Showing papers in "Reviews of Modern Physics in 2013"
[...]
TL;DR: The field of cavity optomechanics explores the interaction between electromagnetic radiation and nano-or micromechanical motion as mentioned in this paper, which explores the interactions between optical cavities and mechanical resonators.
Abstract: We review the field of cavity optomechanics, which explores the interaction between electromagnetic radiation and nano- or micromechanical motion This review covers the basics of optical cavities and mechanical resonators, their mutual optomechanical interaction mediated by the radiation pressure force, the large variety of experimental systems which exhibit this interaction, optical measurements of mechanical motion, dynamical backaction amplification and cooling, nonlinear dynamics, multimode optomechanics, and proposals for future cavity quantum optomechanics experiments In addition, we describe the perspectives for fundamental quantum physics and for possible applications of optomechanical devices
4,031 citations
TL;DR: This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments, and highlights the experimental relevance of various semimicroscopic derivations of the continuum theory for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material.
Abstract: This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are ``dry'' systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or ``wet'' systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.
3,314 citations
[...]
TL;DR: The main theoretical and experimental aspects of quantum simulation have been discussed in this article, and some of the challenges and promises of this fast-growing field have also been highlighted in this review.
Abstract: Simulating quantum mechanics is known to be a difficult computational problem, especially when dealing with large systems However, this difficulty may be overcome by using some controllable quantum system to study another less controllable or accessible quantum system, ie, quantum simulation Quantum simulation promises to have applications in the study of many problems in, eg, condensed-matter physics, high-energy physics, atomic physics, quantum chemistry and cosmology Quantum simulation could be implemented using quantum computers, but also with simpler, analog devices that would require less control, and therefore, would be easier to construct A number of quantum systems such as neutral atoms, ions, polar molecules, electrons in semiconductors, superconducting circuits, nuclear spins and photons have been proposed as quantum simulators This review outlines the main theoretical and experimental aspects of quantum simulation and emphasizes some of the challenges and promises of this fast-growing field
1,941 citations
TL;DR: In this paper, a review of recent theoretical and experimental advances in the fundamental understanding and active control of quantum fluids of light in nonlinear optical systems is presented, from the superfluid flow around a defect at low speeds to the appearance of a Mach-Cherenkov cone in a supersonic flow, to the hydrodynamic formation of topological excitations such as quantized vortices and dark solitons at the surface of large impenetrable obstacles.
Abstract: This article reviews recent theoretical and experimental advances in the fundamental understanding and active control of quantum fluids of light in nonlinear optical systems. In the presence of effective photon-photon interactions induced by the optical nonlinearity of the medium, a many-photon system can behave collectively as a quantum fluid with a number of novel features stemming from its intrinsically nonequilibrium nature. A rich variety of recently observed photon hydrodynamical effects is presented, from the superfluid flow around a defect at low speeds, to the appearance of a Mach-Cherenkov cone in a supersonic flow, to the hydrodynamic formation of topological excitations such as quantized vortices and dark solitons at the surface of large impenetrable obstacles. While the review is mostly focused on a specific class of semiconductor systems that have been extensively studied in recent years (planar semiconductor microcavities in the strong light-matter coupling regime having cavity polaritons as elementary excitations), the very concept of quantum fluids of light applies to a broad spectrum of systems, ranging from bulk nonlinear crystals, to atomic clouds embedded in optical fibers and cavities, to photonic crystal cavities, to superconducting quantum circuits based on Josephson junctions. The conclusive part of the article is devoted to a review of the future perspectives in the direction of strongly correlated photon gases and of artificial gauge fields for photons. In particular, several mechanisms to obtain efficient photon blockade are presented, together with their application to the generation of novel quantum phases.
1,469 citations
TL;DR: Hybrid quantum circuits combine two or more physical systems, with the goal of harnessing the advantages and strengths of the different systems in order to better explore new phenomena and potentially bring about novel quantum technologies as discussed by the authors.
