Quantum-ElectroDynamics (QED) is the quantum field theory believed to describe the electromagnetic interaction (and with some extension the weak nuclear force).

learn more… | top users | synonyms (1)

0
votes
3answers
72 views

Does an electromagnetic wave necessarily contain many photons?

I've often come across people saying from a quantum physics standpoint that an electromagnetic wave necessarily contains many photons. But doesn't the double-slit experiment conducted one photon ...
0
votes
0answers
9 views

Deep Inelastic Scattering - electromagnetic current

When one tries to compute the deep inelastic scattering for the process: where $l$ is a lepton with incoming momentum $k$ and outgoing $k'$, $h$ is an hadron with momentum $P$, $q$ denotes some ...
0
votes
0answers
7 views

Plasmon quenching vs plasmon decay. What is the difference?

I'm reading an article "Quenching, Plasmonic, and Radiative Decays in Nanogap Emitting Devices" (pubs.acs.org/journal/apchd5). I don't understand the following: Counterintuitively, we evidence ...
0
votes
1answer
22 views

Under what conditions does a beam splitter entangle two input photons?

There is a dispute on PhysicsForums related to what are the conditions necessary for two photons to be entangled by a beam splitter. Lots of references given by the forum users but they never arrive ...
1
vote
1answer
22 views

Crossing Symmetry in Bhabha scattering and Moller scattering

Given the amplitude for a particular process, it may be possible to obtain the amplitude for another similar process by a so called crossing symmetry. I know there is a $s \leftrightarrow u$ crossing ...
10
votes
1answer
294 views

Why can't a real scalar couple to the electromagnetic field?

If we have a complex scalar $\phi$ we know that the gauge-invariant interaction with $A$ is given by $A^\mu J_\mu$, where $J$ is the Noether current of the $U(1)$ symmetry of the Lagrangian $$ ...
22
votes
1answer
819 views

How can my window not scramble the image of my yard?

How can an image pass through a window if the atoms in the glass randomly emit photons in any direction? I've read that glass is transparent because the atoms don't readily adsorb visible light, so it ...
0
votes
0answers
44 views

Connection between statistical and quantum mechanics

I am aware of Gibbs measures, given the energy (Hamiltonian) of an arrangement, one can determine the frequency of the arrangement. Plug the energy level in the Boltzman equation and there you go. I ...
0
votes
1answer
82 views

Can the standard model be explained this simply? [closed]

I discussed QED and the standard model with a friend of mine, who has no background in physics, trying to explain it in the simplest terms possible. This is the explanation I ended up with: You have ...
7
votes
1answer
200 views

Are there negative energy states in QED?

I was reading Weinberg I, when I came upon the following statement$^1$ (slightly edited by me): \begin{align} (\not p+m)u=ie\not A\\ (\not p-m)v=ie\not A \tag{1} \end{align} The minus sign on ...
4
votes
1answer
46 views

What is the QED model about half wave plate?

Surely classical electrodynamics (CED) has a good and well-known answer about the change of light polarization in a HWP (or Quarter wave plate). I tried to find how does this look like from point of ...
1
vote
1answer
48 views

Preference of Chirality

I was interested to see that , $$ \gamma^5 \psi = \psi_R - \psi_L $$ By the definition of chirality projection operator and that $\psi = \psi_R + \psi_L$. since $\gamma^5 \psi$ pops up a lot in ...
4
votes
1answer
66 views

How could we describe the electric bound state like hydrogen by QED? [duplicate]

We can solve the Schrodinger equation for the Hamiltonian operator from the classical Hamiltonian of hydrogen bound state, consisting of proton and electron attracting each other electrodynamically, ...
27
votes
4answers
5k views

Why have our eyes not evolved to see “gluons”? [closed]

Bit of a random question...photons are the propagators for QED, and we rely on photons to see the world around us. The gluon is the propagator in QCD. Why have our eyes not evolved to see gluons ...
0
votes
0answers
20 views

1-loop integration for self-energy

I am trying to calculate the following integral that corresponds to 1-loop contribution to electron self-energy for a specific component of the momentum: $$ \Delta_i(q) = \int \frac{dp_1 dp_2 \ldots ...
8
votes
0answers
78 views

Stimulated Emission in QED

The explanations of stimulated emission which I have found all describe the phenomenon in terms of non-relativistic quantum mechanics. How might you describe it in a field theory such as QED? In ...
0
votes
1answer
38 views

One particle infinite manifestation universe [closed]

I know how non-intuitive everything related to quantum physics is and I was thinking on some very unintuitive things like John Wheeler one electron universe theory ...
1
vote
3answers
73 views

What force prevents particles from penetrating other particles?

