The aim of this thesis is to reconsider energy extraction from black hole magnetospheres, and more specifically the Blandford-Znajek (BZ) process from an effective field theory (EFT) perspective. Superradiant instabilities of scalar and vector bound states in the presence of a rotating black hole will be reviewed when the inverse mass of the black hole is much smaller than the Compton wavelength of the bound state particle. Two different matching calculations will be described for the vector bound state case and the overall decay rate will be compared. Force-free electrodynamics will be motivated and discussed in the context of the BZ process. Using a perturbation expansion, the Blandford-Znajek process will be reviewed up to second order in the rotation parameter. The absolute-space/universal-time (3+1) viewpoint will be discussed and applied to the BZ process and an EFT-like description will be discussed when the black hole horizon is parametrically small. Using differential forms, a simplified framework for the BZ process will be introduced in the (3+1) formalism and the field strength F will be simplified in the slow-rotation limit up to first-order in the rotation parameter. Finally, the Blandford-Znajek process will be considered as a superradiant process in the massive vector limit and the total energy flux in this (new) regime will be compared to the known BZ energy flux. / Graduate

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 171-178). Also available for download via the World Wide Web; free to University of Oregon users.

Hybridization of quantum emitters and plasmonic nanostructures has attracted much attention over the last years, due to their potential use as plasmon-based nanolasersor to achieve long-range quantum bit entanglement. Recent theoretical studies suggest that the plasmonic field can induce efficient cross-talking between emitters and lead to the formation of collective superradiant states. In this thesis, we developed a theoretical modelable to analyse collective effects in large ensemble of dipoles coupled by an electromagnetic nanoresonator. We experimentally investigated the plasmon-mediated superradiance of organic emitters grafted at a well-controlled distance from a metal nanosphere at room temperature. We report on the measured decay rates of these hybrid structures at the ensemble and single object levels. We find that the decay rate increases i) with the number ofemitters and ii) as the spacing between the emitters and the metal core decreases, a direct and clear evidence of plasmonic superradiance. This trend was observed for two types of hybrid structures, differing both by the size of the metal core and the type of organic dye used as emitter. The observation of plasmonic superradiance at room temperature opens questions about the robustness of these collective states against decoherence mechanisms.This robustness is of major interest for potential applications of quantum systems at room temperature. / Placer des nanostructures plasmoniques à proximité d’émetteurs quantiques est une approche prometteuse pour concevoir des nanolasers plasmoniques ou réaliser l’intrication de bits quantiques à longue distance. Des études théoriques récentes suggèrent que le champ plasmonique peut induire un couplage efficace entre émetteurs et mener à la formationd’états collectifs superradiants. Dans ce travail de thèse, nous avons développé un modèle théorique afin d’analyser les effets collectifs pour un ensemble de dipoles couplés à un nanorésonateur électromagnétique. Nous avons étudié expérimentalement la superradiance plasmonique d’émetteurs organiques greffés à une distance contrôlée d’une nanosphère metallique,à température ambiante. Nous avons mesuré le taux de relaxation de ces structures hybrides, en ensemble et à l’échelle de l’objet unique. Nous observons que le taux de relaxation augmente i) avec le nombre d’émetteurs et ii) lorsque la distance entre les émetteurs et le coeur métallique diminue, une preuve directe et claire de la superradiance plasmonique.Cette tendance a été observée pour deux types de structure hybride, différentes par la taille du coeur métallique et par le type de molécule utilisée comme émetteur. L’observation de la superradiance plasmonique à température ambiante ouvre des questions sur la robustesse d’un état superradiant contre des mécanismes de décohérence. Cette robustesse présente un intérêt majeur pour des applications potentielles de systèmes quantiques à température ambiante.

