We study the Kuramoto model of globally coupled oscillators with a biharmonic coupling function. We develop an analytic self-consistency approach to find stationary synchronous states in the thermodynamic limit and demonstrate that there is a huge multiplicity of such states, which differ microscopically in the distributions of locked phases. These synchronous regimes already exist prior to the linear instability transition of the fully asynchronous state. In the presence of white Gaussian noise, the multiplicity is lifted, but the dependence of the order parameters on coupling constants remains nontrivial.

The degradation of colors in historical paintings affects our cultural heritage in both museums and archeological sites. Despite intensive experimental studies, the origin of darkening of one of the most ancient pigments known to humankind, vermilion ($\alpha$-HgS), remains unexplained. Here, by combining many-body theoretical spectroscopy and high-resolution microscopic x-ray diffraction, we clarify the composition of the damaged paint work and demonstrate possible physicochemical processes, induced by illumination and exposure to humidity and air, that cause photoactivation of the original pigment and the degradation of the secondary minerals. The results suggest a new path for the darkening process which was never considered by previous studies and prompt a critical examination of their findings.

Spectral homodyne detection, a widely used technique for measuring quantum properties of light beams, cannot retrieve all the information needed to reconstruct the quantum state of spectral field modes. We show that full quantum state reconstruction can be achieved with the alternative measurement technique of resonator detection. We experimentally demonstrate this difference by engineering a quantum state with features that go undetected by homodyne detection but are clearly revealed by resonator detection.

The first observed connection between kinetic instabilities driven by proton temperature anisotropy and estimated energy cascade rates in the turbulent solar wind is reported using measurements from the Wind spacecraft at 1 AU. We find enhanced cascade rates are concentrated along the boundaries of the (${\beta }_{\parallel }$, $T_{\perp }/T_{\parallel }$) plane, which includes regions theoretically unstable to the mirror and firehose instabilities. A strong correlation is observed between the estimated cascade rate and kinetic effects such as temperature anisotropy and plasma heating, resulting in protons 5–6 times hotter and 70%–90% more anisotropic than under typical isotropic plasma conditions. These results offer new insights into kinetic processes in a turbulent regime.

We make an analytic investigation of rapid quenches of relevant operators in $d$-dimensional holographic conformal field theories, which admit a dual gravity description. We uncover a universal scaling behavior in the response of the system, which depends only on the conformal dimension of the quenched operator in the vicinity of the ultraviolet fixed point of the theory. Unless the amplitude of the quench is scaled appropriately, the work done on a system during the quench diverges in the limit of abrupt quenches for operators with dimension $(d/2)\le \Delta <d$.

We present a measurement of the total decay width of the top quark using events with top-antitop quark pair candidates reconstructed in the final state with one charged lepton and four or more hadronic jets. We use the full Tevatron run II data set of $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collisions recorded by the CDF II detector. The top quark mass and the mass of the hadronically decaying $W$ boson are reconstructed for each event and compared with distributions derived from simulated signal and background samples to extract the top quark width (${\Gamma }_{\mathrm{top}}$) and the energy scale of the calorimeter jets with in situ calibration. For a top quark mass $M_{\mathrm{top}}=172.5\mathrm{GeV}/c^2$, we find $1.10<{\Gamma }_{\mathrm{top}}<4.05\mathrm{GeV}$ at 68% confidence level, which is in agreement with the standard model expectation of 1.3 GeV and is the most precise direct measurement of the top quark width to date.

Superior thermal conductivity of graphene is frequently reported and used to justify its technical relevance for ultimately scaled devices. However, this extraordinary property is size dependent, and understanding of graphene’s thermal properties in the quasiballistic thermal transport regime is lacking. To overcome this limitation, we directly probe local heat transfer into graphene by high-resolution scanning thermal microscopy on amorphous silicon oxide (${\mathrm{SiO}}_2$) and crystalline silicon carbide (SiC). We quantify thickness-dependent thermal resistance modulations at sub-10-nm lateral resolution and thermal sensitivity for the individual atomic layers. On ${\mathrm{SiO}}_2$, we observe a decrease of thermal resistance with increasing number of graphene layers. We attribute this trend to the spreading of heat using the thickness dependence of graphene’s thermal conductivity. On SiC, the heated tip-sample contact is scaled below the phonon mean free path of both the graphene and its supporting substrate. Consistently, we find the thermal interface resistances of the graphene top and bottom contacts dominating thermal transport.

