Read about quantum | 387 Discussions | Page 1

  1. A

    I What part of physics describes what happens just outside of an electron?

    Coulomb's law for three dimensional space is an empirical law that describes the forces between two stationary point charges and is defined as: \vec{F}=\frac{K q_1 q_2 (\vec{r}_1-\vec{r}_2)}{|\vec{r}_1-\vec{r}_2|^3} From Coulomb's law, the magnitude and direction of an electric field produced by...
  2. J

    B Does the Higgs Boson really have 0 spin?

    Does the Higgs Boson really have 0 spin or is the spin between 0 and 1/2 x (1.054 571 817... x 10-34 J s)?
  3. A

    A Green's function for tunneling electrons between quantum dots

    Good afternoon! I am writing with such a problem, I hope to find someone who could help me. I'm almost desperate! So, there is such a thing as the Braess paradox, this is a classic paradox for roads and power grids, and there is also such an article...
  4. lelouch_v1

    I How to work in the |F,m_F> states in hyperfine structure

    Suppose that we have two atoms with one proton one electron each, and these electrons interact with each other. The states for the electrons are the singlet(S=0) and the triplet states(S=1). My question is if i have to keep the nuclear spin of the protons parallel when i write the states, for...
  5. lelouch_v1

    A Eigenvalues of Hyperfine Hamiltonian

    I was reading a paper on Radical-Pair mechanism (2 atoms with 1 valence electron each) and the author used the hyperfine hamiltonian $$H_{B}=-B(s_{D_z}+s_{A_z})+As_{D_x}I_x+As_{D_y}I_y+as_{D_z}I_z$$ and found the following eigenvalues: a/4 (doubly degenerate) , a/4±B , (-a-2B±2√(A^2+B^2)) ...
  6. Tuca

    I Solving Schrödinger's equation for a hydrogen atom with Euler's method

    Hi, first-time poster here I'm a student at HS-level in DK, who has decided to write my annual large scale assignment on Schrödinger's equation. My teacher has only given us a brief introduction to the equation and has tasked us to solve it numerically with Euler's method for the hydrogen atom...
  7. Danny Boy

    A Entanglement Witnesses close to GHZ states

    Consider page 2 of Toth's paper Entanglement detection in the stabilizer formalism (2005) . To detect entanglement close to GHZ states, they construct entanglement witnesses of the form $$\mathcal{W} := c_0 I - \tilde{S}_{k}^{(GHZ_N)} - \tilde{S}_{l}^{(GHZ_N)},$$ where...
  8. Y

    Help with the matrix representation of <-|+|->. Does "+"=|+>?

    Trying to use <+|+>=1=<-|-> and <-|+>=0 to prove each iteration of the equation, so I have 6 different versions to prove. But the part I'm currently stuck on is understanding how to simplify any given version. I've written out [S_x,S_y]=S_xS_y\psi-S_yS_x\psi and expanded it in terms of the...
  9. EclogiteFacies

    A Everettian FAPP solipsism

    Travis Norsen in his paper Quantum Solipsism and Non-Locality seems to believe that Everettian QM implies some sort of solipsism. He falls it FAPP (for all present purposes) solipsism. (I must say that as a geologist this goes over my head a bit!) However I have recently read Sean Carrolls...
  10. EclogiteFacies

    I Consistent Histories Interpretation - History

    I have just finished reading the book 'Three Roads to Quantum Gravity' by Lee Smolin. My question interestingly is associated with my geology background. Lee Smolin notes Fay Dowker concludes that if Consistent Histories is true then we cannot deduce the existence of dinosaurs 100 million...
  11. Someone_physics

    A Conditional time evolution entropy and the experimenter?

    Question --- So I've done a calculation which seems to suggest if I combine the system of a measuring apparatus to say an experimenter who "reacts" to the outcome of the the measurement versus one who does not. Then the change in entropy in both these situations is bounded by: $$ \Delta S_R...
  12. Muthumanimaran

    I Is a LASER a classical light source or a coherent state in quantum mechanics only?

    My question is the physics behind the LASER such as stimulated emission can be only explained by quantum mechanics only. We can represent LASER as coherent state in quantum mechanics only. Then how can we say LASER can be thought of a classical light source?
  13. cutecat

    Quantum Do you have a quantum physics book? Can I borrow it?

