Quantum Definition and 998 Threads

  1. K

    Quantum High-level book on scattering in quantum mechanics

    I'm interested in a book which treats scattering in quantum mechanics aimed at the research-level. I'm particularly interested in a text which focuses on mathematical details such as the analytic structure of the S matrix, the relation between the S matrix and various green's/two-point...
  2. Replusz

    30-day Topological Quantum challenge

    Hey everyone, This is more of a motivational thread, and of course if anyone wants to join in, please do! Any comments are welcome. It's also fine if no one comments. Maybe don't remove the thread though please. I hope this might be useful later on for others as motivation. So the challenge is...
  3. Z

    I Could Quantum Physics explain the singularity in a Black Hole?

    If a singularity exists in the center of a black hole, could quantum physics, instead of relativity , explain it?
  4. nomadreid

    I Quantum logic based on closed Hilbert space subspaces

    One proposal that I have read (but cannot re-find the source, sorry) was to identify a truth value for a proposition (event) with the collection of closed subspaces in which the event had a probability of 1. But as I understand it, a Hilbert space is a framework which, unless trivial, keeps...
  5. Jarvis323

    I Modern Assesment of Grete Hermann's Philosophy on Quantum Mechanics

    As a quarantine hobby I've been learning about Grete Hermann and the early history of QM. I find her early philisophical contribution to be interesting, but I lack the background to put it into a modern context. A brief description can be found in the arxiv paper: Grete Hermann: An early...
  6. G

    A Quantum Mechanic/wave function/junction condition

    May i know how do i eliminate C and D and how do i obtain the last two equations? Are there skipping of steps in between 4th to 5th equation? What are the intermediate steps that i should take to transit from 4th equation to the 5th equation?
  7. kellys

    Help with this quantum circuit textbook problem about controlled gates

    Summary:: My skills are very very basic and I'm more a networking major but i had to take a quantum mechanics class, i have trouble with this xcercise from textbook quantum mechanics a general introduction [Mentor Note -- Thread moved from the Technical forums so no Homework Template is shown]...
  8. Adwit

    A Quantum Field Theory: 3-4 Equation Steps Explained

    I understand how do 3 no. equation come from 1 & 2 no. equation. But I am struggling to understand how do 4 no. equation come from 3 no. equation. Will anyone do the steps between 3 no. equation and 4 no. equation, please ?
  9. E

    I Quantum Computing: How are quantum properties exploited?

    To elaborate a little on what I think I do understand / accept: 1. I don't think I have a problem accepting the "weirdness" of quantum concepts. So, for example, I am willing to accept the concept that a quantum system can "exist" in a large number of different states simultaneously. 2. I...
  10. A

    Quantum physics and the theory of evolution

    How did you find PF?: Searching a way to share own thoughts I was wondering if we could gather all the laws of the universe and try to link anything to everything. I'm thinking of the possibility of finding links between quantum physics and the theory of evolution. It reminds me of the...
  11. E

    Quantum motion of a charged particle in a magnetic field

    Once I know the Hamiltonian, I know to take the determinant ##\left| \vec H-\lambda \vec I \right| = 0 ## and solve for ##\lambda## which are the eigenvalues/eigenenergies. My problem is, I'm unsure how to formulate the Hamiltonian. Is my potential ##U(r)## my scalar field ##\phi##? I've seen...
  12. cemtu

    Quantum Mechanics Hydrogen Atom Expectation Value Problem

    I can not solve this problem: However, I have a similar problem with proper solution: Can you please guide me to solve my question? I am not being able to relate Y R (from first question) and U (from second question), and solve the question at the top above...
  13. cemtu

    Quantum Mechanics hydrogen atom eigenfunction problem

    This is a general property of eigenvectors of Hermitian operators. State functions are a particular class of vector, and it is easiest to work in the general formalism (I am hoping to show how ket notation makes qm easier, not just do standard bookwork at this level). Suppose O is a Hermitian...
  14. N

    I Is it possible to explain Quantum tunneling with the HUP?

