Experiments aiming at direct detection of dark matter

We present a review of existing and planned dark matter direct detection experiments. The emphasis is on principle limitations for this detection technique and resulting consequences for future projects. We argue that the near future experiments, CDMS and HDMS, will give such stringent limits on WIMP–nucleon elastic cross sections that the next round of experiments will have to be either massive direction–sensitive detectors or massive ton–scale detectors with almost zero background. Candidate experiments with these requirements are shortly introduced like the newly announced GENIUS proposal. We also shortly discuss the implications of WIMP search results for accelerator experiments and vice versa. Received: 16 April 1998     

Tests of relativistic gravity in space

We review the foundations of Einstein’s general theory of relativity, discuss recent progress in the tests of relativistic gravity, and present motivations for new generation of high-accuracy gravitational experiments. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential of the recently proposed gravitational experiments.     

Superconducting quantum point contacts

We review our experiments on the electronic transport properties of atomic contacts between metallic electrodes, in particular superconducting ones. Despite ignorance of the exact atomic configuration, these ultimate quantum point contacts can be manipulated and well characterized in-situ. They allow performing fundamental tests of the scattering theory of quantum transport. In particular, we discuss the case of the Josephson effect.     

Indications on the mass of the lightest electroweak baryon

In general, an effective low-energy Lagrangian model of composite electroweak symmetry breaking contains soliton solutions that may be identified with technibaryons. We recall how the masses of such states may be related to the coefficients of fourth-order terms in the effective Lagrangian, and review the qualitative success of this approach for baryons in QCD. We then show how the current theoretical and phenomenological constraints on the corresponding fourth-order coefficients in the electroweak theory could be used to estimate qualitative lower and upper bounds on the lightest electroweak baryon mass. We also discuss how the sensitivity of the LHC experiments could enable these bounds to be improved.     

Lasing without inversion: problems and prospects

We review the recent progress both in the theory and in experiments on lasing without inversion and discuss the potential application of this phenomenon for the generation of coherent gamma radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Equation of state of an interacting bose gas confined by a harmonic trap: the role of the "harmonic" pressure

A gas of interacting atoms confined by a three dimensional anisotropic harmonic potential is studied. It is shown that there appear "new" thermodynamic variables instead of the usual pressure and volume: the latter is replaced by (the inverse of) the cube of the geometric average of the oscillator frequencies of the trap, and the former by the harmonic pressure responsible for the mechanical equilibrium of the fluid in the trap. We discuss the origin and physical meaning of these quantities and show that the equation of state of the gas is given in terms of these variables. The equation of state of a cold gas of interacting Bose atoms in the Hartree-Fock approximation is presented. We indicate how the harmonic pressure can be measured in current experiments.     

Spectroscopy of proteins at low temperature. Part I: Experiments with molecular ensembles

We discuss aspects of the physics of proteins at low temperature as they are reflected in highly resolved optical spectra of molecular probes. Typical probe molecules are heme-like dyes, aromatic amino acids, but also extended molecular aggregates in light harvesting complexes. We put emphasis on the interactions of the probe with its protein environment, on the range of these interactions, on their specific behavior in external fields, as well as on the characteristic parameters of the protein which can be determined with optical techniques at low temperatures but are not easily accessible otherwise. However, the focus of the review is on spectral diffusion physics of proteins, i.e. on their motion in conformational phase space, and on how this motion is reflected in the optical spectra. These structure changing-processes reflect the non-ergodic nature of low temperature proteins. They are most clearly detected at low temperature where the resolution of the experiment is close to the ultimate limit as given by the natural linewidth and where the dynamics become slow enough to be conveniently measured. In part I we discuss aspects of ensemble experiments, in part II we focus on experiments with single protein complexes. We offer lines of reasoning which may serve as guidelines for an understanding of the phenomena.     

