This dissertation contains scientific research within the realm of quantum optics, which is a branch of physics. An experimental and theoretical study is made of two-photon interference phenomena... Show moreThis dissertation contains scientific research within the realm of quantum optics, which is a branch of physics. An experimental and theoretical study is made of two-photon interference phenomena in various optical systems. Spatially entangled photon pairs are produced via the nonlinear optical process of spontaneous parametric down-conversion. These entangled photons are then passed through different optical systems to study various aspects of two-photon interference. Firstly, an experimental analysis is made of the high-dimensional entanglement that is present in the orbital angular momentum of the photons. Secondly, we present a comprehensive description of two-photon quantum interference behind a double slit. We demonstrate how to control the quantum correlations and present the first observations of complete two-photon diffraction patterns behind a double slit. Finally, we present pioneering experiments on spatially entangled two-photon states that are scattered of random media. We have observed and theoretically analyzed the structure in the random two-photon interference patterns called two-photon speckle patterns. Spatial entanglement gives two-photon speckle a much richer structure than ordinary one-photon speckle. Our experiments also demonstrate a two-photon interference phenomenon that survives averaging over different realizations of disorder. The latter results are closely related to bosonic, fermionic, and anyonic particle exchange symmetries. Show less
This thesis addresses a variety of systems in which the diffusion is anomalous, mainly motivated by recent experimental developments. The main topics discussed are: * We look at the consequences... Show moreThis thesis addresses a variety of systems in which the diffusion is anomalous, mainly motivated by recent experimental developments. The main topics discussed are: * We look at the consequences that subdiffusion on fractals has for shot noise. * The effects correlations have on superdiffusion in one dimension are examined. * We develop and demonstrate the usefulness of a method to simulate the anomalous diffusion of Dirac fermions in a computer. * A spin precession experiment in topological insulators is proposed and analyzed. * We present the mechanism for the conversion of an ordinary insulator into a topological insulator by disorder which was reported in the literature, on the basis of computer simulations, but had remained unexplained. Show less
Resonant Inelastic X-ray Scattering (RIXS) is an X-ray in, X-ray out technique that enables one to study the dispersion of excitations in solids. In this thesis, we investigated how various... Show moreResonant Inelastic X-ray Scattering (RIXS) is an X-ray in, X-ray out technique that enables one to study the dispersion of excitations in solids. In this thesis, we investigated how various elementary excitations of transition metal oxides show up in RIXS spectra. Show less
As one of the most important developments in string theory, the AdS/CFT correspondence(or in general gauge/gravity correspondence) encodes a way of using string theory to perform non-perturbative... Show moreAs one of the most important developments in string theory, the AdS/CFT correspondence(or in general gauge/gravity correspondence) encodes a way of using string theory to perform non-perturbative calculation in gauge theory which is still a complicated problem. It was firstly formulated as the correspondence between weakly coupled gravity theory with AdS (Anti de Sitter) space-time background and strongly coupled gauge theory with conformal symmetry in one lower dimension. One application of AdS/CFT is to compute some of observables of sQGP such as photon and dilepton production rates, mean-free path time of the plasma constituents, and anisotropic drag force effect to the elliptic flow. Show less
The central topic in this thesis is the effect of topological defects in two distinct types of condensed matter systems. The first type consists of graphene and topological insulators. By... Show moreThe central topic in this thesis is the effect of topological defects in two distinct types of condensed matter systems. The first type consists of graphene and topological insulators. By studying the long-range effect of lattice defects (dislocations and disclinations) we find that the graphene electrons mimic fundamental Dirac electrons in spaces with curvature and torsion. We show that these long-range effects influence interferometric transport measurements: (i) Emphasizing the importance of electron dephasing in graphene; (ii) Enabling a characterization of neutral Majorana states, which are important for quantum computation applications, and conjectured to exist in topological insulators. Considering also the microscopic structure of graphene dislocations, we interpret local tunneling experiments on graphite grain boundaries. The second type of systems we study are the high temperature cuprate superconductors, where the strongly interacting electrons lead to coexisting symmetry breaking orders in the pseudogap phase. We observe and describe the interplay of nematic (orientational) and stripe (translational) orderings in local tunneling experiments, with stripe dislocations playing the key role. We also describe the observed phonon anomaly in cuprates through the effect of metallic stripes. Show less