    I'm a student in South Korea(It is my first English question ever). I found descriptions of quantum tunneling explained by the uncertainty principle in Korea. There are two kinds of descriptions to explain quantum tunneling; position-momentum and time-energy uncertainty principle. First...
  15. The black vegetable

    I Vertex function, quantum action

    I am looking at Srednicki ch 64 , how does equation 64.1 follow from 64.3 as stated. Explicitly in QED how does ## u_{s'}(p')V^{u}(p',p)u_{s}(p)=e\bar{u'}(F_{1}(q^{2})\gamma ^{u}-\frac{i}{m}F_{2}(q^{2})S^{uv}q_{v})u ## follow from the quantum action ## \Gamma =\int d^{4}x(eF_{1}\bar{\varphi...
  16. J

    A Why is the quantum Fisher information useful in quantum metrology?

    I'm getting interested in quantum-enhanced metrology and have come across the quantum Fisher information (QFI) as a measure of how much a quantum state ##|\Psi(\theta)\rangle## changes with respect to some variable, for example, the phase accumulated during an interferometer, ##\theta##. This is...
  17. 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?
  18. J

    Schools Quantum Computing Phd: UNM vs LSU vs WashU

    Hello I am trying to choose a school and am interested in quantum computing theory in the physics department. I haven't decided whether or not I want to stay in academia so I would like the option to go into industry maybe at Google, IBM or a startup. Ideally I'd like the reputation/research to...
  19. A

    A Superluminal origin of Quantum Mechanics

    A relativistic origin of QM is proposed in https://iopscience.iop.org/article/10.1088/1367-2630/ab76f7 It is proposed that lorentz transformation that include superluminal observers (whether those observers exist or not) explain the indeterministic behavior of QM. Not only that, it also would...
  20. J

    B Quantum computing -- How is the relevant solution selected?

    During a quantum computation, all possible solutions exist in a state of superposition. How is the relevant one selected?
  21. L

    A Phonons as a quasiparticles in a quantum LHO

    I am confused with phonons as a quasiparticles in quantum LHO. When I say ##E_n=(n+\frac{1}{2})\hbar \omega## why ##n## is number of phonons? Why no magnons, excitones... And one more question. Why number of maxima of ##|\psi_n(x)|^2## is related to number of phonons, so that number of...
  22. 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...
  23. U

    I Quantum Mechanics Particle in a Box

    I need help .I did not A) E < V0 for T =? (passing coefficient ) B) E = V0 for T = ? C ) E > V0 for T =? A
  24. L

    A Potential step at a Barrier in Quantum mechanics

    In quantum mechanics in books authors discuss only cases ##E<V_0## and ##E>V_0##, where ##E## is energy of the particle and ##V_0## is height of the barrier. Why not ##E=V_0##? In that case for ##x<0## \psi_1(x)=Ae^{ikx}+Be^{-ikx} and for ##x\geq 0## \psi_2(x)=Cx+D and then from...
  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. W

    B Are all quantum fields coherent?

    Is coherence the medium in which quantum waves propagate? Does coherence also exist in the future to flag decoherence events?
  27. LarryS

    I Quantum Measurement under Heisenberg Picture?

    When a quantum measurement occurs under the Schrodinger picture, the wave function collapses to one of the eigenvectors of the operator-observable and the value measured is the corresponding eigenvalue of that eigenvector. What happens during a quantum measurement under the Heisenberg picture...
  28. K

    A Quantum entanglement and quantum foundation

    I was studying about the quantum entanglement phenomena and got introduced to the concept of EPR paradox. From this juncture, I see two schools of thought, one describing quantum mechanics as a probabilistic description and the other brings into question the local hidden variable theory. These...
  29. B

    Principle quantum number n of the excited state

    Here is a question I have been given I have started by setting up the formula and rearranging for n_2 Only problem is that I do not know the quantum number for ground state? What value do I sub in for n_1? Any help would be appreciated! Thanks
  30. K

    A Quantum Information research frontier

    I want to pursue research in Quantum Information Theory. I am surveying research topics before applying for PhD in Physics. Can somebody please enlighten me on the latest broad research problems being pursued in Quantum Information?
  31. G

    B Adjoint Operation in Shankar's "Principles of Quantum Mechanics

    In R Shankar text on “principles of quantum mechanics’ discussing the adjoint operation, 1.3.8 shows that a|V> => <V|a*. Then 1.3.9 then states that <aV| = <V|a*. Is this a typo error?
  32. K

    I Is there some agreement on properties of a theory of quantum gravity?