Quantum Correlations in Systems of Indistinguishable Particles

We discuss quantum correlations in systems of indistinguishable particles in relation to entanglement in composite quantum systems consisting of well separated subsystems. Our studies are motivated by recent experiments and theoretical investigations on quantum dots and neutral atoms in microtraps as tools for quantum information processing. We present analogies between distinguishable particles, bosons, and fermions in low-dimensional Hilbert spaces. We introduce the notion of Slater rank for pure states of pairs of fermions and bosons in analogy to the Schmidt rank for pairs of distinguishable particles. This concept is generalized to mixed states and provides a correlation measure for indistinguishable particles. Then we generalize these notions to pure fermionic and bosonic states in higher-dimensional Hilbert spaces and also to the multi-particle case. We review the results on quantum correlations in mixed fermionic states and discuss the concept of fermionic Slater witnesses. Then the theory of quantum correlations in mixed bosonic states and of bosonic Slater witnesses is formulated. In both cases we provide methods of constructing optimal Slater witnesses that detect the degree of quantum correlations in mixed fermionic and bosonic states.     

All-optical waveguide switching

We present a tutorial review of all-optical switching in fibre and integrated optics waveguides. These switching devices require non-linear refractive index changes in single or coupled waveguides, and involve either the low-power guided modes of the structure or soliton-type waves guided, emitted or captured by waveguides. We discuss the physical principles involved in these all-optical switching schemes, material requirements, recent experiments and limitations. A representative rather than comprehensive list of references is provided.An invited paper     

Majorana准粒子与超导体-半导体异质纳米线

Majorana准粒子是凝聚态物理版本的Majorana费米子.由于Majorana准粒子间的交换操作服从非阿贝尔统计,并基于此可构建更稳定的量子计算机,近年来在凝聚态物理界引起广泛关注.为帮助初学者快速理解Majorana准粒子的形成机理,本文回顾了在一维超导体-半导体异质纳米线系统中Majorana准粒子模型的提出和理论演化过程,介绍Kitaev链模型并分析了模型中各要素所起的作用.还介绍了典型Majorana器件的构成和测量方法,并结合最新的实验进展对探测到的零能电导峰进行了分析和述评.最后对超越一维系统的超导体-半导体异质系统的实验前景进行了展望.     

Stability of thin nematic films. Commentary on "Morphology and structure of thin liquid-crystalline films at nematic-isotropic transition" by P. Ziherl and S. Zumer

We discuss the peculiarity of thin nematic films on solid substrates with a free surface, underlining the differences with what is usually seen in dewetting. We review the thermodynamic basis of the coupled phase/thickness separation that has previously been shown experimentally. We give new experimental evidences for the origin of the coupling force chosen in our previous theoretical model. This additional information contributes to the discussion raised by the article of Ziherl and Zumer in this issue.     

High-resolution photoemission in low-dimensional conductors and superconductors

We review some recent spectroscopic results on low-dimensional systems, including high-T_c superconductors, and charge density wave compounds. We briefly discuss the reasons for the present interest in these materials, and the relevance of band mapping experiments by angle-resolved photoemission spectroscopy. The main focus of the paper is on high-energy resolution, which can be exploited to probe the quasiparticle excitations, and to study the characteristic instabilities of the Fermi surface. Gap spectroscopy in the ordered phases is a prominent part of this research, namely in the cuprates. The normal state properties, however, are often as interesting. This is particularly true in 1D, where the photoemission results indicate strong deviations from a Fermi liquid scenario.     

Femtosecond optical responses of disordered clusters, composites, and rough surfaces: "the ninth wave" effect

We predict that in the course of femtosecond excitation of random clusters, composites, or rough surfaces in the optically linear regime, ultrafast giant fluctuations of local fields occur. These fluctuations cause transient (on a femtosecond scale) formation of highly enhanced fields localized in nanometer-size regions ("the ninth wave effect"). The spatial distribution of those fields is dramatically different from the case of steady-state excitation. We discuss manifestations of this effect and possible experiments.     

Exotic electronic phases in the second Landau level

Recent experiments have shown that two-dimensional electron systems with an externally applied magnetic field are an extremely rich ground for many-body physics. In particular, when only two of the Landau levels (LL) are filled an intricate magnetoresistance is found. This result stems from an interesting competition of electronic phases such as fractional quantum Hall liquids, reentrant integer Hall states, and unique quantized states at even denominator LL filling factors. We present a brief review of the transport properties of these electronic phases and discuss in detail the effects of an added in-plane magnetic field.     

