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. S

    Physics Solid State Physics or Quantum Electronics/Optics

    For which field is there more demand in the industry? And is knowledge of quantum electronics/optics useless without having a phd, as I see most job offers ask for a doctorate degree. Are the skills and knowledge from quantum electronics transferable to engineering positions or is what you...
  2. Vanilla Gorilla

    I Would Black Holes Be Coherent Under Quantum Mechanics?

    I just want to know if Black Holes would be quantumly coherent.
  3. Jamister

    Programs Searching for universities to do my PhD on foundations of quantum mechanics

    I want to do my Phd on foundations of quantum mechanics, but I don't find researchers in the U.S.A that work on that. Is there a good way to search other than to go to each university and go over the PI's? Thanks
  4. L

    I Quantum Measurements with Gravitational Waves

    Would using gravitational waves to measure (it's obviously a gedankenexperiment!) position and momentum of, say, an electron in a specific state, disprove HUP since the quantum of energy of grav. waves does not exist? Would it be possibile to have an arbitrarily small uncertainty in position...
  5. D

    A Suggested reading for quantum information applications in QFT

    What would you say is essential reading for those of us who want to understand how exactly is QFT benefiting from QI? Can anyone give a summary of what is happening, and where to start reading? (at postgraduate/entry-research-level).
  6. Mayan Fung

    I Energy operator in Quantum Mechanics

    I learned that the energy operator is ##\hat{E} = i\hbar \frac{\partial}{\partial t} ## and the Hamiltonian is ##\hat{H} = \frac{-\hbar^2}{2m}\nabla^2+V(r,t)## If the Hamiltonian represents the total energy of the system. I expect the two should be the same. Did I misunderstand the concept of...
  7. ubergewehr273

    I Extraction of a particular quantum state from a quantum circuit

    Hello everyone! I'm trying to implement a quantum circuit that yields a superposition state $$\frac{1}{\sqrt{2}} (|01 \rangle + |10 \rangle)$$ I'm using parameterized gates to achieve this. I have been able to create the state $$\frac{1}{\sqrt{2}}(|01\rangle + e^{i\phi} |10 \rangle)$$ Is there...
  8. P

    B Quantum Entanglement Communication Radio

    Hello, first from all, I am completely new and uneducated in physics. But from nothing I have had idea how to make this invention. And I have quite strong need to share it. My mind found out how we can communicate with no delay through out our universe. Seems quite fancy, isn't it? Yes, quantum...
  9. wolfy

    What Prerequisites do I need in order to understand Quantum Tunneling?

    Summary:: What tools like Calculus, Algebra, etc do I need to Understand how to Write a Quantum Tunneling Equation? I am New to QM however I feel I may have what it takes to do the Math, however, I am not privy to what the Prerequisites are that are needed to perform the...
  10. patric44

    Quantum Dirac notation based quantum books?

    hi i am recently following the nptel course in quantum mechanics (The Course ) and it seems like a really good course , but i can't find the book that it based on . my question is : had anyone saw that course before to suggest a QM book related to it ? - she began by an introduction to vector...
  11. wolfy

    B Simulators for Quantum Mechanics

    A member helped me discover a new quantum tunneling sim online, it's free and quite amazing to look at. https://phet.colorado.edu/en/simulation/quantum-tunneling Are there any other more advance simulators on the net and would anyone like to discuss this program with me as I am new to Quantum...
  12. R

    Quantum What Book Best Explores Quantum Mechanics for Conceptual Thinkers?

    Hi everyone , I am interested in learning quantum mechanics. I want to read a book which explains each and every aspect of quantum physics , gives a conceptual understanding with the help of logical thinking. Also it should be like that if I know the most basic theory and...
  13. S

    I A 5th Dimension May Explain Quantum Theory

    At least according to Tim Anderson Ph.D who wrote the paper in Physics Review. https://news.knowledia.com/US/en/articles/a-5th-dimension-may-explain-quantum-theory-the-infinite-universe-medium-6f1d6fd371e068a07f357b9babe9ab2eec06d034 What do you make of this? "The paper simply presents...
  14. Demystifier

    A Philosophy of quantum field theory

    I usually don't read papers on philosophy of quantum field theory, but this one is really good: http://philsci-archive.pitt.edu/8890/ In particular, the prelude which I quote here is a true gem: "Once upon a time there was a community of physicists. This community be- lieved, and had good...
  15. Keth

    Any studies looking for a quantum bump in human photoreceptors?

