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. A

    A Quantum Gravity Research Group -- any standing in mainstream Physics?

    I would like to know if this group http://www.quantumgravityresearch.org/ and its Emergence Theory has any standing in main stream Physics. Thanks Andrew
  2. M

    What is quantum physics and how can I learn more about it?

    So I love Quantum but unfortunately I don't have much idea of what its about. I would love to grasp the concept better. Can anyone discuss it with me?
  3. O

    I Unitary Processes and Completely Identical Quantum States

    EDIT: Questions have been revised below, those immediately following are for reference, jambaugh's kind reply was in direct response to these original questions. Could a completely unitary (QM) process act on a set of particles in "completely identical quantum states" to cause them to time...
  4. E

    I What does spin quantum number mean?

    A spin quantum number can have a value of 1/2 or -1/2. I assume that the negative means that these two spins are in opposite directions. However, what does the 1/2 mean? Why 1/2, rather than a whole integer? Are there some sort of units associated with this value?
  5. jedishrfu

    Universal Quantum Phenomena found in Strange Metals

    A recent paper in Nature describes a new phenomena found in superconducting materials: https://www.nature.com/articles/s41567-018-0334-2 Quanta magazine wrote about it here: https://www.quantamagazine.org/universal-quantum-phenomenon-found-in-superconductors-20181119/
  6. I

    I Fourier's Trick and calculation of Cn

    I understand that the solutions to the time-independent Schrodinger equation are complete, so a linear combination of the wavefunctions can describe any function (i.e. ##f(x) = \sum_{n = 1}^{\infty}c_n\psi_n(x) = \sqrt{\frac{2}{a}} \sum_{n=1}^{\infty} c_n\sin\left(\frac{n\pi}{a}x\right)## for...
  7. V

    Finding an element using quantum configuration

    havent done this stuff in lile 5-6 years so can't remember half of what to do lel. the first part i would like a yes/no please, Thanks. Given the quantum numbers (6,2,2,+1/2) what is the element, i said UUB becasue the first two numbers indicate 6D and the second would mean its +2 and positive...
  8. MatthijsRog

    I Role of determinate states in quantum mechanics

    Hi, I'm an undergrad, following my very first serious course in QM. We're following Griffith's book, and so far we're staying close to the text in terms of course structure. Griffiths starts out his book by postulating that each and every state for any system \Psi must be a solution to the...
  9. RUTA

    Insights The Quantum Mystery of Wigner's Friend - Comments

    Greg Bernhardt submitted a new blog post Wigner's Friend Continue reading the Original Blog Post.
  10. M

    I Photons and Heisenberg's Uncertainty Principle

    To summarize, my current understanding of how Heisenberg's uncertainty principal works suggests that there would be a contradiction (somewhere down the line) with any way that it applies to (or doesn't apply to) photons, due to the fact that they must always travel the speed of light. I...
  11. L

    I Estimate of ground state energy for the Yukawa potential

    I’ve seen the uncertainty principle used to calculate the ground state energy for things like hydrogen and the harmonic oscillator, but can this be done for the Yukawa potential where you have an exponential?
  12. Mathfan7

    B How to determine the wavefunction of photons?

    Hi, I'm sorry if this question has already been answered somewhere and I'm just too incompetent to find it, buuut: As the title already says, I really do not get that part of quantum physics (if you can even say I'm getting ANY part at all...). As I searched all Google for an answer I just...
  13. Ginosko

    B Does dimensions have the same meaning in the Quantum world?

    Does dimensions and time have the same meaning in the Quantum world? Maybe that explain weird things as the spooky action at distance. What evidence are about the real existence of a 3 geometry dimensions world at quantum level? Maybe even time have a different meaning in the quantum world.
  14. CharlieCW

    2D isotropic quantum harmonic oscillator: polar coordinates

    Homework Statement Find the eigenfunctions and eigenvalues of the isotropic bidimensional harmonic oscillator in polar coordinates. Homework Equations $$H=-\frac{\hbar}{2m}(\frac{\partial^2}{\partial r^2}+\frac{1}{r}\frac{\partial}{\partial r}+\frac{1}{r^2}\frac{\partial^2}{\partial...
  15. O

    I Measurement OF a Beamsplitter - Destroys Quantum Interference?

    In those experiments demonstrating quantum interference which rely on a beam splitter to create a superposition of a photon taking different paths, what would happen if one made a sufficient "measurement" of the momentum of the beamsplitter itself? Would or should it destroy the interference...
  16. Hawkingo

    I Want some suggestions for research papers on quantum entanglement

    I want to know more about quantum entanglement and I am a undergrad student in physics.Can someone suggest some research journals or articles to easily understand the concept deeply?
  17. CMJ96

    A Help Understanding a Quantum Circuit Identity

    Hello I have the following quantum circuit identity for converting a controlled U gate (4x4 matrix) into a series of CNOT gates and single qubit gates $$ U= AXA^{\dagger}X$$ where A is a unitary matrix. Here is a picture of the mentioned identity. Can someone help me understand conceptually...
  18. bbbl67

    Calculating the quantum state of an electron

    Homework Statement An electron in a hydrogen atom falling from an excited state to the ground state has the same wavelength than an electron moving at a speed of 7821 ms^-1. From which excited state did the electron fall from? Homework Equations I used the kinetic energy equation: K = (m...
  19. P

    I How does a nanogenerator work in quantum field theory?

