Single-photon sources are essential building blocks in quantum photonic networks, where quantum-mechanical properties of photons are utilised to achieve quantum technologies such as quantum cryptography and quantum computing. In this thesis, a single-photon source driven by a surface acoustic wave (SAW) is developed and characterised. This single-photon source is based on a SAW-driven lateral n-i-p junction in a GaAs quantum-well structure. On this device, the lateral n-i-p junction is formed by gate-induced electrons and holes in two adjacent regions. The SAW potential minima create dynamic quantum dots in a 1D channel between these two regions, and are able to transport single electrons to the region of holes along the channel. Single-photon emission can therefore be generated as these electrons consecutively recombine with holes. After characterisation and optimisation in four batches of devices, clear SAW-driven charge transport and the corresponding electroluminescence (EL) can be observed on an optimised SAW-driven n-i-p junction. Time-resolved measurements have been carried out to study the dynamics of SAW-driven electrons. Time-resolved EL signals indicate that a packet of electrons is transported to the region of holes in each SAW minimum. In addition, the carrier lifetime of SAW-driven electrons in the region of holes is shown to be $\sim 100$ ps, which is much shorter than the SAW period of $860$ ps. Hence, it is promising to observe single-photon emission in the optimised device. In order to test single-photon emission, a Hanbury Brown-Twiss experimental setup has been employed to record an autocorrelation histogram of the SAW-driven EL signal at the single-electron regime. Suppression of autocorrelation coincidences at time delay $\Delta t = 0$ is evidence of photon antibunching. By fitting theoretical functions describing the SAW-driven EL signal, it is found that the second-order correlation function shows $g^{(2)}(0) = 0.39 \pm 0.05$, which is lower than the common criterion for a single-photon source $g^{(2)}(0) < 0.5$. Moreover, theoretical calculation and simulation suggest that, if a constant background signal can be filtered out, $\sim 80 \%$ of the SAW-driven EL is single-photon emission.

INTRODUÇÃO: O zumbido é um sintoma muito freqüente e de difícil tratamento. Atualmente, algumas evidências mostraram que o zumbido está associado a alterações funcionais do sistema nervoso central. Nos últimos anos, a modulação da atividade cortical relacionada ao zumbido por meio da estimulação magnética transcraniana repetitiva (EMT) tem sido proposta como um tratamento promissor. Entretanto, nenhum estudo avaliou sua eficácia no controle do zumbido em pacientes sem perda auditiva concomitante, nem seu efeito de longa duração. O objetivo do trabalho foi investigar os efeitos imediatos e a longo prazo da estimulação magnética transcraniana repetitiva de baixa freqüência (1 Hz) em pacientes com zumbido e audiometria normal. MÉTODOS: Utilizando um ensaio clínico aleatorizado, duplo cego e paralelo, foram randomizados 20 pacientes para receber a EMT ativa ou placebo. A estimulação foi aplicada no córtex têmporo-parietal esquerdo por cinco dias consecutivos. A avaliação clínica foi feita por meio do Tinnitus Handicap Inventory e da escala análogo-visual. A avaliação por neuroimagem foi feita por meio do SPECT, o qual foi realizado antes e 14 dias após o período de estimulação. RESULTADOS: Clinicamente, o grupo submetido à estimulação magnética transcraniana ativa apresentou uma melhora significativa do zumbido, mantida por até seis meses, quando comparado ao grupo que recebeu a estimulação placebo. A avaliação por SPECT demonstrou redução do fluxo sanguíneo no lobo temporal esquerdo após o período de estimulação ativa. CONCLUSÃO: Os resultados revelam o potencial terapêutico da estimulação magnética transcraniana como nova ferramenta no tratamento do zumbido, proporcionando redução significativa do incômodo provocado pelo zumbido por até seis meses e reduzindo a atividade neuronal no córtex temporal. / INTRODUCTION: Tinnitus is a frequent disorder which is very difficult to treat. There is compelling evidence that tinnitus is associated with functional alterations in the central nervous system. Recently, the targeted modulation of tinnitus-related cortical activity through repetitive transcranial magnetic stimulation (rTMS) has been proposed as a promising new treatment approach. However, its efficacy in patients without hearing loss has never been studied, as well as the long-term duration of its effect. The objective of this study was to investigate both immediate and long-term effect of low frequency (1 Hz) rTMS in patients with tinnitus and normal hearing. METHODS: Using a randomized double-blind and parallel clinical trial, 20 patients were divided to receive either active or placebo transcranial magnetic stimulation over the left temporoparietal cortex for 5 consecutive days. The clinical evaluation was performed by using the Tinnitus Handicap Inventory and the visual analogue scale. The neuroimage evaluation included and ECD-SPECT imaging, which was performed before and 14 days after rTMS. RESULTS: From the clinical point of view, the group submitted to active rTMS presented significant improvement of the tinnitus score, which was sustained up to six months, when compared to the group that received the sham rTMS. SPECT measurements demonstrated a reduction of metabolic activity in the left temporal lobe after active rTMS. CONCLUSION: These results support the potential of rTMS as a new therapeutic tool for the treatment of chronic tinnitus, by demonstrating a significant reduction of tinnitus complaints over a period of at least six months and a significant reduction of neural activity in the temporal cortex.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) is a novel technique for direct analysis of organic and biological molecules. Amino acids, dipeptides, and organoselenium compounds were successfully detected by SALDI on carbon and silicon surfaces. Surface effects, solvent effects, temperature effects and pH effects were studied. A possible mechanism of SALDI is proposed based on observed results. In general, stimulated desorption results in neutral yields that are much larger than ion yields. Thus, we have exploited and further developed laser desorption single photon ionization mass spectrometry (LD/SPI MS) as a means of examining biomolecules. The experimental results clearly demonstrate that LD/SPI MS is a very useful and fast analysis method with uniform selectivity and high sensitivity. Selenium (Se) is an essential ultra-trace element in the human body. In efforts to obtain more useful information of selenium metabolites in human urine, mass determination of unknown organoselenium compounds in biological matrices using SALDI MS was investigated. In another approach, several selenium metabolites in human urine were successfully detected by LD/SPI MS. A HPLC-MS/MS method was also developed for a quantitative case study of selenium metabolites in human urine after ingestion of selenomethionine. Low-energy electrons (LEE, 3-20 eV) have been shown to induce single and double strand breaks (SSB and DSB) in plasmid DNA. To understand the genotoxic effects due to secondary species of high-energy radiation, we investigate the role of transient negative ions and the specificity in LEE-DNA damage by examining the neutral product yields using low electron stimulated dissociation SPI MS. The neutral yields as a function of incident electron energy are also correlated with the SSBs and DSBs measured using post-irradiation gel electrophoresis. The results provide further insight concerning the mechanisms of LEE-induced damage to DNA. Overall, this research provided an in-depth understanding of non-thermal surface processes and the development of new mass spectrometric techniques for the analysis of biomolecules.

