ballistic) thermalization, the island density $N$ obeys scaling $N\propto F^{\alpha }$. In between is found a rich, complex behavior, with various distinctive scaling regimes, characterized by effective exponents ${\alpha }_{\text{eff}}$ and activation energies that we compute exactly. Application to $N(F,T)$ of recent organic-molecule deposition experiments yields an excellent fit.

We report the observation of the Hall effect at hole densities up to $6\times {10}^{13}{\mathrm{cm}}^{-2}$ ($0.3\text{holes}/\text{molecule}$) on the surface of electrolyte-gated rubrene crystals. The perplexing peak in the conductance as a function of gate voltage is confirmed to result from a maximum in mobility, which reaches $4{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at $2.5\times {10}^{13}{\mathrm{cm}}^{-2}$. Measurements to liquid helium temperatures reveal that this peak is markedly asymmetric, with bandlike and hopping-type transport occurring on the low density side, while unconventional, likely electrostatic-disorder-affected transport dominates the high density side. Most significantly, near the mobility peak the temperature coefficient of the resistance remains positive to as low as 120 K, the low temperature resistance becomes weakly temperature dependent, and the conductance reaches within a factor of 2 of $e^2/h$, revealing conduction unprecedentedly close to a two-dimensional metallic state.

The recent observation of ultralow resistivity in highly doped, atomic-scale silicon wires has sparked interest in what limits conduction in these quasi-1D systems. Here we present electron transport measurements of gated $\mathrm{Si}:\mathrm{P}$ wires of widths 4.6 and 1.5 nm. At 4.6 nm we find an electron mobility, ${\mu }_{\mathrm{el}}\simeq 60{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$, in excellent agreement with that of macroscopic Hall bars. Metallic conduction persists to millikelvin temperatures where we observe Gaussian conductance fluctuations of order $\delta G\sim e^2/h$. In thinner wires (1.5 nm), metallic conduction breaks down at $G\lesssim e^2/h$, where localization of carriers leads to Coulomb blockade. Metallic behavior is explained by the large carrier densities in $\mathrm{Si}:\mathrm{P}$ $\delta$-doped systems, allowing the occupation of all six valleys of the silicon conduction band, enhancing the number of 1D channels and hence the localization length.

In few-body physics, Efimov states are an infinite series of three-body bound states that obey universal discrete scaling symmetry when pairwise interactions are resonantly enhanced. Despite abundant reports of Efimov states in recent cold atom experiments, direct observation of the discrete scaling symmetry remains an elusive goal. Here we report the observation of three consecutive Efimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies Feshbach resonance. The positions of the resonances closely follow a geometric series 1, $\lambda$, ${\lambda }^2$. The observed scaling constant ${\lambda }_{\text{exp}}=4.9(4)$ is in good agreement with the predicted value of 4.88.

The Majorana’s stellar representation, which represents the evolution of a quantum state with the trajectories of the Majorana stars on a Bloch sphere, provides an intuitive way to study a physical system with a high dimensional projective Hilbert space. In this Letter, we study the Berry phase by these stars and their loops on the Bloch sphere. It is shown that the Berry phase of a general spin state can be expressed by an elegant formula with the solid angles of Majorana star loops. Furthermore, these results can be used to a general state with arbitrary dimensions. To demonstrate our theory, we study a two mode interacting boson system. Finally, the relation between stars’ correlations and quantum entanglement is discussed.

We show that an electron moving in a uniform magnetic field possesses a time-varying “diamagnetic” angular momentum. Surprisingly this means that the kinetic angular momentum of the electron may vary with time, despite the rotational symmetry of the system. This apparent violation of angular momentum conservation is resolved by including the angular momentum of the surrounding fields.

We describe a Casimir apparatus based on a differential force measurement between a Au-coated sphere and a planar slab divided in two regions, one of which is made of high-resistivity (dielectric) Si, and the other of Au. The crucial feature of the setup is a semitransparent plane parallel conducting overlayer, covering both regions. The setup offers two important advantages over existing Casimir setups. On one hand, it leads to a large amplification of the difference between the Drude and the plasma prescriptions that are currently used to compute the thermal Casimir force. On the other hand, thanks to the screening power of the overlayer, it is in principle immune from electrostatic forces caused by potential patches on the plates surfaces, that plague present large distance Casimir experiments. If a semitransparent conductive overlayer with identical patch structure over the Au-Si regions of the plate can be manufactured, similar to the opaque overlayers used in recent searches of non-Newtonian gravitational forces based on the isoelectronic technique, the way will be paved for a clear observation of the thermal Casimir force up to separations of several microns, and an unambiguous discrimination between the Drude and the plasma prescriptions.

