Quantum dots (QDs) are one of the first nanotechnologies to be integrated into the designing of pharmaceutical and biomedical instruments. This book starts by reviewing their structure, quantum confinement effects, band-gap characteristics and applications to the various branches in nanotechnology (e.g. bioimaging, solar cells, light emitting diodes [1] ). Fabrication methods of QDs are also included in this review, in particular, the droplet epitaxial method [2]. In the case of bulk materials, the energy band-gap is fixed by the choice of material. However, QDs are a special class of semiconductors, they can be regarded as an artificial molecule with a band-gap dependent on its size. The usage of QDs as an attempt to replace bulk materials (e.g. silicon and copper indium gallium selenide) in solar cells is discussed in some detail [3]. QDs size-dependent bandgap allows the fabrication of nanostructured or multi-junction solar cells and, therefore, a variety of materials can be used to improve efficiency by harvesting multiple portions of the solar spectrum. Experiments have demonstrated that, due to unique optical traits within luminescence characteristics and electronic properties, QDs possess multiple potential applications, such as labeling and tracking single biomolecules and cells in real time, in vitro as well as in vivo; assessing cell growth in damaged tissue; pH probes for the study of enzyme reaction kinetics; imaging and sensing of infectious diseases; as well as the detection of cancer biomarkers [4, 5]. A discussion about the toxicity of QDs applications to nanosize drug delivery systems is also discussed [6]. Next, this book overviews of the recent advances in quantum sensors. A technique of filtering a single molecule with an atomic vapor notch results in an improvement of about 15% in a confocal and in a wide-field configuration. This can potentially enhance DNA detection efficiency, better sensing and localization accuracies in material science and applications in microbiology. [7]. The combination of a low milliamperes X-ray source and a microlens-based sensor may potentially reduce dose exposure without compromising the resolution of dental digital images [8]. Ultra-stable quantum cascade lasers can be integrated into a real-time, nanometric displacement sensor with a resolution on the order of ?/1000 [9]. A spectroscopy method combining the use of entangled photon pairs and plasmonic nanoparticle arrays with Fano resonance have been shown to be robust, even in excessively noisy conditions, when compared with conventional broadband transmission spectroscopy [10]. The second part of this book, overviews physics and the technological advances in infrared [11, 12] optical [13] photodetectors based on the quantum tunneling as well as the wide-range of applications these detectors possess: e.g. navigation, night vision, weapons detection, communications, aerospace, medical imaging, atmospheric sounding, pollution control, meteorology, environmental monitoring, astronomy, etc. Last but not the least, the book focuses on the quantum information processing. Magnetic tunnel junction (MJC) have the potential of becoming the basic component of random access memory, logic circuits in quantum computing [15]. MTJ based nanomagnet arrays can offer a highly tunable system with an electrical I/O for logic and sensing applications, including two or three-dimensional field sensing [16]. The efficient detection of single photons are also crucial for quantum information processing. Superconducting nanowire single-photon detectors at a wavelength of 940 nm showed high detection efficiencies (~60%) and fast recovery times (?12 ns) promising a great future for quantum computing [17]. Nitrogen-vacancy centers in diamond are revealed to be a good candidate for solid-state quantum information processing due to their long coherence time and high feasibility in initialization, control, and readout of their spin states. To realize quantum computation, the effects of interactions between qubits and their environment must be minimized, the weak spin-orbit coupling and largely eliminated hyperfine interaction in graphene provides the solution to building highly controllable systems [18]. Finally, the use of Silicon carbide as an alternative material to host deep optically active defects is also suitable for optical and spin quantum bits [19].