# Search results

1. ### Is a perfect circle possible?

You're saying this as if not having an infinite precision number is the only problem of having a perfect circle. I think many students do this and confuse physics with math. There's a very thick line separating physics from math, and that's where you're wrong. A circle is a mathematical...
2. ### Physics in banks -- Is it the right thing to go for?

@bigfooted Thank you very much. Your message made me feel much better. Would you provide me some help on the personal level? Since you work at a very similar thing as I do, you would know what I need to do to get started, and what I need to focus on. I'd appreciate it a lot. Can I PM you?
3. ### Physics in banks -- Is it the right thing to go for?

Dear readers: I would like to share my story with you, and I really appreciate your advice. I graduated last year from ETH Zürich as a PhD in physics. Now I'm doing a Postdoc in a group as my first step in a "science" career. The Problem: As much as I love research and enjoy doing science...
4. ### Finding the density matrix

@vanhees71 I agree the asker asked an ambiguous question. The probability to be in state j is P_j=\langle \psi | o_j \rangle I would say. I think people learning QM always get confused because the concept of preparation of states isn't clear. I guess a logical question for a new learner is...
5. ### Finding the density matrix

@vanhees71 I see. You're talking about the eigenvalues of the density matrix itself. I think the asker meant the eigenvalues of the Hamiltonian, which explains why he provided eigenvalues -1 and 1.
6. ### Finding the density matrix

@vanhees71 Although this is an old post, but I really have to ask: Why are you constructing the density matrix using the eigenvalues and not the probabilities? This makes it like if the eigenvalue has units of energy, the density matrix will have units of energy too... isn't the density matrix...
7. ### EMU sensitivity unit for SQUID magnetometers

Thank you for your response, though I would like to tell you that definitely googling it is the first thing I have done, but it doesn't help, because apparently EMU has many different conventions and I'm looking for something specific used for magnetometer sensitivity. Magnetometer sensitivity...
8. ### EMU sensitivity unit for SQUID magnetometers

In many, many articles about the SQUID magnetometer, I see people referring to the sensitivity of the magnetometer in units of EMU, as in this article: http://iopscience.iop.org/0268-1242/26/6/064006 or this http://link.springer.com/article/10.1007%2FBF02570388 Could someone please explain...
9. ### Advanced atomic physx: From Liouville Equation to the Bloch equations

Thanks to the people who've helped, though the problem was pointed to me by my Professor. The problem was in the definition of raising and lowering operators with respect to spherical basis...
10. ### Advanced atomic physx: From Liouville Equation to the Bloch equations

Thank you for your response. As reasonable as what you're saying sounds, I verified the signs like 5 times in different times to make sure there's no mistake, and I can't find any. Let me give an example. Let's talk about the z equation. The equation is...
11. ### Advanced atomic physx: From Liouville Equation to the Bloch equations

Thanks for your response. I checked it and I found no sign error; though maybe I'm wrong, but this is a secondary problem, since even if a sign error is there, this won't resolve the problem I'm facing where those equations have nothing to do with Bloch equations the way we know them. Any...
12. ### Advanced atomic physx: From Liouville Equation to the Bloch equations

In that line k=1,q=0, which makes the \omega_0 term vanish because it's muliplied by q. Best regards.
13. ### Advanced atomic physx: From Liouville Equation to the Bloch equations

This question was on Stackexchange, and no one was able to solve it. So now I'm posting it here, and I wish someone could help. I'm trying to derive the Bloch equations[1] from the Liouville equation[2]. This should be possible according to this paper[3], where it discusses higher order Bloch...
14. ### Combine Hamiltonians of two different bases

Thank you for your answers, guys. Like Kith said, I need to add components and not have the product. A 63*63 matrix is redundant, where it gives me, for example, a state | F=3,F=4,m_F=3,m_F=-4 \rangle, which is definitely wrong. What I'm doing is adding components... please consider...
15. ### Combine Hamiltonians of two different bases

If I do this product the result's side length will become 7*9=63 elements... while my combined system from F=3 and F=4 has only 7+9=16 elements, since F=3 has side-length 2*3+1=7 and F=4 has 2*4+1=9. So here's the problem right now.
16. ### Combine Hamiltonians of two different bases

Thank you for your time. Wigner D-Matrix for that case will be the following, starting from the eigen-vector |F=3;m_F=-3 \rangle to |F=3;m_F=3 \rangle D^{F=3}=\left( \begin{array}{ccccccc} e^{-3 i \alpha -3 i \gamma } \cos ^6\left(\frac{\beta }{2}\right) & -\sqrt{6} e^{-3 i \alpha -2 i \gamma...
17. ### Combine Hamiltonians of two different bases

