Show filters Hide filters

Refine your search

Publication Year
Publisher
Person found in the video
1-36 out of 334 results
Change view
  • Sort by:
02:58 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Quantum walk on a chimera graph

We analyse a continuous-time quantum walk on a chimera graph, which is a graph of choice for designing quantum annealers, and we discover beautiful quantum walk features such as localization that starkly distinguishes classical from quantum behaviour. Motivated by technological thrusts, we study continuous-time quantum walk on enhanced variants of the chimera graph and on diminished chimera graph with a random removal of vertices. We explain the quantum walk by constructing a generating set for a suitable subgroup of graph isomorphisms and corresponding symmetry operators that commute with the quantum walk Hamiltonian; the Hamiltonian and these symmetry operators provide a complete set of labels for the spectrum and the stationary states. Our quantum walk characterization of the chimera graph and its variants yields valuable insights into graphs used for designing quantum-annealers.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:30 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Theory of electron–phonon–dislon interacting system—toward a quantized theory of dislocations

We provide a comprehensive theoretical framework to study how crystal dislocations influence the functional properties of materials, based on the idea of a quantized dislocation, namely a 'dislon'. In contrast to previous work on dislons which focused on exotic phenomenology, here we focus on their theoretical structure and computational power. We first provide a pedagogical introduction that explains the necessity and benefits of taking the dislon approach and why the dislon Hamiltonian takes its current form. Then, we study the electron–dislocation and phonon–dislocation scattering problems using the dislon formalism. Both the effective electron and phonon theories are derived, from which the role of dislocations on electronic and phononic transport properties is computed. Compared with traditional dislocation scattering studies, which are intrinsically single-particle, low-order perturbation and classical quenched defect in nature, the dislon theory not only allows easy incorporation of quantum many-body effects such as electron correlation, electron–phonon interaction, and higher-order scattering events, but also allows proper consideration of the dislocation's long-range strain field and dynamic aspects on equal footing for arbitrary types of straight-line dislocations. This means that instead of developing individual models for specific dislocation scattering problems, the dislon theory allows for the calculation of electronic structure and electrical transport, thermal transport, optical and superconducting properties, etc, under one unified theory. Furthermore, the dislon theory has another advantage over empirical models in that it requires no fitting parameters. The dislon theory could serve as a major computational tool to understand the role of dislocations on multiple materials' functional properties at an unprecedented level of clarity, and may have wide applications in dislocated energy materials.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:17 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Measuring the deviation from the superposition principle in interference experiments

The Feynman path integral formalism has long been used for calculations of probability amplitudes. Over the last few years, it has been extensively used to theoretically demonstrate that the usual application of the superposition principle in slit based interference experiments is often incorrect. This has caveat in both optics and quantum mechanics where it is often naively assumed that the boundary condition represented by slits opened individually is same as them being opened together. The correction term comes from exotic sub-leading terms in the path integral which can be described by what are popularly called non-classical paths. In this work, we report an experiment where we have a controllable parameter that can be varied in its contribution such that the effect due to these non-classical paths, which we will refer to as sub-leading paths, can be increased or diminished at will. Thus, the reality of these sub-leading paths is brought forth in a classical experiment using microwaves, thereby proving that the boundary condition effect being investigated transcends the classical-quantum divide and that the Feynman path integral formalism is an overarching framework. We report the first measurement of a deviation (as big as 6%) from the superposition principle in the microwave domain using antennas as sources and detectors of the electromagnetic waves. We also show that our results can have potential applications in astronomy.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:24 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Coherent perfect absorption and laser modes in a cylindrical structure of conjugate metamaterials

In this work, we theoretically find that coherent perfect absorption (CPA) and laser modes can be realized in a two-dimensional cylindrical structure composed of conjugate metamaterials (CMs). The required phase factors of CMs for achieving CPA and laser modes are determined by the geometric size of the CM cylinder, which is a unique feature compared with other non-Hermitian optical systems. Based on this property, we also demonstrate that CPA and laser modes can exist simultaneously in a CM cylinder with an extremely large size, where the excitations of CPA and laser modes depend on the angular momentum of coherent incident light. Therefore, compared with the well known parity time symmetry, our work opens up a brand-new path to obtaining CPA and laser modes, and is a significant advance in non-Hermitian optical systems.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:55 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Chaotic signatures of photoconductive Cu2ZnSnS4 nanostructures explored by Lorenz attractors

Photoconductive and third-order nonlinear optical properties exhibited by Cu2ZnSnS4 nanostructures are presented. The samples were synthetized in thin film form by a spray pyrolysis processing route. Distinctions in the photoconductive behavior throughout the samples were clearly noted by modulating their optoelectronic response dependent on electrical frequency. Vectorial two-wave mixing experiments were carried out at a 532 nm wavelength provided by a Nd:YAG laser system to study the optical nonlinearities in the samples. An induced transparency effect was observed during nanosecond single-beam experiments in the nanostructures reported. Quantum and thermal processes were considered to be the main physical mechanism responsible for the photo-electrical phenomena and nonlinear refraction in the nanostructures. Potential applications for developing nanophotonic and nanoelectronic instrumentation systems can be contemplated.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:59 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Flagellar dynamics of chains of active Janus particles fueled by an AC electric field

