ABSTRACT
This chapter gives a broad overview on basics in quantum physics and spin dynamics used to interpret and simulate Nuclear Magnetic Resonance (NMR) experiments. However in NMR, peoples are dealing with macroscopic samples of large sub-ensembles of spins in different pure states, which can be interacting with each other and with external magnetic fields. The spin density operator will evolve in time under the influence of a total Hamiltonian, which is generally the sum of multiple Hamiltonians related to different interactions between the spins themselves or with external factors such as a magnetic field, radiofrequency fields, and other interactions. The Zeeman Hamiltonian describes the interaction of the magnetic moment with main magnetic field. The concept of relaxation describes the process by which the spins return to their equilibrium state after excitation by means of interaction with their environment (such as random temporal fluctuations of the electric and magnetic fields generated by tissue structures, molecules, and other spins in their surroundings).