Four problems in non-equilibrium statistical physics are investigated: 1. The thermodynamics of single-photon gas; 2. Energy of the ground state in Multi-electron atoms; 3. Energy state of the H2 molecule; and 4. The Condensation behavior in N weakly interacting Boson gas. In the single-photon heat engine, we have derived the equation of state similar to that in classical ideal gas and applied it to construct the Carnot cycle with a single photon, and showed the Carnot efficiency in this single-photon heat engine. The energies of the ground state of multi-electron atoms are calculated using the modi ed Bohr model with a shell structure of the bound electrons. The di erential Schrodinger equation is simpli ed into the minimization problem of a simple energy functional, similar to the problem in dimensional scaling in the H-atom. For the C-atom, we got the ground state energy -37:82 eV with a relative error less than 6 %. The simplest molecular ion, H+ 2 , has been investigated by the quasi-classical method and two-center molecular orbit. Using the two-center molecular orbit derived from the exact treatment of the H+ 2 molecular ion problem, we can reduce the number of terms in wavefunction to get the binding energy of the H2 molecule, without using the conventional wavefunction with over-thousand terms. We get the binding energy for the H2 with Hylleraas correlation factor 1 + kr12 as 4:7eV, which is comparable to the experimental value of 4:74 eV. Condensation in the ground state of a weakly interacting Bose gas in equilibrium is investigated using a partial partition function in canonical ensemble. The recursive relation for the partition function developed for an ideal gas has been modi ed to be applicable in the interacting case, and the statistics of the occupation number in condensate states was examined. The well-known behavior of the Bose-Einstein Condensate for a weakly interacting Bose Gas are shown: Depletion of the condensate state, even at zero temperature, and a maximum uctuation near transition temperature. Furthermore, the use of the partition function in canonical ensemble leads to the smooth cross-over between low temperatures and higher temperatures, which has enlarged the applicable range of the Bogoliubov transformation. During the calculation, we also developed the formula to calculate the correlations among the excited states.

In this study, we have developed a high performance multi-photon microscopic system to perform second- harmonic (SH) imaging on a tooth and a KTP crystal . The high sensitivity of the system allows acquisition rate of 300 seconds/frame with resolution at 512¡Ñ512 pixels. The surface SH signal generated from the tooth and the KTP crystal is also carefully verified through micro-spectroscopy, polarization rotation and wavelength tuning. In this way, we can ensure the authenticity of the signal. KTP crystal and the enamel that encapsulates the dentine is known to possess highly ordered structures. The anisotropy of the structure is revealed in the microscopic SH images of the tooth and the KTP crystal samples.

In this study, we have successfully developed a high performance transmission mode Laser scanning for SHG imaging. This setup is capable of acquiring images of size 512¡Ñ512 pixels at a rate of 5.4 seconds/frame. The of samples can thus be imaged, which reflects the samples¡¦ structure and symmetry.