    Homework Statement:: I need a quantum physics book because I am learning it Relevant Equations:: Quantum physics I can borrow a pdf one
  14. dontknow

    A Statistical physics : Irreversibility

    I was reading mehran kardar (books and lectures) it says the concept of irreversibility comes from an assumption (in which we increase the length scale by interaction disctance between two particles). So My question is the concept of irreversibility is still valid in the case of 1 particle...
  15. E

    I Momentum of photons

    We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if: 1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's...
  16. J

    A Griffith's Elementary Particles Section 9.7 Electroweak Unification

    1. On pg. 343 Griffith's expresses the weak current in terms of left-handed doublets. jμ± = ##\bar χ_L##γμτ±##χ_L## ##χ_L## = ##\begin{pmatrix} ν_e \\ e \end{pmatrix}_L## ##\tau^+## = ##\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}## , ## \tau^- ## = ##\begin{pmatrix} 0 & 0 \\ 1 & 0...
  17. S

    Calculating degeneracy of the energy levels of a 2D harmonic oscillator

    Too dim for this kind of combinatorics. Could anyone refer me to/ explain a general way of approaching these without having to think :D. Thanks.
  18. Ishika_96_sparkles

    Mathematica PlotLegend not showing

    Here, are the parts of the plot function p1 = Plot[Normal[g*Exp[-x^2/2] /. solute[[1]] /. en -> 3], {x, -8, 8}, PlotStyle -> {Dashed, Gray}, PlotLegends -> Automatic]; (* Here, g=1 - x^2 - x^4/6 - x^6/30 - x^8/168 - x^10/1080 , energy en =3 and solute is the series solution of g with...
  19. micklat

    I Explaining atoms and bonding using entropy

    I am a biology undergraduate interested in abiogenesis. The entropic explanation for the origin of life is that life is allowed to exist because it increases universal entropy. I am curious about how far we can take this theory down. How can you explain the emergence of atoms and atomic...
  20. SamRoss

    I Seeking better explanation of some quantum stats formulae

    In "Introduction to Quantum Mechanics", Griffiths derives the following formulae for counting the number of configurations for N particles. Distinguishable particles... $$ N!\prod_{n=1}^\infty \frac {d^{N_n}_n} {N_n !} $$ Fermions... $$ \prod_{n=1}^\infty \frac {d_n!} {N_n!(d_n-N_n)!}$$...
  21. victor01

    I Clebsch–Gordan coefficients: An Identity

    Hi, everyone. I'm trying to get the next identity It is in the format <j1, j2; m1, m2 |j, m>. I hope you can help me
  22. E

    Bohr-Sommerfeld, WKB, and current-biased Josephson junction

    I've already found the turning points, in the case of the left turning point, the local minimum of the potential, ##\delta_{min}=1.11977## when evaluating for an arbitrary value of current ##J=0.9I_C##. The left turning point is therefore ##\delta_r=2.48243##. I know the Bohr-Sommerfeld...
  23. B

    Finding energy eigenvalues with perturbation

    I know the basis I should use is |m_1,m_2> and that each m can be 1,0,-1 but how do I get the eigenvalues from this?
  24. E

    S-wave phase shift for quantum mechanical scattering

    a.) The potential is a delta function, so ##V \left( r \right) = \frac {\hbar^2} {2\mu} \gamma \delta \left(r-a \right)##, therefore ##V \left( r \right) = \frac {\hbar^2} {2\mu} \gamma ## at ##r=a##, and ##V \left( r \right) = 0## otherwise. I've tried a few different approaches: 1.) In...
  25. CrosisBH

    Computing the wave function of a square potential

    The book's procedure for the "shooting method" The point of this program is to compute a wave function and to try and home in on the ground eigenvalue energy, which i should expect pi^2 / 8 = 1.2337.... This is my program (written in python) import matplotlib.pyplot as plt import numpy as...
  26. E

    Qubit Operations

    Part a: Gate H X Y Z S T R_x R_y Theta pi pi pi pi pi/2 pi/4 pi/2 pi/2 n_alpha (1/sqrt(2))*(1,0,1) (1,0,0) (0,1,0) (0,0,1) (0,0,1) (0,0,1) (1,0,0) (0,1,0) Using the info from the table and equation 1, I find: U_H=(i/sqrt(2))*[1,1;1,-1] U_X=i*[0,1;1,0] U_Y=i*[0,-i;i,0] U_Z=i*[1,0;0,-1]...
  27. patric44

    Perturbation treatment of hydrogen molecular ion

    hi guys i am a the third year undergrad student and in this 2nd semester in my collage we should start taking quantum mechanics along with molecular physics , our molecular physics professor choose a book that we are going to take which is " molecular physics by wolfgang Demtroder " when i...
  28. TopologyisGeometry

    Plotting the radial wave function of Deuteron in a finite well

    To plot ##u(r)## we need to find the solutions for each region. Which is in the relevant equations part. Now, I have to do this numerically. Using python 3.7 I made an ##u## which is filled with zeros and a for loop with if/elseif statement, basically telling it to plot values for whenever...
  29. Quantum Alchemy

    I What exactly is a measurement device and how does it work?

    What exactly is a measurement device and how does it carry out a measurement? For instance, in the double slit experiment, you always hear about particle/wave duality. When it's not being measured it behaves like a wave but when a measuring device is placed by the slits, it behaves like a...
  30. Cetus

    Five State Quantum System, need help understanding the question

    I’ve never worked with a quantum system with more that two states 1, -1, and I’ve just gotten this homework problem. I'm not sure what it means. Does this mean it has five states? Why are there two 0’s and two 1’s?