Motivated by the recent observation of the shell effect in a nanoscale pure superconductor by Bose et al. [Nat. Mater. 9, 550 (2010)], we explore the possible shell-like effect in a strongly disordered superconductor as it is known to produce nanosize superconducting puddles (SPs). We find a remarkable change in the texture of the pairing amplitudes that is responsible for forming the SP, upon monotonic tuning of the average electron density, $⟨n⟩$, and keeping the disorder landscape unaltered. Both the spatially averaged pairing amplitude and the quasiparticle excitation gap oscillate with $⟨n⟩$. This oscillation is due to a rapid change in the low-lying quasiparticle energy spectra and thereby a change in the shapes and positions of the SPs. We establish a correlation between the formation of SPs and the shell-like effect. The experimental consequences of our theory are also discussed.

By employing rheological experiments, mode coupling theory, and computer simulations based on realistic coarse-grained models, we investigate the effects of small, hard colloids on the glassy states formed by large, soft colloids. Multiarm star polymers mimic hard and soft colloids by appropriately varying the number and size of their arms. The addition of hard colloids leads, depending on their concentration, to either melting of the soft glass or the emergence of two distinct glassy states. We explain our findings by depletion of the colloids adjacent to the stars, which leads to an arrested phase separation when the repulsive glass line meets the demixing binodal. The parameter-free agreement between experiment, theory, and simulations suggests the generic nature of our results and opens the route for designing soft-hard colloidal composites with tunable rheology.

Neoclassical bootstrap current is expected to provide a significant fraction of the equilibrium plasma current in tokamak reactors. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons and thus driving a bootstrap current. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.

A novel way to create a band structure of the quasienergy spectrum for driven systems is proposed based on the discrete symmetry in phase space. The system, e.g., an ion or ultracold atom trapped in a potential, shows no spatial periodicity, but it is driven by a time-dependent field coupling highly nonlinearly to one of its degrees of freedom (e.g., $\sim q^n$). The band structure in quasienergy arises as a consequence of the $n$-fold discrete periodicity in phase space induced by this driving field. We propose an explicit model to realize such a phase space crystal and analyze its band structure in the frame of a tight-binding approximation. The phase space crystal opens new ways to engineer energy band structures, with the added advantage that its properties can be changed in situ by tuning the driving field’s parameters.

We present a single-quadrature feedback scheme able to overcome the conventional 3 dB limit on parametric squeezing. The method is experimentally demonstrated in a micromechanical system based on a cantilever with a magnetic tip. The cantilever is detected at low temperature by a SQUID susceptometer, while parametric pumping is obtained by modulating the magnetic field gradient at twice the cantilever frequency. A maximum squeezing of 11.5 dB and 11.3 dB is observed, respectively, in the response to a sinusoidal test signal and in the thermomechanical noise. So far, the maximum squeezing factor is limited only by the maximum achievable parametric modulation. The proposed technique might be used to squeeze one quadrature of a mechanical resonator below the quantum noise level, even without the need for a quantum limited detector.

We show that the minimum experimental effort to estimate the average error of a quantum gate scales as $2^n$ for $n$ qubits and requires classical computational resources $\sim n^2{2}^{3n}$ when no specific assumptions on the gate can be made. This represents a reduction by $2^n$ compared to the best currently available protocol, Monte Carlo characterization. The reduction comes at the price of either having to prepare entangled input states or obtaining bounds rather than the average fidelity itself. It is achieved by applying Monte Carlo sampling to so-called 2-designs or two classical fidelities. For the specific case of Clifford gates, the original version of Monte Carlo characterization based on the channel-state isomorphism remains an optimal choice. We provide a classification of the available efficient strategies to determine the average gate error in terms of the number of required experimental settings, average number of actual measurements, and classical computational resources.