Laser techniques, such as gain / Q switching, mode-locking, have successfully overcome the energy restriction of gain clamping in the stead-state operated lasers, and allowed the generation of giant pulses with short pulse durations. However, gain saturation further limits the amount of stored energy in a gain medium, and therefore limits the possible maximum pulse energy obtained by laser techniques. Here we circumvent both gain clamping and the capacity limitation of energy storage by operating the double-quantum-well laser diode chips on ultrafast gain-switching model using femtosecond (fs) laser pulses as the optical pump. The advantage of our pumping approach is that the fs pulse can instantly produce a very large number of carriers, and therefore enable the formation of non-equilibrium coherent e-h BCS-like condensate state in a large energy region from the lowest QW subband edges to the highest subband and then obtain the ultra-broadband superrandiant pulses. / Superradiance (SR) or the coherent spontaneous emission is not a new quantum optics phenomenon, which has been proposed in 1954 by R. Dicke, even earlier than the invention of laser. It is famous as by its ultrashort duration, high peak power, high coherence and high timing jitter. Recently, femtosecond SR pulses have been generated from semiconductors. This investigation has revived both theoretical and experimental studies of SR emission. / In this thesis, we have demonstrated the generation of intense, delayed SR pulses from the InP based double quantum well laser diode at room temperature. The 1040 nm femtosecond laser was applied as the optical pumping source, and when the pump power is high enough, the cooperative recombination of e-h pairs from higher order quantum energy levels can occur to generate SR bursts earlier than the cooperative emission from the lower quantum energy levels. Then, ultra-broadband TM polarized SR pulses have been firstly generated at room temperature. Our experiments also provide a well prospect of ultra-high energy light pulse generation based on SR, besides, the ultra-broadband spectrum is promising for applications in a diverse range of fields, including optical coherent tomography and spectroscopy. / Graphene, a truly 2D material, has stimulated a vast amount of research in recent years. In our work, we have wet transferred the CVD grown monolayer graphene onto the top of our LD chips. With the combination of graphene on top of QW LD, the evanescent field of TM polarized modes can well interact with top graphene layer, and therefore, produce a dramatically modulation of the output power, and optical spectra of output pulses. The graphene-on-DQW LD will be promising to explore the novel devices, such as optical modulator, which will greatly promote the applications of SR emission in near future. / 激光技術，諸如增益 / Q調製，鎖模，已經成功克服了穩態激光器存在的增益箝制現象，從而產生了脈寬窄，峰值功率高的巨脈衝。然而，增益飽和現象又進一步限制了增益介質的儲能上限，因而設定了激光技術產生的脈衝的能量上限。在這裡，我們以飛秒激光為光泵,使量子阱激光器工作在超快增益調製模式, 從而有效地規避了增益箝制和儲能限制。这种泵浦方式的优势在于可以瞬间产生极大量的载流子，從而可以在一个很宽的能带区间内（从量子阱的最低能级到最高能级）形成非平衡相干类BCS状态的电子空穴对的凝聚态，从而产生宽频超辐射。 / 超輻射（SR），或稱為相干的自發輻射並非是一個新的量子光學現象，早在1954年就被由R. Dicke提出了，比發明激光器還早。SR以它脈衝時間短，峰值功率高，相干性好，以及脈衝定時抖動高等特點而聞名。近來，不同的研究組報導了他們用半導體材料產生了SR, 復興了理論和實驗雙方面對SR的研究。 / 在這篇論文中，我們論證了如何用飛秒激光泵浦雙量子阱激光二極管產生高功率帶有延時的超辐射脈衝。當泵功率足夠高時，高量子能級的電子空穴對先於低能級的電子空穴對發生超輻射，從而第一次在室溫下得到了超寬頻譜的超輻射脈衝。此外，我們證明了超輻射光是TM偏振的。根據我們的結果可以預測關於SR的超高能量脈衝的研究以及相关应用具有光明的發展前景，比如，SR可用於包括光學相干斷層成像和光譜學等的各種各樣的先進領域。 / 石墨烯，真正的2D材料，近年來激發了巨大的研究熱潮。我們用濕法轉移的方法將化學氣相沉積生長的單層石墨烯鋪到我們的樣品表面。這使TM偏振模式的漸逝場能很好地與石墨烯層作用，因此，顯著調製SR脈衝的功率和頻譜。石墨烯與多量子阱激光二極管的結合將大大推動了新型器件的研究，如光調製器等，這將大大改善SR的應用前景。 / Liu, Jingjing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2015. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 21, December, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Cooperative effect in the radiation process has been studied in for more than half a century. It is important in the sense of both basic physics and applied science. In this work, we study the dynamics of the cooperative spontaneous emission from an ensemble of N atoms which is uniformly excited by absorbing a single photon. We reveal that there are two different regimes in which the system exhibits totally different behaviors. One of them is the superradiance type of behavior: the system decays much quicker than single atom decay, with a decay rate proportional to N(λ/R)2, where N is the atom numbers, R is the size of the atom cloud, and λ is the wavelength. We call it Markovian regime because the sytem does not persist memory effect. The other regime is called non-Markovian regime and the system oscillates with effective Rabi oscillation frequency while slowly decaying with a rate proportional to the photon escaping rate. The effective Rabi oscillation is a new type of dynamics which analogs well known Cavity QED behavior. Particularly in the Markovian regime, we study the system dynamics as a manybody eigenfunction and eigenvalue problem. For a dense cloud, we find analytical solutions for the eigenstates and corresponding eigenvalues, which can help to generally describe the system dynamics for any initial conditions in this regime. One of the applications is in atom microscopy. We propose a scheme to measure the distance between two atoms/molecules beyond diffraction limit. It covers the whole range from half the wavelength to sub-nanometers, utilizing both the atom localization technique and the collective frequency shift effect due to the cooperative effect in the radiation of the two atoms. Another application that we propose is to generate Coherent XUV radiation using Raman-type superradaince. We prove that intense short pulses of XUV radiation can be produced by Raman type superradiance from an ensemble of atoms/ions driven by visible or IR laser pulses.

