We follow the evolution of fermion pairing in the dimensional crossover from three-dimensional to two-dimensional as a strongly interacting Fermi gas of ${}^6\mathrm{Li}$ atoms becomes confined to a stack of two-dimensional layers formed by a one-dimensional optical lattice. Decreasing the dimensionality leads to the opening of a gap in radio-frequency spectra, even on the Bardeen-Cooper-Schrieffer side of a Feshbach resonance. The measured binding energy of fermion pairs closely follows the theoretical two-body binding energy and, in the two-dimensional limit, the zero-temperature mean-field Bose-Einstein-condensation to Bardeen-Cooper-Schrieffer crossover theory.

Entanglement and nonlocality are both fundamental aspects of quantum theory, and play a prominent role in quantum information science. The exact relation between entanglement and nonlocality is, however, still poorly understood. Here we make progress in this direction by showing that, contrary to what previous work suggested, quantum nonlocality does not imply entanglement distillability. Specifically, we present analytically a 3-qubit entangled state that is separable along any bipartition. This implies that no bipartite entanglement can be distilled from this state, which is thus fully bound entangled. Then we show that this state nevertheless violates a Bell inequality. Our result also disproves the multipartite version of a long-standing conjecture made by Peres.

We present molecular dynamics friction calculations for confined hydrocarbon films with molecular lengths from 20 to 1400 carbon atoms. We find that the logarithm of the effective viscosity ${\eta }_{\mathrm{eff}}$ for nanometer-thin films depends linearly on the logarithm of the shear rate: $\log {\eta }_{\mathrm{eff}}=C-n\log \dot{\gamma }$, where $n$ varies from 1 (solidlike friction) at very low temperatures to 0 (Newtonian liquid) at very high temperatures, following an inverse sigmoidal curve. Only the shortest chain molecules melt, whereas the longer ones only show a softening in the studied temperature interval $0<T<900\mathrm{K}$. The results are important for the frictional properties of very thin (nanometer) films and to estimate their thermal durability.

On the example of exceptional families of viruses we (i) show the existence of a completely new type of matter organization in nanoparticles, in which the regions with a chiral pentagonal quasicrystalline order of protein positions are arranged in a structure commensurate with the spherical topology and dodecahedral geometry, (ii) generalize the classical theory of quasicrystals (QCs) to explain this organization, and (iii) establish the relation between local chiral QC order and nonzero curvature of the dodecahedral capsid faces.

Sequences of alternating-sign time-dependent electric field pulses lead to coherent interference effects in Schwinger vacuum pair production, producing a Ramsey interferometer, an all-optical time-domain realization of the multiple-slit interference effect, directly from the quantum vacuum. The interference, obeying fermionic quantum statistics, is manifest in the momentum dependence of the number of produced electrons and positrons along the linearly polarized electric field. The central value grows like $N^2$ for $N$ pulses [i.e., $N$ “slits”], and the functional form is well described by a coherent multiple-slit expression. This behavior is generic for many driven quantum systems.

We report the first observations of the spin-singlet bottomonium states $h_b(1P)$ and $h_b(2P)$. The states are produced in the reaction $e^{+}{e}^{-}\to h_b(nP){\pi }^{+}{\pi }^{-}$ using a $121.4{\mathrm{fb}}^{-1}$ data sample collected at energies near the ${\rm Y}(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We determine $M[h_b(1P)]=({9898.2}_{-1.0-1.1}^{+1.1+1.0})\mathrm{MeV}/c^2$ and $M[h_b(2P)]=(10259.8\pm {0.6}_{-1.0}^{+1.4})\mathrm{MeV}/c^2$, which correspond to $P$-wave hyperfine splittings $\Delta M_{\mathrm{HF}}=(+1.7\pm 1.5)$ and $(+{0.5}_{-1.2}^{+1.6})\mathrm{MeV}/c^2$, respectively. The significances of the $h_b(1P)$ and $h_b(2P)$ are $5.5\sigma$ and $11.2\sigma$, respectively. We find that the production of the $h_b(1P)$ and $h_b(2P)$ is not suppressed relative to the production of the ${\rm Y}(1S)$, ${\rm Y}(2S)$, and ${\rm Y}(3S)$.