Exotic electronic phases in the second Landau level

Recent experiments have shown that two-dimensional electron systems with an externally applied magnetic field are an extremely rich ground for many-body physics. In particular, when only two of the Landau levels (LL) are filled an intricate magnetoresistance is found. This result stems from an interesting competition of electronic phases such as fractional quantum Hall liquids, reentrant integer Hall states, and unique quantized states at even denominator LL filling factors. We present a brief review of the transport properties of these electronic phases and discuss in detail the effects of an added in-plane magnetic field.     

Mind the gap: Turbulent combustion model validation and future needs

This overview collects a range of well characterized experiments used in the step-wise validation of turbulent combustion models, from gas phase non-premixed jet flames to spray flames, and from simple symmetric jets to real device geometries, focusing primarily on statistically steady state experiments. We discuss how the experiments and models are constructed, approaches to modelling, and the tradeoffs between the level of detail and computational demands. The review highlights a number of experiments used for benchmarking models, selecting a few examples where models have clearly succeeded, as well as some areas where there are clear needs in the experimental database. In particular, the areas of turbulent spray combustion and soot prediction, as well as combustion under high pressures appear as the least developed and present the clearest gaps for both models and experiments. Based on the successful application of advanced methods of uncertainty quantification to a number of problems in reacting flows, we suggest that these methods might be used to advantage in the design of experiments. This would enable an upfront examination of the extent to which comparisons between measurable scalars and velocities allow clear distinction between model features.     

Theoretical calculations of the properties of point defects in solids

In accordance with the terms of reference of this series of journals, we have set out in this review to give as far as is possible a critical overview of the methods currently available for the calculation of the various properties of point defects in, first, ionic crystals and, then, in metals. We have restricted ourselves to these two classes of solids since, at present, such calculations as have been made for other materials are relatively few in number and, in our opinion, relatively unreliable. In attempting to write a critical review of this area we have found it impossible to restrict our discussion entirely to relatively recent papers. For example, when we are discussing ionic crystals, it is essential that we review the Mott-Littleton method, and the original paper by these authors appeared in 1938. The real upsurge in interest in the type of calculation we are reviewing largely parallels the development of modern electronic computers. Thus, such calculations as have been made recently can be regarded as computer “experiments.” In a recent short review, Gilman' has justifiably pointed out that there comes a point at whch, from a “cost effectiveness” point of view, it becomes more economical to spend money doing real experiments on real crystals instead of computer experiments on model crystals. This is a valid point and should be borne in mind when assessing the relative merits of the types of defect calculations we discuss. In fact, there is a real danger in writing a “critical” review of this field in that one may convince the reader that the whole subject is an intellectual dead end, and we have tried to bear this in mind in our subsequent discussion.     

Deconstructing the glass transition through critical experiments on colloids

The glass transition is the most enduring grand-challenge problem in contemporary condensed matter physics. Here, we review the contribution of colloid experiments to our understanding of this problem. First, we briefly outline the success of colloidal systems in yielding microscopic insights into a wide range of condensed matter phenomena. In the context of the glass transition, we demonstrate their utility in revealing the nature of spatial and temporal dynamical heterogeneity. We then discuss the evidence from colloid experiments in favor of various theories of glass formation that has accumulated over the last two decades. In the next section, we expound on the recent paradigm shift in colloid experiments from an exploratory approach to a critical one aimed at distinguishing between predictions of competing frameworks. We demonstrate how this critical approach is aided by the discovery of novel dynamical crossovers within the range accessible to colloid experiments. We also highlight the impact of alternate routes to glass formation such as random pinning, trajectory space phase transitions and replica coupling on current and future research on the glass transition. We conclude our review by listing some key open challenges in glass physics such as the comparison of growing static length scales and the preparation of ultrastable glasses that can be addressed using colloid experiments.