This chapter attempts to give a review of the main concepts and principal experimental results on semiconductor microcavities in the strong coupling regime. Atomic single-mode interactions in the strong coupling regime were first achieved using Rydberg transitions in the microwave region of the spectrum, and more recently have been achieved using optical transitions. The assumption that the absorption spectrum in bare quantum wells is coincident with the energy distribution of the excitons amounts to an assumption that the excitonic states are localised. The chapter reviews the basic-quantum mechanical model for two-level atoms in a single-mode cavity and its relation to classical linear dispersion theory. Tests of fundamental issues in quantum optics such as quantum measurement theory become possible when the coupled atom-cavity system is in the strong coupling regime and the average number of atoms in the cavity is one.
This chapter attempts to give a review of the main concepts and principal experimental results on semiconductor microcavities in the strong coupling regime. Atomic single-mode interactions in the strong coupling regime were first achieved using Rydberg transitions in the microwave region of the spectrum, and more recently have been achieved using optical transitions. The assumption that the absorption spectrum in bare quantum wells is coincident with the energy distribution of the excitons amounts to an assumption that the excitonic states are localised. The chapter reviews the basic-quantum mechanical model for two-level atoms in a single-mode cavity and its relation to classical linear dispersion theory. Tests of fundamental issues in quantum optics such as quantum measurement theory become possible when the coupled atom-cavity system is in the strong coupling regime and the average number of atoms in the cavity is one.
Nonlinear optical phenomena in both semiconductor microcavities and sodium vapor are investigated. Systems displaying atomic and excitonic coupling are studied in detail in order to unravel underlying physical principles. Possible applications for these systems are evaluated where appropriate. Normal-mode coupling (NMC) in a semiconductor microcavity is achieved when a narrow-linewidth quantum well exciton resonance is coincident with the cavity mode of a high-finesse microcavity. This interaction leads to a double-peaked spectrum in either transmission, reflection, or photoluminescence (PL). The high-quality microcavities studied here at liquid-Helium temperatures reveal intensity dependent behavior that has not previously been observed. Nonlinear saturation of the exciton leads to a spectral broadening of the excitonic absorption without a significant loss in oscillator strength. This results in a reduction of the two transmission peaks with almost no change in the splitting between the peaks. Such behavior is easily explained using phenomenological nonlinear dispersion theory. In this nonlinear regime, the luminescence from the microcavity shows a gradual transition from the nonperturbative regime of NMC to lasing with increasing excitation. The observed behavior is explained by density-dependent changes in both the transmission of the microcavity and the bare-exciton emission, rather than a boson-condensation of excitons which has been previously proposed. An intermediate-finesse microcavity also modifies the emission distribution from a bulk-semiconductor at room temperature. Angularly resolved emission spectra and quantum efficiency measurements show the PL is strongly dependent on the reflectivity of the microcavity. Unfortunately, the enhancement in the decay rate of excitons due to high-reflectivity mirrors seen previously by our group does not result in an increased quantum efficiency. High-gain optical-wavefront amplification in atomic sodium vapor is demonstrated via both the three-photon effect and stimulated Raman scattering (SRS). In both cases, single-pass weak-field gain of nearly 400 is achieved with only 800 mW of pump power near 589 nm. In the case of SRS, phase preservation of the amplified wavefront, which is necessary in adaptive imaging applications, is also demonstrated.
Semiconductor quantum microcavities are interesting physical systems in which fundamental interactions between light and excitons can be explored. For example, in the weak - coupling limit, modified excitonic spontaneous emission can be observed. In the strong-coupling limit, the cavity field modes and the quantum well exciton modes become coupled; the normal modes of the system are "cavity-polaritons" [1,2]. For in-plane wavevectors k// near zero, the normal modes are split by the dipole coupling between the excitons and the cavity vacuum field. This splitting is often referred to as a vacuum-Rabi splitting (VRS), as it has the same physical origin as the VRS observed in the interactions of atoms with single-mode cavities. The physical system in this work consists of a λ planar microcavity formed by two distributed-Bragg reflectors, with five GaAs quantum wells situated in the center of the cavity. In all the experiments described here, the exciton and cavity modes are on resonance (the low-field VRS is 6 meV for this sample).
Light and matter can be unified under the strong coupling regime, creating superpositions of both, called dressed states or polaritons. After initially being demonstrated in bulk semiconductors and atomic systems ,strong coupling phenomena have been realized in solid state optical microcavities. They form an essential ingredient in the exciting physics spanning from many-body quantum coherence phenomena, like Bose-Einstein condensation and superfluidity, to cavity quantum electrodynamics (cQED). A widely used approach within cQED is the Jaynes-Cummings (JC) model that describes the interaction of a single fermionic two-level system with a single bosonic photon mode. For a photon number larger than one, known as quantum strong coupling (QSC), a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures, first signatures of the quantum strong coupling were recently published. In our latest report we applied advanced coherent nonlinear spectroscopy to explore a strongly coupled exciton-cavity system. Specifically, we measured and simulated its four-wave mixing (FWM) response, granting direct access to the first two rungs of the JC ladder. This paper summarizes the main results of Ref. 15 and adds FWM experiments obtained on a micropillar cavity in which a doublet of quantum dot (QD) excitons interacts with the cavity mode in the limit of weak to strong coupling.
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.
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 optical emission spectrum of a quantum dot in strong coupling with the single mode of a microcavity is obtained in the nonlinear regime. We study how exciton-exciton interactions alter the emission spectrum of the system, bringing the linear Rabi doublet into a multiplet structure that is strongly dependent on the cavity-exciton energy detuning. We emphasize how nonlinearity can be used to evidence the genuine quantum nature of the coupling by producing satellites peaks of the Rabi doublet that originate from the quantized energy levels of the interactions.