1) Quantum mechanic 
. ==Properties== Each set of eigenspinors forms a complete, orthonormal basis. This means that any state can be written as a linear combination of the basis spinors. The eigenspinors are eigenvectors of the Pauli matrices in the case of a single spin 1/2 particle. Griffiths, David J. (2005) Introduction to Quantum Mechanics(2nd ed.). Upper Saddle ...