显示样式:     当前期刊: "热门"类期刊    排序: 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Engineered CRISPR-Cas9 nuclease with expanded targeting space
    Science (IF 41.058) Pub Date : 2018-09-18
    Hiroshi Nishimasu, Xi Shi, Soh Ishiguro, Linyi Gao, Seiichi Hirano, Sae Okazaki, Taichi Noda, Omar O. Abudayyeh, Jonathan S. Gootenberg, Hideto Mori, Seiya Oura, Benjamin Holmes, Mamoru Tanaka, Motoaki Seki, Hisato Hirano, Hiroyuki Aburatani, Ryuichiro Ishitani, Masahito Ikawa, Nozomu Yachie, Feng Zhang, Osamu Nureki

    The RNA-guided endonuclease Cas9 cleaves its target DNA and is a powerful genome-editing tool. However, the widely used Streptococcus pyogenes Cas9 enzyme (SpCas9) requires an NGG protospacer adjacent motif (PAM) for target recognition, thereby restricting the targetable genomic loci. Here, we report a rationally engineered SpCas9 variant (SpCas9-NG) that can recognize relaxed NG PAMs. The crystal structure revealed that the loss of the base-specific interaction with the third G is compensated by newly introduced non-base-specific interactions, enabling the NG PAM recognition. We showed that SpCas9-NG induces indels at endogenous target sites bearing NG PAMs in human cells. Furthermore, we found that the fusion of SpCas9-NG and the activation-induced cytidine deaminase (AID) mediates the C-to-T conversion at target sites with NG PAMs in human cells.

    更新日期:2018-09-19
  • Exciton States in MonolayerMoSe2andMoTe2Probed by Upconversion Spectroscopy
    Phys. Rev. X (IF 14.385) Pub Date : 2018-09-18
    B. Han, C. Robert, E. Courtade, M. Manca, S. Shree, T. Amand, P. Renucci, T. Taniguchi, K. Watanabe, X. Marie, L. E. Golub, M. M. Glazov, and B. Urbaszek
    更新日期:2018-09-19
  • Experimental Observation of Topologically Protected Helical Edge Modes in Patterned Elastic Plates
    Phys. Rev. X (IF 14.385) Pub Date : 2018-09-18
    M. Miniaci, R. K. Pal, B. Morvan, and M. Ruzzene
    更新日期:2018-09-19
  • Erratum: Binary Black Hole Mergers in the First Advanced LIGO Observing Run [Phys. Rev. X6, 041015 (2016)]
    Phys. Rev. X (IF 14.385) Pub Date : 2018-09-18
    B. P. Abbottet al.(LIGO Scientific and Virgo Collaborations)
    更新日期:2018-09-19
  • Certification and quantification of multilevel quantum coherence
    Phys. Rev. X (IF 14.385) Pub Date : 
    Martin Ringbauer, Thomas R. Bromley, Marco Cianciaruso, Ludovico Lami, W. Y. Sarah Lau, Gerardo Adesso, Andrew G. White, Alessandro Fedrizzi, and Marco Piani

    Quantum coherence, present whenever a quantum system exists in a superposition of , marks one of the fundamental departures from classical physics. Quantum coherence has recently been investigated rigorously within a resource-theoretic formalism. However, the finer-grained notion of , which explicitly takes into account the number of superposed classical states, has remained relatively unexplored. A comprehensive analysis of multi-level coherence, which acts as the single-party analogue to multi-partite entanglement, is essential for understanding natural quantum processes as well as for gauging the performance of quantum technologies. Here we develop the theoretical and experimental groundwork for characterizing and quantifying multilevel coherence. We further verify and lower-bound the robustness of multilevel coherence by performing a phase discrimination task, which is implemented experimentally with four-level quantum probes in a photonic setup. Our results contribute to understanding the operational relevance of genuine multilevel coherence, also by demonstrating the key role it plays in enhanced phase discrimination—a primitive for quantum communication and metrology—and suggest new ways to reliably and effectively test the quantum behaviour of physical systems.

    更新日期:2018-09-19
  • Non-perturbative quantum electrodynamics in the Cherenkov effect
    Phys. Rev. X (IF 14.385) Pub Date : 
    Charles Roques-Carmes, Nicholas Rivera, John D. Joannopoulos, Marin Soljačić, and Ido Kaminer

    Quantum Electrodynamics (QED) is one of the most precisely tested theories in the history of science, giving accurate predictions to a wide range of experimental observations. Recent experimental advances have allowed for the ability to probe physics on extremely short attosecond timescales, enabling ultrafast imaging of quantum dynamics. It is of great interest to extend our understanding of short-time quantum dynamics to QED, where the focus is typically on long-time observables such as S-matrices, decay rates, and cross sections. That said, even for the simplest problems, solving the dynamics of the QED hamiltonian can lead to short-time divergences, making it unclear how to arrive at physical predictions. We present an approach to regularize QED at short times, and apply it to the problem of describing the detailed time dynamics of free electron radiation into a medium, known as erenkov radiation. Surprisingly, we find a number of previously unknown phenomena yielding corrections to the conventional erenkov effect that could be observed in current experiments. Specifically, the rate of photon emission near the erenkov velocity threshold decreases relative to the conventional theory, effectively making the minimum velocity for erenkov radiation larger than the phase velocity of light in the medium. Finally, we reveal a bifurcation process creating radiation into new erenkov angles, occurring in the strong-coupling regime, which would be realizable by considering the radiation dynamics of highly-charged ions. Our results shed light on QED phenomena at short times and reveal surprising new physics in the erenkov effect.

