Recent content by IFNT

Can anyone explain to me the definition of canonical and kinetic momentum? The Schrödinger equation for an electron in a laser field can be written in the length gauge or the velocity gauge. In the litterature it is often said that in the length gauge the kinematical momentum is equal to the...

I can only find materials on how to measure the transition frequency accurately, But after you have measured a given transition frequency very accurately, do you then use this frequency to drive an (Rabi) oscillation of the atomic levels? I mean, what does an atomic clock consist of? How do...

Thank you for your replies. I am looking into atomic clocks because I want to know how you can use atomic clocks to get a constraint on the variation of e.g. the fine-structure alpha.

Yeah, thanks. But are there sources with more details?

Does anyone have information on how exactly a atomic clock works? I have had advanced quantum mechanics courses so I am sure I wil understand it. My problem is that I can't find any descriptive materials (with drawings), the wikipedia page is very vague about the different things. So can...

In a RG flow diagram for a physical system where we have two fix points, which one is the most important one and describes the physical theory of the system? Is it the unstable fix point or the "stable" one where some of the flow lines flows towards?

Am I too vague in my question?

I don't seem to grasp the meaning of boundary conditions for Laplace's equation. Consider the Lagendre expansion of the potential at x due to a unit charge 1/|x-x'|, where x' is the position of the unit point charge. To do the expansion, we need to consider a volume in space where the...

Hmm okay you do not understand, I hope some other on this forum will understand and answer.

Now suppose I did two examples and they both give zero. So now I know it is true for all hamiltonians? nice proof

I don't know, but do we know it is zero?

If I have H=p^2/2m+V(x), |a'> are energy eigenkets with eigenvalue E_{a'}, isn't the expectation value of [H,x] wrt |a'> not always 0? Don't I have that <a'|[H,x]|a'> = <a'|(Hx-xH)|a'> = <a'|Hx|a'> - <a'|xH|a'> = 0 ? But if I calculate the commutator, I get: <a'|[H,x]|a'> = <a'|-i p \hbar /...

Hmm okay... I just started a QFT course and the lecturer just starts throwing phrases like "tensor", "covariance" , and so on without defining them properly.

But in the Minkowski space, is \eta^{ab} = \eta _{ab} ?

What is the difference between \eta ^{ab} and \eta _{ab}? Is this true? \partial_a \phi^* \partial^a \phi = \eta^{ab} \partial_a \phi^* \partial_b \phi= \eta _{ab} \partial^a \phi^* \partial ^b \phi and is \eta^{ab} = \eta _{ab} ?