This chapter aims to illustrate how quantum theory provides useful technological solutions – applications that may be more integrated in our everyday lives than we tend to think. Some applications lend themselves to a particularly straightforward outline through examples already seen in the preceding chapters. These include scanning tunnelling microscopy and emission spectroscopy, which utilize tunnelling and energy quantization, respectively. Prior knowledge and readymade implementations allow these applications to be studied in a quantitative manner. Also, nuclear magnetic resonance is, albeit in a somewhat simplified model, studied quantitatively – within the framework of an oscillating spin-½ particle developed in Chapter 5. The remainder of the chapter is dedicated to quantum information technology. Also in this context, the notion of one or two spin-½ particles is applied frequently. A spin-½ particle is one possible realization of a quantum bit, and it serves well as a model even in cases when quantum bits are implemented differently. After having introduced some basic notions, two specific protocols for quantum communication are studied in some detail. The last part of the chapter addresses adiabatic quantum computing. This technology is studied in a manner that lies close to the last example of Chapter 5.

In this chapter we study the primordial process in which nuclei of atoms formed -- the Big Bang nucleosynthesis, or BBN for short. We show that BBN principally leads to the synthesis of hydrogen and helium, along with a trace amount of a few more of the lightest elements. We describe the basic thermodynamical and nuclear-physics conditions in the early universe, and explain how they determine the primordial origin and abundance of nuclei in the universe. Finally, we illustrate how the lightest-element abundances are in spectacularly good agreement with observations, making BBN one of the pillars of the hot Big Bang cosmological model.

For a proper quantum mechanical description of multiple-particle systems, we must account for the indistinguishability of fundamental particles. The symmetrization postulate requires that the quantum state vector of a system of identical particles be either symmetric or antisymmetric with respect to exchange of any pair of identical particles within the system. Nature dictates that integer spin particles – bosons – have symmetric states, while half-integer spin particles – fermions – have antisymmetric states. The best-known manifestation of this is the Pauli exclusion principle, which limits the number of electrons in given atomic levels and leads to the structure of the periodic table.