We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field. Both the speed and direction of the self-propulsion, and the strength of the attractive interaction between particles can be controlled by tuning the frequency of the applied electric field and the ion concentration of the solution. The strong attractive force at high ion concentration gives rise to chain formation of the Janus particles, which can be explained by the quadrupolar charge distribution on the particles. Chain formation is observed irrespective of the direction of the self-propulsion of the particles. When both the position and the orientation of the heads of the chains are fixed, they exhibit beating behavior reminiscent of eukaryotic flagella. The beating frequency of the chains of Janus particles depends on the applied voltage and thus on the self-propulsive force. The scaling relation between the beating frequency and the self-propulsive force deviates from theoretical predictions made previously on active filaments. However, this discrepancy is resolved by assuming that the attractive interaction between the particles is mediated by the quadrupolar distribution of the induced charges, which gives indirect but convincing evidence on the mechanisms of the Janus particles. This signifies that the dependence between the propulsion mechanism and the interaction mechanism, which had been dismissed previously, can modify the dispersion relations of beating behaviors. In addition, hydrodynamic interaction within the chain, and its effect on propulsion speed, are discussed. These provide new insights into active filaments, such as optimal flagellar design for biological functions.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:38 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Quantum probe spectroscopy for cold atomic systems

We study a two-level impurity coupled locally to a quantum gas on an optical lattice. For state-dependent interactions between the impurity and the gas, we show that its evolution encodes information on the local excitation spectrum of the gas at the coupling site. Based on this, we design a nondestructive method to probe the system's excitations in a broad range of energies by measuring the state of the probe using standard atom optics methods. We illustrate our findings with numerical simulations for quantum lattice systems, including realistic dephasing noise on the quantum probe, and discuss practical limits on the probe dephasing rate to fully resolve both regular and chaotic spectra.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:25 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Frequency spectrum of an optical resonator in a curved spacetime

The effect of gravity and proper acceleration on the frequency spectrum of an optical resonator—both rigid or deformable—is considered in the framework of general relativity. The optical resonator is modeled either as a rod of matter connecting two mirrors or as a dielectric rod whose ends function as mirrors. Explicit expressions for the frequency spectrum are derived for the case that it is only perturbed slightly and variations are slow enough to avoid any elastic resonances of the rod. For a deformable resonator, the perturbation of the frequency spectrum depends on the speed of sound in the rod supporting the mirrors. A connection is found to a relativistic concept of rigidity when the speed of sound approaches the speed of light. In contrast, the corresponding result for the assumption of Born rigidity is recovered when the speed of sound becomes infinite. The results presented in this article can be used as the basis for the description of optical and opto-mechanical systems in a curved spacetime. We apply our results to the examples of a uniformly accelerating resonator and an optical resonator in the gravitational field of a small moving sphere. To exemplify the applicability of our approach beyond the framework of linearized gravity, we consider the fictitious situation of an optical resonator falling into a black hole.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:45 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Sensing coherent phonons with two-photon interference

Detecting coherent phonons pose different challenges compared to coherent photons due to the much stronger interaction between phonons and matter. This is especially true for high frequency heat carrying phonons, which are intrinsic lattice vibrations experiencing many decoherence events with the environment, and are thus generally assumed to be incoherent. Two photon interference techniques, especially coherent population trapping (CPT) and electromagnetically induced transparency (EIT), have led to extremely sensitive detection, spectroscopy and metrology. Here, we propose the use of two photon interference in a three-level system to sense coherent phonons. Unlike prior works which have treated phonon coupling as damping, we account for coherent phonon coupling using a full quantum–mechanical treatment. We observe strong asymmetry in absorption spectrum in CPT and negative dispersion in EIT susceptibility in the presence of coherent phonon coupling which cannot be accounted for if only pure phonon damping is considered. Our proposal has application in sensing heat carrying coherent phonons effects and understanding coherent bosonic multi-pathway interference effects in three coupled oscillator systems.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:34 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Superstatistical generalised Langevin equation: non-Gaussian viscoelastic anomalous diffusion

Recent advances in single particle tracking and supercomputing techniques demonstrate the emergence of normal or anomalous, viscoelastic diffusion in conjunction with non-Gaussian distributions in soft, biological, and active matter systems. We here formulate a stochastic model based on a generalised Langevin equation in which non-Gaussian shapes of the probability density function and normal or anomalous diffusion have a common origin, namely a random parametrisation of the stochastic force. We perform a detailed analysis demonstrating how various types of parameter distributions for the memory kernel result in exponential, power law, or power-log law tails of the memory functions. The studied system is also shown to exhibit a further unusual property: the velocity has a Gaussian one point probability density but non-Gaussian joint distributions. This behaviour is reflected in the relaxation from a Gaussian to a non-Gaussian distribution observed for the position variable. We show that our theoretical results are in excellent agreement with stochastic simulations.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:37 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Experimental realization of a relativistic harmonic oscillator

