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 Yearling
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  • 28 votes cast
Oct
1
answered When can a Hilbert space with a given Hamiltonian be decomposed into non-interacting tensor product factors?
Sep
5
comment How to solve bound states of 2D finite rectangular square well?
Maybe a change in variables by a conformal mapping of the square onto the circle helps in the case a = b : math.stackexchange.com/questions/1015205/…
Nov
25
comment Separability of a Hilbert space and its implications for the formalism of QM
For every infinite dimensional Hilbert space there are states which cannot be represented by a density operator (the states that are not normal).
Oct
25
comment Interpreting some domain issues of (potential) momentum operators
Even for a free particle the domain of the momentum operator is larger than the domain of the Hamiltonian. So $p_1$ could be the right momentum operator but I haven't yet found a good argument for this.
Oct
23
comment What is discrete phase space?
An example is the quantization of Arnolds cat map. The phase space is given by the discrete Heisenberg-Weyl group modulo the center of the group.
Aug
13
comment Can observables with discrete and continous eigenvalues be commuting?
The identity operator has discrete spectrum and commutes with every operator.
May
13
comment Why are there gapless excitations in the anti-ferromagnetic Heisenberg model while the true ground state is a singlet?
to "we do have anti-ferromagnetic magnons which are gapless excitations" : not always true if Haldanes conjecture is true : physics.stackexchange.com/questions/59986/…
May
8
awarded  Yearling
May
4
comment What is the precise definition of state of a quantum system?
Note that if you multiply the vector by a phase factor it is still the same state.
Apr
25
answered Complex conjugate of momentum operator
Feb
4
comment Is the second law of thermodynamics a fundamental law, or does it emerge from other laws?
@Lubos Motl : The second law of thermodynamics can't be true for all times if Poincare recurrence occurs. And Poincare recurrence occurs according to your answer in physics.stackexchange.com/questions/94122/… .
Jan
17
comment Is Poincare recurrence relevant to our universe?
The cosmic horizon depends on the observer, so does the finite-dimensional Hilbert space depend on the observer ? If yes, how are the Hilbert spaces related ?
Nov
17
comment Physical Interpretation of Relationship Between Hall Conductivity and Berry Curvature?
@Everett You : It's a counter example to the quantization to the integer value and to Laughlin's Argument.
Nov
16
comment Physical Interpretation of Relationship Between Hall Conductivity and Berry Curvature?
@Everett You : The fractional quantum hall effect is a counter example.
Nov
12
comment What exactly is $\hat{\psi}^\dagger(x)$? An operator or a function?
to "I'd need to think about it, but I believe the notion of an unbounded-operator valued distribution doesn't even make sense mathematically" : It makes sense, see e.g. Streater-Wightman axioms. $\hat{\psi}^\dagger(x)$ must be a distribution since $[\hat{\psi}(y),\hat{\psi}^\dagger(x)]=\delta(y-x)$
Nov
11
comment What exactly is $\hat{\psi}^\dagger(x)$? An operator or a function?
$\hat\psi^\dagger$ is not an operator valued function but an operator valued distribution.
Oct
9
comment The state of Indefinite metric in Quantum Electrodynamics
Do you mean this : en.wikipedia.org/wiki/Gupta%E2%80%93Bleuler_formalism ?
Oct
1
comment Is the Lorentz group compact (and if not, is U(1)?)
to "only compact groups have finite-dimensional representations" : No, all unitary irreducible representations of abelian groups are one dimensional no matter whether they are compact or not.
Sep
30
comment Maximum theoretical data density
Is the answer also true shortly after the big bang ?
Sep
29
answered Applications of Algebraic Topology to physics