# Questions tagged [matrix-elements]

The tag has no usage guidance.

121 questions
Filter by
Sorted by
Tagged with
23 views

### How to determine correct spinor in Feynman diagram

Setup Consider Moller scattering, that is $$e^-(\vec p_1, \alpha)+e^-(\vec p_2, \beta) \quad\longrightarrow\quad e^-(\vec q_1, \gamma)+e^-(\vec q_2, \delta),$$ where the $\vec{p}_i,\vec q_i$ label the ...
117 views

### Physical meaning of the rows and columns matrix representation of operators in Quantum Mechanics

When any operator is written in its matrix form, do the individual rows and columns of the matrices have any physical meaning to them? For example, the rows and columns of momentum and position ...
46 views

### Does a $U(1)$ matrix, as in QED, have a single entry? A $1×1$ matrix ( degree 1)? [closed]

This is a very simple question, but somehow, I am getting confused.... Some examples of Q.E.D U(1) matrices I see gave four (2×2) elements, like the Weak SU(2) matrices....
72 views

### When does a Hermitian operator have real matrix elements?

I will use braket-notation, but my question is not specific to quantum mechanics. Instead, I would be interested in a general answer for operators in some Hilbert space. Let $H$ be a Hermitian ...
74 views

### Matrix elements of powers of the position operator for a SHO [closed]

I'm asked to compute the matrix elements $\left( x^i \right)_{nm}$ where $i=2,3,4$ and $x$ represents the position operator for the quantum harmonic oscillator. I know that for $i=1$: \begin{equation} ...
I started with evaluating the following derivative with respect to a general element of an $n\times n$ matrix, $$\frac{\partial}{\partial X_{ab}}\left(\mathrm{Tr}{(XX)}\right)$$ I wrote out the ...