A big open question in the quantum information theory concerns the feasibility of a self-correcting quantum memory. A quantum state recorded in such memory can be stored reliably for a macroscopic time without need for active error correction, if the memory is in contact with a cold enough thermal bath. Here we report analytic and numerical evidence for self-correcting behavior in the quantum spin lattice model known as the 3D cubic code. We prove that its memory time is at least $L^{c\beta }$, where $L$ is the lattice size, $\beta$ is the inverse temperature of the bath, and $c>0$ is a constant coefficient. However, this bound applies only if the lattice size $L$ does not exceed a critical value which grows exponentially with $\beta$. In that sense, the model can be called a partially self-correcting memory. We also report a Monte Carlo simulation indicating that our analytic bounds on the memory time are tight up to constant coefficients. To model the readout step we introduce a new decoding algorithm, which can be implemented efficiently for any topological stabilizer code. A longer version of this work can be found in Bravyi and Haah, arXiv:1112.3252.

We study the real-time dynamics of string breaking in quantum electrodynamics in one spatial dimension. A two-stage process with a clear separation of time and energy scales for the fermion-antifermion pair creation and subsequent charge separation leading to the screening of external charges is found. Going away from the traditional setup of external static charges, we establish the phenomenon of multiple string breaking by considering dynamical charges flying apart.

We compute the next-to-next-to-leading order QCD corrections for standard model Higgs boson pair production inclusive cross section at hadron colliders within the large top-mass approximation. We provide numerical results for the LHC, finding that the corrections are large, resulting in an increase of $\mathcal{O}(20\%)$ with respect to the next-to-leading order result at c.m. energy $\sqrt{s_H}=14\mathrm{TeV}$. We observe a substantial reduction in the scale dependence, with overlap between the current and previous order prediction. All our results are normalized using the full top- and bottom-mass dependence at leading order. We also provide analytical expressions for the $K$ factors as a function of $s_H$.

We present results for three charmonia states (${\psi }^{\prime }$, ${\chi }_c$, and $J/\psi$) in $d+\mathrm{Au}$ collisions at $|y|<0.35$ and $\sqrt{s_{NN}}=200\mathrm{GeV}$. We find that the modification of the ${\psi }^{\prime }$ yield relative to that of the $J/\psi$ scales approximately with charged particle multiplicity at midrapidity across $p+A$, $d+\mathrm{Au}$, and $A+A$ results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the ${\psi }^{\prime }$ and $J/\psi$, while in small-impact-parameter collisions the more weakly bound ${\psi }^{\prime }$ is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger ${\psi }^{\prime }$ suppression in central events is not explained by an increase of the nuclear absorption owing to meson formation time effects.

We experimentally characterize Hopf bifurcation phenomena at femtojoule energy scales in a multiatom cavity quantum electrodynamical (cavity QED) system and demonstrate how such behaviors can be exploited in the design of all-optical memory and modulation devices. The data are analyzed by using a semiclassical model that explicitly treats heterogeneous coupling of atoms to the cavity mode. Our results highlight the interest of cavity QED systems for ultralow power photonic signal processing as well as for fundamental studies of mesoscopic nonlinear dynamics.

The effects of confinement and electron correlations on the relative time delay between the $3s$ and $3p$ photoemissions of Ar confined endohedrally in ${\mathrm{C}}_{60}$ are investigated using the time-dependent local density approximation—a method that is also found to mostly agree with recent time delay measurements between the $3s$ and $3p$ subshells in atomic Ar. At energies in the neighborhood of $3p$ Cooper minimum, correlations with ${\mathrm{C}}_{60}$ electrons are found to induce opposite temporal effects in the emission of Ar $3p$ hybridized symmetrically versus that of Ar $3p$ hybridized antisymmetrically with ${\mathrm{C}}_{60}$. A recoil-type interaction model mediated by the confinement is found to best describe the phenomenon.

We show theoretically that ultracold hydrogen atoms have very favorable properties for sympathetic cooling of molecules to microkelvin temperatures. We calculate the potential energy surfaces for spin-polarized interactions of H atoms with the prototype molecules $\mathrm{NH}({}^3\Sigma ^{-})$ and $\mathrm{OH}({}^2\Pi )$ and show that they are shallow (50 to $80{\mathrm{cm}}^{-1}$) and only weakly anisotropic. We carry out quantum collision calculations on $\mathrm{H}+\mathrm{NH}$ and $\mathrm{H}+\mathrm{OH}$ and show that the ratio of elastic to inelastic cross sections is high enough to allow sympathetic cooling from temperatures well over 1 K for NH and around 250 mK for OH.