1. ### I Properties of a unitary matrix

So let's say that we have som unitary matrix, ##S##. Let that unitary matrix be the scattering matrix in quantum mechanics or the "S-matrix". Now we all know that it can be defined in the following way: $$\psi(x) = Ae^{ipx} + Be^{-ipx}, x<<0$$ and $$\psi(x) = Ce^{ipx} + De^{-ipx}$$. Now, A and...
2. ### I Calculate a spin state as a function of the base spin states

Practically it is said that, given two spin states |u⟩ (up) and |d⟩ (down) - which are the spin measured along the +z and -z semiaxes - such that they are orthogonal ( ⟨u|d⟩ = ⟨d|u⟩ = 0), it is possible to write any other spin states using a linear combination of these two (because they are a...

29. ### Quantum Book on quantum electrodynamics

Can anyone suggest me a book on quantum electrodynamics for beginners? Thanks in advance
30. ### Electron Scattering Question

Homework Statement A beam of electrons with kinetic energy 50 eV is fired at a 100 nm thick crystalline nickel foil. (a) Calculate the speed of the electrons in the beam. (b) Based on your answer to part (a), state, with justification, whether classical (Newtonian) mechanics correctly...