Hasil untuk "Physics"

J. Fodor

J. Jackson, H. Gove, R. Schwitters et al.

Sh. M. Kogan

J. Shah

T. Kraemer, M. Mark, P. Waldburger et al.

Systems of three interacting particles are notorious for their complex physical behaviour. A landmark theoretical result in few-body quantum physics is Efimov's prediction of a universal set of bound trimer states appearing for three identical bosons with a resonant two-body interaction. Counterintuitively, these states even exist in the absence of a corresponding two-body bound state. Since the formulation of Efimov's problem in the context of nuclear physics 35 years ago, it has attracted great interest in many areas of physics. However, the observation of Efimov quantum states has remained an elusive goal. Here we report the observation of an Efimov resonance in an ultracold gas of caesium atoms. The resonance occurs in the range of large negative two-body scattering lengths, arising from the coupling of three free atoms to an Efimov trimer. Experimentally, we observe its signature as a giant three-body recombination loss when the strength of the two-body interaction is varied. We also detect a minimum in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point with which to explore the universal properties of resonantly interacting few-body systems. While Feshbach resonances have provided the key to control quantum-mechanical interactions on the two-body level, Efimov resonances connect ultracold matter to the world of few-body quantum phenomena.

M. Yankowitz, Q. Ma, P. Jarillo-Herrero et al.

As the first in a large family of 2D van der Waals (vdW) materials, graphene has attracted enormous attention owing to its remarkable properties. The recent development of simple experimental techniques for combining graphene with other atomically thin vdW crystals to form heterostructures has enabled the exploration of the properties of these so-called vdW heterostructures. Hexagonal boron nitride is the second most popular vdW material after graphene, owing to the new physics and device properties of vdW heterostructures combining the two. Hexagonal boron nitride can act as a featureless dielectric substrate for graphene, enabling devices with ultralow disorder that allow access to the intrinsic physics of graphene, such as the integer and fractional quantum Hall effects. Additionally, under certain circumstances, hexagonal boron nitride can modify the optical and electronic properties of graphene in new ways, inducing the appearance of secondary Dirac points or driving new plasmonic states. Integrating other vdW materials into these heterostructures and tuning their new degrees of freedom, such as the relative rotation between crystals and their interlayer spacing, provide a path for engineering and manipulating nearly limitless new physics and device properties.This is an overview of the new physics that emerges in van der Waals heterostructures consisting of graphene and hexagonal boron nitride, including the integer and fractional quantum Hall effects, novel plasmonic states and the effects of emergent moiré superlattices.Key pointsAtomically thin flakes of van der Waals materials such as graphene and hexagonal boron nitride (hBN) can be mixed and matched into heterostructures with fundamentally new optoelectronic properties.Graphene encapsulated in hBN has very high mobility, with very low charge carrier inhomogeneity and ballistic transport characteristics over micrometre length scales at low temperature.High-mobility graphene devices exhibit well-developed multicomponent integer and fractional quantum Hall effects, as well as additional exotic correlated electronic phases in a magnetic field.When the graphene and hBN crystals are rotationally aligned, a long-wavelength moiré superlattice emerges, which creates new, finite-energy Dirac points in the graphene bandstructure and leads to the Hofstadter butterfly spectrum.Graphene–hBN heterostructures host new hybrid polaritons, as well as plasmonic excitations with exceptionally long lifetimes that can be tuned with a moiré superlattice.

Jian-Feng Ge, Zhi-Long Liu, Canhua Liu et al.

Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China. Department of Physics, Tsinghua University, Beijing 100084, China. Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA. *Correspondence to: canhualiu@sjtu.edu.cn; qkxue@mail.tsinghua.edu.cn; jfjia@sjtu.edu.cn.

D. Jaksch, D. Jaksch, P. Zoller

Abstract We review recent theoretical advances in cold atom physics concentrating on strongly correlated cold atoms in optical lattices. We discuss recently developed quantum optical tools for manipulating atoms and show how they can be used to realize a wide range of many body Hamiltonians. Then, we describe connections and differences to condensed matter physics and present applications in the fields of quantum computing and quantum simulations. Finally, we explain how defects and atomic quantum dots can be introduced in a controlled way in optical lattice systems.

J. Alimena, James Beacham, M. Borsato et al.

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity "dark showers", highlighting opportunities for expanding the LHC reach for these signals.

F. Avignone, S. Elliott, J. Engel

The theoretical and experimental issues relevant to neutrinoless double beta decay are reviewed. The impact that a direct observation of this exotic process would have on elementary particle physics, nuclear physics, astrophysics, and cosmology is profound. Now that neutrinos are known to have mass and experiments are becoming more sensitive, even the nonobservation of neutrinoless double beta decay will be useful. If the process is actually observed, we will immediately learn much about the neutrino. The status and discovery potential of proposed experiments are reviewed in this context, with significant emphasis on proposals favored by recent panel reviews. The importance of and challenges in the calculation of nuclear matrix elements that govern the decay are considered in detail. The increasing sensitivity of experiments and improvements in nuclear theory make the future exciting for this field at the interface of nuclear and particle physics.

