In this thesis, carrier dynamics and broadband THz enhancement of photoconduction based THz system are studied with double pulses pump-probe and THz system. The carrier dynamics behavior of the second pulse excitation almost remain unchanged for various temporal spacing of double pulses excitation (from 264fs to 276fs). This is attributed to faster carrier life time of material (around 270fs). Meanwhile, broadband THz enhancement is also investigated under various chirp and temporal spacing of two excitation pulses using shaping pulse THz-TDS system. Compared to typical narrowband THz enhancement, enhanced broadband THz signal both in temporal profile and power is observed at specific temporal spacing and chirp of two excitation pulses. Suitable mechanics is also discussed in this thesis.

The effects of quantum coherence in X-ray optics at nuclear transitions are investigated from a theoretical point of view. First, we introduce the general concept of the decaying dressed states and present a classification of the quantum coherence effects in a three-level coherently driven system. Second, we show that the interference effects may appear in X-ray radiation at the nuclear transitions under the condition of the nuclear level anti-crossing. This effects are similar to electromagnetically induced transparency, which has been widely studied earlier at the electronic transitions in optics. We also suggest a new technique for inhomogeneous line narrowing at nuclear transitions. This technique is based on the combined action of RF and DC fields and adopted to be applied in the M¨ossbauer spectroscopy. Numerical simulation of a simple model with the dipole-dipole interaction is presented in order to demonstrate the efficiency of the technique. Finally, we study the possibility to suppress the nuclear elastic forward scattering in the synchrotron experiments using trains of pulses. A numerical model is developed to confirm this possibility and the main issue of relative phases of consecutive pulses is discussed.

We investigate quantum coherences between excited states induced on quantum systems upon excitation by partially coherent radiation sources. Attempts at rejuvenating coherences using noisy sources are also explored. This work is most relevant to studies of photo-excitation of light harvesting systems under natural conditions as well as to quantum optical experiments using partially coherent lasers. The transient coherent response of a model $V$ system upon irradiation by various models of incoherent light is explored and it was found that it was possible to induce transient excited state coherences upon excitation. These excited state coherences eventually become a small fraction of population and the system reaches a mixed state. Lastly, we critique an existing literature model of excitation by noisy laser and we show that the coherence observed in that scenario is artificial. We propose an alternative using a physical model of noisy excitation.

We investigate quantum coherences between excited states induced on quantum systems upon excitation by partially coherent radiation sources. Attempts at rejuvenating coherences using noisy sources are also explored. This work is most relevant to studies of photo-excitation of light harvesting systems under natural conditions as well as to quantum optical experiments using partially coherent lasers. The transient coherent response of a model $V$ system upon irradiation by various models of incoherent light is explored and it was found that it was possible to induce transient excited state coherences upon excitation. These excited state coherences eventually become a small fraction of population and the system reaches a mixed state. Lastly, we critique an existing literature model of excitation by noisy laser and we show that the coherence observed in that scenario is artificial. We propose an alternative using a physical model of noisy excitation.

Coherent atomic states prepared by laser field can have quantum interference between the different transition amplitudes. Therefore, the medium susceptibility and optical response can be engineered, leading to many interesting phenomena, such as coherent population trapping (CPT), electromagnetically induced transparency (EIT), and lasing without inversion (LWI). We studied the coherence effects in various prototype atomic systems, and found many interesting applications. We solved the slow light bandwidth problem by decomposing the pulse and matching each frequency to its EIT window using a magnetic field gradient. We also considered the probe field deflection induced by the driving field distribution in EIT, and showed that even a broadband pulse can be deflected without serious spreading. In the fast light area, we examined the effects of noise and parameter deviations in a bichromatic Raman type white light cavity. Taking advantage of the adjustable absorption of EIT, we showed that EIT in a laser cavity can have either first-order or second-order phase transitions. Last but not least, we show that the adiabatic population transfer can be used to reverse the weak measurement of an arbitrary field with finite photon number.