I understand that what prevents objects from penetrating each other is the electromagnetic force between the electrons in the respective objects. But if we don't have electrons, for example a proton. ...
0
votes
0answers
25 views

Divergent diagrams in QED

I was reading about how to choose divergent diagrams in QED by using the concept of Superficial degree of divergence. We have an empirical relation $$ D= 4-E_b -\frac{3}{2}E_f $$ where $E_b$ is number ...
2
votes
1answer
78 views

How does QED explain reflection? [duplicate]

By reflection of photons from a mirror, the mirror must get an impulse of 2p=h/pi.l for every photon. This means that the mirror receives kinetic energy. But the photon has the energy it has before ...
1
vote
1answer
45 views

Tree Level Feynman Diagrams of Electron Positron Interaction

Consider the interaction $$e^-+e^- \rightarrow e^-+e^-$$ The following is a tree level Feynman diagram for this: We can also make the paths of the two electrons on the right hand side cross over and ...
0
votes
0answers
34 views

Confusion over trying to understand spinor components

I've been reading about the quantisation of the Dirac field $\psi(x)$ and it is stated that the general solution to the Dirac equation $(i\gamma^{\mu}\partial_{\mu}-m)\psi(x)=0$ is given by the ...
0
votes
0answers
40 views
0
votes
0answers
11 views

Resonance Fluorescence spectrum of a symmetric state of two atoms

So recently I've learned about the fluorescence spectrum of an atom (say a two level system) driven by a laser close to its resonance frequency. You get a dressing of the atom states with the laser, ...
0
votes
0answers
31 views

the probability amplitude of a photon

In one of Richard Feynman's lecture, he says that the angle of amplitude of a given path depends on what time the photon is emitted from the source. How does the angle of amplitude depend on time ...
3
votes
1answer
105 views

Problem understanding electromagnetic interaction with matter (non-relativistic QED)

I'm having trouble understanding the interaction of radiation with matter in (elementary non-relativistic QED) in Coulomb gauge ($\nabla\cdot\boldsymbol{A}=0$). We saw how to quantize the free ...
1
vote
1answer
46 views

Photon one (odd) point function in QED

In Peskin's QFT textbook, when discussing the superficial divergence of loops in QED, the book says (page 317): "To analyse the photon one-point function,note that the external photon must be ...
2
votes
0answers
38 views

Schwinger metals?

Consider an electromagnetic field that does reach values above the Schwinger limit inside a region of space $R$, on each oscillation. Once the field exceeds the Schwinger intensity, the field causes ...
0
votes
0answers
46 views

Exchange of virtual photons [duplicate]

How does the exchange of virtual photons as per QED explain the electrostatic attraction of particles of opposite charge?
0
votes
0answers
56 views

How does the introduction of a new ground affect a circuit?

I was talking today at lunch with a friend about getting shocked by a light socket while changing a light bulb the other day. The glass got separated from the metal threads where the positive and ...
0
votes
1answer
64 views

Does light with opposite spins cancel out the probability of an event?

I'm an A level student and as i was reading QED by Richard Feynman, I came across something really interesting, that light can be reflected from all parts of the mirror according to the quantum ...
1
vote
2answers
54 views

Probability of photon to photon collision

2 photons having sufficient energy can collide and form an electron positron pair (which then annihilate and form a new photon pair - with lower energy?). I assume this means that they can't collide ...
0
votes
2answers
86 views

How does absorption of light by atoms and molecules work?

