Recent content by chafelix

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    Difference in phase convention for Wigner d-function

    Yes, Edmonds has a typo. There should be no (-1)**(j-m) there.
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    Difference in phase convention for Wigner d-function

    I am looking for a way to connect the Condon-Shortley-Wigner to the Edmonds phase convention. Specifically I am writing a program to compute Wigner-d matrix coefficients From tabulated values (e.g. even Wikipedia) d^1/2_{1/2,-1/2}=(-1)^{-1/2-1/2}d^1/2_{-1/2,1/2}=-sin(theta/2) So...
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    FFT vs Filon's Rule: Accuracy Comparison

    Homework Statement Suppose we can calculate a quantity f(t) and we need its Fourier transform F(w). Looks to me that accuracywise Filon's rule, e.g. approximating the computed f(t) by splines and analytically integrating piecewise should be more accurate than an FFT, at least for a smooth...
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    Exploring the Mysteries of Plasma Physics

    Because the mobile plasma charges(i.e. electrons first) will rearrange themselves because of the field, so as to resist it. But if the field changes sign before the electrons can move, they are 'confused', i.e. they start moving one way to resist the field, but the field sign changes sign before...
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    So, I know that spin is very important in quantum mechanics/elementary

    If you have a problem with spin, try some more exotic notion such as charm. It was Feynman who said that if we cannot explain something in simple terms, it means we do not understand it well. And yes, Feynman also said "nobody understands quantum mechanics" and this is normal, because our...
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    Decoherence does not collapse wavefunc.

    Another question on decoherence: Take stat mechanics. There we have an atomic system and an environment(consisting of atomic subsystems that will be traced over) plus an interaction between them, V(t). The atomic system could be for example an atom and the environment could reprsent collisions...
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    Double Slit Experiment: Q&A on Photon Detection

    No, in both cases you detect N1+N2, but that is if you have one HUGE detector that will grab anything past the slits, or alternatively a large number of detectors that cover all space past the slits. The interference pattern has to do with the distribution of photons caught by each such...
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    What Determines the Lineshape in a Two-Level System with Spontaneous Emission?

    Look in my example for Ly-a: Assuming a diagonal density matrix, the Trace is sum_m <21m|rho|21m><21m|d|100><100|d(t)|21m> no parity issue here. The relative contribution to any particular line is proportional to the upper level population, which (for a diagonal density matrix) is...
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    What Determines the Lineshape in a Two-Level System with Spontaneous Emission?

    d is dipole moment. rho is the density matrix. Why is d constant? You need matrix elements of d to do the trace. You can get a constant reduced matrix element out of d, but you still have the Clebsch-Gordan to sum e.g. Ly-a:(sum over m) <100|d|21m><21m|d(t)|100>
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    Are Autoionizing States Necessary for Accurate Wavepacket Representations?

    I don't think that's right. Coulomb waves have the correct asymptotic behavior, but the point is that this is merely a basis; you can use any basis you want to represent the states and clearly bound states +say Coulomb waves is a complete basis. What's the point of non-stationary autoionizing...
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    Degenerate pertubation theory when the first order fails

    Actually when you diagonalize you solve the problem EXACTLY to all orders(in the framework of the set of states you use). It's when you have both degenerate and nondegenerate that order makes sense. To your question, if in the degerenate subspace the perturbation is 0, then to get a nonzero...
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    Are Autoionizing States Necessary for Accurate Wavepacket Representations?

    In terms of stationary states we have bound states and free(plane wave or Coulomb) states Autoionizing states are free(E>0), e.g. continuum, but localized states(resonances). Hence wavepackets consisting of a band of plane or Coulomb waves. I understand they may be long-lived, longer than the...
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    What Determines the Lineshape in a Two-Level System with Spontaneous Emission?

    Lineshape is FT of Tr[d(0).d(t) rho] (if you do not include the omega**4 power which is typically a constant over the line profile)
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    Compute SHO Propagator: Eigenfunction Expansion

    ok, need the Mehler formula
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    Solving an Interesting Problem with Two Hermitian Operators

    If any experiment can only give a single result, then there is no uncertainity. In this case where we start with a prepared state |1>, a measurement of O2 can only give the result |2>. It has 100% |2> character and 0% |1> character. In contrast if O2|1> were a|1>+b|2>, then the outcome would...
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