    I studied the work of a nano generator in quantu mechanics. The generator uses the principle of triboelectrics. How does this work in quantum field theory? I think that the electron (wave packet in the field) is in the atom in a small volume because the nucleus inhibits the propagation of the...
  20. J

    I Would this experiment prove or disprove quantum randomness?

    I was told of a thought experiment by a friend of mine who says that his thought experiment will either prove or disprove randomness in quantum mechanics, and this was in fact verified by several other physicists, who said that if this experiment was ever successfully carried out it would either...
  21. Another

    I Question about Operators in Quantum Mechanics

    I study on quantum mechanics and I have question about operator. In one dimension. How do we know ## \hat{x} = x## and ## \hat{p}_{x} = -i \bar{h} \frac{d}{dx} ## When schrodinger was creating an equation, which later called "the schrodinger equation". How does he know momentum operator equal...
  22. jedishrfu

    B Is the Evidence for Quantum Entanglement in Bacteria Strong Enough?

    In a recent Scientific American article, researchers have claimed to have quantum entangled some bacteria: https://www.scientificamerican.com/article/schroedingers-bacterium-could-be-a-quantum-biology-milestone/
  23. Adrian Tudini

    Power of a Quantum Cascade laser by theory

    hi Just a little question. How does one calculate the power of a QCL by theory? Is there any free software that allows one to calculate the power of a inputted laser medium for a qcl? Thanks. Adrian
  24. C

    Finding the potential inside a semiconductor

    Homework Statement My question is more about understanding the task itself, not about calculation. I am supposed to use the poisson equation, to derive the potential inside a semiconductor for a barrier with potential height ##\phi_B## and a donator doping with ##N1 > N2##. Then I should use...
  25. Ramazan Duzgun

    Stopping Light in Air: Myth or Reality?

    is it possible, i mean can we hold it at a certain distance we want ?
  26. T

    B Quantum Entanglement: Explaining the Logic Behind It

    Hi, I read some about quantum entanglement but I don't really understand the logic behind it. If you quantum entangle 2 particles by for example colliding them and then separate them by a long distance they are both in superposition and you do not know the spin of them. Then you separate them...
  27. 1

    Quantum Textbook for Quantum Computing

    Hello, I am looking for a good textbook to learn quantum computing. My background is that I am a double major in math and computer science, and I pretty much don't know anything about quantum mechanics. I prefer something that is more computer science oriented, like quantum algorithms, rather...
  28. itoero

    B Unraveling Quantum Weirdness: A Guide to Understanding Entanglement Phenomena

    Now for the true quantum weirdness. Even if one single photon is emitted into the medium and that photon is not absorbed or reemitted the photon's wave equation describing where it could be is STILL affected by the prescience of the medium. When all the possible paths through the medium are...
  29. S

    I Understanding Electron Behavior in Quantum Tunneling through Dielectrics

    When an electron leaves a conductor and tunnels through a thin dielectric; how does it behave in the space occupied by the dielectric? Does it behave like a ballistic electron traveling through vacuum? Is it instead that the electron never really occupies the space in the dielectric?
  30. J

    A Are quantum fields real objects in space?

    I always had a tough time understanding how QFT relates to reality. Are these quantum fields (electron field, ect) physically real? Are they things that exist in space or are they just mathematical abstractions that help use calculate things?
  31. Sophrosyne

    B How to think of molecular orbitals quantum mechanically

    The electrons in a molecule are said to be in a quantum superposition state in terms of their position/spin/momentum. But when you look at a molecule like water at a chemical level, it has a very specific shape corresponding to the P orbitals of the outer shell of the Oxygen atom. The two...
  32. Danny Boy

    A Quantum synchronization description used in a paper

    In the paper "Steady-state spin synchronization through the collective motion of trapped ions" it states the following: "Steady-state synchronization of atomic dipoles forms the foundation for ultra-stable optical lasers utilizing narrow-linewidth atoms coupled to a lossy cavity mode. The...
  33. S

    A Quantum Confinement Effect and Density of States

    I've been reading a bit about the quantum confinement effect on nanowires, particularly how it changes the band structure. I'm trying to find an explanation on why the density of states splits into sub-bands. At the moment all I'm running into is 'because of the quantum confinement effect' which...
  34. Alex Petrosyan

    Studying Are there any good exercise books for Quantum Mechanics?

    hi, I’ve been walking through posts on this forum, and found plenty of book recommendations for QM. My problem is, I haven’t had enough practice in a long while. I could go over Solved Problems in e.g. Galitsky, or Gasiorowitz, but they seem to be a little far from what I want to test...
  35. Stu-W

    I Black Hole Singularity: Discussing Quantum Theories

    Hi, I'm new on here and this is my first post, so forgive me if I don't master the threads instantly :) - right, now that's out of way: I want to open a discussion on the singularity in Black Holes, namely in regards to the well known issue of Special Realitivity breaking down at the...
  36. G

    B Computer-simulated quantum physics?

