What is Quantum: Definition and 999 Discussions

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. P

    I According to quantum physics, can our universe be a simulation?

    What does quantum physics say about the simulation hypothesis?
  2. A

    Quantum Theory Of Semiconductor Quantum Dots + other books on this topic

    Hello, I have two questions into one. First I would like to know what books are considered the best to introduce the theory of quantum dots, so for example with the k.p method, tight-binding, empirical pseudopotentials, and other techniques, analytical derivations, optical properties, band...
  3. Auto-Didact

    A Experimental evidence of non-local quantum forces

    Becker et al. 2019, Asymmetry and non-dispersivity in the Aharonov-Bohm effect The paper is open access and published in Nature Communications.
  4. A. Neumaier

    I Exploring Quantum Gravity's Impact on Quantum Mechanics

    See Peter Shor's comments here and here and Urs Schreiber's comments here.
  5. J

    A Does the effective action make sense in Quantum Mechanics?

    I think the effective action should make sense also in Quantum Mechanics, not only in QFT. But I have never seen described in a QM book as such. Could there be a QM book that uses effective actions? Or maybe in QM effective actions are called another name? I think effective actions in QM could...
  6. samalkhaiat

    Insights The Classical Limit of Quantum Mechanical Commutator

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  7. D

    I Compute the optical gain of a quantum well

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  8. E

    Find the atom using a quantum oracle

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  9. A. Neumaier

    I The Philosophy of Quantum Mechanics

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  10. T

    I Problem of time in quantum field theory?

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  11. Haorong Wu

    I Is there a procedure for designing some quantum circuits?

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  12. C

    How can I derive Eq 9.5.11 in Scully's Quantum Optics

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  13. A. Neumaier

    A Jürg Fröhlich on the deeper meaning of Quantum Mechanics

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  14. Ramil

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  15. Hawkingo

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  16. R

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  17. J

    A What does "solving a quantum mechanics problem" mean?

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  18. platosuniverse

    B Is spacetime a quantum error correcting code?

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  19. S

    B Loss of information and Quantum Determinism

    Other than with black holes, are there any other natural ways that quantum information can be lost, and thus jeopardize quantum determinism?
  20. A. Neumaier

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  21. C

    Writing: Input Wanted Ability to influence quantum probability

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  22. binbagsss

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  23. M

    Fermi energy in a quantum well

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  24. M

    I Vector Notation of Quantum States for 2 Qubit System

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  25. Danny Boy

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  26. Haorong Wu

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  27. S

    I Kim's 1999 delayed-choice quantum eraser experiment

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  28. M

    Mass in motivic quantum gravity

    From the proceedings of Group32, the 32nd International Colloquium on Group Theoretical Methods in Physics (9–13 July 2018, Prague): https://iopscience.iop.org/article/10.1088/1742-6596/1194/1/012097 M D Sheppeard Abstract: A physical approach to a category of motives must account for the...
  29. J

    B Proietti 2019 experiment: Doubt in measuring A1(B1)

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  30. L

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  31. A

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  32. A

    I Which operator for reflection in quantum mechanics?

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  33. S

    I Griffiths: Intro To Quantum Example 4.3 clarification , <Sx> =

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  34. Silvio Macedo

    I Wave function of particle / quantum field in space, also in time?

    Quantum fields have wave functions that determine a particle position in space. It solves non-locality, double-slit paradox, tunnel effect, etc. What if the wave function is also in time? Won't it solve the breaking of causality at quantum level? (Delayed Choice/Quantum Eraser/Time) Not much...
  35. L

    I Definition of a symmetry transformations in quantum mechanics

    By the Wigner theorem, symmetries transformations are implemented by operators ##\hat{U}## that are unitary or antiunitary. This is what is written in most books. But I have read somewhere that, to ##\hat{U}## represent a symmetrie, it's necessary that ##\hat{U}^{\dagger} \hat{H} \hat{U} =...
  36. Bure

