Showing papers on "Field (physics) published in 2019"

A quantum engineer's guide to superconducting qubits

Abstract: The aim of this review is to provide quantum engineers with an introductory guide to the central concepts and challenges in the rapidly accelerating field of superconducting quantum circuits. Over the past twenty years, the field has matured from a predominantly basic research endeavor to a one that increasingly explores the engineering of larger-scale superconducting quantum systems. Here, we review several foundational elements—qubit design, noise properties, qubit control, and readout techniques—developed during this period, bridging fundamental concepts in circuit quantum electrodynamics and contemporary, state-of-the-art applications in gate-model quantum computation.

Magnon Spintronics : Fundamentals of Magnon-Based Computing

Abstract: This chapter addresses a selection of fundamental topics that form the basis of the magnon-based computing and are of primary importance for the further development of theconcept. It examines the transport of spin-wave-carried information in one and two dimensions that is required for the realization of logic elements and integrated magnon circuits is covered. The chapter discusses the converters between spin waves and electron currents. It provides a basic knowledge of spin waves in the most commonly used structure, a spin-wave waveguide in the form of a narrow strip. The main spin-wave characteristics can be obtained from the analysis of its dispersion relation, that is, the dependence of the wave frequency on its wavenumber k. Spin waves are usually studied in nanometer-thick and micrometer-wide waveguides and, several additional factors, which define spin-wave properties, should be considered. The fabrication of high-quality spin-wave waveguides in the form of magnetic strips is also one of the primary tasks in the field of magnonics.

The Swampland: Introduction and Review

Abstract: The Swampland program aims to distinguish effective theories which can be completed into quantum gravity in the ultraviolet from those which cannot. This article forms an introduction to the field, assuming only a knowledge of quantum field theory and general relativity. It also forms a comprehensive review, covering the range of ideas that are part of the field, from the Weak Gravity Conjecture, through compactifications of String Theory, to the de Sitter conjecture.

Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and Applications.

Abstract: Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, that is, two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced ...

OpenMolcas : From Source Code to Insight

Abstract: In this Article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations include an array of additional options and functionalities. The paper proceeds and describes developments related to explorations of potential energy surfaces. Here we present methods for the optimization of conical intersections, the simulation of adiabatic and nonadiabatic molecular dynamics, and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the Article describes features unique to simulations of spectroscopic and magnetic phenomena such as the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism, and properties. Finally, the paper describes a number of built-in and add-on features to support the OpenMolcas platform with postcalculation analysis and visualization, a multiscale simulation option using frozen-density embedding theory, and new electronic and muonic basis sets.

Electromagnetic metasurfaces: physics and applications

Abstract: Metasurfaces are ultrathin metamaterials consisting of planar electromagnetic (EM) microstructures (e.g., meta-atoms) with pre-determined EM responses arranged in specific sequences. Based on careful structural designs on both meta-atoms and global sequences, one can realize homogenous and inhomogeneous metasurfaces that can possess exceptional capabilities to manipulate EM waves, serving as ideal candidates to realize ultracompact and highly efficient EM devices for next-generation integration-optics applications. In this paper, we present an overview on the development of metasurfaces, including both homogeneous and inhomogeneous ones, focusing particularly on their working principles, the fascinating wave-manipulation effects achieved both statically and dynamically, and the representative applications so far realized. Finally, we also present our own perspectives on possible future directions of this fast-developing research field in the conclusion.

Tensor networks for complex quantum systems

Abstract: Originally developed in the context of condensed-matter physics and based on renormalization group ideas, tensor networks have been revived thanks to quantum information theory and the progress in understanding the role of entanglement in quantum many-body systems. Moreover, tensor network states have turned out to play a key role in other scientific disciplines. In this context, here I provide an overview of the basic concepts and key developments in the field. I briefly discuss the most important tensor network structures and algorithms, together with an outline of advances related to global and gauge symmetries, fermions, topological order, classification of phases, entanglement Hamiltonians, holografic duality, artificial intelligence, the 2D Hubbard model, 2D quantum antiferromagnets, conformal field theory, quantum chemistry, disordered systems and many-body localization. Understanding entanglement in many-body systems provided a description of complex quantum states in terms of tensor networks. This Review revisits the main tensor network structures, key ideas behind their numerical methods and their application in fields beyond condensed matter physics.

Towards understanding two-level-systems in amorphous solids: insights from quantum circuits.

