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Just here to learn and share.


Oct
31
answered Interpretation of Wigner function in optics
Oct
29
answered Force as gradient of scalar potential energy
Oct
29
comment “Dark” quantities
I asked this at a seminar and the speaker gave me a very dirty look. I guess he thought I was stupid or something. (He did not really answer the question either).
Oct
29
asked “Dark” quantities
Oct
25
answered Is Gravity Energy?
Oct
25
answered Are there any quantities in the physical world that are inherently rational/algebraic?
Oct
25
answered Usefullness of an only qualitative understanding of momentum?
Oct
24
awarded  Teacher
Oct
24
accepted Linearizing Quantum Operators
Oct
24
answered How is squeezed light produced?
Oct
24
awarded  Supporter
Oct
24
awarded  Scholar
Oct
24
accepted Linearizing Quantum Operators
Oct
24
comment Linearizing Quantum Operators
Ron, thank you. I will check out those references. How does the background field method justify decoupling fluctuations from the mean-field to solve them separately? This is the real problem I am having. It almost seems like a vector space formalism, only in this case you describe the space of $\hat{A}$ in terms of two basis, i.e $I$ and $\Delta\hat{a}$. Sorry about my obsession with Groups/Vector Spaces. :)
Oct
24
answered Hyperfine structure vs Lamb shift in the hydrogen atom
Oct
24
comment Linearizing Quantum Operators
Sorry guys. I am new here and I was not sure which site would be appropriate. I saw tons of F=ma questions on the Physics site, so I was not sure if my question would be answered there. Both versions have given me different answers, so thank you.
Oct
24
comment Linearizing Quantum Operators
Thank you for the answer. Can you kindly point me to a book or an article where I can read about this formalism? I have no background in QFT beyond second quantization.
Oct
23
comment Linearizing Quantum Operators
I am aware of the standard calculus reasoning, i.e a Taylor series expansion about the mean and dropping higher order terms, but that does not necessarily mean that any functional expansion is separable. I mean, the author states that a diff eq:$$\frac{d\hat{A}_1}{dz}=-\alpha \hat{A}_1^{\dagger }\hat{A}_2 e^{-{i\Delta kz}}$$ can be solved by treating the average and fluctuations separately. I don't see how you can decouple them?
Oct
23
comment Linearizing Quantum Operators
I don't see how this can be justified based on calculus reasoning alone? The first thing that comes to my mind is Cosets, but I am not sure how to take that anywhere.
Oct
23
comment Linearizing Quantum Operators
Greetings Vladimir, as you have suggested, it makes sense from a pure calculus point of view (continuous and differentiable functions), but would it necessarily apply in the case of quantum operators? I am looking for a Group theoretic reason to justify this operation. The problem I am having is that the author in (pra.aps.org/abstract/PRA/v49/i3/p2157_1) decomposes $$\frac{d\hat{A}_1}{dz}=-\alpha \hat{A}_1^{\dagger }\hat{A}_2 e^{-{i\Delta kz}}$$ into separable differential equations, one involving only the average values and the other involving only fluctuations.