quantum physics

  1. A

    Studying Self-studying plan for modern science

    Hey guys, I want to build a strong and straight plan for my next years of studying and once finish I am able to do something on my own and come up with crazy ideas and actually test them, build some awesome algorithms, all that cool stuff, but I'm kinda stumble so it would be nice if someone...
  2. schwarzg

    A Simultanious eigenstate of Hubbard Hamiltonian and Spin operator in tw

    Please see this page and give me an advice. https://physics.stackexchange.com/questions/499269/simultanious-eigenstate-of-hubbard-hamiltonian-and-spin-operator-in-two-site-mod Known fact 1. If two operators ##A## and ##B## commute, ##[A,B]=0##, they have simultaneous eigenstates. That means...
  3. Futurestar33

    Shelf in a box, treating the shelf as a weak perturbation

    In this problem I am supposed to treat the shelf as a weak perturbation. However it doesn't give us what the perturbed state H' is. At the step V(x) = Vo, but that is all that is given and isn't needed to determine H'. This isn't in a weak magnetic field so I wouldn't you use H'=qEx and then...
  4. P

    Constant of proportionality in probability of superposition of states

    Using the fact that Pa ∝ |α|^2 and Pb ∝ |β|^2, we get: Pa = k|α|^2 and Pb = k|β|^2 Since the probability of measuring the two states must add up to 1, we have Pa + Pb = 1 => k = 1/(|α|^2 + |β|^2). Substituting this in Pa and Pb, we get: Pa = |α|^2/(|α|^2 + |β|^2) and Pb = |β|^2/(|α|^2 + |β|^2)...
  5. lastItem

    I Relation between the momentum operator and the Hamiltonian gradient operator

    Is there a relationship between the momentum operator matrix elements and the following: <φ|dH/dkx|ψ> where kx is the Bloch wave number such that if I have the latter calculated for the x direction as a matrix, I can get the momentum operator matrix elements from it?
  6. J

    How to find von-Klitzing constant based on graph?

    Hi all, Given that the question: From what i know , im not sure how this equation can help me estimate the von-klitzing constant? Or is there another way? Thanks!
  7. B

    A LS vs jj couplings and their selection rules

    Two questions, where the 1st is related to previous discussion regarding thes couplings: The selection rules for LS coupling is quite clear - it's based on calculating the compatible electric dipole matrix element. However, in the case of jj coupling we end up with different selection rules...
  8. C

    I Confusion on binding energy and ionization energy.

    1) I know that the binding energy is the energy that holds a nucleus together ( which equals to the mass defect E = mc2 ). But what does it mean when we are talking about binding energy of an electron ( eg. binding energy = -Z2R/n2 ? ). Some website saying that " binding energy = - ionization...
  9. J

    I David Deutsch (1985) attempt to solve the incoherence problem

    Can anyone elaborate on Deutsch's attempt to solve the incoherence problem? He postulates a continuously infinite set of universes, together with a preferred measure on that set. And so when a measurement occurs, the proportion of universes in the original branch that end up on a given branch...
  10. A. Neumaier

    Insights A Classical View of the Qubit - Comments

    Greg Bernhardt submitted a new blog post A Classical View of the Qubit Continue reading the Original Blog Post.
  11. R

    Evolution and quantum physics

    Is it possible that evolution happens in quantum jumps as no intermediate lifeforms were ever found? Analogous to an electron jumping from lower energy level to higher energy level without intermediary states.
  12. F

    B Quantum entanglement phenomenon

    Hi there, Question from a biologist with very poor background in physics, but willing to understand quantum physics. I think quantum entanglement shocks everyone, even if it has been proven right. I would love to know if there is any hypothesis or crazy theory out there to explain why or how...
  13. Demystifier

    Against "interpretation" - Comments

    Greg Bernhardt submitted a new blog post Against "interpretation" Continue reading the Original Blog Post.
  14. P

    I Van der Waals force in quantum physics

    According to QFT, are there hydrogen bonds or Van der Waals force? Or this an outdated concept of classical physics?
  15. RUTA

    Insights The Quantum Mystery of Wigner's Friend - Comments

    Greg Bernhardt submitted a new blog post Wigner's Friend Continue reading the Original Blog Post.
  16. thariya

    A Quantization of the electric field inside a box

    Hello all, The second quantization of a general electromagnetic field assumes the energy density integration to be performed inside a box in 3D space. Someone mentioned to me recently that the physical significance of the actual volume used is that it should be chosen based on the detector used...
  17. RUTA