Abstract: Amorphous solids show surprisingly universal behaviour at low temperatures. The prevailing wisdom is that this can be explained by the existence of two-state defects within the material. The so-called standard tunneling model has become the established framework to explain these results, yet it still leaves the central question essentially unanswered-what are these two-level defects (TLS)? This question has recently taken on a new urgency with the rise of superconducting circuits in quantum computing, circuit quantum electrodynamics, magnetometry, electrometry and metrology. Superconducting circuits made from aluminium or niobium are fundamentally limited by losses due to TLS within the amorphous oxide layers encasing them. On the other hand, these circuits also provide a novel and effective method for studying the very defects which limit their operation. We can now go beyond ensemble measurements and probe individual defects-observing the quantum nature of their dynamics and studying their formation, their behaviour as a function of applied field, strain, temperature and other properties. This article reviews the plethora of recent experimental results in this area and discusses the various theoretical models which have been used to describe the observations. In doing so, it summarises the current approaches to solving this fundamentally important problem in solid-state physics.

Strong light–matter interactions: a new direction within chemistry

Abstract: It is possible to modify the chemical and physical properties of molecules, not only through chemical modifications but also by coupling molecules strongly to light. More intriguingly, strong coupling between molecules and light is possible even without the presence of a photon. The phenomenon that makes this possible is called vacuum fluctuations, which is the finite zero point energy of the quantized electromagnetic field inside an optical cavity. The light–matter coupling, which can be as large as 1 eV (100 kJ mol−1), leads to the formation of new hybrid states, called polaritons. The formed hybrid states can be viewed as a linear combination of light (vacuum field) and matter (molecules), thus completely changing the energy landscape of the system. Using vacuum fluctuations, strong light–matter interactions have for instance been used to change chemical reactivity, charge conductivity, excited state relaxation pathways and rates of chemical reactions of organic molecules. In this review a brief history of the field is given, followed by a theoretical framework, methods of analysis, and a review of accomplishments. Finally, a personal reflection on the future perspectives and applications within this field is given.

Strategies to break linear scaling relationships

Abstract: The search for new catalytic materials has relied on highly time- and human- resource-consuming procedures. The appearance of theoretical methods that employ density functional theory coupled to kinetic models has allowed the rational understanding of activity volcano plots and selectivity abrupt profiles that resemble cliffs. However, these methodologies present several drawbacks as the optimization is confined to a family of materials, typically metals, and not applied to the overall phase and compositional space, therefore the maximum activity might not be sufficient for practical applications. Volcanos emerge from the symmetry between the adsorption energies of different intermediates on the catalyst, and thus circumventing these dependencies is crucial to identify better catalytic materials. Here we present a revision of the advances in the field that indicate that complexity in the materials is key to identifying alternative paths and thus overcome the drawbacks of scaling relationships. The energies of the species in a given reaction network are linked by linear scaling relationships, limiting the design of catalysts with improved activity and selectivity. In this Perspective, Lopez and Perez-Ramirez discuss strategies to circumvent such scaling relationships.

Quantum Computation as Gravity.

Abstract: We formulate Nielsen's geometric approach to circuit complexity in the context of two-dimensional conformal field theories, where series of conformal transformations are interpreted as ``unitary circuits'' built from energy-momentum tensor gates. We show that the complexity functional in this setup can be written as the Polyakov action of two-dimensional gravity or, equivalently, as the geometric action on the coadjoint orbits of the Virasoro group. This way, we argue that gravity sets the rules for optimal quantum computation in conformal field theories.

High-energy pulse self-compression and ultraviolet generation through soliton dynamics in hollow capillary fibres

Abstract: Optical soliton dynamics can cause extreme alteration of the temporal and spectral shape of a propagating light pulse. This occurs at up to kilowatt peak powers in glass-core optical fibres and at the gigawatt level in gas-filled microstructured hollow-core fibres. Here, we demonstrate optical soliton dynamics in large-core hollow capillary fibres. This enables scaling of soliton effects by several orders of magnitude to the multi-millijoule energy and terawatt peak power level. We experimentally demonstrate two key soliton effects. First, we observe self-compression to sub-cycle pulses and infer the creation of sub-femtosecond field waveforms—a route to high-power optical attosecond pulse generation. Second, we efficiently generate continuously tunable high-energy (1–16 μJ) pulses in the vacuum and deep ultraviolet (110 nm to 400 nm) through resonant dispersive-wave emission. These results promise to be the foundation of a new generation of table-top light sources for ultrafast strong-field physics and advanced spectroscopy. Optical soliton dynamics in large-core hollow capillary fibres is demonstrated. The findings enable the scaling of soliton effects by several orders of magnitude to the multi-millijoule energy and terawatt peak power levels, and open up opportunities for new-generation table-top light sources for ultrafast strong-field physics and advanced spectroscopy.

A Field Guide to Spin Liquids

Abstract: Spin liquids are collective phases of quantum matter that have eluded discovery in correlated magnetic materials for over half a century. Theoretical models of these enigmatic topological phases ar...

