Collective quantum mechanical phenomena such as superfluidity and superconductivity are observed for particles at a high density and low temperature. These collective effects can also take place in optically manipulated materials through a precise control of light-matter interactions. The most successful example is the creation of ultra cold atomic gas prepared by laser cooling and evaporation cooling. Various quantum mechanical phenomena including Bose-Einstein condensation and paring of Fermionic atoms have been extensively studied. The rapid development of ultra cold atom quantum physics stimulates other fields including the study of excitons in semiconductors. Several new experimental results triggered a growing interest to revisit many body phenomena of excitonic particles, BEC of excitons in two-dimensional coupled quantum wells, condensation of cavity polaritons in semiconductor microcavities and exciton BEC in bulk semiconductors. Other new aspects of such quantum degenerate excitonic particles are their potential for manipulating and controlling the quantum coherence of photons, which is a key technique for quantum information technology. Phase-preserving control of photons is possible by the formation of “dark states”, i.e. optically inactive states with a long-lived phase coherence of excitonic particles. Highly quantum degenerate excitonic particles, such as ensemble of ultracold biexcitons and spin-flipped excitons, could be potential candidate for the media for coherence storage. In these lecture notes, we present recent experiments on the creation and detection of high-density and cold excitonic particles into a highly quantum degenerate regime with precise control of optical excitation. We discuss new experimental aspects regarding coherence storage and observation of collective quantum phenomena in semiconductors. We also discuss the prospects of spontaneous Bose Einstein condensation of excitons in a bulk crystal of Cu₂O.