We report the experimental study of a harmonic oscillator in the relativistic regime. The oscillator is composed of Bose-condensed lithium atoms in the third band of an optical lattice, which have an energy–momentum relation nearly identical to that of a massive relativistic particle, with an effective mass reduced below the bare value and a greatly reduced effective speed of light. Imaging the shape of oscillator trajectories at velocities up to 98% of the effective speed of light reveals a crossover from sinusoidal to nearly photon-like propagation. The existence of a maximum velocity causes the measured period of oscillations to increase with energy; our measurements reveal beyond-leading-order contributions to this relativistic anharmonicity. We observe an intrinsic relativistic dephasing of oscillator ensembles, and a monopole oscillation with exactly the opposite phase of that predicted for non-relativistic harmonic motion. All observed dynamics are in quantitative agreement with longstanding but hitherto-untested relativistic predictions.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:08 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

MeV proton acceleration at kHz repetition rate from ultra-intense laser liquid interaction

Laser acceleration of ions to MeV energies has been achieved on a variety of Petawatt laser systems, raising the prospect of ion beam applications using compact ultra-intense laser technology. However, translation from proof-of-concept laser experiment into real-world application requires MeV-scale ion energies and an appreciable repetition rate (>Hz). We demonstrate, for the first time, proton acceleration up to 2 MeV energies at a kHz repetition rate using a milli-joule-class short-pulse laser system. In these experiments, 5 mJ of ultrashort-pulse laser energy is delivered at an intensity near onto a thin-sheet, liquid-density target. Key to this effort is a flowing liquid ethylene glycol target formed in vacuum with thicknesses down to 400 nm and full recovery at 70 μs, suggesting its potential use at kHz rate. Novel detectors and experimental methods tailored to high-repetition-rate ion acceleration by lasers were essential to this study and are described. In addition, particle-in-cell simulations of the laser–plasma interaction show good agreement with experimental observations.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:02 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Quantum control for high-fidelity multi-qubit gates

Quantum control for error correction is critical for the practical use of quantum computers. We address quantum optimal control for single-shot multi-qubit gates by framing it as a feasibility problem for the Hamiltonian model that is then solved with standard global optimization software. Our approach yields faster high-fidelity (>99.99%) single-shot three-qubit-gate control than obtained previously, and it has also enabled us to solve the quantum-control problem for a fast high-fidelity four-qubit gate.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:11 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Networks of non-equilibrium condensates for global optimization

Recently several gain-dissipative platforms based on the networks of optical parametric oscillators, lasers and various non-equilibrium Bose–Einstein condensates have been proposed and realised as analogue Hamiltonian simulators for solving large-scale hard optimisation problems. However, in these realisations the parameters of the problem depend on the node occupancies that are not known a priori, which limits the applicability of the gain-dissipative simulators to the classes of problems easily solvable by classical computations. We show how to overcome this difficulty and formulate the principles of operation of such simulators for solving the NP-hard large-scale optimisation problems such as constant modulus continuous quadratic optimisation and quadratic binary optimisation for any general matrix. To solve such problems any gain-dissipative simulator has to implement a feedback mechanism for the dynamical adjustment of the gain and coupling strengths.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:17 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Protecting solid-state spins from a strongly coupled environment

Quantum memories are critical for solid-state quantum computing devices and a good quantum memory requires both long storage time and fast read/write operations. A promising system is the nitrogen-vacancy (NV) center in diamond, where the NV electronic spin serves as the computing qubit and a nearby nuclear spin as the memory qubit. Previous works used remote, weakly coupled 13C nuclear spins, trading read/write speed for long storage time. Here we focus instead on the intrinsic strongly coupled 14N nuclear spin. We first quantitatively understand its decoherence mechanism, identifying as its source the electronic spin that acts as a quantum fluctuator. We then propose a scheme to protect the quantum memory from the fluctuating noise by applying dynamical decoupling on the environment itself. We demonstrate a factor of 3 enhancement of the storage time in a proof-of-principle experiment, showing the potential for a quantum memory that combines fast operation with long coherence time.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:04 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Curing Braess' paradox by secondary control in power grids

The robust operation of power transmission grids is essential for most of today's technical infrastructure and our daily life. Adding renewable generation to power grids requires grid extensions and sophisticated control actions on different time scales to cope with short-term fluctuations and long-term power imbalance. Braess' paradox constitutes a counterintuitive collective phenomenon that occurs if adding new transmission line capacity to a network increases loads on other lines, effectively reducing the system's performance and potentially even entirely destabilizing its operating state. Combining simple analytical considerations with numerical investigations on a small sample network, we here study dynamical consequences of secondary control in AC power grid models. We demonstrate that sufficiently strong control not only implies dynamical stability of the system but may also cure Braess' paradox. Our results highlight the importance of demand control in conjunction with the grid topology to ensure stable operation of the grid and reveal a new functional benefit of secondary control.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:03 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Magnetic force microscopy with frequency-modulated capacitive tip–sample distance control