Visualizing Poiseuille flow of hydrodynamic electrons

Abstract: Hydrodynamics is a general description for the flow of a fluid, and is expected to hold even for fundamental particles such as electrons when inter-particle interactions dominate. While various aspects of electron hydrodynamics were revealed in recent experiments, the fundamental spatial structure of hydrodynamic electrons, the Poiseuille flow profile, has remained elusive. In this work, we provide the first real-space imaging of Poiseuille flow of an electronic fluid, as well as visualization of its evolution from ballistic flow. Utilizing a scanning nanotube single electron transistor, we image the Hall voltage of electronic flow through channels of high-mobility graphene. We find that the profile of the Hall field across the channel is a key physical quantity for distinguishing ballistic from hydrodynamic flow. We image the transition from flat, ballistic field profiles at low temperature into parabolic field profiles at elevated temperatures, which is the hallmark of Poiseuille flow. The curvature of the imaged profiles is qualitatively reproduced by Boltzmann calculations, which allow us to create a 'phase diagram' that characterizes the electron flow regimes. Our results provide long-sought, direct confirmation of Poiseuille flow in the solid state, and enable a new approach for exploring the rich physics of interacting electrons in real space.

Laser Cavity-Soliton Micro-Combs

Abstract: The field of micro-cavity based frequency combs, or 'micro-combs'[1,2], has recently witnessed many fundamental breakthroughs[3-19] enabled by the discovery of temporal cavity-solitons, self-localised waves sustained by a background of radiation usually containing 95% of the total power[20]. Simple methods for their efficient generation and control are currently researched to finally establish micro-combs as out-of-the-lab widespread tools[21]. Here we demonstrate micro-comb laser cavity-solitons, an intrinsically highly-efficient, background free class of solitary waves. Laser cavity-solitons have underpinned key breakthroughs in semiconductor lasers[22,23] and photonic memories[24-26]. By merging their properties with the physics of both micro-resonators[1,2] and multi-mode systems[27], we provide a new paradigm for the generation and control of self-localised pulses in micro-cavities. We demonstrate 50 nm wide soliton combs induced with average powers one order of magnitude lower than those typically required by state-of-the-art approaches[26]. Furthermore, we can tune the repetition-rate to well over a megahertz with no-active feedback.

The Physics of Gamma-Ray Bursts

Abstract: Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, which within seconds release energy comparable to what the Sun releases in its entire lifetime. The field of GRBs has developed rapidly and matured over the past decades. Written by a leading researcher, this text presents a thorough treatment of every aspect of the physics of GRBs. It starts with an overview of the field and an introduction to GRB phenomenology. After laying out the basics of relativity, relativistic shocks, and leptonic and hadronic radiation processes, the volume covers all topics related to GRBs, including a general theoretical framework, afterglow and prompt emission models, progenitor, central engine, multi-messenger aspects (cosmic rays, neutrinos, and gravitational waves), cosmological connections, and broader impacts on fundamental physics and astrobiology. It is suitable for advanced undergraduates, graduate students, and experienced researchers in the field of GRBs and high-energy astrophysics in general.

New Complex Hyperbolic Structures to the Lonngren-Wave Equation by Using Sine-Gordon Expansion Method

Abstract: In this paper, a powerful sine-Gordon expansion method (SGEM) with aid of a computational program is used in constructing a new hyperbolic function solutions to one of the popular nonlinear evolution equations that arises in the field of mathematical physics, namely; longren-wave equation. We also give the 3D and 2D graphics of all the obtained solutions which are explaining new properties of model considered in this paper. Finally, we submit a comprehensive conclusion at the end of this paper.

Action Principle for Newtonian Gravity

Abstract: We derive an action whose equations of motion contain the Poisson equation of Newtonian gravity. The construction requires a new notion of Newton-Cartan geometry based on an underlying symmetry algebra that differs from the usual Bargmann algebra. This geometry naturally arises in a covariant $1/c$ expansion of general relativity, with $c$ being the speed of light. By truncating this expansion at subleading order, we obtain the field content and transformation rules of the fields that appear in the action of Newtonian gravity. The equations of motion generalize Newtonian gravity by allowing for the effect of gravitational time dilation due to strong gravitational fields.

All-Dielectric Resonant Meta-Optics Lightens up

Abstract: All-dielectric resonant nanophotonics is a rapidly developing research field driven by its exceptional applications for creating low-loss nanoscale metadevices. The tight confinement of the local e...

