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visits member for 2 years, 6 months
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Nov
23
comment Do photons age in a medium?
What is the difference between field velocity and photon velocity? If you quantize a field that propagates with velocity $v<c$, would you still get photons propagating with velocity $c$? How can we see this mathematically?
Nov
21
comment Explaining chirality for spin 1/2 particle
Calling the two states of chirality left and right gives the impression that it has an intuitive meaning similar to helicity, and this intuitive meaning is what I couldn't grasp till now. In nonrelativistic quantum mechanics, the phase associated with rotating around the z-axis depends only on the angle of rotation (the sense of rotation and hence the sign of the phase is encoded in the angle). In relativistic QM, I don't know how this works since I don't know how a relativistic spin operator is defined.
Nov
21
comment Explaining chirality for spin 1/2 particle
Thanks Flip for the answer. It seems from the first part of your answer that you consider chirality just as another quantum number that has different values for particles and anti-particles. Is that true? Otherwise, is it possible to explain chirality without referring to anti-particles at all?
Sep
22
comment Why doesn't gravity act as a measurement?
A related concept to your question is gravitational decoherence, arxiv.org/abs/gr-qc/0306084
Sep
7
comment Are Rabi oscillations a pure quantum process?
Hers it is: copilot.caltech.edu/classes/ee243/Rempe_collapse_revival.pdf
Mar
13
comment Hamiltonian of a simple graph
$\Sigma_z=S_1^z+S_2^z$ The first matrix you wrote for $\Sigma_z$ is consistent with the definitions for$S_1^z$ and $S_2^z$. What is the problem in $S_1^z |ZZ\rangle=-0.5|ZZ\rangle$ ? Isn't this expected?
Feb
12
comment Nuclear Magnetic Resonance (NMR) Conceptual Questions
Are you having difficulty trying to visualize the time evolution of the magnetization? Try to use this simulator: drcmr.dk/BlochSimulator
Jan
6
comment Simulating the evolution of a wavepacket through a crystal lattice
@hwlau I am not an expert in either of them. For sufficiently small systems, direct evolution with a simple 4th order Runge Kutta algorithm is sufficient. This amounts to using a truncated Taylor expansion of the time evolution operator. The Hamiltonian is represented as a sparse matrix.
Dec
31
comment Simulating the evolution of a wavepacket through a crystal lattice
Have you thought of using numerical algorithms, such as tDMRG, TEBD ?
Oct
26
comment What is the spin rotation operator for spin > 1/2?
Of course I am asking about the analogous formula for the expansion of the exponential in terms of cosines and sines not about the spin matrix !
Oct
5
comment Scale invariance symmetry as a simple argument in an electrostatics problem
This is a valid proof, but I doubt that it is the scale invariance symmetry meant by Prof. Preskill. He wrote: "Actually, this problem can also be solved by a symmetry argument, though the symmetry used is less obvious than rotational invariance. Readers may enjoy constructing this symmetry argument, which (in keeping with the theme of this post) I find more elegant than the argument using concentric rings suggested by your hint." Please read the discussion in the post in the question.
Sep
12
comment Driving a solution of optical isomer molecules with the resonant frequency
I am indeed interested in the simulation details of this. If you wish, you can send to [my email]. In order to understand the theory behind this, we should first know how the chiral states are stabilized in the first place. One famous stabilization mechanism is [decoherence] (prl.aps.org/abstract/PRL/v103/i2/e023202). It seems to me that the predictions of this paper can be tested based on the setup in the question.
Sep
12
comment Driving a solution of optical isomer molecules with the resonant frequency
Aren't $\psi_{L/R}$ the chiral states which are not eigenstates of the Hamiltonian, (and hence the paradox of Hund), while $\psi_\pm$ are the true eigenstates (which are not degenerate)?
Sep
12
comment Driving a solution of optical isomer molecules with the resonant frequency
The left and right-handed states are in fact degenerate. The two level system should be thought of as composed of the eigenstates of the hamiltonian/parity operator. Each of these eigenstates is either a sysmmetric or anti-symmetric superposition of the chirality states (left and right handed).
Jul
29
comment How are quantum phenomena in atoms and molecules protected against decoherence?
Is there a proof that the pointer states are energy eigenstates?
Jul
12
comment Are there devices which convert thermal energy to electric energy?
I am seeking an effect which does not require temperature gradient. Can a device be built which captures "flying" phonons and convert them to electric energy without the need for a colder surface? I am aware that such an idea may violate the 2nd law of thermodynamics, but I wish to know from a technological perspective why this is (not) feasible.
Apr
20
comment Partially filled orbitals and strongly correlated electrons
I think you are using the term screening here in a different sense than the usual one, where electrons closer to the nucleus screen the positive nuclear charge from electrons at a larger distance, and hence those later electrons feels a smaller nuclear charge.
Apr
18
comment Partially filled orbitals and strongly correlated electrons
@JohnRennie See: en.wikipedia.org/wiki/Strongly_correlated_material
Feb
10
comment Electrodynamics textbook that emphasizes applications
Thanks Chris. I didn't mean engineering applications like transmission lines and waveguides, but simply applications from everyday life for the curious students.