    更新日期:2018-09-19
  • Author Correction: Higher-order topology in bismuth
    Nat. Phys. (IF 22.727) Pub Date : 2018-09-19
    Frank Schindler, Zhijun Wang, Maia G. Vergniory, Ashley M. Cook, Anil Murani, Shamashis Sengupta, Alik Yu. Kasumov, Richard Deblock, Sangjun Jeon, Ilya Drozdov, Hélène Bouchiat, Sophie Guéron, Ali Yazdani, B. Andrei Bernevig, Titus Neupert

    Author Correction: Higher-order topology in bismuthAuthor Correction: Higher-order topology in bismuth, Published online: 19 September 2018; doi:10.1038/s41567-018-0308-4Author Correction: Higher-order topology in bismuth

    更新日期:2018-09-19
  • An inconsistent friend
    Nat. Phys. (IF 22.727) Pub Date : 2018-09-18
    Matthew F. Pusey

    An inconsistent friendAn inconsistent friend, Published online: 18 September 2018; doi:10.1038/s41567-018-0293-7Are there limits to the applicability of textbook quantum theory? Experiments haven’t found any yet, but a new theoretical analysis shows that treating your colleagues as quantum systems might be a step too far.

    更新日期:2018-09-19
  • Erratum: Tests of General Relativity with GW150914 [Phys. Rev. Lett.116, 221101 (2016)]
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    B. P. Abbottet al.(LIGO Scientific and Virgo Collaboration)
    更新日期:2018-09-19
  • 更新日期:2018-09-19
  • Energy Storage via Topological Spin Textures
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    Yaroslav Tserkovnyak and Jiang Xiao
    更新日期:2018-09-19
  • Unconventional Multiband Superconductivity in BulkSrTiO3andLaAlO3/SrTiO3Interfaces
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    Thaís V. Trevisan, Michael Schütt, and Rafael M. Fernandes
    更新日期:2018-09-19
  • Spectral Evidence for Emergent Order inBa1−xNaxFe2As2
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    M. Yi, A. Frano, D. H. Lu, Y. He, Meng Wang, B. A. Frandsen, A. F. Kemper, R. Yu, Q. Si, L. Wang, M. He, F. Hardy, P. Schweiss, P. Adelmann, T. Wolf, M. Hashimoto, S.-K. Mo, Z. Hussain, M. Le Tacon, A. E. Böhmer, D.-H. Lee, Z.-X. Shen, C. Meingast, and R. J. Birgeneau
    更新日期:2018-09-19
  • Fragile Topology and Wannier Obstructions
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    Hoi Chun Po, Haruki Watanabe, and Ashvin Vishwanath
    更新日期:2018-09-19
  • Observation of Nonlocal Heat Flux Using Thomson Scattering
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    R. J. Henchen, M. Sherlock, W. Rozmus, J. Katz, D. Cao, J. P. Palastro, and D. H. Froula
    更新日期:2018-09-19
  • Painting Nonclassical States of Spin or Motion with Shaped Single Photons
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    Emily J. Davis, Zhaoyou Wang, Amir H. Safavi-Naeini, and Monika H. Schleier-Smith
    更新日期:2018-09-19
  • R'{e}nyi generalization of the accessible entanglement entropy
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Hatem Barghathi, C. M. Herdman, and Adrian Del Maestro

    Operationally accessible entanglement in bipartite systems of indistinguishable particles could be reduced due to restrictions on the allowed local operations as a result of particle number conservation. In order to quantify this effect, Wiseman and Vaccaro [Phys. Rev. Lett. {91}, 097902 (2003)] introduced an operational measure of the von Neumann entanglement entropy. Motivated by advances in measuring entropies in quantum many-body systems subject to conservation laws, we derive a generalization of the operationally accessible entanglement that is both computationally and experimentally measurable. Using the Widom theorem, we investigate its scaling with the size of a spatial subregion for free fermions and find a logarithmically violated area law scaling, similar to the spatial entanglement entropy, with at most, a double-log leading-order correction. A modification of the correlation matrix method confirms our findings in systems of up to 105 particles.

    更新日期:2018-09-19
  • Realization of a cross-linked chiral ladder with neutral fermions in a one-dimensional optical lattice by orbital-momentum coupling
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Jin Hyoun Kang, Jeong Ho Han, and Y. Shin

    We report the experimental realization of a cross-linked chiral ladder with ultracold fermionic atoms in a one-dimensional optical lattice. In the ladder, the legs are formed by the orbital states of the optical lattice and the complex inter-leg links are generated by the orbital-changing Raman transitions that are driven by a moving lattice potential superimposed onto the optical lattice. The effective magnetic flux per ladder plaquette is tuned by the spatial periodicity of the moving lattice, and the chiral currents are observed from the asymmetric momentum distributions of the orbitals. The effect of the complex cross links is demonstrated in quench dynamics by measuring the momentum dependence of the inter-orbital coupling strength. We discuss the topological phase transition of the chiral ladder system for the variations of the complex cross links.

