It is well known that the components of momentum in quantum mechanichs commute, like this $$ [P_x,P_y] = 0 $$ Basically, it means that the momentum components can be measured independently. Since I read this, I've been trying to figure it out how an experiment to measure this components at th...

I'm reading this article about a derivation of the formula that explains the temperature levels according to frequencies, which is the Planck's work that initiated quantum theory. Is explains how in classical mechanichs the energy of an oscillator is given by $$E = \frac{p^2}{2m} + \frac{1}{2}k...

I was just thinking,we know that radio waves transmits through forest areas and urban areas easily so we can also use them in forest region.

For $V(x)=-{a\delta(x)}$, a>0; there is only one bound state for which ${\psi(x)}={\frac{2\pi\sqrt{m\alpha}}{h}}e^{-4\pi^2 m\alpha\vert x\vert/h^2}$; $E=-\frac {2\pi^2 m\alpha^2}{h^2}$. $\psi(x)$ is non-zero at x=0. Since V(x) is infinite at x=0 how can a particle possess infinite poten...

I was going through the solution (provided by the author of the book R.D. Klauber) of Problem 14, Chapter 6 in the link - http://www.quantumfieldtheory.info/Correction_Ch06_prob_14.pdf on Klauber's website - http://www.quantumfieldtheory.info/corrections_to_solutions.htm and I am confused with a...

1) Even with not completely positive maps, if we can find a domain in which the action of the map is positive, why should we restrict the reduced dynamics of an open system to being exclusively completely positive? Also, what could such maps indicate physically about the system? 2) What are the ...

I am reading the book 'Green’s Functions in Quantum Physics' by Economou and in Chapter 1 he deals with density of states. The Green's function of the equation $$ (z-L(r))G(r,r',z) = \delta(r-r') $$ turns out to have the representation $$ G(r,r',z) = \sum_n \frac{\phi_n(r)\phi_n^*(r)}{z-\lambda_...

I'm trying to solve problem 2.38 from Introduction to Quantum Mechanics (2ed) by Griffiths and I'm puzzled by the solution of this problem. My question is why do we take integral bounds to be 0 and a but not 0 and 2a. By taking integral from 0 to a are we not only looking at the first half ...

I have seen antenna not transmitting when i lie over it,so just curious if the singnal gets reflectd

I found lecture notes online that said "Diagonal density matrix elements are the probabilities of finding system in various states." My quantum mechanics textbook doesn't say anything about this, it just says that the probability a state is in $\big|\phi \big>$ can be found from the density opera...

I was given this problem in my Quantum Mechanics course: Compute the 4 lowest energy levels for a system with 2 non-interacting particles inside a box (infinite square well) of length $2a$. Then, show the degeneracy of the 4 lowest energy levels for: 1. Two identical half-spin particles (identi...

ψ=e^iκx Since the wave function is an exponential equation, is there no point with zero probability of finding a given particle? Does that justify quantum tunneling?

so i was doing a quantum physics past paper and there was this question about ionizing atoms with laser. my answeres made reference to the photons within the laser knocking off or transferring their energy to the electrons and allowing them to escape if this energy exceeds their biding energy. I ...

I understand that sound travels faster in water then in air. Water is a liquid, and air is gas. Water still has the ability to roll the molecules over each other (so water can flow), it has some flexibility. But I do not understand how a solid that is inflexible can make sound waves travel fas...