In a step towards routinely achieving 10 nm spatial resolution with magnetic force microscopy, we have developed a robust method for active tip–sample distance control based on frequency modulation of the cantilever oscillation. It allows us to keep a well-defined tip–sample distance of the order of 10 nm within better than nm precision throughout the measurement even in the presence of energy dissipative processes, and is adequate for single-passage non-contact operation in vacuum. The cantilever is excited mechanically in a phase-locked loop to oscillate at constant amplitude on its first flexural resonance mode. This frequency is modulated by an electrostatic force gradient generated by tip–sample bias oscillating from a few hundred Hz up to a few kHz. The sum of the side bands' amplitudes is a proxy for the tip–sample distance and can be used for tip–sample distance control. This method can also be extended to other scanning probe microscopy techniques.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:26 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Stochastic pair approximation treatment of the noisy voter model

We present a full stochastic description of the pair approximation scheme to study binary-state dynamics on heterogeneous networks. Within this general approach, we obtain a set of equations for the dynamical correlations, fluctuations and finite-size effects, as well as for the temporal evolution of all relevant variables. We test this scheme for a prototypical model of opinion dynamics known as the noisy voter model that has a finite-size critical point. Using a closure approach based on a system size expansion around a stochastic dynamical attractor we obtain very accurate results, as compared with numerical simulations, for stationary and time-dependent quantities whether below, within or above the critical region. We also show that finite-size effects in complex networks cannot be captured, as often suggested, by merely replacing the actual system size N by an effective network dependent size N eff.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:00 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Efficient code for relativistic quantum summoning

Summoning retrieves quantum information, prepared somewhere in spacetime, at another specified point in spacetime, but this task is limited by the quantum no-cloning principle and the speed-of-light bound. We develop a thorough mathematical framework for summoning quantum information in a relativistic system and formulate a quantum summoning protocol for any valid configuration of causal diamonds in spacetime. For single-qubit summoning, we present a protocol based on a Calderbank–Shor–Steane code that decreases the space complexity for encoding by a factor of two compared to the previous best result and reduces the gate complexity from scaling as the cube to the square of the number of causal diamonds. Our protocol includes decoding whose gate complexity scales linearly with the number of causal diamonds. Our thorough framework for quantum summoning enables full specification of the protocol, including spatial and temporal implementation and costs, which enables quantum summoning to be a well posed protocol for relativistic quantum communication purposes.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:52 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Transition from electromagnetically induced transparency to Autler–Townes splitting in cold cesium atoms

Electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) are two similar yet distinct phenomena that modify the transmission of a weak probe field through an absorption medium in the presence of a coupling field, featured in a variety of three-level atomic systems. In many applications it is important to distinguish EIT from ATS splitting. We present EIT and ATS spectra in a three-level cascade system, involving cold cesium atoms in the Rydberg state. The EIT linewidth, γ EIT, defined as the full width at half maximum of the transparency window, and the ATS splitting, γ ATS, defined as the peak-to-peak distance between AT absorption peaks, are used to delineate the EIT and ATS regimes and to characterize the transition between the regimes. In the cold-atom medium, in the weak-coupler (EIT) regime γ EIT ≈ A + B( + , where Ω c and Ω p are the coupler and probe Rabi frequencies, Γ eg is the spontaneous decay rate of the intermediate 6P3/2 level, and parameters A and B that depend on the laser linewidth. We explore the transition into the strong-coupler (ATS) regime, which is characterized by the relation γ ATS ≈ Ω c . The experiments are in agreement with numerical solutions of the Master equation. Our analysis accounts for non-ideal conditions that exist in typical realizations of Rydberg-EIT, including laser-frequency jitter, Doppler mismatch of the utilized two-color Rydberg EIT system, and strong probe fields. The obtained criteria to distinguish cold-atom EIT from ATS are readily accessible and applicable in practical implementations.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:57 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Electron hole instability as a primordial step towards sustained intermittent turbulence in linearly subcritical plasmas

Electron and ion holes are highly stable nonlinear structures met omnipresently in driven collisionless hot plasmas. A mechanism destabilizing small perturbations into holes is essential for an often witnessed but less understood subcritically driven intermittent plasma turbulence. In this paper we show how a tiny, eddy-like, non-topological electron seed fluctuation can trigger an unstable evolution deep in the linearly damped region, a process being controlled by the trapping nonlinearity and hence being beyond the realm of the Landau scenario. After a (transient) transition phase modes of the privileged spectrum of cnoidal electron and ion holes are excited which in the present case consist of a solitary electron hole (SEH), two counter-propagating 'Langmuir' modes (plasma oscillation), and an ion acoustic mode. A quantitative explanation involves a nonlinear dispersion relation with a forbidden regime and the negative energy character of the SEH, properties being inherent in Schamel's model of undamped Vlasov–Poisson structures identified here as lowest order trapped particle equilibria. An important role in the final adaption of nonlinear plasma eigenmodes is played by a deterministic response of trapped electrons which facilitates transfer of energy from electron thermal energy to an ion acoustic nonuniformity, accelerating the SEH and positioning it into the right place assigned by the theory.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:22 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Skyrmion glass in a 2D Heisenberg ferromagnet with quenched disorder