Cooperative effects in many-particle systems can be exploited to achieve measurement outcomes not possible with independent probe particles. We explore two measurement applications based on the cooperative phenomenon of superradiance or on correlated quantum states closely related to superradiance. In the first application we study the off-resonant superradiant Raman scattering of light from an ultracold Bose atomic vapor. We investigate the temperature dependence of superradiance for a trapped vapor and show that in the regime where superradiance occurs on a timescale comparable to a trap frequency, scattering takes place preferentially from atoms in the lowest trap levels due to Doppler dephasing. As a consequence, below the critical temperature for Bose condensation, absorption images of transmitted light serve as a direct probe of the condensed state. Subsequently, we consider a pure condensate and study the time-dependent spatial features of transmitted light, obtaining good qualitative agreement with recent imaging experiments. Inclusion of quantum fluctuations in the initial stages of the superradiant emission accounts well for shot-to-shot fluctuations. Secondly, we have used simulated annealing, a global optimization strategy, to systematically search for correlated quantum interferometer input states that approach the Heisenberg limited uncertainty in estimates of the interferometer phase shift. That limit improves over the standard quantum limit to the phase sensitivity of interferometric measurements by a factor of 1√N, where N is the number of interfering particles. We compare the performance of these states to that of other non-classical states already known to yield Heisenberg limited uncertainty.

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Optical precursor is the sharp optical pulse front that does not show delay in absorptive media. In this thesis, optical precursor behavior in rubidium (Rb) vapor was investigated in the picoseconds regime. An amplified femtosecond laser was shaped to a 7-ps square pulse with sharp rising and trailing edges. This pulse was then sent into a hot rubidium vapor, and the center frequency of the laser pulse was absorbed. The output pulses were measured by a fast streak camera with 2-picosecond resolution. By varying the temperature of the Rb vapor, the measured pulse shapes showed the progression of formation of optical precursors. The measured pulses shapes showed good agreement with theory. On the other hand, a connection between optical precursors and femtosecond laser pumped 3-photon superradiance was investigated in this thesis. Maxwell-Bloch equations were numerically solved in two steps with commercial software Mathematica 8. A good agreement was found between simulation and experiment. It was confirmed that, at low excitation regime, superradiance generated from hot rubidium vapor, which were pumped by a femtosecond laser, can be understood as the formation of optical precursors.

We show the scattering of electromagnetic radiation on a rotating cylinder and a rotating sphere using formalism of the vector spherical harmonics in this thesis. If a specific condition is satisfied then we can observe the rotational superradiance, phenomena originally discovered by Y. B. Zel'dovich in 1970s saying that the radiation can gain power by scattering on a rotating body. In this particular case there is an underlying principle of the rotational superradiance, the energy dissipation in the form of Joule heating created due to the induction of surface currents on the conductor. Superradiance can occur in the radiation scattering on the rotating black hole background, although there is no dissipation present. We summarize the results of scattering on the Kerr black hole from the literature, including an application called Black hole bomb, when the black hole is enclosed into a perfectly reflecting mirror. We show that for the lowest modes of the radiation at specific intervals the general relativity results can be approximated by scattering on the flat spacetime.