When an initially entangled pair of qubits undergoes local decoherence processes, there are a number of ways in which the original entanglement can spread throughout the multipartite system consisting of the two qubits and their environments. Here, we report theoretical and experimental results regarding the dynamics of the distribution of entanglement in this system. The experiment employs an all optical setup in which the qubits are encoded in the polarization degrees of freedom of two photons, and each local decoherence channel is implemented with an interferometer that couples the polarization to the path of each photon, which acts as an environment. We monitor the dynamics and distribution of entanglement and observe the transition from bipartite to multipartite entanglement and back, and show how these transitions are intimately related to the sudden death and sudden birth of entanglement. The multipartite entanglement is further analyzed in terms of three- and four-partite entanglement contributions, and genuine four-qubit entanglement is observed at some points of the evolution.

The serious cosmological problems created by the axion-string–axion-domain-wall system in standard axion models are alleviated by positing the existence of a new confining force. The instantons of this force can generate an axion potential that erases the axion strings long before QCD effects become important, thus preventing QCD-generated axion walls from ever appearing. Axion walls generated by the new confining force would decay so early as not to contribute significantly to the energy in axion dark matter.

We report final measurements of direct $CP$-violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using the complete $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collisions data set, corresponding to $9.3{\mathrm{fb}}^{-1}$ of integrated luminosity, we measure $\mathcal{A}({\mathrm{\Lambda }}_b^0\to p{\pi }^{-})=+0.06\pm 0.07(\text{stat})\pm 0.03(\text{syst})$ and $\mathcal{A}({\mathrm{\Lambda }}_b^0\to p{K}^{-})=-0.10\pm 0.08(\text{stat})\pm 0.04(\text{syst})$, compatible with no asymmetry. In addition we measure the $CP$-violating asymmetries in $B_s^0\to K^{-}{\pi }^{+}$ and $B^0\to K^{+}{\pi }^{-}$ decays to be $\mathcal{A}(B_s^0\to K^{-}{\pi }^{+})=+0.22\pm 0.07(\text{stat})\pm 0.02(\text{syst})$ and $\mathcal{A}(B^0\to K^{+}{\pi }^{-})=-0.083\pm 0.013(\text{stat})\pm 0.004(\text{syst})$, respectively, which are significantly different from zero and consistent with current world averages.

We report on measurements of the mass and lifetime of the ${\mathrm{\Xi }}_b^{-}$ baryon using about 1800 ${\mathrm{\Xi }}_b^{-}$ decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected by the LHCb experiment. The decays are reconstructed in the ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}_c^0{\pi }^{-}$, ${\mathrm{\Xi }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+}$ channel and the mass and lifetime are measured using the ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\pi }^{-}$ mode as a reference. We measure $M({\mathrm{\Xi }}_b^{-})-M({\mathrm{\Lambda }}_b^0)=178.36\pm 0.46\pm 0.16\mathrm{MeV}/c^2$, $({\tau }_{{\mathrm{\Xi }}_b^{-}}/{\tau }_{{\mathrm{\Lambda }}_b^0})=1.089\pm 0.026\pm 0.011$, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of 2 better precision on the ${\mathrm{\Xi }}_b^{-}$ mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.

We study neutron matter and symmetric nuclear matter with the quark-meson model for the two-nucleon interaction. The Bethe-Bruckner-Goldstone many-body theory is used to describe the correlations up to the three hole-line approximation with no extra parameters. At variance with other nonrelativistic realistic interactions, the three hole-line contribution turns out to be non-negligible and to have a substantial saturation effect. The saturation point of nuclear matter, the compressibility, the symmetry energy, and its slope are within the phenomenological constraints. Since the interaction also reproduces fairly well the properties of the three-nucleon system, these results indicate that the explicit introduction of the quark degrees of freedom within the considered constituent quark model is expected to reduce the role of three-body forces.

Self-guiding of an ultraintense laser requires the refractive index to build up rapidly to a sufficient value before the main body of the pulse passes by. We show that placing a low-intensity precursor in front of the main pulse mitigates the diffraction of its leading edge and facilitates reaching a self-guided state that remains stable for more than 10 Rayleigh lengths. Furthermore, this precursor slows the phase slippage between the trapped electrons and the wakefield and leads to an accelerating structure that is more stable, contains more energy, and is sustained longer. Examples from three-dimensional particle-in-cell simulations show that the conversion efficiency from the laser to the self-trapped electrons increases by an order of magnitude when using the precursor.