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  • Quantum Correlations in Nonlocal Boson Sampling
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-19
    Farid Shahandeh, Austin P. Lund, and Timothy C. Ralph

    Determination of the quantum nature of correlations between two spatially separated systems plays a crucial role in quantum information science. Of particular interest is the questions of if and how these correlations enable quantum information protocols to be more powerful. Here, we report on a distributed quantum computation protocol in which the input and output quantum states are considered to be classically correlated in quantum informatics. Nevertheless, we show that the correlations between the outcomes of the measurements on the output state cannot be efficiently simulated using classical algorithms. Crucially, at the same time, local measurement outcomes can be efficiently simulated on classical computers. We show that the only known classicality criterion violated by the input and output states in our protocol is the one used in quantum optics, namely, phase-space nonclassicality. As a result, we argue that the global phase-space nonclassicality inherent within the output state of our protocol represents true quantum correlations.

    更新日期:2017-09-19
  • Dark Matter Coannihilation with a Lighter Species
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-19
    Asher Berlin

    We propose a new thermal freeze-out mechanism for ultraheavy dark matter. Dark matter coannihilates with a lighter unstable species that is nearby in mass, leading to an annihilation rate that is exponentially enhanced relative to standard weakly interactive massive particles. This scenario destabilizes any potential dark matter candidate. In order to remain consistent with astrophysical observations, our proposal necessitates very long-lived states, motivating striking phenomenology associated with the late decays of ultraheavy dark matter, potentially as massive as the scale of grand unified theories, MGUT∼1016  GeV.

    更新日期:2017-09-19
  • Characterization of theHo163Electron Capture Spectrum: A Step Towards the Electron Neutrino Mass Determination
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-19
    P. C.-O. Ranitzsch, C. Hassel, M. Wegner, D. Hengstler, S. Kempf, A. Fleischmann, C. Enss, L. Gastaldo, A. Herlert, and K. Johnston

    The isotope Ho163 is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to Dy163 with an energy available to the decay, QEC, of about 2.8 keV. According to the present knowledge, this is the lowest QEC value for such transitions. Here we discuss a newly obtained spectrum of Ho163, taken by cryogenic metallic magnetic calorimeters with Ho163 implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the Dy163 daughter atom following the capture of electrons from the 5s shell in Ho163, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48 eV. In addition, a precise determination of the energy available for the decay QEC=(2.858±0.010stat±0.05syst)  keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between Ho163 and Dy163 obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique.

    更新日期:2017-09-19
  • Simultaneous Deep Tunneling and Classical Hopping for Hydrogen Diffusion on Metals
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-19
    Wei Fang, Jeremy O. Richardson, Ji Chen, Xin-Zheng Li, and Angelos Michaelides

    Hydrogen diffusion on metals exhibits rich quantum behavior, which is not yet fully understood. Using simulations, we show that many hydrogen diffusion barriers can be categorized into those with parabolic tops and those with broad tops. With parabolic-top barriers, hydrogen diffusion evolves gradually from classical hopping, to shallow tunneling, to deep tunneling as the temperature (T) decreases, and noticeable quantum effects persist at moderate T. In contrast, with broad-top barriers quantum effects become important only at low T and the classical-to-quantum transition is sharp, at which classical hopping and deep tunneling both occur. This coexistence indicates that more than one mechanism contributes to the quantum reaction rate. The conventional definition of the classical-to-quantum crossover T is invalid for the broad tops, and we give a new definition. Extending this, we propose a model to predict the transition T for broad-top diffusion, providing a general guide for theory and experiment.

    更新日期:2017-09-19
  • Gaussian Hypothesis Testing and Quantum Illumination
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-18
    Mark M. Wilde, Marco Tomamichel, Seth Lloyd, and Mario Berta

    Quantum hypothesis testing is one of the most basic tasks in quantum information theory and has fundamental links with quantum communication and estimation theory. In this paper, we establish a formula that characterizes the decay rate of the minimal type-II error probability in a quantum hypothesis test of two Gaussian states given a fixed constraint on the type-I error probability. This formula is a direct function of the mean vectors and covariance matrices of the quantum Gaussian states in question. We give an application to quantum illumination, which is the task of determining whether there is a low-reflectivity object embedded in a target region with a bright thermal-noise bath. For the asymmetric-error setting, we find that a quantum illumination transmitter can achieve an error probability exponent stronger than a coherent-state transmitter of the same mean photon number, and furthermore, that it requires far fewer trials to do so. This occurs when the background thermal noise is either low or bright, which means that a quantum advantage is even easier to witness than in the symmetric-error setting because it occurs for a larger range of parameters. Going forward from here, we expect our formula to have applications in settings well beyond those considered in this paper, especially to quantum communication tasks involving quantum Gaussian channels.

    更新日期:2017-09-18
  • Role of Intrapulse Coherence in Carrier-Envelope Phase Stabilization
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-18
    Nils Raabe, Tianli Feng, Tobias Witting, Ayhan Demircan, Carsten Brée, and Günter Steinmeyer

    The concept of coherence is of fundamental importance for describing the physical characteristics of light and for evaluating the suitability for experimental application. In the case of pulsed laser sources, the pulse-to-pulse coherence is usually considered for a judgment of the compressibility of the pulse train. This type of coherence is often lost during propagation through a highly nonlinear medium, and pulses prove incompressible despite multioctave spectral coverage. Notwithstanding the apparent loss of interpulse coherence, however, supercontinua enable applications in precision frequency metrology that rely on coherence between different spectral components within a laser pulse. To judge the suitability of a light source for the latter application, we define an alternative criterion, which we term intrapulse coherence. This definition plays a limiting role in the carrier-envelope phase measurement and stabilization of ultrashort pulses. It is shown by numerical simulation and further corroborated by experimental data that filamentation-based supercontinuum generation may lead to a loss of intrapulse coherence despite near-perfect compressibility of the pulse train. This loss of coherence may severely limit active and passive carrier-envelope phase stabilization schemes and applications in optical high-field physics.