    Having read many times that there is no theory of quantum gravity, yet physicists at Physics Forums must have some ideas of what a theory of quantum gravity will contain. Is it allowed to discuss these questions at Physics Forums? Wikipedia does allow some current theoretical work to be...
  33. E

    Projective measurements of quantum processor

    Am I correct in thinking that the system measures the probability |<f|1>|^2 for some state <f|? Then the probabilities for each of the six states would be: |<0|1>|^2= 0 |<1|1>|^2= 1 |<+x|1>|^2= |(1/√2)|^2 = 1/2 |<-x|1>|^2= |(-1/√2)|^2 = 1/2 |<+y|1>|^2= |(-i/√2)|^2 = 1/2 |<-y|1>|^2= |(i/√2)|^2...
  34. E

    Qubit Operations: Finding U Gates & Probabilities

    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]...
  35. 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...
  36. S

    Quantum physics and philosophy (books)

    Summary:: Looking for recommendations Are there any books on the philosophical implications of quantum theory by people who know what they're talking about?
  37. S

    I How could a quantum system "predict the future"?

    What is nonlocality? How could a quantum system (like a superposition - is that right?) "know" an interaction will take place? Source...
  38. Quark Effect

    B Quantum Computing for Beginners: Understanding Double Hadamard Gates

    Hi guys, I am an absolute beginner in quantum computing. I am really curious about its mechanics but my lack of knowledge in mathematics makes me struggle. I cannot entirely understand why numbers |1> cancel each other out while double Hadamard gates are applied. If the rule is to cancel out the...
  39. Quark Effect

    B What is the significance of 'i' in quantum computation notation?

    Hi guys, I am currently having some difficulties with this quantum state. I don't entirely understand what that letter 'i' means, where it comes from and why it appears in brackets [1, i]. Shouldn't there be a '0' instead? I am an absolute beginner in quantum computation. I've been following a...
  40. V

    I Getting rid of nonlocality from quantum physics

    The main message of this post is that quantum theory is local, that "``spooky action at a distance'' was just shicky Einstein's slogan from a letter to Born in 1947. Einstein directed it against the individual interpretation of a quantum state. This interpretation is often referred as the...
  41. 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...
  42. Adwit

    I Rotation problem in Quantum Mechanics

    How do "sinϕ - cosϕ sinϕ" become 0 ?
  43. J

    Quantum Journal on hardware used to build quantum computers?

    Hi folks, This time is not a book, I would like to know if exists a journal explaining how a qubit is actually built, I mean the hardware not the theory. Indeed I am interested in any hardware related with these technologies. I know this field is still in an early stage and they are still...
  44. jisbon

    Quantum Physics (Electron in infinite deep quantum well)

    Hi all, below is my attempt. Pretty new at quantum so do correct me if I'm wrong. Thanks i) Since 1nm is the wavelength of the electron, Wavelength = 1nm, 1nm=2(2nm)/n , n=4? ii) - iii) From n=1 to n=4, Change in E = 15h^2/8mL where m is the mass of electron and L is 2nm? From the change in E...
  45. Pispi Choudhury

    Courses Math & Physics Courses for Quantum & Statistical Field Theory

    Summary:: What are the relevant mathematics/ mathematical physics courses for studying quantum field theory and statistical field theory? I'm a physics undergraduate currently in my junior(third) year, thanks.
  46. J

    Quantum Books teaching maths more advanced than what is used in quantum physics

    Hello friends. I was thinking that if you study physics, you learn first the basic math to understand it, but you don't go beyond, or deeper, you just learn the minimum math necessary to understand what you are going to see in your physics leassons. For example, if you are going to learn...
  47. entropy1

    I What does it mean to influence a quantum measurement's outcome?

    This just occurred to me and I don't expect to be the first one to address it: It is said that in a specific measurement basis, the outcome of a measurement in this basis is determined by chance. But in how far is this the case, since if the eigenvectors are for example ##\overrightarrow{A}##...
  48. 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...
  49. pinball1970

    A Quantum measurement of a Strontium ion

    I cannot post the science alert article where I saw this. Apologies, this put the study in layman's. @PeterDonis @vanhees71 et al will not need that. Is this significant? Could the wave function not instantaneously collapse?
  50. G

    Programs Quantum Computation and Information Master's Degree

    I'm in a Physics BSc programme and I would like to delve into quantum computation and quantum information. There are two master's degree in Europe that I find interesting in particular: Quantum Engineering MSc at ETH Zurich and Applied Physics MSc at TU Delft (track in Quantum Devices and...
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