    A The uncertainty principle in quantum gravity

    The main role in quantum gravity can be played by the uncertainty principle , where is the gravitational radius, is the radial coordinate, is the Planck length. This uncertainty principle is another form of Heisenberg's uncertainty principle between momentum and coordinate as applied to the...
  37. S

    A Measuring Quantum Vacuum Fluctuations

    I have been reviewing potential methods for measuring Quantum Vacuum Fluctuations that I might be able to implement in a home hobbyist environment. Must be room temperature devices. I have seen that there are only a couple of possibilities: The Tunnel FET and the Single Electron Transistor. I...
  38. P

    Angular momentum quantum number

    n is the principal quantum number. l is the angular momentum quantum number. ml is the magnetic quantum number. The possible values of l are 2, 3, and 4. I'm not sure if l can be equal to 4. On the answer key, it shows l = 2, 3.
  39. Danny Boy

    Quantum synchronization in a cavity

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  40. C

    Hermitian operators in quantum gravity

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  41. A. Neumaier

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    From here: From here: Peres writes on p.11: And on p.58: Note that Peres says that these issues are not yet fully understood! On p.63, Peres writes: On p.424: And on the next page: The footnote quoted by Peres says: And on p.25, where Peres introduces ensembles, he says (like Gibbs...
  42. Haorong Wu

    Courses Is Griffiths' QM sufficient before studying quantum computation?

    Hello, again. My current interest is quantum computation. I've finished Griffiths' QM for the first time. Because it only takes me a month studying the book, I may have study it superficial, so I plan to study it again and complete all the problems after each chapter. Then is this book...
  43. P

    I Lawrence Krauss: Quantum Mechanics is deterministic (video)

    I understand partly what he is saying, but can you discount the measurement effect as a feature of the world? Aren't measurement effects going on all the time between macroscopic and microscopic systems, making it in practice, at times, an indeterministic world? Or is he assuming that...
  44. SolitaryMan

    Studying Fields related to Quantum Information

    I am a master student in theoretical physics from Italy and I would like to know more about fields related to "Quantum Information". I've been to some seminars and I think that these fields are very interesting, but I need to understand before applying for a PhD. What should I do?
  45. B

    B How do I explain quantum superposition?

    I'm a student trying to explain quantum superposition without using Schrodinger's cat. Instead, I'm trying to use the principal of wave particle duality to explain how a particle can be in multiple states (and locations) at once before it is observed due to wave properties. However, I'm unsure...
  46. L

    I Doubt in the quantum harmonic oscillator

    I was reviewing the harmonic oscillator with Sakurai. Using the annihilation and the creation operators ##a## and ##a^{\dagger}##, and the number operator ##N = a^{\dagger}a##, with ##N |n \rangle = n | n \rangle##, he showed that ##a | n \rangle## is an eigenstate of ##N## with eigenvalue ##n -...
  47. A

    Courses Electromagnetism 1 vs. Quantum Mechanics 2

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  48. L

    I How do irrational numbers give incommensurate potential periods?

    I am trying to understand Aubry-Andre model. It has the following form $$H=∑_n c^†_nc_{n+1}+H.C.+V∑_n cos(2πβn)c^†_nc_n$$ This reference (at the 3rd page) says that if ##\beta## is irrational (rational) then the period of potential is quasi-periodic incommensurate (periodic commensurate) with...
  49. A

    A Quantum Espresso Tutorial: h-Boron Phosphide Variable-Cell Relaxation

    Hello my dear fellows, how're you doing? I'm trying to learn how to use Quantum Espresso, and in order to do this, I'm trying to simulate a hexagonal boron phosphide primary cell. At the end of the simulation, the structure seems to be fine, but sometimes the distance of the atoms are too short...
  50. S

    I How to quantum mechanically describe the photon?

    This might sound stupid , but I am wondering how exactly could I describe the momentum eigenfunctions of photons? EDIT: to destroy ambiguity, I am searching for a quantum mechanic description of monochromatic light similar to how we represent it classically as: E-> = a->cos(wt+phi)
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