    更新日期:2017-09-18
  • Mechanism behind Erosive Bursts In Porous Media
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-18
    R. Jäger, M. Mendoza, and H. J. Herrmann

    Erosion and deposition during flow through porous media can lead to large erosive bursts that manifest as jumps in permeability and pressure loss. Here we reveal that the cause of these bursts is the reopening of clogged pores when the pressure difference between two opposite sites of the pore surpasses a certain threshold. We perform numerical simulations of flow through porous media and compare our predictions to experimental results, recovering with excellent agreement shape and power-law distribution of pressure loss jumps, and the behavior of the permeability jumps as a function of particle concentration. Furthermore, we find that erosive bursts only occur for pressure gradient thresholds within the range of two critical values, independent of how the flow is driven. Our findings provide a better understanding of sudden sand production in oil wells and breakthrough in filtration.

    更新日期:2017-09-18
  • Enhanced Second-Order Nonlinearity for THz Generation by Resonant Interaction of Exciton-Polariton Rabi Oscillations with Optical Phonons
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-18
    Katharina Rojan, Yoan Léger, Giovanna Morigi, Maxime Richard, and Anna Minguzzi

    Semiconductor microcavities in the strong-coupling regime exhibit an energy scale in the terahertz (THz) frequency range, which is fixed by the Rabi splitting between the upper and lower exciton-polariton states. While this range can be tuned by several orders of magnitude using different excitonic media, the transition between both polaritonic states is dipole forbidden. In this work, we show that, in cadmium telluride microcavities, the Rabi-oscillation-driven THz radiation is actually active without the need for any change in the microcavity design. This feature results from the unique resonance condition which is achieved between the Rabi splitting and the phonon-polariton states and leads to a giant enhancement of the second-order nonlinearity.

    更新日期:2017-09-18
  • Search for Low Mass Vector Resonances Decaying to Quark-Antiquark Pairs in Proton-Proton Collisions ats=13TeV
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    A. M. Sirunyanet al.(CMS Collaboration)

    A search is reported for a narrow vector resonance decaying to quark-antiquark pairs in proton-proton collisions at s = 13     TeV , collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.7       fb − 1 . The vector resonance is produced at large transverse momenta, with its decay products merged into a single jet. The resulting signature is a peak over background in the distribution of the invariant mass of the jet. The results are interpreted in the framework of a leptophobic vector resonance and no evidence is found for such particles in the mass range of 100–300 GeV. Upper limits at 95% confidence level on the production cross section are presented in a region of mass-coupling phase space previously unexplored at the LHC. The region below 140 GeV has not been explored by any previous experiments.

    更新日期:2017-09-15
  • Dissecting Reactor Antineutrino Flux Calculations
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    A. A. Sonzogni, E. A. McCutchan, and A. C. Hayes

    Current predictions for the antineutrino yield and spectra from a nuclear reactor rely on the experimental electron spectra from U 235 , Pu 239 , Pu 241 and a numerical method to convert these aggregate electron spectra into their corresponding antineutrino ones. In the present work we investigate quantitatively some of the basic assumptions and approximations used in the conversion method, studying first the compatibility between two recent approaches for calculating electron and antineutrino spectra. We then explore different possibilities for the disagreement between the measured Daya Bay and the Huber-Mueller antineutrino spectra, including the U 238 contribution as well as the effective charge and the allowed shape assumption used in the conversion method. We observe that including a shape correction of about + 6 %     MeV − 1 in conversion calculations can better describe the Daya Bay spectrum. Because of a lack of experimental data, this correction cannot be ruled out, concluding that in order to confirm the existence of the reactor neutrino anomaly, or even quantify it, precisely measured electron spectra for about 50 relevant fission products are needed. With the advent of new rare ion facilities, the measurement of shape factors for these nuclides, for many of which precise beta intensity data from TAGS experiments already exist, would be highly desirable.

    更新日期:2017-09-15
  • Enhancement of the Triple Alpha Rate in a Hot Dense Medium
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Mary Beard, Sam M. Austin, and Richard Cyburt

    In a sufficiently hot and dense astrophysical environment the rate of the triple-alpha ( 3 α ) reaction can increase greatly over the value appropriate for helium burning stars owing to hadronically induced deexcitation of the Hoyle state. In this Letter we use a statistical model to evaluate the enhancement as a function of temperature and density. For a density of 10 6     g   cm − 3 enhancements can exceed a factor of 100. In high temperature or density situations, the enhanced 3 α rate is a better estimate of this rate and should be used in these circumstances. We then examine the effect of these enhancements on production of C 12 in the neutrino wind following a supernova explosion and in an x-ray burster.

    更新日期:2017-09-15
  • Atomic Clock Measurements of Quantum Scattering Phase Shifts Spanning Feshbach Resonances at Ultralow Fields
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Aaron Bennett, Kurt Gibble, Servaas Kokkelmans, and Jeremy M. Hutson

    We use an atomic fountain clock to measure quantum scattering phase shifts precisely through a series of narrow, low-field Feshbach resonances at average collision energies below 1     μ K . Our low spread in collision energy yields phase variations of order ± π / 2 for target atoms in several F , m F states. We compare them to a theoretical model and establish the accuracy of the measurements and the theoretical uncertainties from the fitted potential. We find overall excellent agreement, with small statistically significant differences that remain unexplained.