    There is so much discussion about what does "really happen" at the quantum level, because we can not directly observe the most minute details of quantum systems, and much is left to inference and to the "interpretations". Does the system really collapse by transferring state information to its...
  37. J

    I Causality and quantum physics

    Let me present what I think is the understanding of a particular situation in quantum mechanics, and ask people to tell me whether I am right or wrong. To say that everything happens randomly in QM would be misleading at best. We get at least statistical prediction. But discussions such as the...
  38. DarMM

    A Structure of Matter in Quantum Field Theory

    This is a topic I've mentioned a few times before. Essentially the structure of matter in quantum gauge field theories is unclear to me. I have no clear question here, just some initial discussion points. So at the first level, it seems a particle based view of quantum field theory is difficult...
  39. Y

    A Quantum Gravity -- intro papers for 2nd year MSc student?

    Basically, I'm a Physics/Math MSc student. Currently strengthening my background in Diff. Geo., QFT, GR. I feel like I should start reading some research papers on Quantum Gravity but I do not know where to start. What papers should I start with? I need papers that are accessible to 2nd year...
  40. jedishrfu

    Could Quantum Artificial Life Unlock the Secrets of Evolution?

    For the first time, an international team of researchers has used a quantum computer to create artificial life—a simulation of living organisms that scientists can use to understand life at the level of whole populations all the way down to cellular interactions. With the quantum computer...
  41. Anne Ross

    I Is Quantum Electrodynamics relevant to every electromagnetic field?

    Is Quantum Electrodynamics relevant to every electromagnetic field?
  42. B

    I Quantum eraser in Bohmian Mechanics and many worlds theory

    All the literature on the quantum eraser that I've seen is grounded in the Copenhagen interpretation of quantum mechanics. It's very easy to understand the experiment in those terms. Do you know how quantum eraser experiments are interpreted by the de Broglie–Bohm theory? What is erased in this...
  43. LarryC

    How Can Quantum Mechanics Explain the Eigenstates of a Spherical Pendulum?

    I have trouble with finding the eigenstates of a spherical pendulum (length $l$, mass $m$) under the small angle approximation. My intuition is that the final result should be some sort of combinations of a harmonic oscillator in $\theta$ and a free particle in $\phi$, but it's not obvious to...
  44. Ghost

    Can Quantum Physics Explain Paranormal Phenomena?

    I am fascinated by quantum physics but, I can't do the math to save my life. I teach psychology for Grambling State University. I am putting together a research grant with the NSF for a Social Science experiment. The work I am doing now is in the paranormal - or better put, prediction of...
  45. C

    Expanding the original commutator on the LHS

    Homework Statement Using [x,eiap]=-ħaeiap show that xneiap = eiap(x-ħa)n Homework Equations [x,eiap]=-ħaeiap From which it follows that, xeiap = eiap(x-ħa) The Attempt at a Solution [xn,eiap] = [xxn-1,eiap] = [x,eiap]xn-1 + x[xn-1,eiap]...
  46. bachir1994

    Quantum Starting in quantum field theory

    Hi , I need to enrich my knowledge in quantum field theory, please refer me to reference books in this branch. Thank's.
  47. C

    Can Glass Registers Enhance Quantum Computer Security?

    I was wondering, I recently discovered, but don't have the article, that there is a security technology that involves the superposition of photons across a fiber optic link. I was wondering could a glass register more adequately create a quantum computer for peoples usage than an actual atomic...
  48. V

    B Quantum oscillator algebra help

    Hi. I am working on the quantum harmonic oscillator Schrodinger's equation and need help with the algebra or whatever it is I am missing. Here are the 2 steps I can't understand: d^2psi/dx^2 + (2mE/h^2 - m^2w^2/h^2 * x^2)psi = 0 You substitute this into it: y = sqrt(mw/h)*x I...
  49. W

    I Time-dependence in probability amplitudes

    Hi all, I am rather confused about the following concept. Assistance is greatly appreciated! A time-dependent probability amplitude can be written as $$\langle a_k| e^{-\frac{i}{\hbar}\hat{H}t} |\psi\rangle$$ where ##a_k## is an eigenvalue. Suppose I want the x-representation of the ket, I can...
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