Abstract: Hybrid quantum circuits combine two or more physical systems, with the goal of harnessing the advantages and strengths of the different systems in order to better explore new phenomena and potentially bring about novel quantum technologies. This article presents a brief overview of the progress achieved so far in the field of hybrid circuits involving atoms, spins, and solid-state devices (including superconducting and nanomechanical systems). How these circuits combine elements from atomic physics, quantum optics, condensed matter physics, and nanoscience is discussed, and different possible approaches for integrating various systems into a single circuit are presented. In particular, hybrid quantum circuits can be fabricated on a chip, facilitating their future scalability, which is crucial for building future quantum technologies, including quantum detectors, simulators, and computers.
1,439 citations
TL;DR: An overview of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives are given in this article. But the main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.
Abstract: Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.
1,221 citations
TL;DR: In this paper, a review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and highlights the remarkable advances in Sibased quantum physics that have occurred in the past few years.
Abstract: This review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade, and single-shot readout of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress toward the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics.
998 citations
TL;DR: In this article, a review is given of an experimentally falsifiable phenomenological proposal, known as continuous spontaneous collapse, which is a stochastic nonlinear modification of the Schrodinger equation.
Abstract: Quantum mechanics is an extremely successful theory that agrees with every experimental test. However, the principle of linear superposition, a central tenet of the theory, apparently contradicts a commonplace observation: macroscopic objects are never found in a linear superposition of position states. Moreover, the theory does not explain why during a quantum measurement, deterministic evolution is replaced by probabilistic evolution, whose random outcomes obey the Born probability rule. In this article a review is given of an experimentally falsifiable phenomenological proposal, known as continuous spontaneous collapse: a stochastic nonlinear modification of the Schr\"odinger equation, which resolves these problems, while giving the same experimental results as quantum theory in the microscopic regime. Two underlying theories for this phenomenology are reviewed: trace dynamics and gravity-induced collapse. As the macroscopic scale is approached, predictions of this proposal begin to differ appreciably from those of quantum theory and are being confronted by ongoing laboratory experiments that include molecular interferometry and optomechanics. These experiments, which test the validity of linear superposition for large systems, are reviewed here, and their technical challenges, current results, and future prospects summarized. It is likely that over the next two decades or so, these experiments can verify or rule out the proposed stochastic modification of quantum theory.
901 citations
TL;DR: In this paper, state-of-the-art theory and experiment of the motion of cold and ultracold atoms coupled to the radiation field within a high-finesse optical resonator in the dispersive regime of the atom-field interaction with small internal excitation is reviewed.
Abstract: We review state-of-the-art theory and experiment of the motion of cold and ultracold atoms coupled to the radiation field within a high-finesse optical resonator in the dispersive regime of the atom-field interaction with small internal excitation The optical dipole force on the atoms together with the back-action of atomic motion onto the light field gives rise to a complex nonlinear coupled dynamics As the resonator constitutes an open driven and damped system, the dynamics is non-conservative and in general enables cooling and confining the motion of polarizable particles In addition, the emitted cavity field allows for real-time monitoring of the particle's position with minimal perturbation up to sub-wavelength accuracy For many-body systems, the resonator field mediates controllable long-range atom-atom interactions, which set the stage for collective phenomena Besides correlated motion of distant particles, one finds critical behavior and non-equilibrium phase transitions between states of different atomic order in conjunction with superradiant light scattering Quantum degenerate gases inside optical resonators can be used to emulate opto-mechanics as well as novel quantum phases like supersolids and spin glasses Non-equilibrium quantum phase transitions, as predicted by eg the Dicke Hamiltonian, can be controlled and explored in real-time via monitoring the cavity field In combination with optical lattices, the cavity field can be utilized for non-destructive probing Hubbard physics and tailoring long-range interactions for ultracold quantum systems
727 citations
TL;DR: In this paper, a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed.
Abstract: Spinor Bose gases form a family of quantum fluids manifesting both magnetic order and superfluidity. This article reviews experimental and theoretical progress in understanding the static and dynamic properties of these fluids. The connection between system properties and the rotational symmetry properties of the atomic states and their interactions are investigated. Following a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed. These states serve as the starting point for understanding low-energy dynamics, spin textures and topological defects, effects of magnetic dipole interactions, and various non-equilibrium collective spin-mixing phenomena. The paper aims to form connections and establish coherence among the vast range of works on spinor Bose gases, so as to point to open questions and future research opportunities.
671 citations
TL;DR: In this paper, a unified formalism is presented for the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser accelerated electrons.