A 2D Heisenberg ferromagnet with exchange J and random magnetic anisotropy of strength has been studied. Analytical theory for the dependence of the average size of a pinned skyrmion on the magnetic field H, and for stability of such skyrmions on a lattice, has been developed. It has been complemented by numerical studies of 2D lattices containing up to 40 million spins. At low fields the average size of the skyrmion, λ, is determined by the average size of Imry–Ma domains. On increasing the field the skyrmions first shrink, with , and then collapse at fields distributed around . The concentration of the skyrmions goes down with the field as .
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:17 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Fast-forward scaling theory for phase imprinting on a BEC: creation of a wave packet with uniform momentum density and loading to Bloch states without disturbance

We study phase imprinting on Bose–Einstein condensates (BECs) with the fast-forward scaling theory revealing a nontrivial scaling property in quantum dynamics. We introduce a wave packet with uniform momentum density (WPUM) which has peculiar properties but is short-lived. The fast-forward scaling theory is applied to derive the driving potential for creation of the WPUMs in a predetermined time. Fast manipulation is essential for the creation of WPUMs because of the instability of the state. We also study loading of a BEC into a predetermined Bloch state in the lowest band from the ground state of a periodic potential. Controlled linear potential is not sufficient for creation of the Bloch state with large wavenumber because the change in the amplitude of the order parameter is not negligible. We derive the exact driving potential for creation of predetermined Bloch states using the obtained theory.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:01 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Engineering drag currents in Coulomb coupled quantum dots

The Coulomb drag phenomenon in a Coulomb-coupled double quantum dot system is revisited with a simple model that highlights the importance of simultaneous tunneling of electrons. Previously, cotunneling effects on the drag current in mesoscopic setups have been reported both theoretically and experimentally. However, in both cases the sequential tunneling contribution to the drag current was always present unless the drag level position were too far away from resonance. Here, we consider the case of very large Coulomb interaction between the dots, whereby the drag current needs to be assisted by cotunneling events. As a consequence, a quantum coherent drag effect takes place. Further, we demonstrate that by properly engineering the tunneling probabilities using band tailoring it is possible to control the sign of the drag and drive currents, allowing them to flow in parallel or antiparallel directions. We also show that the drag current can be manipulated by varying the drag gate potential and is thus governed by electron- or hole-like transport.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:18 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Record high-gradient SRF beam acceleration at Fermilab

Many modern and future particle accelerators employ high gradient superconducting RF (SRF) to generate beams of high energy, high intensity and high brightness for research in high energy and nuclear physics, basic energy sciences, etc. In this paper we report the record performance large-scale SRF system with average beam accelerating gradient matching the International Linear Collider (ILC) specification of 31.5 MV m−1. Design of the eight cavity 1.3 GHz SRF cryomodule, its performance without the beam and results of the system commissioning with high intensity electron beam at Fermilab Accelerator Science and Technology (FAST) facility are presented. We also briefly discuss opportunities for further beam studies and tests at FAST including those on even higher gradient and more efficient SRF acceleration, as well as exploration of the system performance with full ILC-type beam specifications.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
05:01 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Freeze-thaw cycles induce content exchange between cell-sized lipid vesicles

Early protocells are commonly assumed to consist of an amphiphilic membrane enclosing an RNA-based self-replicating genetic system and a primitive metabolism without protein enzymes. Thus, protocell evolution must have relied on simple physicochemical self-organization processes within and across such vesicular structures. We investigate freeze-thaw (FT) cycling as a potential environmental driver for the necessary content exchange between vesicles. To this end, we developed a conceptually simple yet statistically powerful high-throughput procedure based on nucleic acid-containing giant unilamellar vesicles (GUVs) as model protocells. GUVs are formed by emulsion transfer in glass bottom microtiter plates and hence can be manipulated and monitored by fluorescence microscopy without additional pipetting and sample handling steps. This new protocol greatly minimizes artefacts, such as unintended GUV rupture or fusion by shear forces. Using DNA-encapsulating phospholipid GUVs fabricated by this method, we quantified the extent of content mixing between GUVs under different FT conditions. We found evidence of nucleic acid exchange in all detected vesicles if fast freezing of GUVs at −80 °C is followed by slow thawing at room temperature. In contrast, slow freezing and fast thawing both adversely affected content mixing. Surprisingly, and in contrast to previous reports for FT-induced content mixing, we found that the content is not exchanged through vesicle fusion and fission, but that vesicles largely maintain their membrane identity and even large molecules are exchanged via diffusion across the membranes. Our approach supports efficient screening of prebiotically plausible molecules and environmental conditions, to yield universal mechanistic insights into how cellular life may have emerged.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:53 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Generation of mechanical interference fringes by multi-photon counting