I found this question on a hobby science forum (mainly about chemistry) and found embarrassingly that I couldn't answer the question. A few searches along the lines of 'photons absorption' here on ...
1
vote
0answers
40 views

Change in energy eigenvalue of Schrödigner-Pauli equation

If I apply a uniform magnetic field to a paramagnetic material, I will re-orient the quantum spins of the electrons on the atoms to create a net magnetic dipole moment. When the re-orientation occurs ...
1
vote
0answers
21 views

Finding the dependence of dephasing time on flux noise in Transmon Qubits

Before introducing some relevant concepts I'll begin by stating my question. What I am looking for is the connection between the noise the flux through the SQUID in my transmon qubit (related to the ...
2
votes
0answers
51 views

Angular momentum of the Photon

I am reading the QED book by Landau and Lifshitz and I am having a confusion with the angular momentum of a photon. In the book, they show that the total angular momentum $j$ cannot be zero and takes ...
0
votes
0answers
26 views

Book Recommendations on Perturbation Theory

I am interested in studying Quantum Electrodynamics and figure I should begin by learning Perturbation theory and Asymptotic expansions. If anyone could recommend some books, or starting points for ...
0
votes
1answer
36 views

Magnetic field of a current carrying wire reduce/increase exterior magnetic field?

If we place a wire within a uniform exterior magnetic field ($B_x$) that's perpendicular to it's length, and allowed current to flow withing the that conductive medium, there is another magnetic field ...
1
vote
0answers
34 views

Lamb shift and logarithmic corrections

Radiative corrections (Lamb shift) to the energy level (1S state) of a hydrogen atom can be written as a power series in $Z\alpha$ and $\ln(Z\alpha)$: $$\Delta E = \frac{\alpha}{\pi}(Z\alpha)^4 ...
3
votes
1answer
62 views

Atom - light field coupling and emission process

Suppose a "2-state atom" and a light field are quantized with the following Hamiltonians, respectively: $$\hat{H}_A=\hbar\omega_{21}\hat{\sigma}^{\dagger}\hat{\sigma}$$ and ...
3
votes
1answer
119 views

Quantized light-atom Hamiltonian

Suppose a "2-state atom" and a light field are quantized with the following Hamiltonians, respectively: $$\hat{H}_A=\hbar\omega_{21}\hat{\sigma}^{\dagger}\hat{\sigma}$$ and ...
1
vote
0answers
39 views

Implications for measurement of an initially localized free particle's wavefunction spreading out to infinity?

So, I have been attempting to wrap my head around what happens to a free particle that is initially localized to one spot. It seems that due to their different frequencies, the particle's wavefunction ...
2
votes
1answer
49 views

Absorption of photon as particle by an electron

As the photon gets absorbed by the electron and goes to higher energy state, does the photon remains in the electron itself in some form (radiation energy), thereby increasing the mass of electron?
4
votes
3answers
93 views

Do we know why the field produced by charge extends to infinity?

Do we have any model to show why charge field or magnetic field extends till infinity. Edit: I agree that according to coulombs law $1/r^2$ cannot be 0 but do we know why this happens.I think I am ...
0
votes
0answers
18 views

NLO compton scattering

I have a question about the NLO processes, that contribute to ${\mid M \mid}^2$ with ${\alpha}^3$ in compton scattering. I can see, that an extra radiative $\gamma$ gives terms $\propto {\alpha}^3$. ...
1
vote
0answers
20 views

How to calculate the magnetic field due to orbital angular momentum in the fine structure

How to calculate effective magnetic field due to the angular momentum L in an atom like Na(23)? I found an answer that we could imagine the case that the atom was orbiting the electron now and ...
2
votes
2answers
69 views

Is Huygens's Wave Theory still correct?

We have to study on details about Huygens's Wave Theory though we have Electromagnetic theory, quantum theory today. Is it still correct or not?
1
vote
0answers
57 views

Electron matrix element in a most simple QFT problem, the e+ e- annihilation

In the beginning of my new QFT book there is this short chapter called Invitation: Pair Production in $e^{+}$ $e^{-}$ Annihilation. An electron and a positron collide and a couple muon & antimuon ...
1
vote
0answers
38 views

Does energy transmission depend on the speed of incoming particle?

Since a few past days , I am struggling with finding an in depth atomic model of force exchange between colliding paricles (originally newtons third law) , because at this point of time i am unable to ...
1
vote
0answers
48 views

What would happen if a monochromatic light falls on an electron?

An electron is not strictly free, but in terms of QFT, we consider scattering events in an asymptotic framework where free particles would arise at $t \rightarrow \pm \infty$. So, I would like to know ...