This work focuses on the many-body properties of semiconductor nanostructures for quantum engineering of infrared optoelectronic devices. In particular, we theoretically investigate the optical response accounting for collective effects in systems of tunnel-coupled quantum wells. A clear manifestation of these effects appears in the optical spectrum of highly doped quantum wells, where the absorption peaks are at completely different energies with respect to the single-particle electronic transitions. We calculate light-matter interaction in two steps. First, we consider the microscopic polarization associated with the electronic transitions between confined levels of the wells, which are all coupled by dipole-dipole Coulomb interaction. Then we calculate the interaction of the resulting collective states with the electromagnetic field. The absorption spectrum is finally expressed in terms of microscopic currents, describing the collective charge oscillations. The theoretical model is applied to a series of relevant systems, and its outcomes are compared with experimental results. As the collective states are issued from the coherent superposition of several electronic excitations, they have the properties of superradiant states. They are thus a promising entity for the realization of efficient light emitters in the mid- and far-infrared frequency range.
This work focuses on the many-body properties of semiconductor nanostructures for quantum engineering of infrared optoelectronic devices. In particular, we theoretically investigate the optical response accounting for collective effects in systems of tunnel-coupled quantum wells. A clear manifestation of these effects appears in the optical spectrum of highly doped quantum wells, where the absorption peaks are at completely different energies with respect to the single-particle electronic transitions. We calculate light-matter interaction in two steps. First, we consider the microscopic polarization associated with the electronic transitions between confined levels of the wells, which are all coupled by dipole-dipole Coulomb interaction. Then we calculate the interaction of the resulting collective states with the electromagnetic field. The absorption spectrum is finally expressed in terms of microscopic currents, describing the collective charge oscillations. The theoretical model is applied to a series of relevant systems, and its outcomes are compared with experimental results. As the collective states are issued from the coherent superposition of several electronic excitations, they have the properties of superradiant states. They are thus a promising entity for the realization of efficient light emitters in the mid- and far-infrared frequency range.
Nanotechnologically fabricated structures out of compound semiconductor materials make up the functional parts in LEDs, in semiconductor lasers and in electronics components. The small size of the structures evidently leads to requiring the modeling to look at phenomena at the quantum level. Especially for optoelectronical devices, one needs to treat the interaction between light and semiconductor material. This research adds to the understanding of inter-pretations of light-matter interaction phenomena and makes it possible to find totally new and undiscovered functionalities in semiconductor nanostructures. \nThis thesis presents work on modeling and creates new theoretical foundations for phenom-ena appearing in semiconductor quantum structures. Of special interest has been to generate a theoretical description to such phenomena that have been caused by an optical field and in which one sees changes, e.g., in angular momentum or spatial distribution of excited states. Basically, two kinds of structures are examined, quantum rings and wells. A quantum ring is a toroidal object of which volume is very small, but its diameter can be significant when com-pared to the wavelength of light. Another class of systems under study is a double quantum well structure, where there are two quantum wells on both sides of a tunnel barrier. In this system, the type-I and type-II semiconductor band-structure properties become combined in spatial coordinates, since the electrons and holes can occupy either the same or the separate quantum wells. \nThe two most interesting results are the angle-of-emission dependent photoluminescence from the quantum rings and the coherent control of vertical transport of desired quasiparticles through material interfaces in the quantum-well system in a selective manner. Since the ob-tained results on quantum rings are closely connected to the orbital-angular-momentum coupling between light and matter, they can prove to be important in different quantum infor-mation schemes where this angular-momentum aspect of light has been found to be highly beneficial. In quantum optics, there already are visible trends towards this direction. The predicted coherent control in a double-quantum-well system may mean a large technological progress, since by utilizing this effect one can study transport properties between materials over an interface, one of the most interesting examples of such phenomena being the transfer of quantum correlations through the interface without changing the local densities of electrons.
This dissertation addresses both fundamental aspects of Coulomb correlations in semiconductor quantum wells and more practical aspects of theoretical analysis of semiconductor optoelectronic devices. After introducing the subject, we present and evaluate a state-of-the-art theory of the third order coherent optical response of a semiconductor quantum well based on the Dynamics Controlled Truncation (DCT) scheme. Already in the third order (the so-called chi (3)) regime, semiconductors exhibit a number of many-body Coulomb correlation effects. Their manifestation in various multi-pulse experimental configurations, customarily used in ultrafast semiconductor spectroscopy, has been an important component of this thesis. Coherent optical effects in a semiconductor 3-band system based on the heavy-hole, light-hole and conduction bands were investigated. The quantum beats in the time-integrated differential transmission signal were analyzed and compared with experimental data obtained at the University of Iowa. Fundamental differences from corresponding quantum beats in atomic 3-level systems were found. Also, the analysis of experimental data (obtained at the University of Arizona) of the coupled heavy-hole-light-hole optical Stark shift revealed evidence of intervalence band coherences, an analog of Raman coherences in atomic 3-levels systems. A scheme for realization of electromagnetically-induced transparency (EIT) based on the interference of excitonic and biexcitonic coherences was proposed. Corresponding experiments performed at the University of Oregon showed indeed a considerable coherent reduction of excitonic absorption. Furthermore, an extension of the chi(3) analysis revealed an energy renormalization of the biexciton, in good agreement with the corresponding experiment. A microscopic analysis of polarization dynamics in time-resolved four-wave mixing signals was performed, revealing interesting implications for the biexciton dephasing in addition to the significance of many-body correlations. In the case of four-wave mixing in semiconductor microcavities, our theoretical analysis in conjunction with experimental data obtained at the University of Tokyo gave us indications for a significant shortcoming of the second Born approximation (2nd BA) applied to two-exciton Coulomb correlations in a thin semiconductor quantum well, in agreement with the general knowledge of the qualitative failure of the 2nd BA in systems with short-range interaction in two dimensions. We also analyzed a novel all-optical switching technique based on the nonlinear polarization rotation. Apart from identifying the many-particle processes relevant for the switch operation in the chi(3) regime, we proposed ways to further optimize the switch.