Exploring the quantum behaviour of macroscopic objects provides an intriguing avenue to study the foundations of physics and to develop a suite of quantum-enhanced technologies. One prominent path of study is provided by quantum optomechanics which utilizes the tools of quantum optics to control the motion of macroscopic mechanical resonators. Despite excellent recent progress, the preparation of mechanical quantum superposition states remains outstanding due to weak coupling and thermal decoherence. Here we present a novel optomechanical scheme that significantly relaxes these requirements allowing the preparation of quantum superposition states of motion of a mechanical resonator by exploiting the nonlinearity of multi-photon quantum measurements. Our method is capable of generating non-classical mechanical states without the need for strong single-photon coupling, is resilient against optical loss, and offers more favourable scaling against initial mechanical thermal occupation than existing schemes. Moreover, our approach allows the generation of larger superposition states by projecting the optical field onto NOON states. We experimentally demonstrate this multi-photon-counting technique on a mechanical thermal state in the classical limit and observe interference fringes in the mechanical position distribution that show phase super-resolution. This opens a feasible route to explore and exploit quantum phenomena at a macroscopic scale.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:02 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Dynamical response of Bose–Einstein condensates to oscillating gravitational fields

A description of the dynamical response of uniformly trapped Bose–Einstein condensates (BECs) to oscillating external gravitational fields is developed, with the inclusion of damping. Two different effects that can lead to the creation of phonons in the BEC are identified; direct driving and parametric driving. Additionally, the oscillating gravitational field couples phonon modes, which can lead to the transition of excitations between modes. The special case of the gravitational field of a small, oscillating sphere located closely to the BEC is considered. It is shown that measurement of the effects may be possible for oscillating source masses down to the milligram scale, with a signal to noise ratio of the order of 10. To this end, noise terms and variations of experimental parameters are discussed and generic experimental parameters are given for specific atom species. The results of this article suggest the utility of BECs as sensors for the gravitational field of very small oscillating objects which may help pave the way towards gravity experiments with masses in the quantum regime.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:52 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

A quantum retrograde canon: complete population inversion in n 2-state systems

We present a novel approach for analytically reducing a family of time-dependent multi-state quantum control problems to two-state systems. The presented method translates between related n 2-state systems and two-state systems, such that the former undergo complete population inversion (CPI) if and only if the latter reach specific states. For even n, the method translates any two-state CPI scheme to a family of CPI schemes in n 2-state systems. In particular, facilitating CPI in a four-state system via real time-dependent nearest-neighbors couplings is reduced to facilitating CPI in a two-level system. Furthermore, we show that the method can be used for operator control, and provide conditions for producing several universal gates for quantum computation as an example. In addition, we indicate a basis for utilizing the method in optimal control problems.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:53 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Two-bunch operation with ns temporal separation at the FERMI FEL facility

In the last decade, a continuous effort has been dedicated to extending the capabilities of existing free-electron lasers (FELs) operating in the x-ray and vacuum ultraviolet regimes. In this framework, the generation of two-color (or multi-color) temporally separated FEL pulses, has paved the way to new x-ray pump and probe experiments and several two-color two-pulse schemes have been implemented at the main facilities, but with a generally limited time-separation between the pulses, from 0 to few hundreds of fs. This limitation may be overcome by generating light with two independent electron bunches, temporally separated by integral multiples of the radio-frequency period. This solution was investigated at FERMI, measurements and characterization of this two-bunch mode of operation are presented, including trajectory control, impact of longitudinal and transverse wakefields, manipulation of the longitudinal phase space and finally a demonstration of suitability of the scheme to provide extreme ultraviolet light by using both bunches.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:24 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Topological and magnetic phase transition in silicene-like zigzag nanoribbons

Spin–orbital interactions (SOI) in silicene results in the quantum-spin-Hall effect, while the Hubbard-induced Coulomb interaction in zigzag nanoribbons often generates a band gap with the anti-ferromagnetic (AF) spin orders on two edges. In this paper we systematically study these two joint contributions to the zigzag silicene-like nanoribbons (zSiNR). Some topological and magnetic phase transitions are investigated with different material parameters and external fields. We find when the ribbon width or the SOI value exceeds some critical value, the SOI may overcome the Coulomb interaction and the system transits from a band insulator to a topological insulator: the quantum-spin-Hall or the spin quantum-anomalous Hall state. We also find some magnetic phase transition exists in the Hubbard-dominated zSiNR systems when the exchange field or the electric field goes beyond some critical values. Lastly we observe a double topological/magnetic phase transition in a Hubbard–SOI-balanced zSiNR system before the magnetic and topological phases are destroyed by a strong electric field.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
49:11 Bibcast German 2017