Beyond Toy Models: Distilling Tensor Networks in Full AdS/CFT

Abstract: We present a general procedure for constructing tensor networks that accurately reproduce holographic states in conformal field theories (CFTs). Given a state in a large-N CFT with a static, semiclassical gravitational dual, we build a tensor network by an iterative series of approximations that eliminate redundant degrees of freedom and minimize the bond dimensions of the resulting network. We argue that the bond dimensions of the tensor network will match the areas of the corresponding bulk surfaces. For “tree” tensor networks (i.e., those that are constructed by discretizing spacetime with non­ intersecting Ryu-Takayanagi surfaces), our arguments can be made rigorous using a version of one-shot entanglement distillation in the CFT. Using the known quantum error correcting properties of AdS/CFT, we show that bulk legs can be added to the tensor networks to create holographic quantum error correcting codes. These codes behave similarly to previous holographic tensor network toy models, but describe actual bulk excitations in continuum AdS/CFT. By assuming some natural generalizations of the “holographic entanglement of purification” conjecture, we are able to construct tensor networks for more general bulk discretizations, leading to finer-grained networks that partition the information content of a Ryu-Takayanagi surface into tensor-factorized subregions. While the granularity of such a tensor network must be set larger than the string/Planck scales, we expect that it can be chosen to lie well below the AdS scale. However, we also prove a no-go theorem which shows that the bulk-to-boundary maps cannot all be isometries in a tensor network with intersecting Ryu-Takayanagi surfaces.

Emergence of a field-driven U(1) spin liquid in the Kitaev honeycomb model.

Abstract: In the field of quantum magnetism, the exactly solvable Kitaev honeycomb model serves as a paradigm for the fractionalization of spin degrees of freedom and the formation of [Formula: see text] quantum spin liquids. An intense experimental search has led to the discovery of a number of spin-orbit entangled Mott insulators that realize its characteristic bond-directional interactions and, in the presence of magnetic fields, exhibit no indications of long-range order. Here, we map out the complete phase diagram of the Kitaev model in tilted magnetic fields and report the emergence of a distinct gapless quantum spin liquid at intermediate field strengths. Analyzing a number of static, dynamical, and finite temperature quantities using numerical exact diagonalization techniques, we find strong evidence that this phase exhibits gapless fermions coupled to a massless U(1) gauge field. We discuss its stability in the presence of perturbations that naturally arise in spin-orbit entangled candidate materials.

Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory.

Abstract: High-energy nuclear collisions produce a nonequilibrium plasma of quarks and gluons which thermalizes and exhibits hydrodynamic flow. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution. We build such a framework using nonequilibrium Green's functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. We demonstrate that this approach can be easily incorporated into existing hydrodynamic simulations, leading to stronger constraints on the energy density at early times and the transport properties of the QCD medium. Based on (conformal) scaling properties of the Green's functions, we further obtain pragmatic bounds for the applicability of hydrodynamics in nuclear collisions.

Effective action of dilaton gravity as the classical double copy of Yang-Mills theory

Abstract: We compute the classical effective action of color charges moving along worldlines by integrating out the Yang-Mills gauge field to next-to-leading order in the coupling. An adapted version of the Bern-Carrasco-Johansson (BCJ) double-copy construction known from quantum scattering amplitudes is then applied to the Feynman integrands, yielding the prediction for the classical effective action of point masses in dilaton gravity. We check the validity of the result by independently constructing the effective action in dilaton gravity employing field redefinitions and gauge choices that greatly simplify the perturbative construction. Complete agreement is found at next-to-leading order. Finally, upon performing the post-Newtonian expansion of our result, we find agreement with the corresponding action of scalar-tensor theories known from the literature. Our results represent a proof of concept for the classical double-copy construction of the gravitational effective action and provides another application of a BCJ-like double copy beyond scattering amplitudes.

Double copy structure of CFT correlators

Abstract: We consider the momentum-space 3-point correlators of currents, stress tensors and marginal scalar operators in general odd-dimensional conformal field theories. We show that the flat space limit of these correlators is spanned by gauge and gravitational scattering amplitudes in one higher dimension which are related by a double copy. Moreover, we recast three-dimensional CFT correlators in terms of tree-level Feynman diagrams without energy conservation, suggesting double copy structure beyond the flat space limit.

Modern Condensed Matter Physics

Abstract: Modern Condensed Matter Physics brings together the most important advances in the field of recent decades. It provides instructors teaching graduate-level condensed matter courses with a comprehensive and in-depth textbook that will prepare graduate students for research or further study as well as reading more advanced and specialized books and research literature in the field. This textbook covers the basics of crystalline solids as well as analogous optical lattices and photonic crystals, while discussing cutting-edge topics such as disordered systems, mesoscopic systems, many-body systems, quantum magnetism, Bose–Einstein condensates, quantum entanglement, and superconducting quantum bits. Students are provided with the appropriate mathematical background to understand the topological concepts that have been permeating the field, together with numerous physical examples ranging from the fractional quantum Hall effect to topological insulators, the toric code, and majorana fermions. Exercises, commentary boxes, and appendices afford guidance and feedback for beginners and experts alike.