Questions tagged [quantum-electrodynamics]
Quantum electrodynamics (QED) is the quantum field theory believed to describe electromagnetic interaction. It is the simplest example of a quantum gauge theory, where the gauge group is abelian, U(1).
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Is the annihilation operator an observable (it is non-Hermitian)?
In most treatments of quantum mechanics that I have seen, observables of a quantum system are defined using Hermitian operators. The most intuitive reason for this is that Hermitian operators have ...
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In dispersive readout of a qubit coupled to a resonator, how is the measured phase shift used to determine the resonant frequency of the resonator?
In the dispersive readout of a qubit coupled to a resonator, a microwave pulse is applied to the resonator and the phase shift of the reflected pulse is used to determine the resonant frequency of the ...
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What is the observable for the optical field?
Typically, observables in quantum mechanics are associated with Hermitian operators. However, Glauber argues in 1963 ([1]) that the electric field operator $\hat{\mathbf{E}}(x,t)$ is not the relevant ...
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Are electric fields a physical input of the real world or a mathematical elaboration of Coulomb's law? If it is real what is it?
If the electric field is real, how does it affect the way we see the world? Or does nothing change? Is there a different interpretation between classical and quantum view of the electric field?
I am ...
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Some integrals in QED Renormalisation
I am currently leaning the renormalisation of QED and I have met some tricky integral that seems unsolvable. The integrals are shown in Quantum Field Theory and the Standard Model by Schwartz, page ...
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Equivalence of Pauli equation and photon picture
The motion of a charge in EM potential is described by the Pauli equation ( which is the non relativistic limit of Dirac eqn). On the other hand, we know that the EM potential is nothing else than the ...
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Feynman trajectories of a photon from entangled pair
In a pair of Entangled photons does any of the two photons has the Feynman trajectories of the other one? Must the possible trajectories of photon 2 be taken in the Feynman's path integral for the ...
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Classical limits of Quantum Electrodynamics?
Quantum Electrodynamics is the theory that studies the interactions between matter and radiation (somewhat).
How would one explain for example the movement of an electron in a constant electric field ...
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Going to momentum space from Hamiltonian equation 17.4 chapter 17 in Schwartz
I'm reading the chapter 17 on the anomalous magnetic moment in QFT and the SM (Schwartz).
In the section "17.1 Extracting the moment" he says
"Going to momentum space,the Dirac equation ...
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How does a photon look like in QFT? [closed]
It is very well known that in QFT the particles are excitations of the field. But how exactly is a free photon looking like in spacetime? What is it shape in free space? And what is in fact in the ...
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How can I count diagrams (in this scalar QED example) at a particular order without drawing all the Feynman diagrams?
Here's a 3-loop diagram for light-by-light scattering in scalar QED (from Schwartz textbook question 9.2):
The question 9.2 asks approximately how many other diagrams contribute at the same order in ...
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Quantizing the electric field without quantizing vector potential
I am trying to quantize the electromagnetic field, without using the vector potential. I start with a Fourier expansion:
$$\begin{equation}
\vec{E}(\vec{r},t) = \sum_{\epsilon} \vec{\epsilon} \int \...
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Equations of motion for Lagrangian of scalar QED [closed]
I really would appreciate your help with this exercise.
I have the Lagrangian for scalar electrodynamics given by:
$$\mathcal{L}=-\frac{1}{4}F_{\mu\nu}(x)F^{\mu\nu}(x)+(D_\mu\varphi(x))^*(D^\mu\varphi(...
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Renormalisation in quantum optics
When reading about QED in QFT books, renormalisation seems to be essential to get results eventually. It also seems absolutely necessary even for low energies, since the internal lines lead to ...
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QFT view of lower light speed of light in medium [duplicate]
In classical EM theory, if we have a medium whose dielectric coefficient is independent of wavelengths (suppose we filter the incoming signal to a certain frequency band), then the waveform gets to ...
