The field of quantum computation currently lacks a formal proof of experimental feasibility. Qubits are fragile and sophisticated quantum error correction is required to achieve reliable quantum computation. The surface code is a promising quantum error correction code, requiring only a physically reasonable 2D lattice of qubits with nearest neighbor interactions. However, existing proofs that reliable quantum computation is possible using this code assume the ability to measure four-body operators and, despite making this difficult to realize assumption, require that the error rate of these operator measurements is less than ${10}^{-9}$, an unphysically low target. High error rates have been proved tolerable only when assuming tunable interactions of strength and error rate independent of distance, which is also unphysical. In this work, given a 2D lattice of qubits with only nearest neighbor two-qubit gates, and single-qubit measurement, initialization, and unitary gates, all of which have error rate $p$, we prove that arbitrarily reliable quantum computation is possible provided $p<7.4\times {10}^{-4}$, a target that many experiments have already achieved. This closes a long-standing open problem, formally proving the experimental feasibility of quantum computation under physically reasonable assumptions.

We propose a protocol for conditional suppression of losses in direct quantum state transmission over a lossy quantum channel. The method works by noiselessly attenuating the input state prior to transmission through a lossy channel followed by noiseless amplification of the output state. The procedure does not add any noise; hence, it keeps quantum coherence. We experimentally demonstrate it in the subspace spanned by vacuum and single-photon states, and consider its general applicability.

We establish the fluctuation theorem in the presence of information exchange between a nonequilibrium system and other degrees of freedom such as an observer and a feedback controller, where the amount of information exchange is added to the entropy production. The resulting generalized second law sets the fundamental limit of energy dissipation and energy cost during the information exchange. Our results apply not only to feedback-controlled processes but also to a much broader class of information exchanges, and provide a unified framework of nonequilibrium thermodynamics of measurement and feedback control.

We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso for 13 months during 2011 and 2012. XENON100 features an ultralow electromagnetic background of $(5.3\pm 0.6)\times {10}^{-3}\mathrm{events}/({\mathrm{keV}}_{\mathrm{ee}}\times \mathrm{kg}\times \mathrm{day})$ in the energy region of interest. A blind analysis of $224.6\mathrm{\text{live days}}\times 34\mathrm{kg}$ exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the predefined nuclear recoil energy range of $6.6–30.5{\mathrm{keV}}_{\mathrm{nr}}$ are consistent with the background expectation of ($1.0\pm 0.2$) events. A profile likelihood analysis using a $6.6–43.3{\mathrm{keV}}_{\mathrm{nr}}$ energy range sets the most stringent limit on the spin-independent elastic weakly interacting massive particle–nucleon scattering cross section for weakly interacting massive particle masses above $8\mathrm{GeV}/c^2$, with a minimum of $2\times {10}^{-45}{\mathrm{cm}}^2$ at $55\mathrm{GeV}/c^2$ and 90% confidence level.

In a three-dimensional Fermi liquid, quasiparticles near the Fermi surface may possess a Berry curvature. We show that if the Berry curvature has a nonvanishing flux through the Fermi surface, the particle number associated with this Fermi surface has a triangle anomaly in external electromagnetic fields. We show how Landau’s Fermi liquid theory should be modified to take into account the Berry curvature. We show that the “chiral magnetic effect” also emerges from the Berry curvature flux.

We show that more than two generations of quarks and leptons are required to have an anomaly free discrete $R$ symmetry larger than $R$ parity, provided that the supersymmetric standard model can be minimally embedded into a grand unified theory. This connects an explanation for the number of generations with seemingly unrelated problems such as supersymmetry breaking, proton decay, the $\mu$ problem, and the cosmological constant through a discrete $R$ symmetry. We also show that three generations is uniquely required by a nonanomalous discrete $R$ symmetry in classes of grand unified theories such as the ones based on (semi)simple gauge groups.

A search is presented for the standard model Higgs boson produced in association with top quarks using the full Run II proton-antiproton collision data set, corresponding to $9.45{\mathrm{fb}}^{-1}$, collected by the Collider Detector at Fermilab. No significant excess over the expected background is observed, and $95\%$ credibility-level upper bounds are placed on the cross section $\sigma (t\overline{t}H\to \mathrm{\text{lepton}}+\mathrm{\text{missing transverse energy}}+\mathrm{\text{jets}})$. For a Higgs boson mass of $125\mathrm{GeV}/c^2$, we expect to set a limit of 12.6 and observe a limit of 20.5 times the standard model rate. This represents the most sensitive search for a standard model Higgs boson in this channel to date.