    更新日期:2018-09-19
  • Periodic Motion of Sedimenting Flexible Knots
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-18
    Magdalena Gruziel, Krishnan Thyagarajan, Giovanni Dietler, Andrzej Stasiak, Maria L. Ekiel-Jeżewska, and Piotr Szymczak
    更新日期:2018-09-18
  • Dynamical control of order in a cavity-BEC system
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Jayson G. Cosme, Christoph Georges, Andreas Hemmerich, and Ludwig Mathey

    We demonstrate dynamical control of the superradiant transition of cavity-BEC system via periodic driving of the pump laser. We show that the dominant density wave order of the superradiant state can be suppressed, and that the subdominant competing order of Bose-Einstein condensation emerges in the steady state. Furthermore, we show that additional, non-equilibrium density wave orders, which do not exist in equilibrium, can be stabilized dynamically. Finally, for strong driving, chaotic dynamics emerges.

    更新日期:2018-09-18
  • Theory of the drift-wave instability at arbitrary collisionality
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    R. Jorge, P. Ricci, and N. F. Loureiro

    A numerically efficient framework that takes into account the effect of the Coulomb collision operator at arbitrary collisionalities is introduced. Such model is based on the expansion of the distribution function on a Hermite-Laguerre polynomial basis, to study the effects of collisions on magnetized plasma instabilities at arbitrary mean-free path. Focusing on the drift-wave instability, we show that our framework allows retrieving established collisional and collisionless limits. At the intermediate collisionalities relevant for present and future magnetic nuclear fusion devices, deviations with respect to collision operators used in state-of-the-art turbulence simulation codes show the need for retaining the full Coulomb operator in order to obtain both the correct instability growth rate and eigenmode spectrum, which, for example, may significantly impact quantitative predictions of transport. The exponential convergence of the spectral representation that we propose makes the representation of the velocity space dependence, including the full collision operator, more efficient than standard finite difference methods.

    更新日期:2018-09-18
  • Dynamo effect and turbulence in hydrodynamic Weyl metals
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Victor Galitski, Mehdi Kargarian, and Sergey Syzranov

    The dynamo effect is a class of macroscopic phenomena responsible for generation and maintaining magnetic fields in astrophysical bodies. It hinges on hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials -- in particular, hydrodynamic metals -- may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental developments, this paper focuses on hydrodynamic Weyl semimetals, where the dominant scattering mechanism is due to interactions. We derive Navier-Stokes equations along with equations of magneto-hydrodynamics that describe transport of Weyl electron-hole plasma appropriate in this regime. We estimate the hydrodynamic and magnetic Reynolds numbers for this system. The latter is a key figure of merit of the dynamo mechanism. We show that it can be relatively large to enable observation of the dynamo-induced magnetic field bootstrap in experiment. Finally, we generalize the simplest dynamo instability model -- Ponomarenko dynamo -- to the case of a hydrodynamic Weyl semimetal and show that the chiral anomaly term reduces the threshold magnetic Reynolds number for the dynamo instability.

    更新日期:2018-09-18
  • Mass difference for charged quarks from asymptotically safe quantum gravity
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Astrid Eichhorn and Aaron Held

    We propose a scenario to retrodict the top and bottom mass and the Abelian gauge coupling from first principles in a microscopic model including quantum gravity. In our approximation, antiscreening quantum-gravity fluctuations induce an asymptotically safe fixed point for the Abelian hypercharge leading to a uniquely fixed infrared value that is observationally viable for a particular choice of microscopic gravitational parameters. The unequal quantum numbers of the top and bottom quark lead to different fixed-point values for the top and bottom Yukawa under the impact of gauge and gravity fluctuations. This results in a dynamically generated mass difference between the two quarks. To work quantitatively, the preferred ratio of electric charges of bottom and top in our approximation lies in close vicinity to the Standard-Model value of $Q_b/Q_t =-1/2$.

    更新日期:2018-09-18
  • From birefringent electrons to marginal or non-Fermi liquid of relativistic spin-1/2 fermions: An emergent superuniversality
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Bitan Roy, Malcolm P. Kennett, Kun Yang, and Vladimir JuričIć

    We present the quantum critical theory of an interacting nodal Fermi-liquid of quasi-relativisitc pseudo-spin-3/2 fermions that have a non-interacting \emph{birefringent} spectrum with \emph{two} distinct Fermi velocities. When such quasiparticles interact with gapless bosonic degrees of freedom that mediate either the long-range Coulomb interaction or its short range component (responsible for spontaneous symmetry breaking), in the deep infrared or quantum critical regime in two dimensions the system is respectively described by a \emph{marginal-} or a \emph{non-Fermi liquid} of relativistic spin-1/2 fermions (possessing a \emph{unique} velocity), and is always a \emph{marginal Fermi liquid} in three dimensions. We consider a possible generalization of these scenarios to fermions with an arbitrary half-odd-integer spin, and conjecture that critical spin-1/2 excitations represent a \emph{superuniversal} description of the entire family of interacting quasi-relativistic fermions.