    更新日期:2017-09-15
  • Vibrational Feshbach Resonances Mediated by Nondipole Positron-Molecule Interactions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    M. R. Natisin, J. R. Danielson, G. F. Gribakin, A. R. Swann, and C. M. Surko

    Measurements of energy-resolved positron-molecule annihilation show the existence of positron binding and vibrational Feshbach resonances. The existing theory describes this phenomenon successfully for the case of infrared-active vibrational modes that allow dipole coupling between the incident positron and the vibrational motion. Presented here are measurements of positron-molecule annihilation made using a recently developed cryogenic positron beam capable of significantly improved energy resolution. The results provide evidence of resonances associated with infrared-inactive vibrational modes, indicating that positron-molecule bound states may be populated by nondipole interactions. The anticipated ingredients for a theoretical description of such interactions are discussed.

    更新日期:2017-09-15
  • Emergence of Type-II Dirac Points in Graphynelike Photonic Lattices
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Georgios G. Pyrialakos, Nicholas S. Nye, Nikolaos V. Kantartzis, and Demetrios N. Christodoulides
    更新日期:2017-09-15
  • Spontaneous Formation of Vector Vortex Beams in Vertical-Cavity Surface-Emitting Lasers with Feedback
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Jesus Jimenez-Garcia, Pedro Rodriguez, T. Guillet, and T. Ackemann
    更新日期:2017-09-15
  • Optically Controlled Orbital Angular Momentum Generation in a Polaritonic Quantum Fluid
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    S. M. H. Luk, N. H. Kwong, P. Lewandowski, S. Schumacher, and R. Binder

    Applications of the orbital angular momentum (OAM) of light range from the next generation of optical communication systems to optical imaging and optical manipulation of particles. Here we propose a micron-sized semiconductor source that emits light with predefined OAM pairs. This source is based on a polaritonic quantum fluid. We show how in this system modulational instabilities can be controlled and harnessed for the spontaneous formation of OAM pairs not present in the pump laser source. Once created, the OAM states exhibit exotic flow patterns in the quantum fluid, characterized by generation-annihilation pairs. These can only occur in open systems, not in equilibrium condensates, in contrast to well-established vortex-antivortex pairs.

    更新日期:2017-09-15
  • Two-Dimensional Pulse Propagation without Anomalous Dispersion
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Carl M. Bender, Francisco J. Rodríguez-Fortuño, Sarben Sarkar, and Anatoly V. Zayats

    Anomalous dispersion is a surprising phenomenon associated with wave propagation in an even number of space dimensions. In particular, wave pulses propagating in two-dimensional space change shape and develop a tail even in the absence of a dispersive medium. We show mathematically that this dispersion can be eliminated by considering a modified wave equation with two geometric spatial dimensions and, unconventionally, two timelike dimensions. Experimentally, such a wave equation describes pulse propagation in an optical or acoustic medium with hyperbolic dispersion, leading to a fundamental understanding and new approaches to ultrashort pulse shaping in nanostructured metamaterials.

    更新日期:2017-09-15
  • Shapes and Fissility of Highly Charged and Rapidly Rotating Levitated Liquid Drops
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    L. Liao and R. J. A. Hill

    We use diamagnetic levitation to investigate the shapes and the stability of free electrically charged and spinning liquid drops of volume ∼ 1 ml. In addition to binary fission and Taylor cone-jet fission modes observed at low and high charge density, respectively, we also observe an unusual mode which appears to be a hybrid of the two. Measurements of the angular momentum required to fission a charged drop show that nonrotating drops become unstable to fission at the amount of charge predicted by Lord Rayleigh. This result is in contrast to the observations of most previous experiments on fissioning charged drops, which typically exhibit fission well below Rayleigh’s limit.

    更新日期:2017-09-15
  • Extraordinary Indentation Strain Stiffening Produces Superhard Tungsten Nitrides
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Cheng Lu, Quan Li, Yanming Ma, and Changfeng Chen

    Transition-metal light-element compounds are a class of designer materials tailored to be a new generation of superhard solids, but indentation strain softening has hitherto limited their intrinsic load-invariant hardness to well below the 40 GPa threshold commonly set for superhard materials. Here we report findings from first-principles calculations that two tungsten nitrides, hP4-WN and hP 6 − WN 2 , exhibit extraordinary strain stiffening that produces remarkably enhanced indentation strengths exceeding 40 GPa, raising exciting prospects of realizing the long-sought nontraditional superhard solids. Calculations show that hP4-WN is metallic both at equilibrium and under indentation, marking it as the first known intrinsic superhard metal. An x-ray diffraction pattern analysis indicates the presence of hP4-WN in a recently synthesized specimen. We elucidate the intricate bonding and stress response mechanisms for the identified structural strengthening, and the insights may help advance rational design and discovery of additional novel superhard materials.

    更新日期:2017-09-15
  • Mapping Isobaric Aging onto the Equilibrium Phase Diagram
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Kristine Niss

    The linear volume relaxation and the nonlinear volume aging of a glass-forming liquid are measured, directly compared, and used to extract the out-of-equilibrium relaxation time. This opens a window to investigate how the relaxation time depends on temperature, structure, and volume in parts of phase space that are not accessed by the equilibrium liquid. It is found that the temperature dependence of relaxation time is non-Arrhenius even in the isostructural case—challenging the Adam-Gibbs entropy model. Based on the presented data and the idea that aging happens through quasiequilibrium states, we suggest a mapping of the out-of-equilibrium states during isobaric aging to the equilibrium phase diagram. This mapping implies the existence of isostructural lines in the equilibrium phase diagram. The relaxation time is found to depend on the bath temperature, density, and a just single structural parameter, referred to as an effective temperature.