Abstract: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent, and femtosecond radiation. In this article, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons are reviewed. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.
TL;DR: In this paper, a review of molecular observations in various spectral windows and summarizes the chemical and physical processes involved in the formation and evolution of interstellar molecules is presented, focusing on the characteristics of complex polycyclic aromatic hydrocarbon molecules and fullerenes.
Abstract: Molecular absorption and emission bands dominate the visible, infrared, and submillimeter spectra of most objects with associated gas. These observations reveal a surprisingly rich array of molecular species and attest to a complex chemistry taking place in the harsh environment of the interstellar medium of galaxies. Molecules are truly everywhere and an important component of interstellar gas. This review surveys molecular observations in the various spectral windows and summarizes the chemical and physical processes involved in the formation and evolution of interstellar molecules. The rich organic inventory of space reflects the multitude of chemical processes involved that, on the one hand, build up molecules an atom at a time and, on the other hand, break down large molecules injected by stars to smaller fragments. Both this bottom-up and the trickle-down chemistry are reviewed. The emphasis is on understanding the characteristics of complex polycyclic aromatic hydrocarbon molecules and fullerenes and their role in chemistry as well as the intricate interaction of gas-phase ion-molecule and neutral-neutral reactions and the chemistry taking place on grain surfaces in dense clouds in setting the organic inventory of regions of star and planet formation and their implications for the chemical history of the Solar System. Many aspects of molecular astrophysics are illustrated with recent observations of the HIFI instrument on the Herschel Space Observatory.
TL;DR: A wide range of analytical methods and models of intracellular transport is presented, including Brownian ratchets, random walk models, exclusion processes, random intermittent search processes, quasi-steady-state reduction methods, and mean-field approximations for active transport.
Abstract: The interior of a living cell is a crowded, heterogenuous, fluctuating environment. Hence, a major challenge in modeling intracellular transport is to analyze stochastic processes within complex environments. Broadly speaking, there are two basic mechanisms for intracellular transport: passive diffusion and motor-driven active transport. Diffusive transport can be formulated in terms of the motion of an overdamped Brownian particle. On the other hand, active transport requires chemical energy, usually in the form of adenosine triphosphate hydrolysis, and can be direction specific, allowing biomolecules to be transported long distances; this is particularly important in neurons due to their complex geometry. In this review a wide range of analytical methods and models of intracellular transport is presented. In the case of diffusive transport, narrow escape problems, diffusion to a small target, confined and single-file diffusion, homogenization theory, and fractional diffusion are considered. In the case of active transport, Brownian ratchets, random walk models, exclusion processes, random intermittent search processes, quasi-steady-state reduction methods, and mean-field approximations are considered. Applications include receptor trafficking, axonal transport, membrane diffusion, nuclear transport, protein-DNA interactions, virus trafficking, and the self-organization of subcellular structures.
TL;DR: In this paper, the physics of a variety of device concepts that have been introduced to realize white organic light-emitting diodes based on both polymer and small-molecule organic materials are discussed.
Abstract: White organic light-emitting diodes (OLEDs) are ultrathin, large-area light sources made from organic semiconductor materials. Over the past decades, much research has been spent on finding suitable materials to realize highly efficient monochrome and white OLEDs. With their high efficiency, color tunability, and color quality, white OLEDs are emerging as one of the next-generation light sources. In this review, the physics of a variety of device concepts that have been introduced to realize white OLEDs based on both polymer and small-molecule organic materials are discussed. Owing to the fact that about 80% of the internally generated photons are trapped within the thin-film layer structure, a second focus is put on reviewing promising concepts for improved light outcoupling.
TL;DR: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors and combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings as mentioned in this paper.
Abstract: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors. Combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings. Also charge states and defect levels in the band gap are accessible. In this review the main experimental and theoretical analysis techniques are described. The usage of these methods is illustrated through examples in technologically important elemental and compound semiconductors. Future challenges include the analysis of noncrystalline materials and of transient defect-related phenomena.
TL;DR: In this paper, a review of the properties of single and two delay-coupled laser systems is presented, with a particular emphasis on emerging complex behavior, deterministic chaos, synchronization phenomena, and application of these properties that range from encrypted communication and fast random bit sequence generators to bioinspired information processing.