    更新日期:2018-09-18
  • Beliaev damping of spin-orbit coupled Bose-Einstein condensate
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Rukuan Wu and Zhaoxin Liang

    Beliaev damping provides a fundamental mechanism for dissipation of quasiparticles. Previous research has shown that the two-component internal degrees of freedom has no nontrivial effect on Beliaev damping. Here we provide the first example where the spinor nature of Bose gases can manifest itself in the Beliaev damping by way of spin-obit coupling. We identify novel features of Beliaev decay rate due to spin-orbit coupling, in particular, it shows explicit dependence on the spin-density interaction and diverges at the interaction-modified phase boundary between the zero-momentum and plane-wave phases. This represents a manifestation of the effect of spin-orbit coupling in the beyond-mean-field regime, which by breaking Galilean invariance couples excitations in the density- and spin-channels. We further show that the measurement of Beliaev damping rate is experimentally feasible through the measurement of spin polarizability susceptibility which has been already achieved in spin-orbit-coupled Bose gases.

    更新日期:2018-09-18
  • Secure quantum key distribution over 421 km of optical fiber
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Alberto Boaron, Gianluca Boso, Davide Rusca, Cédric Vulliez, Claire Autebert, Misael Caloz, Matthieu Perrenoud, Gaëtan Gras, Félix Bussières, Ming-Jun Li, Daniel Nolan, Anthony Martin, and Hugo Zbinden

    We present a quantum key distribution system with a 2.5~GHz repetition rate using a three-state time-bin protocol combined with a one-decoy approach. Taking advantage of superconducting single-photon detectors optimized for quantum key distribution and ultra low-loss fiber, we can distribute secret keys at a maximum distance of 421~km and obtain secret key rates of 6.5~bps over 405~km.

    更新日期:2018-09-18
  • Diffusion Dynamics and Optimal Coupling in Multiplex Networks with Directed Layers
    Phys. Rev. X (IF 14.385) Pub Date : 2018-09-17
    Alejandro Tejedor, Anthony Longjas, Efi Foufoula-Georgiou, Tryphon T. Georgiou, and Yamir Moreno
    更新日期:2018-09-18
  • Strength of Correlations in Strongly Recurrent Neuronal Networks
    Phys. Rev. X (IF 14.385) Pub Date : 2018-09-17
    Ran Darshan, Carl van Vreeswijk, and David Hansel
    更新日期:2018-09-18
  • Deterministic and generalized framework for unsupervised learning with restricted Boltzmann machines
    Phys. Rev. X (IF 14.385) Pub Date : 
    Eric W. Tramel, Marylou Gabrié, Andre Manoel, Francesco Caltagirone, and Florent Krzakala

    Restricted Boltzmann machines (RBMs) are energy-based neural-networks which are commonly used as the building blocks for deep architectures neural architectures. In this work, we derive a deterministic framework for the training, evaluation, and use of RBMs based upon the Thouless-Anderson-Palmer (TAP) mean-field approximation of widely-connected systems with weak interactions coming from spin-glass theory. While the TAP approach has been extensively studied for fully-visible binary spin systems, our construction is generalized to latent-variable models, as well as to arbitrarily distributed real-valued spin systems with bounded support. In our numerical experiments, we demonstrate the effective deterministic training of our proposed models and are able to show interesting features of unsupervised learning which could not be directly observed with sampling. Additionally, we demonstrate how to utilize our TAP-based framework for leveraging trained RBMs as joint priors in denoising problems.

    更新日期:2018-09-18
  • Competing inversion-based lasing and Raman lasing in doped silicon
    Phys. Rev. X (IF 14.385) Pub Date : 
    S. G. Pavlov, N. Deßmann, B. Redlich, A. F. G. van der Meer, N. V. Abrosimov, H. Riemann, R. Kh. Zhukavin, V. N. Shastin, and H. -W. Hübers

    We report on an optically pumped laser where photons are simultaneously generated by population inversion and by stimulated Raman scattering in the same active medium, namely crystalline silicon doped by bismuth (Si:Bi). The medium utilizes three electronic levels: ground state (\textbar 1$\rangle $: 1s(A$_{1})$ in Si:Bi), upper (\textbar 3$\rangle $: 2p$_{\pm })$ and lower (\textbar 2$\rangle $: 1s(E)) laser levels. The \textbar 1$\rangle \leftrightarrow $\textbar 3$\rangle $ and \textbar 2$\rangle \leftrightarrow $\textbar 3$\rangle $ transitions are optically allowed and the \textbar 1$\rangle \leftrightarrow $\textbar 2$\rangle $ transition is Raman active. Lasing based on population inversion occurs between the states \textbar 3$\rangle $ and \textbar 2$\rangle $ while Raman scattering benefits from the Raman-active transition. At high pump power the inversion-based stimulated emission \textbar 3$\rangle \to $\textbar 2$\rangle $ disappears, because electronic scattering from \textbar 1$\rangle $~to~\textbar 2$\rangle $ via a virtual state dominates and the electrons are excited into \textbar 2$\rangle $ rather than into \textbar 3$\rangle $. Starting as population inversion based lasing, it ends as stimulated Raman scattering. Our model shows that such a competition occurs on the time scale of the 10~ps long pump pulse.