    更新日期:2017-09-15
  • Echoes of the Glass Transition in Athermal Soft Spheres
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Peter K. Morse and Eric I. Corwin

    Recent theoretical advances have led to the creation of a unified phase diagram for the thermal glass and athermal jamming transitions. This diagram makes clear that, while related, the mode-coupling—or dynamic—glass transition is distinct from the jamming transition, occurring at a finite temperature and significantly lower density than the jamming transition. Nonetheless, we demonstrate a prejamming transition in athermal frictionless spheres which occurs at the same density as the mode-coupling transition and is marked by percolating clusters of locally rigid particles. At this density in both the thermal and athermal systems, individual motions of an extensive number of particles become constrained, such that only collective motion is possible. This transition, which is well below jamming, exactly matches the definition of collective behavior at the dynamical transition of glasses. Thus, we reveal that the genesis of rigidity in both thermal and athermal systems is governed by the same underlying topological transition in their shared configuration space.

    更新日期:2017-09-15
  • Evidence That Strain-Rate Softening Is Not Necessary for Material Instability Patterns
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-15
    Julio R. Valdes, François Guillard, and Itai Einav

    Strain-rate softening has been associated with a wide variety of material instabilities, from the Portevin–Le Chatelier effect in metal alloys to stick-slip motion in crust faults. Dynamic instability patterns have been recently discovered in brittle porous media: diffused, oscillatory, and erratic compaction. Using model simulations inspired by experiments with puffed rice, we question the link between these dynamic patterns and strain-rate sensitivity in such media. An important feature of our model is that it can recover strain-rate softening as an emergent phenomenon, without imposing it a priori at its microstructural scale. More importantly, the model also demonstrates that the full range of dynamic patterns can develop without presenting macroscopic strain-rate softening. Based on this counterexample model, we therefore argue that strain-rate softening should not be taken as a necessary condition for the emergence of instability patterns. Our findings in brittle porous media have implications on models that require strain-rate softening to explain earthquake and metal alloy instabilities.

    更新日期:2017-09-15
  • Monogamy Inequality for Any Local Quantum Resource and Entanglement
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    S. Camalet

    We derive a monogamy inequality for any local quantum resource and entanglement. It results from the fact that there is always a convex measure for a quantum resource, as shown here, and from the relation between entanglement and local entropy. One of its consequences is an entanglement monogamy different from that usually discussed. If the local resource is nonuniformity or coherence, it is satisfied by familiar resource and entanglement measures. The ensuing upper bound for the local coherence, determined by the entanglement, is independent of the basis used to define the coherence.

    更新日期:2017-09-15
  • Diffusion in Deterministic Interacting Lattice Systems
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Marko Medenjak, Katja Klobas, and Tomaž Prosen

    We study reversible deterministic dynamics of classical charged particles on a lattice with hard-core interaction. It is rigorously shown that the system exhibits three types of transport phenomena, ranging from ballistic, through diffusive to insulating. By obtaining an exact expressions for the current time-autocorrelation function we are able to calculate the linear response transport coefficients, such as the diffusion constant and the Drude weight. Additionally, we calculate the long-time charge profile after an inhomogeneous quench and obtain diffusive profilewith the Green-Kubo diffusion constant. Exact analytical results are corroborated by Monte Carlo simulations.

    更新日期:2017-09-15
  • Scaling Theory of Entanglement at the Many-Body Localization Transition
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Philipp T. Dumitrescu, Romain Vasseur, and Andrew C. Potter

    We study the universal properties of eigenstate entanglement entropy across the transition between many-body localized (MBL) and thermal phases. We develop an improved real space renormalization group approach that enables numerical simulation of large system sizes and systematic extrapolation to the infinite system size limit. For systems smaller than the correlation length, the average entanglement follows a subthermal volume law, whose coefficient is a universal scaling function. The full distribution of entanglement follows a universal scaling form, and exhibits a bimodal structure that produces universal subleading power-law corrections to the leading volume law. For systems larger than the correlation length, the short interval entanglement exhibits a discontinuous jump at the transition from fully thermal volume law on the thermal side, to pure area law on the MBL side.

    更新日期:2017-09-15
  • Realizing and Detecting a Topological Insulator in the AIII Symmetry Class
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Carlos G. Velasco and Belén Paredes

    Topological insulators in the AIII (chiral unitary) symmetry class lack experimental realization. Moreover, fractionalization in one-dimensional topological insulators has not been yet directly observed. Our work might open possibilities for both challenges. We propose a one-dimensional model realizing the AIII symmetry class which can be realized in current experiments with ultracold atomic gases. We further report on a distinctive property of topological edge modes in the AIII class: in contrast to those in the well-studied BDI (chiral orthogonal) class, they have nonzero momentum. Exploiting this feature we propose a path for the detection of fractionalization. A fermion added to an AIII system splits into two halves localized at opposite momenta, which can be detected by imaging the momentum distribution.

    更新日期:2017-09-15
  • Disappearance of the Hexatic Phase in a Binary Mixture of Hard Disks
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    John Russo and Nigel B. Wilding

    Recent studies of melting in hard disks have confirmed the existence of a hexatic phase occurring in a narrow window of density which is separated from the isotropic liquid phase by a first-order transition, and from the solid phase by a continuous transition. However, little is known concerning the melting scenario in mixtures of hard disks. Here we employ tailored Monte Carlo simulations to elucidate the phase behavior of a system of large ( l ) and small ( s ) disks with diameter ratio σ l / σ s = 1.4 . We find that as small disks are introduced to a system of large ones, the stability window of the hexatic phase shrinks progressively until the line of continuous transitions terminates at an end point beyond which melting becomes a first-order liquid-solid transition. This occurs at surprisingly low concentrations of the small disks, c ≲ 1 % , emphasizing the fragility of the hexatic phase. We speculate that the change to the melting scenario is a consequence of strong fractionation effects, the nature of which we elucidate.