Abstract: Complex phenomena in photonics, in particular, dynamical properties of semiconductor lasers due to delayed coupling, are reviewed. Although considered a nuisance for a long time, these phenomena now open interesting perspectives. Semiconductor laser systems represent excellent test beds for the study of nonlinear delay-coupled systems, which are of fundamental relevance in various areas. At the same time delay-coupled lasers provide opportunities for photonic applications. In this review an introduction into the properties of single and two delay-coupled lasers is followed by an extension to network motifs and small networks. A particular emphasis is put on emerging complex behavior, deterministic chaos, synchronization phenomena, and application of these properties that range from encrypted communication and fast random bit sequence generators to bioinspired information processing.
TL;DR: The experiments performed with this ''photon box'' at Ecole Normale Superieure (ENS) belong to the domain of quantum optics called ''cavity quantum electrodynamics'' as discussed by the authors, and have led to the demonstration of basic steps in quantum information processing, including the deterministic entanglement of atoms and the realization of quantum gates using atoms and photons as quantum bits.
Abstract: Microwave photons trapped in a superconducting cavity constitute an ideal system to realize some of the thought experiments imagined by the founding fathers of quantum physics. The interaction of these trapped photons with Rydberg atoms crossing the cavity illustrates fundamental aspects of measurement theory. The experiments performed with this ``photon box'' at Ecole Normale Sup\'erieure (ENS) belong to the domain of quantum optics called ``cavity quantum electrodynamics.'' We have realized the nondestructive counting of photons, the recording of field quantum jumps, the preparation and reconstruction of ``Schr\"odinger cat'' states of radiation and the study of their decoherence, which provides a striking illustration of the transition from the quantum to the classical world. These experiments have also led to the demonstration of basic steps in quantum information processing, including the deterministic entanglement of atoms and the realization of quantum gates using atoms and photons as quantum bits. This lecture starts by an introduction stressing the connection between the ENS photon box and the ion-trap experiments of David Wineland, whose accompanying lecture recalls his own contribution to the field of single particle control. I give then a personal account of the early days of cavity quantum electrodynamics before describing the main experiments performed at ENS during the last 20 years and concluding by a discussion comparing our work to other researches dealing with the control of single quantum particles.
TL;DR: The physics of sliding friction is gaining impulse from nanoscale and mesoscale experiments, simulations, and theoretical modeling as discussed by the authors, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems.
Abstract: The physics of sliding friction is gaining impulse from nanoscale and mesoscale experiments, simulations, and theoretical modeling This Colloquium reviews some recent developments in modeling and in atomistic simulation of friction, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems
TL;DR: Frustration, the presence of competing interactions, is ubiquitous in the physical sciences and is a source of degeneracy and disorder, which in turn gives rise to new and interesting physical phenomena as mentioned in this paper.
Abstract: Frustration, the presence of competing interactions, is ubiquitous in the physical sciences and is a source of degeneracy and disorder, which in turn gives rise to new and interesting physical phenomena. Perhaps nowhere does it occur more simply than in correlated spin systems, where it has been studied in the most detail. In disordered magnetic materials, frustration leads to spin-glass phenomena, with analogies to the behavior of structural glasses and neural networks. In structurally ordered magnetic materials, it has also been the topic of extensive theoretical and experimental studies over the past two decades. Such geometrical frustration has opened a window to a wide range of fundamentally new exotic behavior. This includes spin liquids in which the spins continue to fluctuate down to the lowest temperatures, and spin ice, which appears to retain macroscopic entropy even in the low-temperature limit where it enters a topological Coulomb phase. In the past seven years a new perspective has opened in the study of frustration through the creation of artificial frustrated magnetic systems. These materials consist of arrays of lithographically fabricated single-domain ferromagnetic nanostructures that behave like giant Ising spins. The nanostructures' interactions can be controlled through appropriate choices of their geometric properties and arrangement on a (frustrated) lattice. The degrees of freedom of the material can not only be directly tuned, but also individually observed. Experimental studies have unearthed intriguing connections to the out-of-equilibrium physics of disordered systems and nonthermal ``granular'' materials, while revealing strong analogies to spin ice materials and their fractionalized magnetic monopole excitations, lending the enterprise a distinctly interdisciplinary flavor. The experimental results have also been closely coupled to theoretical and computational analyses, facilitated by connections to classic models of frustrated magnetism, whose hitherto unobserved aspects have here found an experimental realization. Considerable experimental and theoretical progress in this field is reviewed here, including connections to other frustrated phenomena, and future vistas for progress in this rapidly expanding field are outlined.