    更新日期:2018-09-18
  • Entanglement entropy: Holography and renormalization group
    Rev. Mod. Phys. (IF 36.367) Pub Date : 2018-09-17
    Tatsuma Nishioka
    更新日期:2018-09-18
  • Membrane-induced hydroelastic migration of a particle surfing its own wave
    Nat. Phys. (IF 22.727) Pub Date : 2018-09-17
    Bhargav Rallabandi, Naomi Oppenheimer, Matan Yah Ben Zion, Howard A. Stone

    While coupling between fluid flow and soft elastic surfaces is common in biology and engineering, an analytical description is challenging as it often involves non-linear dynamics. Here we show using theory and experiments that a small particle moving along an elastic membrane through a viscous fluid is repelled from the membrane due to hydroelastic forces. The flow field produces an elastic disturbance in the membrane leading to particle–wave coupling. We derive an analytic expression for the particle trajectory and find that the normal migration velocity of the particle is quadratic in its speed and depends on a combination of the tension and bending resistance of the membrane. Experimentally, we measure the normal displacement of spheres sedimenting under gravity along a suspended elastic membrane and find quantitative agreement with the theoretical predictions with no fitting parameters. We experimentally demonstrate that the effect is strong enough for separation and sorting of particles on the basis of both their size and density. We discuss the significance of our results for particles interacting with biological membranes, and propose the use of our model for membrane elasticity measurements.

    更新日期:2018-09-18
  • Visualization of the periodic modulation of Cooper pairing in a cuprate superconductor
    Nat. Phys. (IF 22.727) Pub Date : 2018-09-17
    Wei Ruan, Xintong Li, Cheng Hu, Zhenqi Hao, Haiwei Li, Peng Cai, Xingjiang Zhou, Dung-Hai Lee, Yayu Wang

    In cuprate superconductors, the existence of various intertwined orders associated with spin, charge and Cooper pairs1,2 is an obstacle in understanding the mechanism of Cooper pairing. The ubiquitous charge order is particularly important2,3,4,5,6,7. Various theories have been proposed to explain the origin of the charge order and its implications for the superconducting phase, including charge stripes8, electronic nematicity8,9 and Fermi surface instability5,10. A highly appealing physical picture is the ‘pair density wave’, a spatially periodic modulation of Cooper pairing, which may also induce a charge order2,11,12,13,14,15,16,17,18,19,20,21. To elucidate the existence and nature of the pair density wave, we use scanning tunnelling microscopy to investigate a severely underdoped cuprate, in which superconductivity just emerges on top of a pronounced chequerboard charge order. We observe a periodic modulation of both the superconducting coherence peak and gap depth, indicating the existence of a density wave order of Cooper pairing based on the empirical relationship between superconducting coherence and superfluid density22,23,24,25,26,27. The pair density wave has the same spatial periodicity as the charge order, and the amplitudes of the two orders exhibit clear positive correlation. These results shed new light on the origin of and interplay between the charge order and Cooper pairing modulation in the cuprates.

    更新日期:2018-09-18
  • Collective mechanical adaptation of honeybee swarms
    Nat. Phys. (IF 22.727) Pub Date : 2018-09-17
    O. Peleg, J. M. Peters, M. K. Salcedo, L. Mahadevan

    Honeybee Apis mellifera swarms form large congested tree-hanging clusters made solely of bees attached to each other1. How these structures are maintained under the influence of dynamic mechanical forcing is unknown. To address this, we created pendant clusters and subject them to dynamic loads of varying orientation, amplitude, frequency and duration. We find that horizontally shaken clusters adapt by spreading out to form wider, flatter cones that recover their original shape when unloaded. Measuring the response of a cluster to an impulsive pendular excitation shows that flattened cones deform less and relax faster than the elongated ones (that is, they are more stable). Particle-based simulations of a passive assemblage suggest a behavioural hypothesis: individual bees respond to local variations in strain by moving up the strain gradient, which is qualitatively consistent with our observations of individual bee movement during dynamic loading. The simulations also suggest that vertical shaking will not lead to significant differential strains and thus no shape adaptation, which we confirmed experimentally. Together, our findings highlight how a super-organismal structure responds to dynamic loading by actively changing its morphology to improve the collective stability of the cluster at the expense of increasing the average mechanical burden of an individual.

    更新日期:2018-09-18
  • Non-reciprocal interband Brillouin modulation
    Nat. Photon. (IF 32.521) Pub Date : 2018-09-17
    Eric A. Kittlaus, Nils T. Otterstrom, Prashanta Kharel, Shai Gertler, Peter T. Rakich

    Non-reciprocal light propagation is essential to control optical crosstalk and back-scatter in photonic systems. However, realizing high-fidelity non-reciprocity in low-loss integrated photonic circuits remains challenging. Here, we experimentally demonstrate a form of non-local acousto-optic light scattering to produce non-reciprocal single-sideband modulation and mode conversion in an integrated silicon photonic platform. In this system, a travelling-wave acoustic phonon driven by optical forces in a silicon waveguide spatiotemporally modulates light in a separate waveguide through linear interband Brillouin scattering. This process extends narrowband optomechanics-based schemes for non-reciprocity to travelling-wave physics, enabling large operation bandwidths of more than 125 GHz and up to 38 dB of non-reciprocal contrast between forward- and backward-propagating optical waves. The modulator operation wavelength is tunable over a 35-nm range by varying the optical drive wavelength. Such travelling-wave acousto-optic interactions provide a promising path toward the realization of broadband, low-loss isolators and circulators within integrated photonics.

