Quantum Definition and 999 Threads

In physics, a quantum (plural quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a physical property can be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum.
For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation). Similarly, the energy of an electron bound within an atom is quantized and can exist only in certain discrete values. (Atoms and matter in general are stable because electrons can exist only at discrete energy levels within an atom.) Quantization is one of the foundations of the much broader physics of quantum mechanics. Quantization of energy and its influence on how energy and matter interact (quantum electrodynamics) is part of the fundamental framework for understanding and describing nature.

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  1. wolfy

    B Quantum Tunneling different individual transmission probabilities

    I have gone through all the videos on Youtube about Quantum Tunneling and became interested in it, so any helpful feedback would be appreciated. Do all the different individual transmission probabilities of electrons, protons, and such remain constant? May I ask what is the "formula" or...
  2. jjson775

    How can I accurately calculate the quantum number of a pendulum?

    Summary:: Calculate the quantum number of a pendulum I want to calculate the quantum number of pendulum. L = 1m, m = 1 kg., A= 3cm. I get a period of 2.01 sec. and f = 1/T = .498 sec. E =nhf gives me 2.67x10^31. The correct answer is 1.33x10^31, Where am I going wrong? [Thread moved from...
  3. Ishika_96_sparkles

    Mathematica Troubleshooting 'PlotLegend not showing' in Plot Function: Solutions & Examples

    Here, are the parts of the plot functionp1 = 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 unknown...
  4. mahonskey

    B Quantum total eclipse of the sun?

    This might be total nonsense, but the thought popped into my head while I was trying to get to sleep, so I thought I see if I could find any advanced help with the following hypothetical: If light were instantaneous, how far from Earth would the sun have to be to cause a quark orbiting in place...
  5. forever_physicist

    I Quantum operators and trasformation under rotations

    Good morning! I have a problem in understanding the steps from vectors to operators. Imagine you are given a vectorial observable. In classical mechanics, after rotating the system it transform with a rotation matrix R. If we go to quantum mechanics, this observable becomes an operator that is...
  6. M

    What are the prerequisites to study quantum field theory?

    Summary:: What are the prerequisites to study quantum field theory? What are the prerequisites to study quantum field theory?
  7. 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...
  8. L

    A Quantum computers and Annular Josephson junctions

    Are annular Josephson junctions qubits in some quantum computer right now? https://www.nature.com/articles/425133aI found this article from 2003. What is the progress right now? Also are vortices and fluxons same thing?
  9. Haorong Wu

    Courses I am a graduate student in quantum optics. Should I learn QFT?

    I am particularly interesting in QFT, and I am going to be a graduate student in quantum optics and quantum information this autumn. Strangely, I find that there is no courses for QFT. After all, I though QFT are about quantum and field, and quantum optics are about quantum and field, too...
  10. AndreasC

    Quantum Hilbert spaces and quantum operators being infinite dimensional matrices

    I just realized quantum operators X and P aren't actually just generalizations of matrices in infinite dimensions that you can naively play with as if they're usual matrices. Then I learned that the space of quantum states is not actually a Hilbert space but a "rigged" Hilbert space. It all...
  11. bob012345

    I Is Quantum Mechanics Infinitely More Complex than Classical Mechanics?

    Please critique this text. It came from a research article* I found but I'm only interested if the sentence is 100% accurate or not and not in the specifics of the article itself. Are they suggesting Hilbert space is always infinite? Thanks. Quantum mechanics is infinitely more complicated than...
  12. mktsgm

    Quantum of cells directly infected by a virus?

    In any viral infection, we know that an invading virus enters the cell and damages them (cytolytic/cytopathic). This may be a starting point for inflammation down the road. Though initial inflammation may be beneficial, a longer than necessary inflammatory process proves more damaging than...
  13. Y

    A Quantum finance equation explanation please

    Dear all, Dr. Raymond S. T. Lee in his book on Quantum Finance (page 112), normalizes quantum price return QPR(n) using the following scaling: Normalized QPR(n)=1+0.21*sigma*QPR(n). I don't know of any way of explaining this equation. sigma is the standard deviation of the wave function...
  14. G Delta

    I Quantum Realism and Bell Locality

    I would like to pose a question (previously posed to DrChinese in a personal message) regarding Bell Locality. From PeterDonis in another thread: Bell assumes that local realism requires the factorizability of the joint probability function. Most of the efforts to justify this assumption have...
  15. A. Neumaier

    I Steven Weinberg on the interpretation of quantum mechanics

    I think Weinberg is quite clear about this: On p.87 of the second edition of his quantum mechanics book, he says, and on p.88: After having discussed decoherence, he says on p.92: For the instrumentalist approach (apparently your view of the matter), he states on p.92f this drawback: Then...
  16. B

    A Quantum Period is Compression Robust

    https://arxiv.org/abs/1905.10074 The paper finds that one can reduce the number of qubits to a constant (just one works) used in the last, modular exponential register of the variants of Shor's algorithm, used to factor integers and find discrete logarithms, by applying a universal hash...
  17. G

    I How does Bohmian mechanics explain quantum bomb testing?