    Insights The Unreasonable Effectiveness of the Popescu-Rohrlich Correlations - Comments

    Greg Bernhardt submitted a new blog post The Unreasonable Effectiveness of the Popescu-Rohrlich Correlations Continue reading the Original Blog Post.
  18. J

    I Causality and quantum physics

    Let me present what I think is the understanding of a particular situation in quantum mechanics, and ask people to tell me whether I am right or wrong. To say that everything happens randomly in QM would be misleading at best. We get at least statistical prediction. But discussions such as the...
  19. Warda Anis

    Expectation value <p> of the ground state of hydrogen

    1. Homework Statement How should I calculate the expectation value of momentum of an electron in the ground state in hydrogen atom. 2. Homework Equations 3. The Attempt at a Solution I am trying to apply the p operator i.e. ##-ihd/dx## over ##\psi##. and integrating it from 0 to infinity...
  20. A

    I Dressed electrons are not defined as point masses...

    In @A. Neumaier 's excellent Physics FAQ, he notes under "Are electrons pointlike/structureless?" that "Physical, measurable particles are not points but have extension. By definition, an electron without extension would be described exactly by the 1-particle Dirac equation, which has a...
  21. Pouyan

    Finding state vectors for pure states!

    1. Homework Statement Is the following matrix a state operator ? and if it is a state operator is it a pure state ? and if it is so then find the state vectors for the pure state. If you dont see image here is the matrix which is 2X2 in matlab code: [9/25 12/25; 12/25 16/25] 2. Homework...
  22. D

    I Finding expansion coefficient of a 3-d Gaussian wave packet

    I'm having trouble with trying to find the expansion coefficients of a superposition of a Gaussian wave packet. First I'm decomposing a Gaussian wave packet $$\psi(\textbf{r},0) = \frac{1}{(2\pi)^{3/4}\sigma^{3/2}}\text{exp}\left[ -\frac{(\textbf{r} - \textbf{r}_0)^2}{4\sigma^2} + i\textbf{k}_0...
  23. P

    I Why do you need infinite size matrix which commute...

    ...to give a number? https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2016/lecture-notes/MIT8_04S16_LecNotes5.pdf On page 6, it says, " Matrix mechanics, was worked out in 1925 by Werner Heisenberg and clarified by Max Born and Pascual Jordan. Note that, if we were to write xˆ...
  24. Safder Aree

    Wave packet width given a wave function

    1. Homework Statement Find the wave packet Ψ(x, t) if φ(k) = A for k0 − ∆k ≤ k ≤ k0 + ∆k and φ(k) = 0 for all other k. The system’s dispersion relation is ω = vk, where v is a constant. What is the wave packet’s width? 2. Homework Equations I solved for Ψ(x, t): $$\Psi(x,t) =...
  25. Safder Aree

    Harmonic Oscillator violating Heisenberg's Uncertainity

    1. Homework Statement Does the n = 2 state of a quantum harmonic oscillator violate the Heisenberg Uncertainty Principle? 2. Homework Equations $$\sigma_x\sigma_p = \frac{\hbar}{2}$$ 3. The Attempt at a Solution I worked out the solution for the second state of the harmonic oscillator...
  26. J

    I Can something be caused and be ontologically random?

    Or does ontological probability exist? I was reading an article that came up in my google searches ( https://breakingthefreewillillusion.com/ontic-probability-doesnt-exist/ ) ignore the free will philosophy stuff. But the author makes the claim that ontological probability simply does not...
  27. Giulio Prisco

    I Einstein-Bohr "photon box" debate and general relativity

    I see this has been already discussed but the old threads are closed. EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited "In this example, Einstein presents a paradox in QM suggesting that QM is inconsistent, while Bohr attempts to save consistency of QM by combining QM with the...
  28. Greg Bernhardt

    Insights Interview with Astrophysicist: Adam Becker - Comments

    Greg Bernhardt submitted a new PF Insights post Interview with Astrophysicist: Adam Becker Continue reading the Original PF Insights Post.
  29. J

    B Reason for the speed of light

    Is it possible that the speed of light exists because we cannot move faster than our particles? I.e. the speed of electrons that create the electromagnetic force that hold matter together.
  30. Arik Salehi

    B Explanation of Quantum Entanglement Please

    Hello, I am 12 years old in 6th grade and love physics and Quantum Physics, I would love an explanation of Quantum Physics and Topological Quantum Matter.