Thank you, I appreciate your help so far. You could though (if you're interested) look at this further. Wigner-D matrices are simply the matrices that provide rotations in the angular momentum basis with Euler angles. So you have a basis of F=3 and m_F=-3,...,3, the Wigner-D matrix will be...
18. ### Combine Hamiltonians of two different bases

Hmmmmmmm... Thank you so much. Though I thought this approach would solve my problem, but apparently it doesn't. I have Hyperfine states with F=3,4 (where F=I+J is the sum of the total angular momentum and the nuclear spin), and I want to separate them, do a rotation with Wigner-D matrices, and...
19. ### Combine Hamiltonians of two different bases

Thank you so much for your answer. Let me though put an example to make this clear, because I got some result that I don't believe. Say I have the Hamiltonian matrices H_1 and H_2 H_1=\left( \begin{array}{cccc} \text{s1} & 0 & 0 & 0 \\ 0 & \text{s2} & 0 & 0 \\ 0 & 0 & \text{s3} & 0 \\ 0 & 0...
20. ### Combine Hamiltonians of two different bases

I'm trying to solve a dynamical quantum mechanics problem related to the Cs atom, but I'm having trouble in the following, and I'm afraid I'm doing it wrong. Say I have the matrix form of the Hamiltonian on a basis for a system | \psi \rangle to be H_\psi, and another system with bases |...
21. ### Adding Angular Momentum is commutative, right?

Ah, I see! So the Hamiltonian changes but the Eigenvalues don't change. Thank you so much.
22. ### Adding Angular Momentum is commutative, right?

Thank you for your reply. I still have a little problem understanding how those two cases are equivalent physically. You're telling me that both cases are equivalent up to a phase factor, but I see there's different physics there, because one gets different energy splitting/displacement...
23. ### Adding Angular Momentum is commutative, right?

I have angular momenta S=\frac{1}{2} for spin, and I=\frac{1}{2} for nuclear angular momentum, which I want to add using the Clebsch-Gordon basis, so the conversion looks like:  \begin{align} \lvert 1,1\rangle &= \lvert\bigl(\tfrac{1}{2}\tfrac{1}{2}\bigr)\tfrac{1}{2}\tfrac{1}{2}...
24. ### Hamiltonian matrix off diagonal elements?

Thank you so much for your answer. There's something weird happening when I do this calculation that I don't understand. Now we are adding I and S, and this addition is supposed to be commutative, right? Look at the expectation value that you wrote there: \left\langle 1 0 \frac{1}{2}...
25. ### Hamiltonian matrix off diagonal elements?

Thank you for your reply. The problem is exactly the way you understood it. Actually my problem is how to create the Hamiltonian matrix in the \left| {{I^2}{I_z}{S^2}{S_z}} \right\rangle basis. Can you please explain how to create that hamiltonian?
26. ### Hamiltonian matrix off diagonal elements?

I'm trying to understand how Hamiltonian matrices are built for optical applications. In the excerpts below, from the book "Optically polarized atoms: understanding light-atom interaction", what I don't understand is: Why are the \mu B parts not diagonal? If the Hamiltonian is \vec{\mu} \cdot...
27. ### Magnetic field from a coil (on Mathematica)

@lpetrich Thanks a lot! what a stupid mistake!
28. ### Magnetic field from a coil (on Mathematica)

Hello guys, I'm trying to find the configuration of two circular coils in a configuration similar to Helmholtz coils that would homogenize the magnetic field best at a volume between them. So the first thing step I took in that is use the Biot-Savart law to calculate the magnetic field...
29. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

I'm not an expert (as you see here in my discussion), but I'd like to contribute to this. I've just read this website explaining the Quantum Eraser in detail http://grad.physics.sunysb.edu/~amarch/ [Broken] And I got convinced that the experiment proves that the setup of the experiment is...
30. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Thank you for your response. Let me see if I understand this correctly. You're telling me that the states of the apparatus and the states of the system are superposed rather than being tensor-multiplied, which causes the new big system (which consists of both the apparatus and the system being...
31. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

@Ger Thank you for the link, but I was given the link in the few first comments.
32. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Thanks for the answer. But why would you think that an incomplete basis should give you a unity probability, thus claiming that the Copenhagen interpretation is problematic? I mean you're simply giving your state/probability current a path to escape to a state that you haven't taken into...
33. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