Mobile Makerspaces in kleineren Bibliotheken: Bericht zu einem Forschungsprojekt

Makerspaces haben sich als Thema in der bibliothekarischen Literatur etabliert, in vielen Fällen haben Bibliotheken solche inden letzten Jahren aufgebaut oder betreffende Veranstaltungen durchgeführt. Es scheint, dass es Zeit ist, über die reine Frage, ob sie für Bibliotheken möglich wären (das sind sie) hinauszugehen. Während viele Makerspaces in grösseren Bibliotheken eingerichtet wurde, untersuchte ein Projekt an der HTW Chur, ob und wie sich Makerspaces für kleine und kleinste (schweizerische) Bibliotheken umsetzen lassen. Hierbei ging es vor allem darum, funktionierende Techniken zufinden, die sich in den Arbeitsalltag der Kolleginnen und Kollegen in kleinen Bibliotheken, die wenig Zeit zum „Lernen“ von Technik für Makerspaces und wenig Ressourcen für den Kauf dieser Techniken aufbringen können, integrieren lassen. Das Projekt wurde Ende 2016 in vier schweizerischen Gemeindebibliotheken durchgeführt. Es zeigte sich, dass die Idee, was ein Makerspace ist und können soll, in den Bibliotheken unterschiedlich interpretiert wird und am Ende wenig mit dem, was in der Literatur vorhergesagt wird, zu tun hat; aber auch, das grundsätzlich in kleinen Bibliotheken Veranstaltungen dieser Art durchgeführt werden können, wenn diese Zugang zu den betreffenden Technologien haben. Prägend für die Veranstaltungen war immer der lokale Rahmen, gleichzeitig liessen sich Gemeinsamkeiten beobachten. Makerspaces werden z.B. nicht als feste, sondern als temporäre Angebote gut geheissen; es geht eher um kurzfristige interessante Veranstaltungen als um direkte langfristige Wirkungen. Die Potentiale der Technologien werden nur z.T. genutzt. Im Vortrag werden die Ergebnisse des Projektes berichtet und sowohl in die Beiträge zu Makerspaces in Bibliotheken eingeordnet als auch die mögliche Umsetzung in anderen Bibliotheken diskutiert.
  • Published: 2017
  • Publisher: Bibcast
  • Language: German
46:41 Bibcast German 2017

Ein umfassendes Verzeichnis deutscher Informationseinrichtungen

Ein umfassendes Verzeichnis von Bibliotheken und verwandten Einrichtungen in Deutschland - das hat es bisher nicht gegeben. Zwar existieren zwei umfangreiche Verzeichnisse bibliothekarischer Einrichtungen: das Sigelverzeichnis mit Fokus auf den Bereich "Wissenschaftliche Bibliotheken" und die Deutsche Bibliotheksstatistik (DBS), deren Stammdatenbank hauptsächlich Beschreibungen Öffentlicher Bibliotheken umfasst. Es war bisher aber nicht möglich, beide Verzeichnisse gemeinsam abzufragen. Das Hochschulbibliothekszentrum des Landes Nordrhein-Westfalen (hbz) hat durch eine Zusammenführung beider Verzeichnisse ein umfassendes Organisationsverzeichnis hergestellt und im Web verfügbar gemacht. Seit 2010 bietet das hbz mit dem Dienst "lobid" verschiedene bibliothekarisch relevante Informationen als Linked Data an. Mitte 2014 begann das lobid-Team damit, durch die Integration der Stammdaten der Deutschen Bibliotheksstatistik (DBS) ein umfassendes Verzeichnis deutscher Bibliotheken bereitszustellen. Der Vortrag stellt das Ergebnis vor: http://lobid.org/organisations, eine webbasierte Programmierschnittstelle mit intuitiver Benutzeroberfläche. Die lobid-organisations-API leistet einen nützlichen Beitrag für die deutschlandweite Informationsinfrastruktur, indem sie strukturierte Beschreibungen von knapp 30.000 Organisationen bereitstellt und vielfältige Datenabfragen ermöglicht. Beispiele für Anwendungen, die auf der API aufsetzen (können), sind etwa einfache Statistiken, die u. a. eine Antwort auf folgende Fragen bieten: Wie viele Bibliotheken eines bestimmten Typs gibt es in Deutschland oder in einem bestimmten Bundesland oder Landkreis? Aufsetzend auf der API bietet das hbz eine Rechercheoberfläche an, die zum Entdecken von Informationseinrichtungen in Deutschland einlädt. Filterung von Suchergebnissen nach Standort ist über eine Kartenansicht möglich, mit verschiedenen weiteren Facetten lässt sich nach Bibliothekstyp oder Unterhaltsträger filtern.
  • Published: 2017
  • Publisher: Bibcast
  • Language: German
1:02:44 Bibcast German 2017