TL;DR: In this paper, theoretical and experimental developments for one-dimensional Fermi gases are discussed. But the exact results obtained for Bethe ansatz integrable models of this kind enable the study of the nature and microscopic origin of a wide range of quantum many-body phenomena driven by spin population imbalance, dynamical interactions, and magnetic fields.
Abstract: This article reviews theoretical and experimental developments for one-dimensional Fermi gases. Specifically, the experimentally realized two-component delta-function interacting Fermi gas-the Gaudin-Yang model-and its generalizations to multicomponent Fermi systems with larger spin symmetries is discussed. The exact results obtained for Bethe ansatz integrable models of this kind enable the study of the nature and microscopic origin of a wide range of quantum many-body phenomena driven by spin population imbalance, dynamical interactions, and magnetic fields. This physics includes Bardeen-Cooper-Schrieffer-like pairing, Tomonaga-Luttinger liquids, spin-charge separation, Fulde-Ferrel-Larkin-Ovchinnikov-like pair correlations, quantum criticality and scaling, polarons, and the few-body physics of the trimer state (trions). The fascinating interplay between exactly solved models and experimental developments in one dimension promises to yield further insight into the exciting and fundamental physics of interacting Fermi systems.
TL;DR: Core collapse theory brings together many facets of high energy and nuclear astrophysics and the numerical arts to present theorists with one of the most important, yet frustrating, astronomical questions: ''What is the mechanism of core-collapse supernova explosions?'' A review of all the physics and the 50-year history involved would soon bury the reader in minutiae that could easily obscure the essential elements of the phenomenon, as we understand it today as discussed by the authors.
Abstract: Core-collapse theory brings together many facets of high-energy and nuclear astrophysics and the numerical arts to present theorists with one of the most important, yet frustrating, astronomical questions: ``What is the mechanism of core-collapse supernova explosions?'' A review of all the physics and the 50-year history involved would soon bury the reader in minutiae that could easily obscure the essential elements of the phenomenon, as we understand it today. Moreover, much remains to be discovered and explained, and a complicated review of an unresolved subject in flux could grow stale fast. Therefore, this paper describes various important facts and perspectives that may have escaped the attention of those interested in this puzzle. Furthermore, an attempt to describe the modern theory's physical underpinnings and a brief summary of the current state of play are given. In the process, a few myths that have crept into modern discourse are identified. However, there is much more to do and humility in the face of this age-old challenge is clearly the most prudent stance as its eventual resolution is sought.
TL;DR: In this paper, the authors review the present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon.
Abstract: This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. Present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements, and the open questions and challenges for future investigation are discussed.
TL;DR: Experimental control of quantum systems has been pursued widely since the invention of quantum mechanics as mentioned in this paper, with many of these works focusing on the control of internal and external states of trapped atomic ions, such as Bose-Einstein condensation.