We perform a nonperturbative calculation of the ${\pi }^0\to \gamma \gamma$ transition form factor and the associated decay width using lattice QCD. The amplitude for a two-photon final state, which is not an eigenstate of QCD, is extracted through a Euclidean time integral of the relevant three-point function. We utilize the all-to-all quark propagator technique to carry out this integration as well as to include the disconnected quark diagram contributions. The overlap fermion formulation is employed on the lattice to ensure exact chiral symmetry on the lattice. After examining various sources of systematic effects, except for a possible discretization effect, we obtain ${\Gamma }_{{\pi }^0\to \gamma \gamma }=7.83(31)(49)\mathrm{eV}$ for the pion decay width, where the first error is statistical and the second is our estimate of the systematic error.

Excited states in ${}^{38,40,42}\mathrm{Si}$ nuclei have been studied via in-beam $\gamma$-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of ${}^{40}\mathrm{S}$ and ${}^{44}\mathrm{S}$ provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled $\gamma \mathrm{\text{−}}\gamma$ coincidence measurements. A prominent $\gamma$ line observed with an energy of 742(8) keV in ${}^{42}\mathrm{Si}$ confirms the $2^{+}$ state reported in an earlier study. Among the $\gamma$ lines observed in coincidence with the $2^{+}\to 0^{+}$ transition, the most probable candidate for the transition from the yrast $4^{+}$ state was identified, leading to a $4_1^{+}$ energy of 2173(14) keV. The energy ratio of 2.93(5) between the $2_1^{+}$ and $4_1^{+}$ states indicates well-developed deformation in ${}^{42}\mathrm{Si}$ at $N=28$ and $Z=14$. Also for ${}^{38,40}\mathrm{Si}$ energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for ${}^{42}\mathrm{Si}$, the results show a rapid deformation development of Si isotopes from $N=24$ to $N=28$.

A novel kind of nanostructured optical fiber, displaying an extremely high and optically broadband optomechanical nonlinearity, is presented. It comprises two closely spaced ultrathin glass membranes (webs) suspended in air and attached to the inner walls of a glass fiber capillary. Light guided in this dual-web structure can exert attractive or repulsive pressure on the webs, causing them to be pushed together or pulled apart. The elastic deflection of the webs is, in turn, coupled to the electromagnetic field distribution and results in a change in the effective refractive index within the fiber. Employing a pump-probe technique in an interferometric setup, optomechanically induced refractive index changes more than ${10}^4$ times larger than the Kerr effect are detected. Theoretical estimates of the optomechanical nonlinearity agree well with the experimental results. The dual-web fiber combines the sensitivity of a microoptomechanical device with the versatility of an optical fiber and could trigger new developments in the fields of nonlinear optics, optical metrology, and sensing.

The coalescence of viscous drops on a substrate is studied experimentally and theoretically. We consider cases where the drops can have different contact angles, leading to a very asymmetric coalescence process. Side view experiments reveal that the “bridge” connecting the drops evolves with self-similar dynamics, providing a new perspective on the coalescence of sessile drops. We show that the universal shape of the bridge is accurately described by similarity solutions of the one-dimensional lubrication equation. Our theory predicts that, once the drops are connected on a microscopic scale, the bridge grows linearly in time with a strong dependence on the contact angles. Without any adjustable parameters, we find quantitative agreement with all experiments.

Global electromagnetic gyrokinetic simulations show the existence of near threshold conditions for both a high-$n$ kinetic ballooning mode (KBM) and an intermediate-$n$ kinetic version of peeling-ballooning mode (KPBM) in the edge pedestal of two DIII-D H-mode discharges. When the magnetic shear is reduced in a narrow region of steep pressure gradient, the KPBM is significantly stabilized, while the KBM is weakly destabilized and hence becomes the most-unstable mode. Collisions decrease the KBM’s critical $\beta$ and increase the growth rate.

Self-consistent turbulent transport of high-concentration impurities in magnetically confined fusion plasmas is studied using a three-dimensional nonlinear fluid global turbulence model which includes ion-temperature gradient and trapped electron mode instabilities. It is shown that the impurity concentration can have a dramatic feedback in the turbulence and, as a result, it can significantly change the transport properties of the plasma. High concentration impurities can trigger strong intermittency that manifests in non-Gaussian heavy tails of the probability density functions of the $\mathbf{E}\times \mathbf{B}$ fluctuations and of the ion-temperature flux fluctuations. At the heart of this self-consistent coupling is the existence of inward propagating ion-temperature fronts with a sharp gradient at the leading edge that give rise to instabilities and avalanchelike bursty transport. Numerical evidence of time nonlocality (i.e., history dependence) in the delayed response of the flux to the gradient is presented.