P. Bechtle, O. Brein, S. Heinemeyer et al.

27 paginas, 5 figuras, 16 tablas.-- This paper and its associated computer program are available via the Computer Physics Communications homepage on ScienceDirect (http://www.sciencedirect.com/ science/journal/00104655).-- El Pdf del articulo es la version pre-print: arXiv:1102.1898v1

P. Milonni, M. Nieto

We concisely review the history, physics and significance of coherent states.

M. Pretko, Xie Chen, Yizhi You

Fractons are a new type of quasiparticle which are immobile in isolation, but can often move by forming bound states. Fractons are found in a variety of physical settings, such as spin liquids and elasticity theory, and exhibit unusual phenomenology, such as gravitational physics and localization. The past several years have seen a surge of interest in these exotic particles, which have come to the forefront of modern condensed matter theory. In this review, we provide a broad treatment of fractons, ranging from pedagogical introductory material to discussions of recent advances in the field. We begin by demonstrating how the fracton phenomenon naturally arises as a consequence of higher moment conservation laws, often accompanied by the emergence of tensor gauge theories. We then provide a survey of fracton phases in spin models, along with the various tools used to characterize them, such as the foliation framework. We discuss in detail the manifestation of fracton physics in elasticity theory, as well as the connections of fractons with localization and gravitation. Finally, we provide an overview of some recently proposed platforms for fracton physics, such as Majorana islands and hole-doped antiferromagnets. We conclude with some open questions and an outlook on the field.

S. Rachel

The discovery of the quantum spin Hall effect and topological insulators more than a decade ago has revolutionized modern condensed matter physics. Today, the field of topological states of matter is one of the most active and fruitful research areas for both experimentalists and theorists. The physics of topological insulators is typically well described by band theory and systems of non-interacting fermions. In contrast, several of the most fascinating effects in condensed matter physics merely exist due to electron–electron interactions, examples include unconventional superconductivity, the Kondo effect, and the Mott–Hubbard transition. The aim of this review article is to give an overview of the manifold directions which emerge when topological bandstructures and correlation physics interfere and compete. These include the study of the stability of topological bandstructures and correlated topological insulators. Interaction-induced topological phases such as the topological Kondo insulator provide another exciting topic. More exotic states of matter such as topological Mott insulator and fractional Chern insulators only exist due to the interplay of topology and strong interactions and do not have any bandstructure analogue. Eventually the relation between topological bandstructures and frustrated quantum magnetism in certain transition metal oxides is emphasized.

N. Brambilla, S. Eidelman, P. Foka et al.

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

G. Hagen, G. Hagen, Thomas Papenbrock et al.

In the past decade, coupled-cluster theory has seen a renaissance in nuclear physics, with computations of neutron-rich and medium-mass nuclei. The method is efficient for nuclei with product-state references, and it describes many aspects of weakly bound and unbound nuclei. This report reviews the technical and conceptual developments of this method in nuclear physics, and the results of coupled-cluster calculations for nucleonic matter, and for exotic isotopes of helium, oxygen, calcium, and some of their neighbors.

Changfeng Chen, Andrew J. Cornelius

Foreword Physics and physicists play a vital role in underpinning our way of life, improving its quality and contributing in a major way to wealth creation. Innovations as powerful and diverse as the World Wide Web and magnetic resonance imaging (MRI) have emerged from studies in basic physics, becoming everyday technologies in just two decades. It is, therefore, a worthwhile challenge to speculate where similar explorations today will lead us in the future. This booklet, the first in a series covering the main areas of physics, attempts to do just that: highlight and showcase world-class UK work that has the greatest potential for commercial exploitation. It is jointly sponsored by the Institute of Physics – the professional body and learned society for physics and physicists – and the Engineering and Physical Sciences Research Council (EPSRC) – one of the largest UK funders of physics research. We hope that this booklet illustrates how the research investment made by the EPSRC and the support provided by the Institute to its membership, will enable the UK's economy, and society at large, to benefit from the discoveries and advances in physics being made. Foreword Introduction Nanoparticles in medicine The optical, electronic and magnetic properties of minute metal particles are being exploited to diagnose and cure disease Wonderful carbon One of the most mundane materials, carbon, could be the future of nano-electronics Quantum dots light up the future A novel type of semiconductor nano-structure is set to become a key element in future optoelectronic technology A new spin on electronics Future computer-processing elements, as well as memory devices, could be based on the electron's property of spin Going with the flow What controls how easily a molten plastic squeezes through a nozzle or whether mayonnaise separates? Keeping up with Moore's law Is there a limit to the number and size of devices on an electronic chip? Industry and university research groups are exploring the possibilities

J. Engel, M. Ramsey-Musolf, U. V. Kolck

Searches for the permanent electric dipole moments (EDMs) of molecules, atoms, nucleons and nuclei provide powerful probes of CP violation both within the Standard Model and beyond the Standard Model (BSM). The interpretation of experimental EDM limits requires careful delineation of physics at a wide range of scales, from the long-range atomic and molecular scales to the short-distance dynamics of physics at or beyond the Fermi scale. In this review, we provide a framework for disentangling contributions from physics at these disparate scales, building out from the set of dimension four and six effective operators that embody CP violation at the Fermi scale. We survey computations of hadronic and nuclear matrix elements associated with Fermi-scale CP violation in systems of experimental interest and quantify the present level of theoretical uncertainty in these calculations. Using representative BSM scenarios of current interest, we discuss ways in which the interplay of physics at various scales can generate EDMs at a potentially observable level.

