This chapter discusses the spin degrees of freedom in an atom. We first review how atomic energy levels can be classified in terms of the electron spin and orbital angular momenta and how this couples to the nuclear spin. We then describe how atoms interact with each other, and how the spins affect this interaction. The effect of electromagnetic radiation on the energy levels of an atom is described, and the Hamiltonian for energy levels transitions . After briefly describing how the important phenomena of the ac Stark shift and Feshbach resonances occur, we then turn to describing how dissipative dynamics affect atomic systems. Specifically, we examine master equations for spontaneous emission and atom loss, and look at these can be solved. Finally, we consider an alternative framework for solving such open systems using the quantum jump method, which allows for a stochastic approach to solving the dynamics

This chapter discusses the basic physics of atom diffraction. Starting with a short review on the diffraction of light, we describe the absorption of photons by an atom and its subsequent emission, where the atom to changes its momentum and internal state. Assuming a two-level atom, we describe the coherent interactions of atoms with light, showing its effect on the ground state of the atoms. We further illustrate how the light impacts forces on the atom that can be used for trapping it in the light field. Next, we discuss Bragg diffraction of atoms, where the internal state of an atom is unchanged after diffraction. Here the external motional state of the atom is put in a linear superposition of its movement. Finally, we describe the diffraction of atoms by Raman pulses, where the internal state of the atom is changed after diffraction, while achieving directed motion.