The acceleration of ions from ultrathin foils has been investigated by using 250 TW, subpicosecond laser pulses, focused to intensities of up to $3\times {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}$. The ion spectra show the appearance of narrow-band features for protons and carbon ions peaked at higher energies (in the $5–10\mathrm{MeV}/\mathrm{\text{nucleon range}}$) and with significantly higher flux than previously reported. The spectral features and their scaling with laser and target parameters provide evidence of a multispecies scenario of radiation pressure acceleration in the light sail mode, as confirmed by analytical estimates and 2D particle-in-cell simulations. The scaling indicates that monoenergetic peaks with more than $100\mathrm{MeV}/\mathrm{\text{nucleon}}$ are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.

Current filamentation instability is observed and studied in a laboratory environment with a 60 MeV electron beam and a plasma capillary discharge. Multiple filaments are observed and imaged transversely at the plasma exit with optical transition radiation. By varying the plasma density the transition between single and multiple filaments is found to be $k_p{\sigma }_r\sim 2.2$. Scaling of the transverse filament size with the plasma skin depth is predicted in theory and observed over a range of plasma densities. Lowering the bunch charge, and thus the bunch density, suppresses the instability.

Collisional relaxation of Coulomb systems is studied in the strongly coupled regime. We use an optical pump-probe approach to manipulate and monitor the dynamics of ions in an ultracold neutral plasma, which allows direct measurement of relaxation rates in a regime where common Landau-Spitzer theory breaks down. Numerical simulations confirm the experimental results and display non-Markovian dynamics at early times.

Optimized growth of single wall carbon nanotubes requires full knowledge of the actual state of the catalyst nanoparticle and its interface with the tube. Using tight binding based atomistic computer simulations, we calculate carbon adsorption isotherms on nanoparticles of nickel, a typical catalyst, and show that carbon solubility increases for smaller nanoparticles that are either molten or surface molten under experimental conditions. Increasing carbon content favors the dewetting of Ni nanoparticles with respect to $s{p}^2$ carbon walls, a necessary property to limit catalyst encapsulation and deactivation. Grand canonical Monte Carlo simulations of the growth of tube embryos show that wetting properties of the nanoparticles, controlled by carbon solubility, are of fundamental importance to enable the growth, shedding new light on the growth mechanisms.

The availability of ultrafast pulses of coherent hard x rays from the Linac Coherent Light Source opens new opportunities for studies of atomic-scale dynamics in amorphous materials. Here, we show that single ultrafast coherent x-ray pulses can be used to observe the speckle contrast in the high-angle diffraction from liquid Ga and glassy ${\mathrm{Ni}}_2{\mathrm{Pd}}_2\mathrm{P}$ and ${\mathrm{B}}_2{\mathrm{O}}_3$. We determine the thresholds above which the x-ray pulses disturb the atomic arrangements. Furthermore, high contrast speckle is observed in scattering patterns from the glasses integrated over many pulses, demonstrating that the source and optics are sufficiently stable for x-ray photon correlation spectroscopy studies of dynamics over a wide range of time scales.

The melting curve of lithium between ambient pressure and 64 GPa is measured by detection of an abrupt change in its electrical resistivity at melting and by visual observation. Here we have used a quasi-four-point resistance measurement in a diamond anvil cell and measured the resistance of lithium as it goes through melting. The resistivity near melting exhibits a well documented sharp increase which allowed us to pinpoint the melting transition from ambient pressure to 64 GPa. Our data show that lithium melts clearly above 300 K in all pressure regions and its melting behavior adheres to the classical model. Moreover, we observed an abrupt increase in the slope of the melting curve around 10 GPa. The onset of this increase fits well to the linear extrapolation of the lower temperature bcc-fcc phase boundary.

We used ultrafast electron diffraction and density-functional theory calculations to gain insight into the charge density wave (CDW) formation on $\mathrm{In}/\mathrm{Si}(111)$. Weak excitation by a femtosecond-laser pulse results in the melting of the CDW. The immediate freezing is hindered by a barrier for the motion of atoms during the phase transition: The melted CDW constitutes a long-lived, supercooled phase and is strong evidence for a first-order transition. The freezing into the CDW is triggered by preexisting adsorbates. Starting at these condensation nuclei, the CDW expands one dimensionally on the $\mathrm{In}/\mathrm{Si}(111)$ surface, with a constant velocity of more than $80\mathrm{m}/\mathrm{s}$.