We address the fundamental question: how are pair correlations and structure factors of hard-sphere fluids affected by confinement between hard planar walls at close distance? For this purpose, we combine x-ray scattering from colloid-filled nanofluidic channel arrays and first-principles inhomogeneous liquid-state theory within the anisotropic Percus-Yevick approximation. The experimental and theoretical data are in remarkable agreement at the pair-correlation level, providing the first quantitative experimental verification of the theoretically predicted confinement-induced anisotropy of the pair-correlation functions for the fluid. The description of confined fluids at this level provides, in the general case, important insights into the mechanisms of particle-particle interactions in dense fluids under confinement.

In this Letter we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy $2.6\pm 0.2$), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number.

We present a particle separation mechanism which induces the motion of particles of different sizes in opposite directions. The mechanism is based on the combined action of a driving force and an entropic rectification of the Brownian fluctuations caused by the asymmetric form of the channel along which particles proceed. The entropic splitting effect shown could be controlled upon variation of the geometrical parameters of the channel and could be implemented in narrow channels and microfluidic devices.

We study the conductivity and shear viscosity tensors of a strongly coupled $\mathcal{N}=4$ super-Yang-Mills plasma which is kept anisotropic by a $\theta$ parameter that depends linearly on one of the spatial dimensions. Its holographic dual is given by an anisotropic axion-dilaton-gravity background and has recently been proposed by Mateos and Trancanelli as a model for the preequilibrium stage of quark-gluon plasma in heavy-ion collisions. By applying the membrane paradigm which we also check by numerical evaluation of Kubo formula and lowest lying quasinormal modes, we find that the shear viscosity purely transverse to the direction of anisotropy saturates the holographic viscosity bound, whereas longitudinal shear viscosities are smaller, providing the first such example not involving higher-derivative theories of gravity and, more importantly, with fully known gauge-gravity correspondence.

Results of a new series of experiments on the study of production cross sections and decay properties of the isotopes of element 115 in the reaction ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ are presented. Twenty-one new decay chains originating from ${}^{288}115$ were established as the product of the $3n$-evaporation channel by measuring the excitation function at three excitation energies of the compound nucleus ${}^{291}115$. The decay properties of all newly observed nuclei are in full agreement with those we measured in 2003. At the lowest excitation energy $E^{*}=33\mathrm{MeV}$, for the first time we registered the product of the $2n$-evaporation channel, ${}^{289}115$, which was also observed previously in the reaction ${}^{249}\mathrm{Bk}+{}^{48}\mathrm{Ca}$ as the daughter nucleus of the decay of ${}^{293}117$. The maximum cross section for the production of ${}^{288}115$ is found to be 8.5 pb at $E^{*}\approx 36\mathrm{MeV}$.

Electrical conductivity of FeO was measured up to 141 GPa and 2480 K in a laser-heated diamond-anvil cell. The results show that rock-salt (B1) type structured FeO metallizes at around 70 GPa and 1900 K without any structural phase transition. We computed fully self-consistently the electronic structure and the electrical conductivity of B1 FeO as a function of pressure and temperature, and found that although insulating as expected at ambient condition, B1 FeO metallizes at high temperatures, consistent with experiments. The observed metallization is related to spin crossover.

Combining two indirect-gap materials—with different electronic and optical gaps—to create a direct gap material represents an ongoing theoretical challenge with potentially rewarding practical implications, such as optoelectronics integration on a single wafer. We provide an unexpected solution to this classic problem, by spatially melding two indirect-gap materials (Si and Ge) into one strongly dipole-allowed direct-gap material. We leverage a combination of genetic algorithms with a pseudopotential Hamiltonian to search through the astronomic number of variants of ${\mathrm{Si}}_n/{\mathrm{Ge}}_m/\dots /{\mathrm{Si}}_p/{\mathrm{Ge}}_q$ superstructures grown on (001) ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$. The search reveals a robust configurational motif—${\mathrm{SiGe}}_2{\mathrm{Si}}_2{\mathrm{Ge}}_2{\mathrm{SiGe}}_n$ on (001) ${\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}$ substrate ($x\le 0.4$) presenting a direct and dipole-allowed gap resulting from an enhanced $\Gamma \mathrm{\text{−}}X$ coupling at the band edges.

We study an open quantum system of atoms with a long-range Rydberg interaction, laser driving, and spontaneous emission. Over time, the system occasionally jumps between a state of low Rydberg population and a state of high Rydberg population. The jumps are inherently collective, and in fact, exist only for a large number of atoms. We explain how entanglement and quantum measurement enable the jumps, which are otherwise classically forbidden.