    更新日期:2017-09-15
  • Temperature Scaling Law for Quantum Annealing Optimizers
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Tameem Albash, Victor Martin-Mayor, and Itay Hen
    更新日期:2017-09-14
  • Heat Transport via Low-Dimensional Systems with Broken Time-Reversal Symmetry
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Shuji Tamaki, Makiko Sasada, and Keiji Saito

    We consider heat transport via systems with broken time-reversal symmetry. We apply magnetic fields to the one-dimensional charged particle systems with transverse motions. The standard momentum conservation is not satisfied. To focus on this effect clearly, we introduce a solvable model. We exactly demonstrate that the anomalous transport with a new exponent can appear. We numerically show the violation of the standard relation between the power-law decay in the equilibrium correlation and the diverging exponent of the thermal conductivity in the open system.

    更新日期:2017-09-14
  • Constraining Quirky Tracks with Conventional Searches
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Marco Farina and Matthew Low

    Quirks are particles that are charged both under the standard model and under a new confining group. The quirk setup assumes there are no light flavors of the new confining group, so that while the theory is in a confining phase, the quirk-antiquirk distance can be macroscopic. In this Letter, we reinterpret existing collider limits, those from monojet and heavy stable charged particle searches, as limits on quirks. Additionally, we propose a new search in the magnetic-field-less CMS data for quirks and estimate the sensitivity. We focus on the region where the confinement scale is roughly between 1 and 100 eV and find mass constraints in the TeV range, depending on the quirk’s quantum numbers.

    更新日期:2017-09-14
  • Incommensurate Chirality Density Wave Transition in a Hybrid Molecular Framework
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Joshua A. Hill, Kirsten E. Christensen, and Andrew L. Goodwin

    Using single-crystal x-ray diffraction we characterize the 235 K incommensurate phase transition in the hybrid molecular framework tetraethylammonium silver(I) dicyanoargentate, [ NEt 4 ] Ag 3 ( CN ) 4 . We demonstrate the transition to involve spontaneous resolution of chiral [ NEt 4 ] + conformations, giving rise to a state in which molecular chirality is incommensurately modulated throughout the crystal lattice. We refer to this state as an incommensurate chirality density wave (XDW) phase, which represents a fundamentally new type of chiral symmetry breaking in the solid state. Drawing on parallels to the incommensurate ferroelectric transition of NaNO 2 , we suggest the XDW state arises through coupling between acoustic (shear) and molecular rotoinversion modes. Such coupling is symmetry forbidden at the Brillouin zone center but symmetry allowed for small but finite modulation vectors q = [ 0 , 0 , q z ] * . The importance of long-wavelength chirality modulations in the physics of this hybrid framework may have implications for the generation of mesoscale chiral textures, as required for advanced photonic materials.

    更新日期:2017-09-14
  • Self-Averaging Fluctuations in the Chaoticity of Simple Fluids
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Moupriya Das and Jason R. Green

    Bulk properties of equilibrium liquids are a manifestation of intermolecular forces. Here, we show how these forces imprint on dynamical fluctuations in the Lyapunov exponents for simple fluids with and without attractive forces. While the bulk of the spectrum is strongly self-averaging, the first Lyapunov exponent self-averages only weakly and at a rate that depends on the length scale of the intermolecular forces; short-range repulsive forces quantitatively dominate longer-range attractive forces, which act as a weak perturbation that slows the convergence to the thermodynamic limit. Regardless of intermolecular forces, the fluctuations in the Kolmogorov-Sinai entropy rate diverge, as one expects for an extensive quantity, and the spontaneous fluctuations of these dynamical observables obey fluctuation-dissipation-like relationships. Together, these results are a representation of the van der Waals picture of fluids and another lens through which we can view the liquid state.

    更新日期:2017-09-14
  • Nanoparticle Superlattices as Quasi-Frank-Kasper Phases
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-14
    Alex Travesset

    I show that all phases reported experimentally in binary nanoparticle superlattices can be described as networks of disclinations in an ideal lattice of regular tetrahedra. A set of simple rules is provided to identify the different disclination types from the Voronoi construction, and it is shown that those disclinations completely screen the positive curvature of the ideal tetrahedral lattice. In this way, this study provides a generalization of the well-known Frank-Kasper phases to binary systems consisting of two types of particles, and with a more general type of disclinations, i.e., quasi-Frank-Kasper phases. The study comprises all strategies in nanoparticle self-assembly, whether driven by DNA or hydrocarbon ligands, and establishes the universal tendency of superlattices to develop icosahedral order, which is facilitated by the asymmetry of the particles. Besides its interest in predicting nanoparticle self-assembly, I discuss the implications for models of the glass transition, micelles of diblock polymers, and dendritic molecules, among many others.

    更新日期:2017-09-14
  • Correlation Decay in Fermionic Lattice Systems with Power-Law Interactions at Nonzero Temperature
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-13
    Senaida Hernández-Santana, Christian Gogolin, J. Ignacio Cirac, and Antonio Acín

    We study correlations in fermionic lattice systems with long-range interactions in thermal equilibrium. We prove a bound on the correlation decay between anticommuting operators and generalize a long-range Lieb-Robinson-type bound. Our results show that in these systems of spatial dimension D with, not necessarily translation invariant, two-site interactions decaying algebraically with the distance with an exponent α ≥ 2 D , correlations between such operators decay at least algebraically to 0 with an exponent arbitrarily close to α at any nonzero temperature. Our bound is asymptotically tight, which we demonstrate by a high temperature expansion and by numerically analyzing density-density correlations in the one-dimensional quadratic (free, exactly solvable) Kitaev chain with long-range pairing.

