Reviews in Physics最新文献

Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emission and the radiation induced refractive index change. Depending on the fiber profile of use, these phenomena differently contribute to the degradation of the fiber performances and then have to be either mitigated for radiation tolerant systems or exploited to design radiation detectors and dosimeters. Considering the strong impact of radiation on key applications such as data transfer or sensing in space, fusion and fission-related facilities or high energy physics facilities, since 1970′s numerous experimental and theoretical studies have been conducted to identify the microscopic origins of these changes. The observed degradation can be explained through the generation by ionization or displacement damages of point defects in the differently doped amorphous glass (SiO₂) of the fiber's core and cladding layers. Indeed, the fiber chemical composition (dopants/concentrations) and elaboration processes play an important role. Consequently, identifying the nature, the properties and the generation and bleaching mechanisms of these point defects is mandatory in order to imagine ways to control the fiber radiation behaviors. In this review paper, the responses of the main classes of silica-based optical fibers are presented: radiation tolerant pure-silica core or fluorine doped optical fibers, germanosilicate optical fibers and radiation sensitive phosphosilicate and aluminosilicate optical fibers. Our current knowledge about the nature and optical properties of the point defects related to silica and these main dopants is presented. The efficiency of the known defects to reproduce the transient and steady state radiation induced attenuation between 300 nm and 2 µm wavelength range is discussed. The main parameters, related to the fibers themselves or extrinsic - harsh environments, profile of use - affecting the concentration, growth and decay kinetics of those defects are also reviewed. Finally, the main remaining challenges are discussed, including the increasing needs for accurate and multi-physics modeling tools.

The standard model of particle physics is an extremely successful theory of fundamental interactions, but it has many known limitations. It is therefore widely believed to be an effective field theory that describes interactions near the TeV scale. A plethora of strategies exist to extend the standard model, many of which contain predictions of new particles or dynamics that could manifest in proton-proton collisions at the Large Hadron Collider (LHC). As of now, none have been observed, and much of the available phase space for natural solutions to outstanding problems is excluded. If new physics exists, it is therefore either heavy (i.e. above the reach of current searches) or hidden (i.e. currently indistinguishable from standard model backgrounds). We summarize the existing searches, and discuss future directions at the LHC.

The enhanced local electromagnetic field (EM) excited on the noble metallic nanostructure exhibits potential application in various areas, particularly in surface-enhanced spectroscopy (SES). Resonant coupling of SPs to luminous centers can strongly moderate the emission spectra properties, including the angular distribution, the intensity, the speed of radiative decay, and even the spectrum radiation polarization, or so-called plasmon-enhanced fluorescence (PEF). Due to the low efficiency of emission and small absorption section of rare earth ions, plasmon-enhanced upconversion photoluminescence (PUCPL) has attracted increasing attention recently. In this review, we focus on recent advanced reports on PUCPL. First, the mechanism of the conventional upconversion process and related reports will be introduced. We will then demonstrate that the introduction of plasmonic nanostructure, including nonperiodic and periodic metallic nanostructures, has a critical effect on upconversion nanoparticles (UCNPs). The recent advances in plasmon-enhanced fluorescence with metallic tip configuration are also noted. Finally, the recent applications of PUCPL are introduced. As a result, the combination of a rare-earth luminescent center with plasmonic nanostructure can largely expand the application of upconversion materials.

Initially proposed to achieve strong noise isolation levels beyond the mass-density law, acoustic metamaterials (AMMs) have now overturned the conventional views in all aspects of sound propagation and manipulation. In fact, within the last two decades, these artificial materials have enabled improved control over the propagation of sound waves by allowing one to engineer macroscopic effective properties well beyond what is naturally available. In this review, we first trace the development of passive AMMs from their initial realizations based on locally resonant structures to their more advanced versions, like space-coiling, holey and labyrinthine metamaterials, Willis materials, and subwavelength crystalline metamaterials, highlighting their basic working principles and applications. We then survey more recent research topics, including non-Hermitian, non-reciprocal, and topological acoustic metamaterials. Altogether, this paper provides a comprehensive overview of research on acoustic metamaterials, and highlights prominent future directions in the field, including topological and active metamaterials.