    更新日期:2018-09-18
  • Thermal Critical Points and Quantum Critical End Point in the Frustrated Bilayer Heisenberg Antiferromagnet
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    J. Stapmanns, P. Corboz, F. Mila, A. Honecker, B. Normand, and S. Wessel
    更新日期:2018-09-18
  • Binary Two-Dimensional Honeycomb Lattice with Strong Spin-Orbit Coupling and Electron-Hole Asymmetry
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    Jian Gou, Bingyu Xia, Hang Li, Xuguang Wang, Longjuan Kong, Peng Cheng, Hui Li, Weifeng Zhang, Tian Qian, Hong Ding, Yong Xu, Wenhui Duan, Kehui Wu, and Lan Chen
    更新日期:2018-09-18
  • Fractional Excitonic Insulator
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    Yichen Hu, Jörn W. F. Venderbos, and C. L. Kane
    更新日期:2018-09-18
  • Quantum Spin Hall Effect and Spin Bott Index in a Quasicrystal Lattice
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    Huaqing Huang and Feng Liu
    更新日期:2018-09-18
  • Observation of Higgs Boson Decay to Bottom Quarks
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    A. M. Sirunyanet al.(CMS Collaboration)
    更新日期:2018-09-18
  • Quantum Anomaly and 2D-3D Crossover in Strongly Interacting Fermi Gases
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    T. Peppler, P. Dyke, M. Zamorano, I. Herrera, S. Hoinka, and C. J. Vale
    更新日期:2018-09-18
  • Anomalous Breaking of Scale Invariance in a Two-Dimensional Fermi Gas
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    M. Holten, L. Bayha, A. C. Klein, P. A. Murthy, P. M. Preiss, and S. Jochim
    更新日期:2018-09-18
  • Stochastic polarization instability in PbTiO$_3$
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    K. Datta, I. Margaritescu, D. A. Keen, and B. Mihailova

    Although discussions of structural phase transitions in prototypical ferroelectric systems with the perovskite structure, such as BaTiO$_3$ and PbTiO$_3$, started almost seventy years ago, an atomic-level description of the polar characteristics as a function of temperature, pressure and composition remains topical. Here we provide a novel quantitative description of the temperature-driven local structural correlations in PbTiO$_3$ via the development of characteristic relative cationic shifts. The results give new insights into the phase transition beyond those reliant on the long-range order. The ferroelectric-to-paraelectric transition of PbTiO$_3$ is realized by the extent of a stochastic polarization instability driven by a progressive misalignment instead of a complete disappearance of the local dipoles, which further suggests that such polarization instability is chemically induced at the morphotropic phase boundary of PbTiO$_3$-based solid solutions with giant piezoelectric effect. As such, our results not only identify the evolving atomistic disorder in a perovskite-based ferroelectric system, but also suggest that polarization-instability can serve as a generic fingerprint for phase transitions as well as for better understanding structure-property relationships in PbTiO$_3$-based ferroelectric solid solutions.

    更新日期:2018-09-18
  • High-dimensional quantum communication complexity beyond strategies based on Bell's theorem
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Daniel Martínez, Armin Tavakoli, Mauricio Casanova, Gustavo Cañas, Breno Marques, and Gustavo Lima

    Quantum resources can improve communication complexity problems (CCPs) beyond their classical constraints. One quantum approach is to share entanglement and create correlations violating a Bell inequality, which can then assist classical communication. A second approach is to resort solely to the preparation, transmission and measurement of a single quantum system; in other words quantum communication. Here, we show the advantages of the latter over the former in high-dimensional Hilbert space. We focus on a family of CCPs, based on facet Bell inequalities, study the advantage of high-dimensional quantum communication, and realise such quantum communication strategies using up to ten-dimensional systems. The experiment demonstrates, for growing dimension, an increasing advantage over quantum strategies based on Bell inequality violation. For sufficiently high dimensions, quantum communication also surpasses the limitations of the post-quantum Bell correlations obeying only locality in the macroscopic limit. We find that the advantages are tied to the use of measurements that are not rank-one projective, and provide an experimental semi-device-independent falsification of such measurements in Hilbert space dimension six.

    更新日期:2018-09-18
  • Initiating and monitoring the evolution of single electrons within atom-defined structures
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Mohammad Rashidi, Wyatt Vine, Thomas Dienel, Lucian Livadaru, Jacob Retallick, Taleana Huff, Konrad Walus, and Robert A. Wolkow

    Using a non-contact atomic force microscope we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds on the hydrogen terminated silicon surface. An attractive tip surface interaction mechanically manipulates the equilibrium position of a surface silicon atom, causing rehybridization that stabilizes a negative charge at the dangling bond. This is applied to controllably switch the charge state of individual dangling bonds. Because this mechanism is based on short range interactions and can be performed without applied bias voltage, we maintain both site-specific selectivity and single-electron control. We extract the short range forces involved with this mechanism by subtracting the long range forces acquired on a dimer vacancy site. As a result of relaxation of the silicon lattice to accommodate negatively charged dangling bonds, we observe charge configurations of dangling bond structures that remain stable for many seconds at 4.5~K. Subsequently, we use charge manipulation to directly prepare the ground state and metastable charge configurations of dangling bond structures composed of up to six atoms.