I'm sorry, but I still don't see the problem. Whenever you see a state you haven't accounted for, can't you simply add it and renormalize again? Why can't this be done?
34. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Ah, you're right. I'm sorry. That identity is obvious, I don't know why I got confused. But doesn't this mean already that if ∥ψ′∥<∥ψ∥, then ∑|a,α><a,α| < 1, which means that the vector space isn't complete and still requires more bases, bringing us back to my cross-product example?
35. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Thank you for your answer. I'm confused a little bit, and apparently I'm not as good as I thought in Quantum Mechanics, even after reading 3 Quantum Field Theory books and having a QFT course. Can you please clarify, why should ∥ψ′∥≤∥ψ∥? Do the books you mentioned explain this paradigm of...
36. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Thank you dextercioby and UltrafastPED; your comments were helpful. vanhees71: I'm not sure how to answer your argument, but you left the main topic and went far away; maybe I'm wrong, but you probably have some problems understanding Quantum Mechanics. I'm not willing to go into a discussion...
37. ### Can Quantum Mechanics be studied without the Copenhagen interpretation

Hello everyone, I'm a doctoral student of particle physics in ETH Zurich, and have a question in fundamental QM. I remember a friend telling me that the professor that taught him Quantum Mechanics in ETH Zurich did not believe in the Copenhagen interpretation, and thus taught the class...
38. ### Is mathematics a separate entity from nature?

Dear micromass, thank you for your answer and your time. First, I would like to express my extreme disagreement with the article in the link you provided. The guy in the article is completely mixing two different things: 1- The mathematics as an entity, 2- and the way we understand...
39. ### Is mathematics a separate entity from nature?

Hello guys: A very known fact we live is that mathematics is not falsifiable. There hasn't been a day in history when someone came up and made an experiment to prove that the equation "x^2-5x+6=0" has solutions different than 2 and 3. In science, if we find something that doesn't comply...
40. ### Is the Big Bang a theory or a hypothesis?

Thank you all for the replies. They are all great, except the one from "Xyooj", which was hilarious. If anyone has more to say about this, please feel free to do it :)
41. ### Is the Big Bang a theory or a hypothesis?

Hello everyone: I'm a doctoral student in particle physics, confused about something pretty fundamental and need your help. From what I know, the only evidence we have from the Big Bang is the Cosmic Microwave Background radiation (CMB), which showed up around 300k years after the...
42. ### Two level system Schrodinger Equation problem

Got it. Thanks man :)
43. ### Two level system Schrodinger Equation problem

Hello guys, in the attached file, I can't understand how the guy arrived to the equation in the red rectangle. My problem is: how could there not be dC2/dt term. Why only dC1/dt term? ψ contains both C1 and C2, and when the derivative is applied, both have to be influenced, and both are...
44. ### Beam splitters cubes configurations

Hello guys, I'm not sure this is the right place to ask the question, but I hope someone would have experience with beam splitters cubes. If I want to split a laser beam over more than one level with more than one beam splitter cube, so the first beam splitter splits to two beams with 50%...
45. ### Normals of a Dodecahedron

Hello guys, I need the normals of a Dodecahedron (fully symmetric 12 facets' polyhedron) given in rational numbers. I got tired searching the internet for that, so I expect something like: {-Sqrt[1 + 2/Sqrt[5]], 0, 1/2 Sqrt[1/10 (5 - Sqrt[5])]]} I tried Mathematica, but it gives 20 Faces for...
46. ### Cesium Atom quantum mechanical description

Thank you again for your replies. We're doing a very specific research about Cesium magnetometers. The transitions I'm looking for are depicted in the attachment please take a look at it. We're currently solving the Bloch's equation numerically to simulate the responce of the gas to the...
47. ### Cesium Atom quantum mechanical description

Has anyone made such a Hamiltonian and solved it? I would like to see previous contributions to this field, so that I could start working. I found nothing so far, and that's why I'm asking for help!
48. ### Cesium Atom quantum mechanical description

Well that's my question. What are the available methods for obtaining the wave-function of Cs? I have a problem where I have a Cs gas in a chamber under a magnetic field and pumped by a laser beam. I need at least some wave function to put it in my density matrix to start doing this. But this...
49. ### Cesium Atom quantum mechanical description

I didn't find any particular thing available for the wave-function of the Cesium atom... that's why I'm surprised. If you know any reference that would help, please let me know.
50. ### Cesium Atom quantum mechanical description

OK... let me rephrase the question... Has anyone in the history of physics solved the Schrodinger equation of a Cesium Atom? Why can't I find anything about that? Any references would help. Thanks!