    更新日期:2017-09-13
  • Self-Interacting Dark Matter Can Explain Diverse Galactic Rotation Curves
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-13
    Ayuki Kamada, Manoj Kaplinghat, Andrew B. Pace, and Hai-Bo Yu
    更新日期:2017-09-13
  • Gauss-Bonnet Supergravity in Six Dimensions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-13
    Joseph Novak, Mehmet Ozkan, Yi Pang, and Gabriele Tartaglino-Mazzucchelli

    The supersymmetrization of curvature squared terms is important in the study of the low-energy limit of compactified superstrings where a distinguished role is played by the Gauss-Bonnet combination, which is ghost-free. In this Letter, we construct its off-shell N = ( 1 , 0 ) supersymmetrization in six dimensions for the first time. By studying this invariant together with the supersymmetric Einstein-Hilbert term, we confirm and extend known results of the α ′ -corrected string theory compactified to six dimensions. Finally, we analyze the spectrum about the AdS 3 × S 3 solution.

    更新日期:2017-09-13
  • Derivation of the Time-Reversal Anomaly for (2+1)-Dimensional Topological Phases
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-13
    Yuji Tachikawa and Kazuya Yonekura

    We prove an explicit formula conjectured recently by Wang and Levin for the anomaly of time-reversal symmetry in ( 2 + 1 )-dimensional fermionic topological quantum field theories. The crucial step is to determine the cross-cap state in terms of the modular S matrix and T 2 eigenvalues, generalizing the recent analysis by Barkeshli et al. in the bosonic case.

    更新日期:2017-09-13
  • Unexpected Large Hole Effective Masses in SnSe Revealed by Angle-Resolved Photoemission Spectroscopy
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-13
    Qiangsheng Lu, Minghui Wu, Di Wu, Cheng Chang, Yan-Ping Guo, Chun-Sheng Zhou, Wei Li, Xiao-Ming Ma, Gan Wang, Li-Dong Zhao, Li Huang, Chang Liu, and Jiaqing He

    SnSe has emerged as an efficient thermoelectric material since a high value of the thermoelectric figure of merit ( Z T ) has been reported recently. Here we show with systematic angle resolved photoemission spectroscopy data that the low-lying electronic structures of undoped and hole-doped SnSe crystals exhibit noticeable temperature variation from 80 to 600 K. In particular, the hole effective masses for the two lowest lying valence band maxima are found to be very large and increase with decreasing temperature. Thermoelectric parameters derived from such hole-mass enhancement agree well with the transport values, indicating comprehensively a reduced impact of multivalley transport to the system’s thermoelectric performance.

    更新日期:2017-09-13
  • Large Spin Perturbation Theory for Conformal Field Theories
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Luis F. Alday

    We consider conformal field theories around points of large twist degeneracy. Examples of this are theories with weakly broken higher spin symmetry and perturbations around generalized free fields. At the degenerate point we introduce twist conformal blocks. These are eigenfunctions of certain quartic operators and encode the contribution, to a given four-point correlator, of the whole tower of intermediate operators with a given twist. As we perturb around the degenerate point, the twist degeneracy is lifted. In many situations this breaking is controlled by inverse powers of the spin. In such cases the twist conformal blocks can be decomposed into a sequence of functions which we systematically construct. Decomposing the four-point correlator in this basis turns crossing symmetry into an algebraic problem. Our method can be applied to a wide spectrum of conformal field theories in any number of dimensions and at any order in the breaking parameter. As an example, we compute the spectrum of various theories around generalized free fields.

    更新日期:2017-09-12
  • Induced Cavities for Photonic Quantum Gates
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Ohr Lahad and Ofer Firstenberg

    Effective cavities can be optically induced in atomic media and employed to strengthen optical nonlinearities. Here we study the integration of induced cavities with a photonic quantum gate based on Rydberg blockade. Accounting for loss in the atomic medium, we calculate the corresponding finesse and gate infidelity. Our analysis shows that the conventional limits imposed by the blockade optical depth are mitigated by the induced cavity in long media, thus establishing the total optical depth of the medium as a complementary resource.

    更新日期:2017-09-12
  • Conductance and Kondo Interference beyond Proportional Coupling
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Luis G. G. V. Dias da Silva, Caio H. Lewenkopf, Edson Vernek, Gerson J. Ferreira, and Sergio E. Ulloa

    The transport properties of nanostructured systems are deeply affected by the geometry of the effective connections to metallic leads. In this work we derive a conductance expression for a class of interacting systems whose connectivity geometries do not meet the Meir-Wingreen proportional coupling condition. As an interesting application, we consider a quantum dot connected coherently to tunable electronic cavity modes. The structure is shown to exhibit a well-defined Kondo effect over a wide range of coupling strengths between the two subsystems. In agreement with recent experimental results, the calculated conductance curves exhibit strong modulations and asymmetric behavior as different cavity modes are swept through the Fermi level. These conductance modulations occur, however, while maintaining robust Kondo singlet correlations of the dot with the electronic reservoir, a direct consequence of the lopsided nature of the device.

    更新日期:2017-09-12
  • Quantum Criticality in Resonant Andreev Conduction
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    M. Pustilnik, B. van Heck, R. M. Lutchyn, and L. I. Glazman

    Motivated by recent experiments with proximitized nanowires, we study a mesoscopic s-wave superconductor connected via point contacts to normal-state leads. We demonstrate that at energies below the charging energy the system is described by the two-channel Kondo model, which can be brought to the quantum critical regime by varying the gate potential and conductances of the contacts.