Abstract: Experimental control of quantum systems has been pursued widely since the invention of quantum mechanics In the first part of the 20th century, atomic physics helped provide a test bed for quantum mechanics through studies of atoms’ internal energy differences and their interaction with radiation The advent of spectrally pure, tunable radiation sources such as microwave oscillators and lasers dramatically improved these studies by enabling the coherent control of atoms’ internal states to deterministically prepare superposition states, as, for example, in the Ramsey method (Ramsey, 1990) More recently this control has been extended to the external (motional) states of atoms Laser cooling and other refrigeration techniques have provided the initial states for a number of interesting studies, such as Bose-Einstein condensation Similarly, control of the quantum states of artificial atoms in the context of condensed-matter systems is achieved in many laboratories throughout theworld To give proper recognition to all of these works would be a daunting task; therefore, I will restrict these notes to experiments on quantum control of internal and external states of trapped atomic ions The precise manipulation of any system requires lownoise controls and isolation of the system from its environment Of course the controls can be regarded as part of the environment, so we mean that the system must be isolated from the uncontrolled or noisy parts of the environment A simple example of quantum control comes from nuclear magnetic resonance, where the spins of a macroscopic ensemble of protons in the state j #i (spin antiparallel to an applied magnetic field) can be deterministically placed in a superposition state j #i þ j "i (j j2 þ j j2 1⁄4 1) by application of a resonant rf field for a specified duration Although the ensemble is macroscopic, in this example each spin is independent of the others and behaves as an individual quantum system But already in 1935, Erwin Schrodinger (Schrodinger, 1935) realized that, in principle, quantum mechanics should apply to a macroscopic system in a more complex way, which could then lead to bizarre consequences In his specific example, the system is composed of a single radioactive particle and a cat placed together with a mechanism such that if the particle decays, poison is released, which kills the cat Quantum mechanically we represent the quantum states of the radioactive particle as undecayed 1⁄4 j "i or decayed 1⁄4 j #i, and live and dead states of the cat as jLi and jDi If the system is initialized in the state represented by the wave function j "ijLi, then after a duration equal to the half life of the particle, quantum mechanics says the system evolves to a superposition state where the cat is alive and dead simultaneously, expressed by the superposition wave function
TL;DR: The variational principles called maximum entropy (MaxEnt) and maximum caliber (MaxCal) are reviewed in this paper, and the different historical justifications for the entropy $S = \ensuremath{-}\ensurem{-} √ √ p √ i √ log √ ǫ(p) √ I √ n) and its corresponding variational principle are reviewed.
Abstract: The variational principles called maximum entropy (MaxEnt) and maximum caliber (MaxCal) are reviewed. MaxEnt originated in the statistical physics of Boltzmann and Gibbs, as a theoretical tool for predicting the equilibrium states of thermal systems. Later, entropy maximization was also applied to matters of information, signal transmission, and image reconstruction. Recently, since the work of Shore and Johnson, MaxEnt has been regarded as a principle that is broader than either physics or information alone. MaxEnt is a procedure that ensures that inferences drawn from stochastic data satisfy basic self-consistency requirements. The different historical justifications for the entropy $S=\ensuremath{-}\ensuremath{\sum}_{i}{p}_{i}\mathrm{log} {p}_{i}$ and its corresponding variational principles are reviewed. As an illustration of the broadening purview of maximum entropy principles, maximum caliber, which is path entropy maximization applied to the trajectories of dynamical systems, is also reviewed. Examples are given in which maximum caliber is used to interpret dynamical fluctuations in biology and on the nanoscale, in single-molecule and few-particle systems such as molecular motors, chemical reactions, biological feedback circuits, and diffusion in microfluidics devices.
TL;DR: In this paper, a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays or disordered nanotube mats is presented.
Abstract: The extremely high thermal conductivities of carbon nanotubes have motivated a wealth of research. Progress includes innovative conduction metrology based on microfabricated platforms and scanning thermal probes as well as simulations exploring phonon dispersion and scattering using both transport theory and molecular dynamics. This article highlights these advancements as part of a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays of nanotubes or disordered nanotube mats. Nanotube length, diameter, and chirality strongly influence the thermal conductivities of individual nanotubes and the transition from primarily diffusive to ballistic heat transport with decreasing temperature. A key experimental challenge, for both individual nanotubes and aligned films, is the separation of intrinsic and contact resistances. Molecular dynamics simulations have studied the impacts of specific types of imperfections on the nanotube conductance and its variation with length and chirality. While the properties of aligned films fall short of predictions based on individual nanotube data, improvements in surface engagement and postfabrication nanotube quality are promising for a variety of applications including mechanically compliant thermal contacts.
TL;DR: A review of the physics of direct detection of dark matter, discussing the roles of both the particle physics and astrophysics in the expected signals, is given in this article, where the authors discuss the practical formulas needed to interpret a modulating signal.