The Standard Model of particles and fields describes the fundamental particles and their interactions to high level of precision. The SM is nevertheless considered to be a low energy effective theory as it leaves many open questions including: What is the origin of the dark matter in the Universe? What is the origin of the matter-antimatter asymmetry in the Universe? What is the origin of mass? Supersymmety is one of the most appealing theories of physics beyond the Standard Model as it can address the SM shortcomings in an elegant framework. This paper reviews the most recent direct searches for supersymmetry developed by the ATLAS and CMS collaborations at the Large Hadron Collider.

We discuss how quantum computation can be applied to financial problems, providing an overview of current approaches and potential prospects. We review quantum optimization algorithms, and expose how quantum annealers can be used to optimize portfolios, find arbitrage opportunities, and perform credit scoring. We also discuss deep-learning in finance, and suggestions to improve these methods through quantum machine learning. Finally, we consider quantum amplitude estimation, and how it can result in a quantum speed-up for Monte Carlo sampling. This has direct applications to many current financial methods, including pricing of derivatives and risk analysis. Perspectives are also discussed.

Owing to their low density, high aspect ratio and excellent charge transport properties, Carbon nanotubes (CNTs) are proven to be one of the best reinforcing materials in the fabrication of composite materials. CNTs dispersed in a non-conducting matrix is an interesting system for condensed matter physicists and materials scientists; CNT based composites offer an opportunity to physicists to design different experiments for fundamental studies while these composites are suitable for several technological applications that are of interest to materials scientists. In this review article, we summarize interesting experimental results on low temperature charge transport properties of composites based on multi-wall carbon nanotubes (MWCNTs) that have been reported in the past decade. In particular, we critically review different conduction mechanisms that have been identified through detailed investigations of charge transport characteristics as functions of MWCNT loading in the composites, temperature, and magnetic field.

An explosive development of quantum technologies since 1999 allowed the creation of arrays of natural and artificial quantum unit elements (viz. trapped ions and superconducting qubits), which maintain certain degree of quantum coherence and allow a degree of control over their quantum state. A natural application of such structures is towards simulating quantum systems, which are too big or too complex to allow a simulation with the means of classical computers. A digital quantum simulation promises a controlled accuracy, scalability and versatility, but it imposes practically as strict requirements on the hardware as a universal quantum computation. The other approach, analogue quantum simulation, is less demanding and thus more promising in short-to-medium term. It has already provided interesting results within the current experimental means and can be used as a stopgap approach as well as the means towards the perfecting of quantum technologies. Here I review the status of the field and discuss its prospects and the role it will play in the development of digital quantum simulation, universal quantum computing and, more broadly, quantum engineering.

This document summarises the talks and discussions happened during the VBSCan Split17 workshop, the first general meeting of the VBSCan COST Action network. This collaboration is aiming at a consistent and coordinated study of vector-boson scattering from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.

In interacting one-dimensional (1D) systems, the quasi-particle picture in Fermi-liquid theory cannot successfully describe low-energy physics. Instead, electron dynamics in one dimension can be described as collective excitations, i.e., charge- and/or spin-density waves, which are elementary excitations in a Tomonaga-Luttinger (TL) liquid. Integer quantum Hall (QH) edge channels, which are chiral 1D electron states formed along the periphery of integer QH systems, provide a unique opportunity for studying TL-liquid physics. When edge channels lie parallel to each other, inter-channel interactions induce significant TL-liquid behaviors in coupled plasmons. One can prepare an arbitrary number of co- and/or counter-propagating channels of spin-up or -down electrons to form such a multiple edge-channel system. The plasmon dynamics can be experimentally investigated by using various functional devices such as charge injectors, detectors, and spin filters to select spin and bidirectional-momentum degrees of freedom. This article reviews electron dynamics in such QH TL liquids. We first introduce the chiral distributed-element circuit model for describing interactions in single and multiple integer-edge-channel systems. This simple model captures the TL-liquid nature of the 1D plasmon transport. We then review experimental studies on TL-liquid behaviors. These experiments show that plasmon velocity is significantly enhanced by the intra-channel interaction. In addition, they show that co-propagating channels with spin degrees of freedom exhibit TL-liquid behavior known as spin-charge separation, in which spin and charge excitations behave differently. This is demonstrated with a novel time- and spin-resolved charge detection technique. They also reveal that charge fractionalization occurs at the boundaries of counter-propagating channels with bidirectional-momentum degrees of freedom. A charge excitation even as small as an electron charge is fractionalized into smaller charges to form coupled plasmons in the interacting region. These experiments highlight the intriguing quantum many-body nature of QH TL liquids.