    更新日期:2018-09-18
  • Breakdown of nonrelativistic QCD factorization in processes involving two quarkonia and its cure
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Zhi-Guo He, Bernd A. Kniehl, and Xiang-Peng Wang

    We study inclusive processes involving two heavy quarkonia in nonrelativisitic QCD (NRQCD) and demonstrate that, in the presence of two P-wave Fock states, NRQCD factorization breaks down, leaving uncanceled infrared singularities. As phenomenologically important examples, we consider the decay $\Upsilon \to \chi_{cJ}+X$ via $b\bar{b}(^3P_{J_b}^{[8]})\to c\bar{c}(^3P_J^{[1]})+gg$ and the production process $e^+e^-\to J/\psi+\chi_{cJ}+X$ via $e^{+}e^{-}\to c\bar{c}(^3P_{J_1}^{[8]})+c\bar{c}(^3P_J^{[1]})+g$. We infer that such singularities will appear for double quarkonium hadroproduction at next-to-leading order. As a solution to this problem, we introduce to NRQCD effective field theory new types of operators whose quantum corrections absorb these singularities.

    更新日期:2018-09-18
  • Quantization of the thermal Hall conductivity at small Hall angles
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Mengxing Ye, Gábor B. Halász, Lucile Savary, and Leon Balents

    We consider the effect of coupling between phonons and a chiral Majorana edge in a gapped chiral spin liquid with Ising anyons (e.g., Kitaev's non-abelian spin liquid on the honeycomb lattice). This is especially important in the regime in which the longitudinal bulk heat conductivity $\kappa_{xx}$ due to phonons is much larger than the expected quantized thermal Hall conductance $\kappa_{xy}^{\rm q}=\frac{\pi T}{12} \frac{k_B^2}{\hbar}$ of the ideal isolated edge mode, so that the thermal Hall angle, i.e., the angle between the thermal current and the temperature gradient, is small. By modeling the interaction between a Majorana edge and bulk phonons, we show that the exchange of energy between the two subsystems leads to a transverse component of the bulk current and thereby an {\em effective} Hall conductivity. Remarkably, the latter is equal to the quantized value when the edge and bulk can thermalize, which occurs for a Hall bar of length $L \gg \ell$, where $\ell$ is a thermalization length. We obtain $\ell \sim T^{-5}$ for a model of the Majorana-phonon coupling. We also find that the quality of the quantization depends on the means of measuring the temperature and, surprisingly, a more robust quantization is obtained when the lattice, not the spin, temperature is measured. We present general hydrodynamic equations for the system, detailed results for the temperature and current profiles, and an estimate for the coupling strength and its temperature dependence based on a microscopic model Hamiltonian. Our results may explain recent experiments observing a quantized thermal Hall conductivity in the regime of small Hall angle, $\kappa_{xy}/\kappa_{xx} \sim 10^{-3}$, in $\alpha$-RuCl$_3$.

    更新日期:2018-09-18
  • Confinement of positrons exceeding one second in a supported magnetic dipole trap
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    J. Horn-Stanja, S. Niß l, U. Hergenhahn, T. Sunn Pedersen, H. Saitoh, E. V. Stenson, M. Dickmann, C. Hugenschmidt, M. Singer, M. R. Stoneking, and J. R. Danielson

    An ensemble of low-energy positrons injected into a supported magnetic dipole trap can remain trapped for more than a second. Trapping experiments with and without a positive magnet bias yield confinement times up to $\tau_A=(1.5\pm0.1)\,$s and $\tau_B=(0.28\pm0.04)\,$s, respectively. Supported by single-particle simulations, we conclude that the dominant mechanism limiting the confinement in this trap is scattering off of neutrals, which can lead to both radial transport and parallel losses onto the magnet surface. These results provide encouragement for plans to confine an electron-positron plasma in a levitated dipole trap.

    更新日期:2018-09-18
  • Short note on the density of states in 3D Weyl semimetals
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    K. Ziegler and A. Sinner

    The average density of states in a disordered three-dimensional Weyl system is discussed in the case of a continuous distribution of random scattering. Our results clearly indicate that the average density of states does not vanish, reflecting the absence of a critical point for a metal-insulator transition. This calculation supports recent suggestions of an avoided quantum critical point in the disordered three-dimensional Weyl semimetal. However, the effective density of states can be very small such that the saddle-approximation with a vanishing density of states might be valid for practical cases.