    Has there been a study looking for a quantum bump in human photoreceptors. I've done some searching and haven't crossed anything as of yet.
  16. thegroundhog

    Unanswered Questions in Popular Science: Exploring the Gaps in Quantum Physics

    I read a lot of popular science books, especially on quantum physics. My favourite authors are Brian Cox, Sean Carroll, Jim Al-Khalili, Marcus du Sautoy and Brian Greene. I have joined this forum as the more I read the more questions I have that are not covered in detail by the above writers...
  17. ChrisVer

    A Search for literature on Quantum Gravity

    Hi all, I am looking for a pedagogical (or maybe also historical) paper that describes the attempts of quantizing gravity and the problems that appear along the lines. It is quite interesting to hear from public talks that "when we try to canonically quantize gravity as we did EM we get...
  18. E

    I Photon Momentum: The Impact of Light on Movement in Space

    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...
  19. allisrelative

    B Time-reversal of an unknown quantum state

    A very interesting paper was recently released that's a follow up to the paper that talked about Time Reversal to a known state. If you remember a lot of papers talked about how they reversed time. Here's more from the new article. Basically, Schrodinger's equation is reversable and there's no...
  20. Leonardo Muzzi

    I Quantum Eraser: do entangled photons arrive at different moments?

    Considering a Delayed Choice Quantum Eraser experiment such as the one in the picture above: It is said that paired photons arriving at the detectors A,B,C,or D, reach the detectors after the entangled pair has reached the interference screen. Are we actually able to measure the time interval...
  21. ohwilleke

    I Trouble for Loop Quantum Gravity?

    A new preprint establishes that almost all models implementing loop quantum gravity violate the principle of general covariance, and can only satisfy a more limited condition. Is this the huge problem for loop quantum gravity theory that it appears to be? Or is the less strict condition that can...
  22. Danny Boy

    A Quantum Ising model correlation function query

    In this paper, on quantum Ising model dynamics, they consider the Hamiltonian $$\mathcal{H} = \sum_{j < k} J_{jk} \hat{\sigma}_{j}^{z}\hat{\sigma}_{k}^{z}$$ and the correlation function $$\mathcal{G} = \langle \mathcal{T}_C(\hat{\sigma}^{a_n}_{j_n}(t_n^*)\cdot\cdot\cdot...
  23. F

    B Does the future affect the past in a quantum world?

    Is this true?
  24. 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...
  25. S

    I Forces (Fields) of Nature and Quantum Foundations

    Is it possible for new forces or fields of nature to be connected to quantum foundations? For example, new forces or fields that choose the decoherent histories or branches. Or generally actualize one of the decoherence branches? Or should new forces or fields of nature be reserved for...
  26. F

    B Quantum Entanglement spin measurement

    Hi, When a quantum entangled photon is measured to determine spin does it's spin stay in that orientation as long as it's measured it or does it immediately go back to a superpositioned state? In other words if you determined the spin of a quantum entangled particle at say 12:00 pm and...
  27. N

    A General Covariance in Quantum Field Theory

    All physical laws have to be Lorentz invariant according to a lecture I just watched. Why is general covariance (which is more general than Lorentz invariance) not a requirement for all laws of physics? Are there any quantum gravity theories that take the approach of adding general covariance to...
  28. Leonardo Muzzi

    I Can an electron quantum tunnel inside the potential barrier?

    When I see explanations for quantum tunneling, the discussion is around the probability of an electron manifesting itself before the potential barrier, and after the potential barrier. However, looking at the curves draw, there is a non-zero probability (the evanescent part of the wave) inside...
  29. T

    B Exploring Quantum Decay: Understanding Energy Changes and Fixed Barriers

    For a system to undergo quantum decay, is the energy change and energy barrier fixed?
  30. Mondayman

    Quantum Intro to Quantum Electrodynamics

    Hi folks, Electricity and magnetism have always been my favorite subjects, and I am just getting to learn the basics of quantum theory and it is absolutely terrific going. I was always fascinated by the story of Feynman, Schwinger, and Tomonaga tackling QED from the books Genius by James Gleick...
  31. Jehannum

    B Are electromagnetic wavelength and quantum wavelength the same thing?