FWB-Online - Die Erschließung eines Wörterbuchschatzes

Die Akademie der Wissenschaften zu Göttingen (AdWG) ist eine traditionsreiche Gelehrtengesellschaft und eine außeruniversitäre Forschungseinrichtung. Als Forschungseinrichtung betreut sie in einer schnelllebigen Zeit wissenschaftliche Langzeitprojekte. Die niedersächsische Staats- und Universitätsbibliothek Göttingen (SUB) ist eine der größten wissenschaftlichen Bibliotheken in Deutschland und führend in der Forschung und Entwicklung von Forschungsinfrastrukturen im Bereich eResearch. Die AdWG und die SUB haben ihre Kooperation intensiviert und bieten gemeinsam eine Digitale Bibliothek für die AdWG an. Im Rahmen dieser Kooperation wird eine Online-Version des Frühneuhochdeutschen Wörterbuchs (FWB) FWB-online umgesetzt. Das FWB beschreibt den Wortschatz der hochdeutschen Sprache von etwa 1350 bis 1650. Für FWB-online wurden die typographisch ausgezeichneten Satzdaten der Buchproduktion in ein semantisch tiefstrukturiertes TEI-XML transformiert. Über einen Suchindex wird es den Nutzern ermöglicht, Abfragen zu formulieren, die das FWB in einem völlig neuen Ausmaß erschließen. FWB-online bietet die Wahl zwischen einer Standardsuche, die alle Teile der Artikel einbezieht und einer erweiterten Suche, welche die Tiefenstruktur des Wörterbuchs gezielt abfragen kann. So kann der Nutzende beispielsweise eine exakte Suche, eine unscharfe Suche, die Suche nach exotischen Unicode-Zeichen oder eine Suche nur in frühneuhochdeutschen Zitaten anstoßen. Bei der Softwareentwicklung wurden aktuelle Entwicklungsmethoden und ein agiles Projektmanagement eingesetzt, um die Anforderungen der Nutzenden an den Dienst als auch an die Usability zu gewährleisten. Die Entwicklung erfolgt mit Scrum: In kurzen Iterationsschritten werden jeweils Zwischenergebnisse klar definiert und vorgestellt. Der Vortrag geht neben der technischen Umsetzung eines solchen Projektes vor allem auf die inhaltlichen Funktionen des FWB-online ein und gibt einen Einblick in die vielfältigen Funktionen des Wörterbuchs.
  • Published: 2017
  • Publisher: Bibcast
  • Language: German
1:03:20 Bibcast German 2017

Offene Lernskripte mit Gitbook - Erfahrungsbericht aus einem Seminar

Viele Skripte zu Seminaren und Vorlesungen liegen versteckt in Lernplattformen, die genauso gut frei im Netz veröffentlicht werden könnten. Dann wären Sie auch für Selbstlernende und als Vorlage für andere Lehrende zugänglich. Der Aufwand für die Erstellung von Open Educational Resources schreckt aber wohl viele ab. Abhilfe versprechen aktuelle Publikationswerkzeuge wie die kostenfreie Software Gitbook. Im Seminar „Wir bauen uns einen Bibliothekskatalog“ im Studiengang Bibliotheks- und Informationsmanagement der HAW Hamburg haben wir Erfahrungen mit der Software Gitbook gesammelt. Das Skript [1] steht als HTML mit Suchfunktion sowie als PDF und ePub zur Verfügung und kann vom Dozenten schnell und leicht editiert werden. Andere Lehrende können es über Github kopieren und anpassen. Im Vortrag erwarten Sie eine Live-Demo der Software, ein Erfahrungsbericht und Empfehlungen zur Nachnutzung. Außerdem werden die offenen Lerntagebücher [2] der Studierenden vorgestellt, die sie mit WordPress angelegt haben. [1] https://www.gitbook.com/read/book/felixlohmeier/seminar-wir-bauen-uns-einen-bibliothekskatalog [2] https://felixlohmeier.gitbooks.io/seminar-wir-bauen-uns-einen-bibliothekskatalog/content/lerntagebucher.html
  • Published: 2017
  • Publisher: Bibcast
  • Language: German
52:00 Bibcast German 2017

Einführung zum NMC Horizon Report 2017 Library Edition

Einführungsvortrag zum NMC Horizon Report 2017 Library Edition. Der Vortrag dient der Vorbereitung auf das Hands-On-Lab „Ausblick auf Bibliotheken im Jahr 2027: Keytrends aus dem NMC Horizon Report 2017 Library Edition weiter gedacht" auf dem Bibliothekartag 2017.
  • Published: 2017
  • Publisher: Bibcast
  • Language: German
out of 10 pages
Loading...
Feedback

Timings

  191 ms - page object
   51 ms - search
    1 ms - highlighting
    0 ms - highlighting/38860
    0 ms - highlighting/31038
    0 ms - highlighting/38869
    0 ms - highlighting/38859
    0 ms - highlighting/38864
    0 ms - highlighting/38862
    0 ms - highlighting/38857
    0 ms - highlighting/38884
    0 ms - highlighting/38883
    0 ms - highlighting/38881
    0 ms - highlighting/38882
    0 ms - highlighting/38858
    0 ms - highlighting/38861
    0 ms - highlighting/38863
    0 ms - highlighting/38856
    0 ms - highlighting/38872
    0 ms - highlighting/31043
    0 ms - highlighting/31041
    0 ms - highlighting/31044
    0 ms - highlighting/38875
    0 ms - highlighting/38871
    0 ms - highlighting/38866
    0 ms - highlighting/38877
    0 ms - highlighting/38868
    1 ms - highlighting/38880
    0 ms - highlighting/31039
    0 ms - highlighting/38865
    0 ms - highlighting/38873
    0 ms - highlighting/38886
    0 ms - highlighting/38878
    0 ms - highlighting/38879
    0 ms - highlighting/38885
    0 ms - highlighting/38876
    0 ms - highlighting/38874
    0 ms - highlighting/38870
    1 ms - highlighting/38867

Version

AV-Portal 3.8.0 (dec2fe8b0ce2e718d55d6f23ab68f0b2424a1f3f)