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visits member for 2 years, 2 months
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Currently doing a PhD in Controlled Quantum Dynamics at Imperial College and the University of Oxford.


1d
comment Does quantum entanglement arise from quantum theory or is it merely an experimental observation?
Yeah I see your point and I quite agree that could cause some difficulty. I'll have to remember that!
1d
comment Does quantum entanglement arise from quantum theory or is it merely an experimental observation?
Rod, I'm curious why you think that 2D Hilbert spaces are bad for illustrating the tensor product, pedagogically speaking. Is it because $2^2 = 2\times 2$, in contrast to $3^2 \neq 3\times 3$, for example?
2d
comment About the nonlocality of QM and faster-than-light/backward-in-time machines
@Sofia Read the proof carefully, it is completely general. The possible transformations include non-unitary ones.
2d
comment About the nonlocality of QM and faster-than-light/backward-in-time machines
Sofia, the proof on Wiki does not make any assumption that the transformations are unitary. It merely assumes that they are completely positive and trace preserving, as they must of course always be. @Hypnosifl, yes, the point I was sort of getting at is that the no-communication theorem in the context of non-relativistic QM has nothing to do with that question, and therefore some of the answers were misguided.
2d
comment About the nonlocality of QM and faster-than-light/backward-in-time machines
Hi Sofia, are you unhappy with the general proof given on Wiki? If so, could you explain exactly why? Note that this theorem and the situation to which it pertains are completely unrelated to this recent question.
2d
comment Why does the group velocity of 2D plasmon diverge at small wave number?
Please could you give the proportionality constant which appears in $v_g^{2D}$? This should tell us at which wavelengths the group velocity approaches $c$. Presumably this is also a length scale at which the effective theory you are using becomes invalid.
2d
answered Why drops form spheres?
Dec
16
comment How did the operators come about?
Do you know what a Poisson bracket is? The operator representation of variables with a classical limit are found by demanding that their commutator is given by $i\hbar$ times the classical Poisson bracket. Spin operators can be derived by self-consistency arguments and some minimal physical input, see Dirac's Principles of Quantum Mechanics.
Dec
15
comment A conceptual question about scattering theory in quantum mechanics
These expressions are derived in the asymptotic limit $r\to\infty$; you keep only the lowest order term in $1/r$ when calculating the current.
Dec
12
comment Plants and Quantum Mechanics!
About textbooks on open quantum systems, I would recommend Breuer & Petruccione and Gardiner & Zoller
Dec
12
comment Plants and Quantum Mechanics!
The relevant excitations to study from the point of view of quantum transport in chromophores are excitons, not photons. Modelling the absorption of thermal photons in this context is extremely interesting, and as far as I know hardly anything is known about this question. However, I doubt this has anything to do with the OP's question.
Dec
12
revised Plants and Quantum Mechanics!
added 124 characters in body
Dec
12
answered Plants and Quantum Mechanics!
Dec
11
awarded  Tumbleweed
Dec
11
answered Is $\phi_n =\left\langle \vec r | n \right\rangle $ the photon wave function?
Dec
4
asked Independent boson model with an arbitrary finite-dimensional impurity
Dec
4
comment How is decoherence due to the environment compatible with the Copenhagen interpretation?
The "collapse" bit is when the observation picks out a single component of the mixed state. This is not the same as a pure state superposition decohering into a mixture.
Dec
2
comment How was it proven that a quantum entanglement measurement of particle A, affects properties of particle B
@ACuriousMind Bell's theorem is about realism vs. locality, not determinism vs. locality. Determinism has nothing to do with it.
Nov
28
comment Why is the ground state energy of the Heisenberg XXZ Model unbounded for some values of $J$?
The XXZ model as $J\to 0$ becomes equivalent to a free Fermi lattice system via the Jordan-Wigner transformation. This certainly has a finite ground state energy, so it looks like you have made a mistake somewhere. I would suggest calculating the ground state in the $J=0$ limit analytically, using the JW transformation, and then comparing with your numerical results to find the error.
Nov
24
comment How to rebut denials of the existence of photons?
@WetSavannaAnimalakaRodVance I'm afraid I know nothing about SED. What I mean is the following. Many states of the radiation field can be described by a classical electric and magnetic field distributed according to a positive semi-definite quasi-probability distribution, e.g. the Wigner function. Perhaps such a description is equivalent to some formulation of stochastic electrodynamics. However, Fock states cannot be described in this way: their quasi-probability distributions will be negative or singular.