Organisms show a remarkable variation in sizes, yet cell sizes are surprisingly similar across species, typically ranging from 10 _m to 100 _m. A striking exception are the giant cells of the algal... Show moreOrganisms show a remarkable variation in sizes, yet cell sizes are surprisingly similar across species, typically ranging from 10 _m to 100 _m. A striking exception are the giant cells of the algal weed Chara, which can exceed 10 cm in length and 1 mm in diameter. A circulation known as cytoplasmic streaming takes place inside these cells, which has been hypothesised to mitigate the slowness of diffusion on these scales. Our work has sought to quantify how this circulation allows the organism to circumvent the diffusional bottleneck that appears to limits cell size in most organisms. We examine the circulation pattern in the cylindrical internodal cells that make up the shoot of this organism. Along the surface of these cells, two twisting bands carry the cellular fluid up and down, forming a pattern much like the red and white ribbon on a barber pole. Hydrodynamic analysis reveals that this twisting of the bands, which is most prominent during growth, may serve to enhance mixing in the cell, thereby aiding diffusional transport. Flow measurements by means of injected tracers, as well as an MRI technique known as Magnetic Resonance Velocimetry, are consistent with our hydrodymic description of the flow field. Show less
This thesis concerns the vibrational properties of different classical disordered condensed matter systems. In the first part we focus on materials that exhibit a rigidity transition as their... Show moreThis thesis concerns the vibrational properties of different classical disordered condensed matter systems. In the first part we focus on materials that exhibit a rigidity transition as their density is increased. By introducing a new method into the field, we were able to look into the localization behavior of vibrational modes of jammed packings of soft spherical particles, both in the localized regime where the localization length is much less and in the regime where it is grater than the linear system size. We also analyze the nature of vibrational modes of jammed packings of soft elliptical particles, where we uncover the change of the structure of the spectrum, compared to the simplest model of sphere packings, due to the rotational degrees of freedom of the particles. In the second part of this thesis we explore the localization properties of collective modes and response to uniform driving of bubble clouds. We find that the response is often very different from that of a typical mode because the frequency response of each mode is sufficiently wide that many modes are excited when the cloud is driven by an ultrasound. Show less
Doped manganese oxides such as La0.67Ca0.33MnO3 (LCMO) are strongly correlated electron systems which display an insulator to metal transition upon cooling at a temperature T_MI. At low temperature... Show moreDoped manganese oxides such as La0.67Ca0.33MnO3 (LCMO) are strongly correlated electron systems which display an insulator to metal transition upon cooling at a temperature T_MI. At low temperature the material is ferromagnetic. Above the transition the material is a paramagnetic insulator in which conduction is governed by activated polaron hopping. As yet, the fundamental question of conductance on micrometer length scales (the scale on which electronic phase separation can occur) has been little studied. We investigate this question of electrical transport in LCMO, which requires the fabrication of micron sized structures in LCMO thin films. We measure current-voltage (I-V) characteristics as function of temperature, in high magnetic fields, in electric fields and with varying film thickness. In warming from the metallic to the insulating state we find strong non-linear effects in the steep part of the transition. The differential resistance is largest at zero bias, then drops with increasing current, and saturates at a current density which is the same for different samples. Resistance drops of up to 80 % are observed upon increasing the applied current. We propose that the nonlinear behavior is a direct signature of an intervening phase involving the formation of short range polaron correlations (electron-glass). The nonlinear behavior occurs when the homogeneous glass phase which now encompasses the entire microstructure is melted by the applied electrical current. We also associate the formation of inhomogeneities in the microstructure with the appearance of a strong electric field effect. Show less
This thesis describes a series of measurements and a theoretical analysis to get more insight into the fundamental working of superconducting systems when these are brought into close proximity... Show moreThis thesis describes a series of measurements and a theoretical analysis to get more insight into the fundamental working of superconducting systems when these are brought into close proximity with ferromagnetic systems, or when they are driven into a non-equilibrium state. The main focus is on the electronic transport properties of such coupled systems, from which the working of the individual part are well known. Show less
The growing field of bio-electronics holds many promises with regard to the integration of various organic molecules onto printed circuit-boards. These include a decrease in the cost of production,... Show moreThe growing field of bio-electronics holds many promises with regard to the integration of various organic molecules onto printed circuit-boards. These include a decrease in the cost of production, an increased sensitivity and specificity to molecular detection from various solutions (i.e. blood) and ultra-miniaturization. However, numerous challenges still face such prospects, chief among which is the retention of biological activity of the adsorbed molecules. To circumvent the possible harmful effects of the bare surfaces, we have made use of self-assembled molecular films that not only shield the proteins (i.e. azurin) off surfaces, but also help establish a spatially-defined conductive path to electrodes. At the same time, the protein itself was engineered such that the active cavity is directly connected via such molecular __wires__. Our results may help in the adsorption of more complex enzymes into future molecular devices, that will retain their activity on the surfaces and are able to integrate into biosensors. Show less