Abstract: Direct detection experiments, which are designed to detect the scattering of dark matter off nuclei in detectors, are a critical component in the search for the Universe’s missing matter. This Colloquium begins with a review of the physics of direct detection of dark matter, discussing the roles of both the particle physics and astrophysics in the expected signals. The count rate in these experiments should experience an annual modulation due to the relative motion of the Earth around the Sun. This modulation, not present for most known background sources, is critical for solidifying the origin of a potential signal as dark matter. The focus is on the physics of annual modulation, discussing the practical formulas needed to interpret a modulating signal. The dependence of the modulation spectrum on the particle and astrophysics models for the dark matter is illustrated. For standard assumptions, the count rate has a cosine dependence with time, with a maximum in June and a minimum in December. Well-motivated generalizations of these models, however, can affect both the phase and amplitude of the modulation. Shown is how a measurement of an annually modulating signal could teach us about the presence of substructure in the galactic halo or about the interactions between dark and baryonic matter. Although primarily a theoretical review, the current experimental situation for annual modulation and future experimental directions is briefly discussed.
TL;DR: Recent progress in the understanding of the role of forces in cell adhesion is reviewed from the viewpoint of theoretical soft matter physics and in close relation to the relevant experiments.
Abstract: One of the most unique physical features of cell adhesion to external surfaces is the active generation of mechanical force at the cell-material interface. This includes pulling forces generated by contractile polymer bundles and networks, and pushing forces generated by the polymerization of polymer networks. These forces are transmitted to the substrate mainly by focal adhesions, which are large, yet highly dynamic adhesion clusters. Tissue cells use these forces to sense the physical properties of their environment and to communicate with each other. The effect of forces is intricately linked to the material properties of cells and their physical environment. Here a review is given of recent progress in our understanding of the role of forces in cell adhesion from the viewpoint of theoretical soft matter physics and in close relation to the relevant experiments.
TL;DR: In this article, it is shown how to view the Born rule as a normative rule in addition to usual Dutch-book coherence, and the extent to which the general form of the new normative rule implies the full state-space structure of quantum mechanics is explored.
Abstract: In the quantum-Bayesian interpretation of quantum theory (or QBism), the Born rule cannot be interpreted as a rule for setting measurement-outcome probabilities from an objective quantum state. But if not, what is the role of the rule? In this paper, the argument is given that it should be seen as an empirical addition to Bayesian reasoning itself. Particularly, it is shown how to view the Born rule as a normative rule in addition to usual Dutch-book coherence. It is a rule that takes into account how one should assign probabilities to the consequences of various intended measurements on a physical system, but explicitly in terms of prior probabilities for and conditional probabilities consequent upon the imagined outcomes of a special counterfactual reference measurement. This interpretation is exemplified by representing quantum states in terms of probabilities for the outcomes of a fixed, fiducial symmetric informationally complete measurement. The extent to which the general form of the new normative rule implies the full state-space structure of quantum mechanics is explored.
TL;DR: In this article, a review of the physical and technical constraints that influence single-electron charge transport is presented, and a broad variety of proposed realizations are presented, some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently "just" wild ideas, still often potentially competitive if technical constraints can be lifted.
Abstract: The control electrons at the level of the elementary charge e was demonstrated experimentally already in the 1980s. Ever since, the production of an electrical current ef, or its integer multiple, at a drive frequency f has been in a focus of research for metrological purposes.This review discusses the generic physical phenomena and technical constraints that influence single-electron charge transport and presents a broad variety of proposed realizations. Some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently ‘‘just’’ wild ideas, still often potentially competitive if technical constraints can be lifted. The important issues of readout of singleelectron events and potential error correction schemes based on them are also discussed. Finally, an account is given of the status of single-electron current sources in the bigger framework of electric quantum standards and of the future international SI system of units, and applications and uses of single-electron devices outside the metrological context are briefly discussed.
TL;DR: In this article, the authors highlight the importance and challenges of three-nucleon forces for nuclear structure and reactions, including applications to astrophysics and fundamental symmetries, and illustrate that three and higher-body forces enter naturally in effective field theories and are especially prominent in strongly interacting quantum systems.
Abstract: It is often assumed that few- and many-body systems can be accurately described by considering only pairwise two-body interactions of the constituents. We illustrate that three- and higher-body forces enter naturally in effective field theories and are especially prominent in strongly interacting quantum systems. We focus on three-body forces and discuss examples from atomic and nuclear physics. In particular, we highlight the importance and the challenges of three-nucleon forces for nuclear structure and reactions, including applications to astrophysics and fundamental symmetries.