    The classical picture of the electromagnetic wave has electric and magnetic field oscillations which give the wavelength of the light. In the quantum picture, is the wavelength of the (de Broglie) wave function of the photon the same thing?
  32. redtree

    I Relativistic quantum mechanics

    Given that the Minkowski metric implies the Lorentz transformations and special relativity, why do the equations of relativistic quantum mechanics, i.e., the Dirac and Klein-Gordon equations, require a mass term to unite quantum mechanics and special relativity? Shouldn't their formulation in...
  33. R

    I Consciousness and quantum mechanics

    Reading book, “God? Very Probable”. The author quotes Wigners comments in his book, “Remarks on the Mind- Body Question” 169, 171, 173. “The very study of the external world led to the conclusion that the content of consciousness is an ultimate reality. Given the ultimate priority of...
  34. darthgoon

    B Dumb Q, let's discuss :: How would quantum communications work at the speed of light?

    I feel like the emerging idea of quantum communications; is that you can exchange data via the synchronous states of entangled particles, across any distance, in real-time. But, there's also this dilation in the physical world, at the speed of light, according to relativity. So- how would the...
  35. Ssnow

    I Quantum spaces without classical counterparts?

    Hi to all members! From few days that I am thinking on this question: there are finite-dimensional spaces that are quantum spaces (models for QM) but without the classical counterpart in classical mechanics ? For example I know that entanglement have not a ''clearly'' classical counterpart ...
  36. Phylosopher

    Quantum Is Zuber's Quantum Field Theory textbook any good?

    Hi, I have been studying Quantum Field Theory this semester! It seems that Shwartz and Peskin are the most popular choices when it comes to studying QFT. But apparently my professor have another "old" preference. He strongly suggested that we learn QFT from Zuber's book. I have looked at the...
  37. P

    I Necessity of Quantum Gravity given Planck scales for nuclear physics

    In the solutions (page 6, points ii) and iii)), https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2013/assignments/MIT8_04S13_ps1_sol.pdf, it is mentioned that given that the Planck mass is about 20 orders of magnitude larger than a proton and that the Planck length is about 20...
  38. atommo

    B Quantum Micro-Blackholes: Fact or Fiction?

    This is more of a general question than technical (but since its still physics-related I feel it still belongs in this section of the forum). Many of you probably remember back in 2008 the headlines in newspapers threatening CERN would make an 'Earth consuming' black hole - of course that...
  39. Superposed_Cat

    I Pair production via Quantum Tunneling has negative Kinetic energy?

    If we have a photon being converted to a positron-electron pair, but we lack enough energy for this to happen (hv<2Me*c^2) but the difference is smaller than the uncertainty amount, such that tunneling may be possible, would the resultant pair have net negative energy? Would tunneling even be...
  40. phun_physics

    I Representing Quantum Gates in Tensor Product Space

    Where do I start. I want to write the matrix form of a single or two qubit gate in the tensor product vector space of a many qubit system. Ill outline a simple example: Both qubits, ##q_0## and ##q_1## start in the ground state, ##|0 \rangle =\begin{pmatrix}1 \\ 0 \end{pmatrix}##. Then we...
  41. JD_PM

    Quantum Optics Question Involving Coherent States

    I've tried to square and compare ##\Delta X## and ##\Delta P## but they are not equal I have to say I am pretty lost here and a hint would be appreciated. I have studied coherent states and I know how to proof some properties related to it. For instance, I see how to proof that the state is...
  42. H

    I Does quantum theory describe light as a wave?

    Hello! I recently had a discussion with a person who's well-read on quantum physics and I was suprised by his claim that "light is in no sense regarded as a wave" in quantum mechanics. His support for this claim was that there are no wave crest or wave trough, there is nothing moving. What...
  43. 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.
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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?
  50. 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...
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