    更新日期:2017-09-12
  • Mechanisms for Strong Anisotropy of In-Planeg-Factors in Hole Based Quantum Point Contacts
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    D. S. Miserev, A. Srinivasan, O. A. Tkachenko, V. A. Tkachenko, I. Farrer, D. A. Ritchie, A. R. Hamilton, and O. P. Sushkov

    In-plane hole g factors measured in quantum point contacts based on p-type heterostructures strongly depend on the orientation of the magnetic field with respect to the electric current. This effect, first reported a decade ago and confirmed in a number of publications, has remained an open problem. In this work, we present systematic experimental studies to disentangle different mechanisms contributing to the effect and develop the theory which describes it successfully. We show that there is a new mechanism for the anisotropy related to the existence of an additional B+k−4σ+ effective Zeeman interaction for holes, which is kinematically different from the standard single Zeeman term B−k−2σ+ considered until now.

    更新日期:2017-09-12
  • Emergent Berezinskii-Kosterlitz-Thouless Phase in Low-Dimensional Ferroelectrics
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Y. Nahas, S. Prokhorenko, I. Kornev, and L. Bellaiche

    Using first-principles-based simulations merging an effective Hamiltonian scheme with scaling, symmetry, and topological arguments, we find that an overlooked Berezinskii-Kosterlitz-Thouless (BKT) phase sustained by quasicontinuous symmetry emerges between the ferroelectric phase and the paraelectric one of BaTiO3 ultrathin film, being under tensile strain. Not only do these results provide an extension of BKT physics to the field of ferroelectrics, but they also unveil their nontrivial critical behavior in low dimensions.

    更新日期:2017-09-12
  • Shear-Induced Heterogeneity in Associating Polymer Gels: Role of Network Structure and Dilatancy
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Ahmad K. Omar and Zhen-Gang Wang

    We study associating polymer gels under steady shear using Brownian dynamics simulation to explore the interplay between the network structure, dynamics, and rheology. For a wide range of flow rates, we observe the formation of shear bands with a pronounced difference in shear rate, concentration, and structure. A striking increase in the polymer pressure in the gradient direction with shear, along with the inherently large compressibility of the gels, is shown to be a crucial factor in destabilizing homogeneous flow through shear-gradient concentration coupling. We find that shear has only a modest influence on the degree of association, but induces marked spatial heterogeneity in the network connectivity. We attribute the increase in the polymer pressure (and polymer mobility) to this structural reorganization.

    更新日期:2017-09-12
  • Dynamical Scaling and Phase Coexistence in Topologically Constrained DNA Melting
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Y. A. G. Fosado, D. Michieletto, and D. Marenduzzo

    There is a long-standing experimental observation that the melting of topologically constrained DNA, such as circular closed plasmids, is less abrupt than that of linear molecules. This finding points to an important role of topology in the physics of DNA denaturation, which is, however, poorly understood. Here, we shed light on this issue by combining large-scale Brownian dynamics simulations with an analytically solvable phenomenological Landau mean field theory. We find that the competition between melting and supercoiling leads to phase coexistence of denatured and intact phases at the single-molecule level. This coexistence occurs in a wide temperature range, thereby accounting for the broadening of the transition. Finally, our simulations show an intriguing topology-dependent scaling law governing the growth of denaturation bubbles in supercoiled plasmids, which can be understood within the proposed mean field theory.

    更新日期:2017-09-12
  • Erratum: Reduced Limit on the Permanent Electric Dipole Moment ofHg199[Phys. Rev. Lett.116, 161601 (2016)]
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    B. Graner, Y. Chen, E. G. Lindahl, and B. R. Heckel

    DOI:https://doi.org/10.1103/PhysRevLett.119.119901

    更新日期:2017-09-12
  • Improved Noninterferometric Test of Collapse Models Using Ultracold Cantilevers
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    A. Vinante, R. Mezzena, P. Falferi, M. Carlesso, and A. Bassi
    更新日期:2017-09-12
  • All Entangled States can Demonstrate Nonclassical Teleportation
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Daniel Cavalcanti, Paul Skrzypczyk, and Ivan Šupić
    更新日期:2017-09-12
  • Gravitational Wave Oscillations in Bigravity
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Kevin Max, Moritz Platscher, and Juri Smirnov

    We derive consistent equations for gravitational wave oscillations in bigravity. In this framework a second dynamical tensor field is introduced in addition to general relativity and coupled such that one massless and one massive linear combination arise. Only one of the two tensors is the physical metric coupling to matter, and thus the basis in which gravitational waves propagate is different from the basis where the wave is produced and detected. Therefore, one should expect—in analogy to neutrino oscillations—to observe an oscillatory behavior. We show for the first time how this behavior arises explicitly, discuss phenomenological implications, and present new limits on the graviton parameter space in bigravity.

    更新日期:2017-09-12
  • First Measurement of Transverse-Spin-Dependent Azimuthal Asymmetries in the Drell-Yan Process
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    M. Aghasyanet al.(COMPASS Collaboration)

    The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190  GeV/c π− beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3  GeV/c2 and 8.5  GeV/c2. Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.

    更新日期:2017-09-12
  • Probing the Hardest Branching within Jets in Heavy-Ion Collisions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-12
    Yang-Ting Chien and Ivan Vitev

    Heavy ion collisions present exciting opportunities to study the effects of quantum coherence in the formation of subatomic particle showers. We report on the first calculation of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet in such collisions. These observables are directly sensitive to the hardest branching within jets and can probe the early stage of the jet formation. We find that the leading-order medium-induced splitting functions, here obtained in the framework of soft-collinear effective theory with Glauber gluon interactions, capture the essential many-body physics, which is different from proton-proton reactions. Qualitative and in most cases quantitative agreement between theory and preliminary CMS measurements suggests that hard parton branching in strongly interacting matter can be dramatically modified. We also propose a new measurement that will illuminate its angular structure.