    Hi. In an Elitzur–Vaidman bomb tester, will the guiding wave be different in a situation with a live bomb compared to one with only a dud? And if yes, how does the bomb interact with the guiding wave? Because usually it is described as a pointlike device that only explodes when hit by the...
  18. 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... $$ \prod_{n=1}^\infty \frac {d_n!} {N_n!(d_n-N_n)!}$$...
  19. PGaccount

    I Partition function of quantum mechanics

    In quantum mechanics, we have the partition function Z[j] = e-W[j] = ∫ eiS+ jiOi. The propagator between two points 1 and 2 can be calculated as ## \frac{\delta}{\delta j_1}\frac{\delta}{\delta j_2} Z = \langle O_1 O_2 \rangle## The S in the path integral has been replaced by S → S + jiOi...
  20. P

    I Help! I Don't Understand Quantum Darwinism

    I have been trying to understand quantum Darwinism and I just don't get it. It seems to be like decoherence yet I don't see any value added. I don't think I'm even understanding it. I cannot even understand what a pointer state is supose to be. Apologies if this is the wrong place to ask but I...
  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. K

    I Quantum Field Operators for Bosons

    Consider the field creation operator ψ†(x) = ∫d3p ap†exp(-ip.x) My understanding is that this operator does not add particles from a particular momentum state. Rather it coherently (in-phase) adds a particle created from |0> expanded as a superposition of momentum eigenstates states...
  23. troglodyte

    I Struggling with one step to show quantum operator equality

    Hello guys, I struggle with one step in a calculation to show a quantum operator equality .It would be nice to get some help from you.The problematic step is red marked.I make a photo of my whiteboard activities.The main problem is the step where two infinite sums pops although I work...
  24. AndreasC

    I Exploring Foundations of Quantum Mechanics & QFT

    Hey, applied maths and physics student here. I started wondering recently what the meaning of measurement was in quantum mechanics, and I remembered that I had once heard of the bohmian interpretation which challenged the impression I had so far (which was that hidden variables had been...
  25. E

    Extended Essay IB - Quantum Physics Oriented

    Summary:: - IB Extended Essay - Physics - Quantum Mechanics and Electricity/ Electrical Components I've been asked to pick a topic for my IB Extended Essay. Basically the extended essay is a piece of independent research done during the course of IB. It's meant to be 4000 words and you have to...
  26. T

    A Evaluating Matrix Spin Dependent Term in Dirac Quadratic Equation

    I derive the quadratic form of Dirac equation as follows $$\lbrace[i\not \partial-e\not A]^2-m^2\rbrace\psi=\lbrace\left( i\partial-e A\right)^2 + \frac{1}{2i} \sigma^{\mu\nu}F_{\mu \nu}-m^2\rbrace\psi=0$$ And I need to find the form of the spin dependent term to get the final expression $$g...
  27. shintashi

    B Is there a Relativistic Quantum Chemistry Table?

    Wiki said "Arnold Sommerfeld calculated that, for a 1s orbital electron of a hydrogen atom with an orbiting radius of 0.0529 nm, α ≈ 1/137. That is to say, the fine-structure constant shows the electron traveling at nearly 1/137 the speed of light.[9] One can extend this to a larger element with...
  28. 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...
  29. 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...
  30. 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?
  31. 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...
  32. 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...
  33. 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?
  34. 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]...
  35. 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 ?
  36. 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...
  37. 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...
  38. 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...
  39. 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...
  40. 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...
  41. 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...
  42. 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...
  43. 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...
  44. A

    A Quantum vacuum fluctuation in BEC

    Hi, I have some problems with visualization (I'm trying to understand Jeff Steinhauer's experiment, but my questions are general). Why the quantum vacuum fluctuations are guaranteed by the underlying pointlike atoms composing a BEC? And if vacuum fluctuations generate excitations (i.e...
  45. 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...
  46. 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?
  47. 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...
  48. 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...
  49. 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?
  50. 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...
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