E. Cohen, H. Larocque, F. Bouchard et al.

Whenever a quantum system undergoes a cyclic evolution governed by a slow change of parameters, it acquires a phase factor: the geometric phase. Its most common formulations are known as the Aharonov–Bohm phase and the Pancharatnam and Berry phase, but both earlier and later manifestations exist. Although traditionally attributed to the foundations of quantum mechanics, the geometric phase has been generalized and become increasingly influential in many areas from condensed-matter physics and optics to high-energy and particle physics and from fluid mechanics to gravity and cosmology. Interestingly, the geometric phase also offers unique opportunities for quantum information and computation. In this Review, we first introduce the Aharonov–Bohm effect as an important realization of the geometric phase. Then, we discuss in detail the broader meaning, consequences and realizations of the geometric phase, emphasizing the most important mathematical methods and experimental techniques used in the study of the geometric phase, in particular those related to recent works in optics and condensed-matter physics. The geometric phase is a deep and influential concept in modern physics and related sciences. This Review briefly discusses its origin, mathematical formulation and various forms, some of which are topological; then elaborates on contemporary optical and condensed-matter applications. The Aharonov–Bohm phase, acquired by charged particles encircling a confined magnetic flux, is topological, gauge invariant and realistic, highlighting the unique role of electromagnetic potentials in quantum mechanics. The Aharonov–Bohm phase can be seen as a manifestation of Berry’s geometric phase accumulated whenever a quantum system is adiabatically transported around a cyclic circuit on an abstract surface in the parameter space (with additional generalizations to degenerate and open systems, and to non-adiabatic, non-cyclic, non-unitary evolutions). The geometric phase is an example of a holonomy (failure of parallel transport around closed cycles to preserve the geometrical information being transported) and its profound role in physics. The two main types of geometric phase in optics originate from ‘spin redirection’ (when light with a fixed state of polarization is changing direction) and from a slow change in polarization (of light propagating through an anisotropic medium in a fixed direction), giving rise to the Pancharatnam–Berry phase. In condensed-matter physics, the geometric phase manifests itself in the electronic Bloch states, quantum Hall effect, electric polarization, exchange statistics and many other phenomena. The Aharonov–Bohm phase, acquired by charged particles encircling a confined magnetic flux, is topological, gauge invariant and realistic, highlighting the unique role of electromagnetic potentials in quantum mechanics. The Aharonov–Bohm phase can be seen as a manifestation of Berry’s geometric phase accumulated whenever a quantum system is adiabatically transported around a cyclic circuit on an abstract surface in the parameter space (with additional generalizations to degenerate and open systems, and to non-adiabatic, non-cyclic, non-unitary evolutions). The geometric phase is an example of a holonomy (failure of parallel transport around closed cycles to preserve the geometrical information being transported) and its profound role in physics. The two main types of geometric phase in optics originate from ‘spin redirection’ (when light with a fixed state of polarization is changing direction) and from a slow change in polarization (of light propagating through an anisotropic medium in a fixed direction), giving rise to the Pancharatnam–Berry phase. In condensed-matter physics, the geometric phase manifests itself in the electronic Bloch states, quantum Hall effect, electric polarization, exchange statistics and many other phenomena.

Mathieu Calvat, Chris Bean, Dhruv Anjaria et al.

Abstract To leverage advancements in machine learning for metallic materials design and property prediction, it is crucial to develop a data-reduced representation of metal microstructures that surpasses the limitations of current physics-based discrete microstructure descriptors. This need is particularly relevant for metallic materials processed through additive manufacturing, which exhibit complex hierarchical microstructures that cannot be adequately described using the conventional metrics typically applied to wrought materials. Furthermore, capturing the spatial heterogeneity of microstructures at the different scales is necessary within such framework to accurately predict their properties. To address these challenges, we propose the physical spatial mapping of metal diffraction latent space features. This approach integrates (i) point diffraction data encoding via variational autoencoders or contrastive learning and (ii) the physical mapping of the encoded values. Together, these steps offer a method to comprehensively describe metal microstructures. We demonstrate this approach on a wrought and additively manufactured alloy, showing that it effectively encodes microstructural information and enables direct identification of microstructural heterogeneity not directly possible by physics-based models. This data-reduced microstructure representation opens the application of machine learning models in accelerating metallic material design and accurately predicting their properties.