    更新日期:2017-09-12
  • Diffusion and Signatures of Localization in Stochastic Conformal Field Theory
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-11
    Denis Bernard and Benjamin Doyon

    We define a simple model of conformal field theory in random space-time environments, which we refer to as stochastic conformal field theory. This model accounts for the effects of dilute random impurities in strongly interacting critical many-body systems. On one hand, surprisingly, although impurities are separated by macroscopic distances, we find that the infinite-time steady state is factorized on microscopic lengths, a signature of the emergence of localization. The stationary state also displays vanishing energy current and strong uncorrelated spatial fluctuations of local observables. On the other hand, at finite times, the transient shows a crossover from ballistic to diffusive energy propagation. In this regime and a Markovian limit, concentrating on current-generating initial states with a temperature imbalance, we show that the energy current and density satisfy simple dissipative hydrodynamic equations. We describe the space-time scales at which nonequilibrium currents exist. We show that a light-cone effect subsists in the presence of impurities although a momentum burst propagates transiently on a diffusive scale only.

    更新日期:2017-09-11
  • Observation of the Doubly Charmed BaryonΞcc++
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-11
    R. Aaijet al.(LHCb Collaboration)
    更新日期:2017-09-11
  • Enhancement of the Upper Critical Field in Disordered Transition Metal Dichalcogenide Monolayers
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-11
    Stefan Ilić, Julia S. Meyer, and Manuel Houzet

    We calculate the effect of impurities on the superconducting phase diagram of transition metal dichalcogenide monolayers in the presence of an in-plane magnetic field. Because of strong intrinsic spin-orbit coupling, the upper critical field greatly surpasses the Pauli limit at low temperatures. We find that it is insensitive to intravalley scattering and, ultimately, limited by intervalley scattering.

    更新日期:2017-09-11
  • Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture: Local Charge Separation and Surface Phase Transition
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-11
    Shunsuke Yabunaka and Akira Onuki

    We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ > 0 the anions remain accumulated, but for σ < 0 the cations are attracted to the wall with increasing | σ | . Furthermore, the electric potential drop Ψ ( σ ) is nonmonotonic when the solvent interaction parameter χ ( T ) exceeds a critical value χ c determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ . In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

    更新日期:2017-09-11
  • General Galilei Covariant Gaussian Maps
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-08
    Giulio Gasbarri, Marko Toroš, and Angelo Bassi

    We characterize general non-Markovian Gaussian maps which are covariant under Galilean transformations. In particular, we consider translational and Galilean covariant maps and show that they reduce to the known Holevo result in the Markovian limit. We apply the results to discuss measures of macroscopicity based on classicalization maps, specifically addressing dissipation, Galilean covariance and non-Markovianity. We further suggest a possible generalization of the macroscopicity measure defined by Nimmrichter and Hornberger [Phys. Rev. Lett. 110, 16 (2013)].

    更新日期:2017-09-08
  • Experimental Detection of Quantum Channel Capacities
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-08
    Álvaro Cuevas, Massimiliano Proietti, Mario Arnolfo Ciampini, Stefano Duranti, Paolo Mataloni, Massimiliano F. Sacchi, and Chiara Macchiavello

    We present an efficient experimental procedure that certifies nonvanishing quantum capacities for qubit noisy channels. Our method is based on the use of a fixed bipartite entangled state, where the system qubit is sent to the channel input. A particular set of local measurements is performed at the channel output and the ancilla qubit mode, obtaining lower bounds to the quantum capacities for any unknown channel with no need of quantum process tomography. The entangled qubits have a Bell state configuration and are encoded in photon polarization. The lower bounds are found by estimating the Shannon and von Neumann entropies at the output using an optimized basis, whose statistics is obtained by measuring only the three observables σ x ⊗ σ x , σ y ⊗ σ y , and σ z ⊗ σ z .

    更新日期:2017-09-08
  • Polynomial-Time Classical Simulation of Quantum Ferromagnets
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-08
    Sergey Bravyi and David Gosset

    We consider a family of quantum spin systems which includes, as special cases, the ferromagnetic X Y model and ferromagnetic Ising model on any graph, with or without a transverse magnetic field. We prove that the partition function of any model in this family can be efficiently approximated to a given relative error ε using a classical randomized algorithm with runtime polynomial in ε − 1 , system size, and inverse temperature. As a consequence, we obtain a polynomial time algorithm which approximates the free energy or ground energy to a given additive error. We first show how to approximate the partition function by the perfect matching sum of a finite graph with positive edge weights. Although the perfect matching sum is not known to be efficiently approximable in general, the graphs obtained by our method have a special structure which facilitates efficient approximation via a randomized algorithm due to Jerrum and Sinclair.

    更新日期:2017-09-08
  • Hybrid Semiclassical Theory of Quantum Quenches in One-Dimensional Systems
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-09-08
    Cătălin Paşcu Moca, Márton Kormos, and Gergely Zaránd

    We develop a hybrid semiclassical method to study the time evolution of one-dimensional quantum systems in and out of equilibrium. Our method handles internal degrees of freedom completely quantum mechanically by a modified time-evolving block decimation method while treating orbital quasiparticle motion classically. We can follow dynamics up to time scales well beyond the reach of standard numerical methods to observe the crossover between preequilibrated and locally phase equilibrated states. As an application, we investigate the quench dynamics and phase fluctuations of a pair of tunnel-coupled one-dimensional Bose condensates. We demonstrate the emergence of soliton-collision-induced phase propagation, soliton-entropy production, and multistep thermalization. Our method can be applied to a wide range of gapped one-dimensional systems.

    更新日期:2017-09-08
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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