All Questions
17
questions
0
votes
2
answers
162
views
Electromagnetic field affect on hydrogen atom energy levels
If hydrogen atom is in the ground energy state it must be hitted by photon with energy higher than electron proton energy binding which is 13,6 eV according quantum mechanics. Proton have positive ...
- 119
4
votes
3
answers
304
views
What makes a photon a photon?
As i understand photons are excitation of the electromagnetic field. Therefore charged particles are affected by this excitation. But what if we have (highly theoretically) a particle that has the ...
- 793
1
vote
1
answer
92
views
Phase and group velocities in QFT / Quantum Optics
How does one define phase and group velocities in QFT? More precisely, are they referring to the mode structure of the field or do they characterize excitations?
The question is motivated by question ...
- 60.3k
1
vote
3
answers
162
views
Friction in photon absorption/emission process
Question: Is photon emission/absorption by an atom always accompanied by emission of soft photons (i.e. photons of very low energy)?
On the one hand, we can consider a scattering problem where at $t=-\...
- 60.3k
4
votes
2
answers
395
views
What is the connection between quantum optical photons and particle physics' photons?
There has been quite some debate amongst users with different backgrounds about the usage of the word photon.[1, 2] The most apparent disagreement was on whether a photon has a wavelength. I don't ...
- 3,260
7
votes
3
answers
1k
views
What is the physical meaning of the operators of the positive and negative frequency components?
In quantum optics, after performing the quantization of the radiation field, the field operator $E$ is often split into the positive- and negative-frequency parts as
$$ E(\mathbf{r},t) = E^{\left(+\...
- 143
0
votes
1
answer
70
views
Can a photons wavelength be independent of its associated temporal wavefunction?
Typically a traveling photon is described as being in a superposition of frequency modes $\hat{E} = \int g(\omega) a^\dagger_\omega d\omega + h.c. $ where often the $g(\omega)$ is some kind of pulse. ...
- 2,193
3
votes
0
answers
83
views
How is magnetic flux viewed in QED?
I know that QED is formulated in terms of Lagrangian density. So when we solve for a physical system we ultimately ends up finding $\psi$ and $A_{\mu}$. I'm not interested in $\psi$ for now. Since I ...
- 3,043
0
votes
1
answer
35
views
What type of scattering happens, when the "free" electrons in conductor receive the em wave?
We know for sure, that antennas(depending on their parameters), or just simple wires can receive(and emit) a large spectrum frequencies of em waves(from 1 Hz to 300 GHz for sure). But to excite an ...
user205695
0
votes
2
answers
891
views
Evaluation of the expectation value of a product of operators
In studying the the interaction of a single mode electromagnetic field in a coherent state with a two state atomic system (initially in its ground state), the problem is reduced to evaluating the ...
- 87
5
votes
3
answers
4k
views
How is a photon measured?
If photons transmit the electromagnetic force, which is observable: the photon or the electron? Do we ever directly measure a photon, or do we only measure it's effect on electrons. For example ...
- 75
9
votes
3
answers
3k
views
Why aren't all photons virtual particles even in the "vacuum" of empty space? [duplicate]
I'm thoroughly confused about the nature of electromagnetic radiation. Light is supposed to exhibit both wave and particle characteristics. But does that mean that it is both a wave and a particle or ...
- 1,141
5
votes
1
answer
751
views
Photon Angular Momentum
Essentially I am wanting to evaluate $$\langle j\, m \mid a^\dagger(\mathbf{k}, \lambda) \mid 0 \rangle \,,$$ where $\lambda$ indicates the circular polarization (about $\mathbf{k}$). We have that $\...
- 724
14
votes
3
answers
4k
views
If photons carry 1 spin unit, why does visible light seem to have no angular momentum?
Spin 1 silver atoms have a definite spin axis, e.g. up or down along an axis labeled X. This in turn means that they carry angular momentum in an overt, visible fashion.
However, spin 1 photons do ...
- 22.1k
0
votes
1
answer
288
views
The electron jumps and lets loose photons
Where is the source of the photon.
If the photon propagates from within the electrons transit does this point to some sort of field?
Does the energy come from a boundary being broken in laymens ...
- 1,241