    更新日期:2018-09-18
  • Generation of a cat state in an optical sideband
    Phys. Rev. Lett. (IF 8.839) Pub Date : 
    Takahiro Serikawa, Jun-ichi Yoshikawa, Shuntaro Takeda, Hidehiro Yonezawa, Timothy C. Ralph, Elanor H. Huntington, and Akira Furusawa

    We propose a method to subtract a photon from a double sideband mode of continuous-wave light. The central idea is to use phase modulation as a frequency sideband beamsplitter in the heralding photon subtraction scheme, where a small portion of the sideband mode is downconverted to 0\,Hz to provide a trigger photon. An optical cat state is created by applying the proposed method to a squeezed state at 500MHz sideband, which is generated by an optical parametric oscillator. The Wigner function of the cat state reconstructed from a direct homodyne measurement of the 500\,MHz sideband modes shows the negativity of $W(0,0) = -0.088\pm0.001$ without any loss corrections.

    更新日期:2018-09-18
  • Time-asymmetric loop around an exceptional point over the full optical communications band
    Nature (IF 41.577) Pub Date : 2018-09-17
    Jae Woong Yoon, Youngsun Choi, Choloong Hahn, Gunpyo Kim, Seok Ho Song, Ki-Yeon Yang, Jeong Yub Lee, Yongsung Kim, Chang Seung Lee, Jai Kwang Shin, Hong-Seok Lee, Pierre Berini
    更新日期:2018-09-17
  • Sensation, movement and learning in the absence of barrel cortex
    Nature (IF 41.577) Pub Date : 2018-09-17
    Y. Kate Hong, Clay O. Lacefield, Chris C. Rodgers, Randy M. Bruno
    更新日期:2018-09-17
  • Structure of the membrane-assembled retromer coat determined by cryo-electron tomography
    Nature (IF 41.577) Pub Date : 2018-09-17
    Oleksiy Kovtun, Natalya Leneva, Yury S. Bykov, Nicholas Ariotti, Rohan D. Teasdale, Miroslava Schaffer, Benjamin D. Engel, David. J. Owen, John A. G. Briggs, Brett M. Collins
    更新日期:2018-09-17
  • The role of miniaturization in the evolution of the mammalian jaw and middle ear
    Nature (IF 41.577) Pub Date : 2018-09-17
    Stephan Lautenschlager, Pamela G. Gill, Zhe-Xi Luo, Michael J. Fagan, Emily J. Rayfield
    更新日期:2018-09-17
  • Spectrally resolved specular reflections of thermal phonons from atomically rough surfaces
    Phys. Rev. X (IF 14.385) Pub Date : 
    Navaneetha K. Ravichandran, Hang Zhang, and Austin J. Minnich

    The reflection of waves from rough surfaces is a fundamental process that plays a role in diverse fields such as optics, acoustics, and seismology. While a quantitative understanding of the process has long been established for many types of waves, the precise manner in which thermal phonons of specific wavelengths reflect from atomically rough surfaces remains unclear owing to limited control over THz frequency phonon generation and detection. Knowledge of these processes is critical for many applications, however, and is particularly important for recent attempts to create novel materials by coherently interfering thermal phonons. Here, we report measurements of a key property for these efforts, the phonon wavelength-dependent specularity parameter, which describes the probability of specular reflection of thermal phonons at a surface. Our observations demonstrate that THz thermal phonons specularly reflect from surfaces with Angstrom-scale roughness, and further show that completely diffuse reflections occur with surface imperfections on the scale of only a few atomic planes. Our work provides key insights into the surface perfection required for coherent manipulation of heat and demonstrates a general approach to probe thermal phonon interactions with surfaces with considerable microscopic detail.

    更新日期:2018-09-17
  • The conformal bootstrap: Theory, numerical techniques, and applications
    Rev. Mod. Phys. (IF 36.367) Pub Date : 
    David Poland, Slava Rychkov, and Alessandro Vichi

    Conformal field theories have been long known to describe the fascinating universal physics of scale invariant critical points. They describe continuous phase transitions in fluids, magnets, and numerous other materials, while at the same time sit at the heart of our modern understanding of quantum field theory. For decades it has been a dream to study these intricate strongly coupled theories nonperturbatively using symmetries and other consistency conditions. This idea, called the conformal bootstrap, saw some successes in two dimensions but it is only in the last ten years that it has been fully realized in three, four, and other dimensions of interest. This renaissance has been possible both due to significant analytical progress in understanding how to set up the bootstrap equations and the development of numerical techniques for finding or constraining their solutions. These developments have led to a number of groundbreaking results, including world record determinations of critical exponents and correlation function coecients in the Ising and O(N) models in three dimensions. This article will review these exciting developments for newcomers to the bootstrap, giving an introduction to conformal field theories and the theory of conformal blocks, describing numerical techniques for the bootstrap based on convex optimization, and summarizing in detail their applications to fixed points in three and four dimensions with no or minimal supersymmetry.

    更新日期:2018-09-17
  • 更新日期:2018-09-17
  • Constraint-Based Approach to Granular Dispersion Rheology
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    B. M. Guy, J. A. Richards, D. J. M. Hodgson, E. Blanco, and W. C. K. Poon
    更新日期:2018-09-17
  • Anomalous Hall Effect in 2D Dirac Materials
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    Manuel Offidani and Aires Ferreira
    更新日期:2018-09-17
  • Avalanche Behavior in Creep Failure of Disordered Materials
    Phys. Rev. Lett. (IF 8.839) Pub Date : 2018-09-17
    D. F. Castellanos and M. Zaiser
    更新日期:2018-09-17
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.
down
wechat
bug