Gegenstand dieser Diplomarbeit ist die Untersuchung der Dynamik in dünnen Polymerfilmen anhand von einzelnen Molekülen. Zu diesem Zweck wurden dünne Filme (kleiner 100nm) hergestellt und mittels Einzelmoleküldetektion und zeitaufgelöster Einzelphotonenzählung analysiert, was eine orts- und zeitaufgelöste Untersuchung einzelner Farbstoffmoleküle ermöglicht. Ziel war es, festzustellen ob, und auf welchem Weg, die Dynamik der Umgebung in Fluktuationen der Fluoreszenzlebensdauer einzelner Moleküle sichtbar wird. Neben der Evaluierung der Untersuchungsmethoden wurden in dieser Arbeit zwei Arten von Sensormolekülen - DiD und Malachit Grün - näher untersucht. / The subject of this diploma thesis is the analysis of dynamics in thin polymer films using single molecules. Thin polymer films (less than 100nm) were produced and analysed by Single Molecule Detection (SMD) and Time Correlated Single Photon Counting (TCSPC). This allows a spatial and time resolved investigation of the single dye molecule. The aim was to ascertain if, and in which way, the dynamics of the environment are reflected by fluctuations of the fluorescence lifetime of the single molecule. In addition to evaluating the investigation methods two kinds of molecules - DiD and Malachite Green - were also analysed.

This dissertation details the development and experimental implementation of single-photon atomic cooling. In this scheme atoms are transferred from a large-volume magnetic trap into a small-volume optical trap via a single spontaneous Raman transition that is driven near each atom's classical turning point. This arrangement removes nearly all of an atomic ensemble's kinetic energy in one dimension. This method does not rely on a transfer of momentum from photon to atom to cool. Rather, single-photon atomic cooling achieves a reduction in temperature and an increase in the phase-space density of an atomic ensemble by the direct reduction of the system's entropy. Presented here is the application of this technique to a sample of magnetically trapped ⁸⁷Rb. Transfer efficiencies between traps of up to 2.2% are demonstrated. It is shown that transfer efficiency can be traded for increased phase-space compression. By doing so, the phase-space density of a magnetically trapped ensemble is increased by a factor of 350 by the single-photon atomic cooling process. / text

The work covered in this thesis deals with the problem of automatically registering 3D images acquired from different medical imaging modalities. The approach taken is to develop generic measures of image registration derived from the co-occurence of values in the two images. The development of statistical alignment measures is reviewed. The registration problem is then expressed in terms of entropy and developed using tools from information theory. The problem of the optimization of the registration process in the different types of algorithms is identified as important and the power of Genetic Algorithms is applied. The application of image registration techniques, implemented during this thesis, in complex situations is evaluated. The cases of patients with brain ischemia and brain tumour residual disease are elaborated. This is accomplished with the formation of Groupwares where the tacit knowledge, owned by the individual specialists that take part in the collaboration, is exposed and made explicit in the process of the evaluation of the findings, provided by the fused images. This is performed in a high performance computer network that has been developed between the Department of Medicine and the University Hospital. / Η παρούσα εργασία ασχολείται με το πρόβλημα της αυτοματοποιημένης προσαρμογής και σύντηξης τρισδιάστατων απεικονίσεων από διαφορετικές ιατρικές απεικονιστικές μεθοδολογίες.

In many medical imaging modalities, as photons travel from the emission source to the detector, they are scattered by the biological tissue. Often this scatter is viewed as a phenomenon that degrades image quality, and most research is focused on designing methods for either discarding the scattered photons or correcting for scatter. However, the scattered photons also carry information about the tissue that they pass through, which can perhaps be extracted. In this research, we investigate methods to retrieve information from the scattered photons in two specific medical imaging modalities: diffuse optical tomography (DOT) and single photon emission computed tomography (SPECT). To model the scattering of photons in biological tissue, we investigate using the Neumann-series form of the radiative transport equation (RTE). Since the scattering phenomenon are different in DOT and SPECT, the models are individually designed for each modality. In the DOT study, we use the developed photon-propagation model to investigate signal detectability in tissue. To study this detectability, we demonstrate the application of a surrogate figure of merit, based on Fisher information, which approximates the Bayesian ideal observer performance. In the SPECT study, our aim is to determine if only the SPECT emission data acquired in list-mode (LM) format, including the scattered-photon data, can be used to compute the tissue-attenuation map. We first propose a path-based formalism to process scattered photon data, and follow it with deriving expressions for the Fisher information that help determine the information content of LM data. We then derive a maximum-likelihood expectation-maximization algorithm that can jointly reconstruct the activity and attenuation map using LM SPECT emission data. While the DOT study can provide a boost in transition of DOT to clinical imaging, the SPECT study will provide insights on whether it is worth exposing the patient to extra X-ray radiation dose in order to obtain an attenuation map. Finally, although the RTE can be used to model light propagation in tissues, it is computationally intensive and therefore time consuming. To increase the speed of computation in the DOT study, we develop software to implement the RTE on parallel computing architectures, specifically the NVIDIA graphics processing units (GPUs).