<p>Liposomes are excellent chemotherapy drug delivery agents, on the cutting edge of cancer treatment technology. Since liposomes are already used to deploy cancer drugs in patients, imaging capacity would make them dual-purpose "theranostic" vesicles. Intermolecular double quantum coherence (iDQC) MRI is uniquely suited to this application, as its contrast does not require any additional chemicals. Adding contrast agents to liposomes can be time-consuming, add to toxicity, interfere with membrane function, or adversely affect drug loading. Furthermore, iDQC contrast measures diffusion and thus directly depends on membrane permeability and related properties. In this set of experiments, it has been shown that iDQC signal from intra-liposomal water can be distinguished from that of bulk water, and that the T2 dynamics of intra-liposomal water are predictable and dependent on the percent of water encapsulated. These techniques to distinguish between water molecules based on their current physical circumstances lead to many novel possibilities in MRI, as nearly all the signal in conventional MRI is from water protons. Based on the signal to noise ratio in the aforementioned iDQC experiments, we predict that iDQC contrast from liposomes will be visible in vivo, and propose to prove this in a murine model. By examining intra-liposomal water, iDQC can be used to improve chemotherapy delivery via real time monitoring of liposome location and drug release.</p> / Thesis

Dans les année récentes, les systèmes d'atomes froids ont été reconnus comme des outils prometteurs pour réaliser des simulateurs quantiques, ainsi que pour différentes applications en information quantique. Parmi eux notamment la jonction Josephson bosonique, un système de bosons ultrafroids dilués pouvant occuper deux modes, a été employée pour réaliser un interféromètre atomique, qui a permi d'estimer un déphasage avec une précision dépassant la limite classique. Dans cette thèse, nous étudions d'un point de vue théorique la production, la détection et la décohérence d'états intriqués qui peuvent être utilisés pour l'interférométrie de haute précision dans une jonction Josephson bosonique. Parmi ces états quantiques utiles se trouvent les états comprimés et les superpositions macroscopiques d'états cohérents. Dans la première du manuscrit, nous démontrons que les superpositions macroscopiques d'états cohérents peuvent être créées pendant la dynamique qui suit un arrêt soudain du couplage entre les deux modes de la jonction, puis nous étudions des protocoles de détection expérimentale. Il existe inévitablement dans chaque expérience des sources de bruit, les principaux étant le bruit de phase, induit par des fluctuations des énergies des deux modes, et la perte d'atomes. La présence de bruit induit de la décohérence et dégrade les corrélations quantiques des états manipulés. Dans la deuxième partie du manuscrit nous analysons en détail la façon dont les corrélations quantiques utiles des états comprimés et des superpositions macroscopiques sont dégradées par le bruit de phase. Nous montrons que, pour des intensités de bruit modérées, les superpositions d'états cohérents à plusieurs composantes sont des candidats intéressantes pour l'interférométrie de précision. Enfin, nous étudions l'effet de la perte d'atomes sur la formation des superpositions macroscopiques, en montrant comment la décohérence agit sur la matrice densité du système / In recent years, cold atomic systems have been recognized as very promising tools for quantum simulators and for applications in quantum technology. In particular, a Bose Josephson junction (BJJ) - a system of ultracold dilute bosons which can occupy two modes - has been used to realize an atomic interferometer, allowing to estimate a phase shift with a precision beyond the classical limit. In this thesis we study theoretically the production, detection and decoherence of entangled states which can be used for high-precision interferometry in a Bose Josephson junction. Among such useful quantum states are atomic squeezed states and macroscopic superpositions of coherent states. In the first part of the thesis, after demonstrating that macroscopic superpositions of coherent states can be created during the dynamics following a "quench" of the coupling between the two modes of the junction, we study protocols for their experimental detection. In the experiments there are unavoidable sources of noise, the major sources being phase noise, induced by stochastic fluctuations of the energies of the two modes of the BJJ, and particle losses. The presence of noise induces decoherence and degrades the quantum correlations of these states. In the second part of the thesis we analyze in detail how the useful quantum correlations of squeezed states and macroscopic superpositions are degraded by phase noise. We show that for moderate phase noise intensities multicomponent superpositions of coherent states are interesting candidates for high-precision atom interferometry. Finally, we address the effect of atom losses on the formation of macroscopic superpositions, showing how decoherence affects the system density matrix.

