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.
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.
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.
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.
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.
This dissertation addresses both fundamental aspects of the coherent exciton kinetics in single semiconductor quantum wells and more application-oriented aspects of the collective excitonic optical properties in quantum well Bragg structures. We use a bosonic theory to investigate the ultrafast coherent exciton dynamics after an optical excitation in a single semiconductor quantum well. It is shown that, on intermediate time scales, nonlinear mean-field interactions between excitons lead to a coherent, wave-like evolution in the momentum distribution of optically inactive excitons, which can survive for some time before dephasing sets in. Driven by two-exciton correlations, this coherent quantum kinetic effect bridges the well-known kinetics associated with optical excitation on the one hand and incoherent relaxation on the other. We also study more general dynamical properties of bosonic mean field systems with N-species of excitons (in a single semiconductor quantum well). We find that the momentum-conserving exciton mean field equations, including the coupling to external fields and fermionic corrections, have the dynamical structure su(N,N). We show that one can define a non-real generalized "Bloch vector" and a non-hermitian "density matrix" description, which allow us to explicitly obtain all the constants of motion associated with the su(N,N) symmetry. The many-body effects and correlations of excitons in a single quantum well are mainly induced by the Coulomb interactions. In the case of a semiconductor quantum well Bragg structure, the light induced coupling between different quantum wells also dramatically affects the excitons' behavior, especially through the collective excitations of excitons in the whole structure. We investigate the linear excitonic optical properties of the quantum well Bragg structure induced by the collective excitations using the transfer matrix approach. We show that the so called "intermediate band" (IB) created by the exciton resonance, which does not exist in conventional photonic crystals, can be used for the stopping, storing and releasing of light, which is important in information processing devices. We also discuss the compensation of the dispersive distortion in the light delay process through reversing the IB band structure. Other conceptual and practical issues such as the decay rate of the IB modes and the generalized anti-reflection coating are also investigated.
The optically generated excitations in semiconductors constitute a genuine many-body system. To describe its quantum-optical features, we have to expand significantly the theoretical models used so far. However, the important insights of Chapters 16–23 are already presented in a form in which most of them can directly be used and generalized to analyze central properties of the optical excitations in solids. As for atoms, the optical transitions in semiconductors are induced via dipole interaction between photons and electrons. We can thus efficiently construct a systematic quantum-optical theory for semiconductors by following the cluster-expansion approach. One of the main differences from atoms is that the electronic excitations in semiconductors form a strongly interacting many-body system. Thus, we must systematically treat the arising Coulomb-induced hierarchy problem together with the quantum-optical one. Moreover, the coupling of electrons to lattice vibrations, i.e., the phonons, produces yet another hierarchy problem. In addition, in solid-state spectroscopy one often uses multimode light fields such that one cannot rely on the single-mode simplifications to study semiconductor quantum optics. As shown in Chapter 15, the Coulomb-, phonon-, and photon-induced hierarchy problems have formally an identical structure. Thus, we start the analysis by investigating how semiconductor quantum optics emerges from the dynamics of correlated clusters. We first focus on the basic properties of the optical transitions in the classical regime. This means investigating the fundamental optical phenomena resulting from the singlets. The full singlet–doublet approach is presented in Chapters 28–30.
The emerging field of semiconductor quantum optics combines semiconductor physics and quantum optics, with the aim of developing quantum devices with unprecedented performance. In this book researchers and graduate students alike will reach a new level of understanding to begin conducting state-of-the-art investigations. The book combines theoretical methods from quantum optics and solid-state physics to give a consistent microscopic description of light-matter- and many-body-interaction effects in low-dimensional semiconductor nanostructures. It develops the systematic theory needed to treat semiconductor quantum-optical effects, such as strong light-matter coupling, light-matter entanglement, squeezing, as well as quantum-optical semiconductor spectroscopy. Detailed derivations of key equations help readers learn the techniques and nearly 300 exercises help test their understanding of the materials covered. The book is accompanied by a website hosted by the authors, containing further discussions on topical issues, latest trends and publications on the field. The link can be found at www.cambridge.org/9780521875097.