The flow structure of strongly turbulent Taylor-Couette flow with Reynolds numbers up to ${\mathrm{Re}}_i=2\times {10}^6$ of the inner cylinder is experimentally examined with high-speed particle image velocimetry (PIV). The wind Reynolds numbers ${\mathrm{Re}}_w$ of the turbulent Taylor-vortex flow is found to scale as ${\mathrm{Re}}_w\propto {\mathrm{Ta}}^{1/2}$, exactly as predicted by Grossmann and Lohse [Phys. Fluids 23, 045108 (2011).] for the ultimate turbulence regime, in which the boundary layers are turbulent. The dimensionless angular velocity flux has an effective scaling of ${\mathrm{Nu}}_{\omega }\propto {\mathrm{Ta}}^{0.38}$, also in correspondence with turbulence in the ultimate regime. The scaling of ${\mathrm{Nu}}_{\omega }$ is confirmed by local angular velocity flux measurements extracted from high-speed PIV measurements: though the flux shows huge fluctuations, its spatial and temporal average nicely agrees with the result from the global torque measurements.

Measurements of the Nusselt number Nu and of a Reynolds number ${\mathrm{Re}}_{\mathrm{eff}}$ for Rayleigh-Bénard convection (RBC) over the Rayleigh-number range ${10}^{12}\lesssim \mathrm{Ra}\lesssim {10}^{15}$ and for Prandtl numbers Pr near 0.8 are presented. The aspect ratio $\Gamma \equiv D/L$ of a cylindrical sample was 0.50. For $\mathrm{Ra}\lesssim {10}^{13}$ the data yielded $\mathrm{Nu}\propto {\mathrm{Ra}}^{{\gamma }_{\mathrm{eff}}}$ with ${\gamma }_{\mathrm{eff}}\simeq 0.31$ and ${\mathrm{Re}}_{\mathrm{eff}}\propto {\mathrm{Ra}}^{{\zeta }_{\mathrm{eff}}}$ with ${\zeta }_{\mathrm{eff}}\simeq 0.43$, consistent with classical turbulent RBC. After a transition region for ${10}^{13}\lesssim \mathrm{Ra}\lesssim 5\times {10}^{14}$, where multistability occurred, we found ${\gamma }_{\mathrm{eff}}\simeq 0.38$ and ${\zeta }_{\mathrm{eff}}=\zeta \simeq 0.50$, in agreement with the results of Grossmann and Lohse for the large-Ra asymptotic state with turbulent boundary layers which was first predicted by Kraichnan.

By measuring the stable charge on oil drops in air, Millikan demonstrated the discrete nature of electric charge. We extend his approach to the charge on solid-liquid interfaces, and focus on the dynamics of the discrete fluctuations. Our measurements are accurate and fast enough to observe changes of one elementary charge. Experiments over thousands of seconds yield information about the fast dynamics of electrochemical reactions, relevant for physicochemical and biological systems. As an example, we study (dis)charging processes on colloidal particles in a nonpolar liquid.

We investigate the growth of a crystal that is built by depositing cubes inside a corner. The interface of this crystal approaches a deterministic growing limiting shape in the long-time limit. Building on known results for the corresponding two-dimensional system and accounting for basic three-dimensional symmetries, we conjecture a governing equation for the evolution of the interface profile. We solve this equation analytically and find excellent agreement with simulations of the growth process. We also present a generalization to arbitrary spatial dimension.

The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers $R(m,n)$ with $m$, $n\ge 3$, only nine are currently known. We present a quantum algorithm for the computation of the Ramsey numbers $R(m,n)$. We show how the computation of $R(m,n)$ can be mapped to a combinatorial optimization problem whose solution can be found using adiabatic quantum evolution. We numerically simulate this adiabatic quantum algorithm and show that it correctly determines the Ramsey numbers $R(3,3)$ and $R(2,s)$ for $5\le s\le 7$. We then discuss the algorithm’s experimental implementation, and close by showing that Ramsey number computation belongs to the quantum complexity class quantum Merlin Arthur.

Quantum walk represents one of the most promising resources for the simulation of physical quantum systems, and has also emerged as an alternative to the standard circuit model for quantum computing. Here we investigate how the particle statistics, either bosonic or fermionic, influences a two-particle discrete quantum walk. Such an experiment has been realized by exploiting polarization entanglement to simulate the bunching-antibunching feature of noninteracting bosons and fermions. To this scope a novel three-dimensional geometry for the waveguide circuit is introduced, which allows accurate polarization independent behavior, maintaining remarkable control on both phase and balancement.