Disertacijos santraukoje reziumuojamas sužadinimo energijos pernašos eksitoniniame dimere tyrimas. Nagrinėjamas kvantinio koherentiškumo vaidmuo energijos pernašos procesų hierarchijoje: virpesinėje relaksacijoje, sužadinimo pernašoje vieneksitoninėje juostoje bei relaksacijoje į pagrindinę būseną. Glaustai aprašomas naujas metodas, išplėtotas koherentiniams efektams silpnos rezonansinės sąveikos riboje aprašyti. Pristatomas eksitoninio dimero tyrimas įvariuose sistemos ir termostato sąveikos režimuose, kuomet stebima tiek koherentinė, tiek nekoherentinė sužadinimo evoliucija. Nustatyta, jog esant skirtingoms chromoforų reorganizacijos energijoms ir stipriam eksitoniniam maišymuisi, eksitoninių būsenų potencinės energijos paviršių minimumai gali susikeisti vietomis lygininat su nesąveikaujančių chromoforų minimumais. Pristatomas relaksacijos į pagrindinę būseną eksitoniniame dimere tyrimas, kuris atskleidė, jog rezonansinė sąveika ir būsenų energijų skirtumas daugiausia turi įtakos procesų spartai, bet ne pobūdžiui. Darbe paaiškintas disipacijos mechanizmas sintetinėse karotenoido-ftalocianino diadose; gauti rezultatai naudingi aiškinant apsauginį fotosintezės mechanizmą, vadinamą nefotocheminiu gesimu. / The summary of doctoral dissertation presents the investigation of excitation energy transfer, studied in an excitonic dimer under various conditions of inter-chromophore resonance interaction and in different regimes of the system-bath coupling. The manifestation of quantum coherence in the energy transfer in molecular dimer is considered within the hierarchy of the relaxation processes: vibrational relaxation, energy redistribution within single exciton manifold and relaxation to the ground state. A new method to capture the coherence effects in the limit of weak resonance interaction is presented. The study of an excitonic heterodimer under various system-bath coupling conditions, which revealed both coherent and incoherent excitation evolutions, is summarized. An outline of the study of the relaxation of the excitonic dimer to the ground state is given, which revealed that the resonance coupling strength and the energy gap between the states control the rate of the process but not the character. The dissipation mechanism in the artificial carotenoid-pthalocyanine dyads is explained, and the results may be helpful in determining the mechanism of energy dissipation during photosynthesis, known as the non-photochemical quenching.

In the dissertation, excitation energy transfer was studied in an excitonic dimer under various conditions of inter-chromophore resonance interaction and in different regimes of the system-bath coupling. We examine the manifestation of quantum coherence in the energy transfer in molecular dimer, within the hierarchy of the relaxation processes: vibrational relaxation, energy redistribution within single exciton manifold and relaxation to the ground state. In order to capture the coherence effects in the limit of weak resonance interaction a novel technique has been presented. We are able to reproduce the coherence effects in the simulation of static and dynamic spectroscopic experiments. The study of an excitonic heterodimer under various system-bath coupling conditions revealed both coherent and incoherent excitation evolutions. In the situation of different reorganization energies, in the case of strong excitonic mixing, the vibrationally relaxed excited state energy levels may become swapped with respect to the monomeric counterparts. The study of the relaxation of the excitonic dimer to the ground state revealed that the resonant coupling strength and the energy gap between the states control the rate of the process but not the character. We have explained the dissipation mechanism in the artificial carotenoid-pthalocyanine dyads, and the results may be helpful in determining the mechanism of energy dissipation during photosynthesis, known as the non-photochemical... [to full text] / Šioje disertacijoje nagrinėjama sužadinimo energijos pernaša eksitoniniame dimere, esant įvairaus stiprio rezonansinei sąveikai tarp chromoforų skirtinguose sistemos ir termostato sąveikos režimuose. Nagrinėjamas kvantinio koherentiškumo vaidmuo energijos pernašos procesų hierarchijoje: virpesinėje relaksacijoje, sužadinimo pernašoje vieneksitoninėje juostoje bei relaksacijoje į pagrindinę būseną. Koherentiniams efektams silpnose rezonansinės sąveikos riboje aprašyti buvo išplėtotas naujas metodas. Juo remiantis modeliuojami koherentiškumo nulemti efektai statinės ir dinaminės spektroskopijos eksperimentuose. Tiriant eksitoninį dimerą įvariuose sistemos ir termostato sąveikos režimuose stebima tiek koherentinė, tiek nekoherentinė sužadinimo evoliucija. Nustatyta, jog esant skirtingoms chromoforų reorganizacijos energijoms ir stipriam eksitoniniam maišymuisi, eksitoninių būsenų potencinės energijos paviršių minimumai gali susikeisti vietomis lygininat su nesąveikaujančių chromoforų minimumais. Relaksacijos į pagrindinę būseną eksitoniniame dimere tyrimas atskleidė, jog rezonansinė sąveika ir būsenų energijų skirtumas daugiausia turi įtakos procesų spartai, bet ne pobūdžiui. Darbe paaiškintas disipacijos mechanizmas sintetinėse karotenoido-ftalocianino diadose; gauti rezultatai naudingi aiškinant apsauginį fotosintezės mechanizmą, vadinamą nefotocheminiu gesimu.

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