In this paper, exciting progress of quantum optics in solid state is reviewed. The focus is on semiconductor microcavities with self-assembled quantum dots embedded in the active layer. Due to enormous progress in semiconductor nanotechnology, such photonic structures have become a model system for the study of quantum optics on a scalable and integrable technology platform with high potential for future applications in quantum information technology. Quantum optical phenomena have become accessible due to 3-D confinement of light and matter on the length scale of their wavelength in state-of-the-art semiconductor micro- and nanostructures. This confinement leads to a quantization of the associated photonic and electronic energy levels and requires a quantum mechanical description of the system in the framework of cavity quantum electrodynamics (cQED). This approach considers the dipole interaction between two-level quantum emitters and discrete photonic states of a microcavity. Within the well-known Jaynes-Cummings model, the dipole interaction is described in terms of a coherent exchange of energy between the emitter and the resonator mode. This coherent interaction in the so-called strong coupling regime of cQED is reflected in a normal mode splitting, the vacuum Rabi splitting, of the involved modes and represents a central feature of quantum optics in solid state. Another important example of quantum optics in semiconductor nanostructures is the generation of nonclassical light in specific quantum devices. Of particular interest is the realization of Fock states which represent states containing a well-defined number of photons. Single-photon sources, for instance, allow for the generation of single photons on demand, which is highly desirable for quantum communication systems. In this context, this review paper will present recent experimental studies of quantum optics in solid state. This paper is meant for readers who would like to become familiar with this topic and for experts being interested in the progress in this field. It will cover a broad range of studies ranging from examples of fundamental light-matter interaction in the quantum limit to devices capable of emitting single photons and entangled photon pairs on demand.
We theoretically study quantum-optical properties of one- and two-dimensional semiconductor nanostructures, where the electronic band structure is described by a two-band tight-binding model. Since the focus of our work is on analyzing quantum-optical effects of systems with a continuous band structure, many-body processes like electron-electron and electron-phonon interactions are neglected. The quantum-optical interband excitations are fully incorporated and described by a Jaynes-Cummings-type model. The exciting quantum light can be a state with arbitrary photon statistics. For simplicity, the results discussed here are limited to single-photon and two-photon Fock states. Our analytical approach is based on the eigenvalue problem and can be utilized to obtain explicit expressions for the steady-state properties of the system. Numerical simulations are based on solutions of the equations of motion and allow for a more precise analysis of the dynamics and nonresonant excitations of the system. We demonstrate that during the interaction process, a collective excitation of the conduction band is formed. For nonresonant excitations, this collective dynamics results in interesting steady states, in which the resonantly addressed eigenstates are occupied. The presented model provides a framework for microscopic simulations of quantum-optically excited extended semiconductor nanostructures.
We present a microscopic and fully quantized model to investigate the interaction between semiconductor nanostructures and quantum light fields including the many-body Coloumb interaction between photoexcited electrons and holes. Our approach describes the coupled dynamics of the quantum light field and single and double electron-hole pairs, i.e., excitons and biexcitons, and exactly accounts for Coulomb many-body correlations and carrier band dispersions. Using a straightforward yet exact approach, we study a one-dimensional two-band system interacting with a single-mode, two-photon quantum state within a Tavis-Cummings framework. By employing an exact coherent factorization scheme, the computational complexity is reduced significantly enabling numerical simulations. We also derive a simplified model that includes only the bound 1s-exciton and biexciton states for comparison. Our simulations reveal distinct single- and two-photon Rabi oscillations, corresponding to photon-exciton and exciton-biexciton transitions. We demonstrate, in particular, that biexciton continuum states significantly modify the dynamics in a way that cannot be captured by simplified models that consider only bound states. Our findings emphasize the importance of a comprehensive microscopic modeling in order to accurately describe quantum optical phenomena of interacting electronic many-body systems.
Quantum spectroscopy utilizes the quantum fluctuations of the light source to characterize and control matter. More specifically, desired many-body states can be directly excited to the semiconductor by adjusting light source's quantum fluctuations. The method is experimentally realizable by projecting an extensive set of classical measurements into a quantum-optical response resulting from any possible quantum source. In this work, quantum spectroscopy is used to identify new classes of many-body states and quantum processes in semiconductor nanostructures. In the first part of this Thesis, the optical properties of semiconductor quantum wells are analyzed with quantum spectroscopy by projecting high-precision optical measurements into quantum-optical responses. It is shown that quantum spectroscopy can characterize the properties of specific stable electron-hole cluster – called quasiparticles – much more sensitively than traditional ultrafast laser spectroscopy. In particular, unambiguous evidence is demonstrated for the identification of a new highly correlated quasiparticle in direct-gap Galliumarsenide quantum wells, the dropleton, that is a quantum droplet consisting of four-to-seven electron-hole pairs. To determine the detectable excitation energetics of such correlated quasiparticles in optically excited semiconductor quantum wells, a new theoretical framework is presented which allows for the computation of the excitation spectrum based on a pair-correlation function formulation of the quasiparticle state. Another study in this Thesis deals with the emission properties of optically pumped quantum-dot microcavities. Experimental and theoretical evidence is shown for a new intriguing quantum-memory effect that is controllable by adjusting pump source's quantum fluctuations. The last part of this Thesis presents a fundamental study about the general applicability of quantum spectroscopy in dissipative systems.