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. MC Theerth

    A new idea in Quantum mechanics

    In "Dual Behavior of Matter", De Broglie referred electrons are waves and particles simultaneously. But, If 2 things are opposite, then should not there be something in the middle of it. So should not there be the middle of waves and particles, I call this warticle. So, if there is a warticle...
  2. MC Theerth

    3

    In "Dual Behavior of Matter", De Broglie referred electrons are waves and particles simultaneously. But, If 2 things are opposite, then should not there be something in the middle of it. So should not there be the middle of waves and particles, I call this warticle. So, if there is a warticle...
  3. Q

    "Retired" but still active

    I am a long-retired physics lecturer, with the bulk of my lecturing focused on quantum and relativity. I am still active in research. I have completely lost contact with the challenge of explaining this stuff to students, and was curious to see how these challenges are met on this forum, not...
  4. Penny57

    Show that energy E always exists such that junction conditions have a solution

    I know this wavefunction should behave as a symmetric cosine function (possibly as Cos( (k∗x)/(hbar) ?). I also know for a bound state, the wavefunction must decay exponentially outside the well. Additionally, r = (-β+ik)/(β−ik) . However, aside from that, I do not know how to get this question...
  5. S

    I Does entanglement always conserve something?

    IIUC, entanglement sometimes plays a role in conserving come quantity like momentum or spin: the quantities measured for two particles must be correlated in order to get a certain total value. But is this always the case? For example, what, if anything, is conserved in the Hong-Ou-Mandel...
  6. M

    B Can objects in nature store light information on the quantum level?

    In the 1934 novel by John Taine, Before the Dawn, scientists are able to retrieve images of the past by accessing the light absorbed by stones throughout history. While this is fictional, 1934 was really before the dawn of quantum physics. In the far future, could we retrieve images from light...
  7. K

    I Two recent tests of loop quantum gravity theory

    2 recent gains on loop quantum gravity theory arXiv:2403.18606 (gr-qc) [Submitted on 27 Mar 2024] Test the Loop Quantum Gravity Theory via the Lensing Effect Lai Zhao, Meirong Tang, Zhaoyi Xu https://doi.org/10.48550/arXiv.2403.18606 and [Submitted on 7 Dec 2023 (v1), last revised 28 Dec...
  8. RUTA

    Insights Schrödinger’s Cat and the Qbit

    Continue reading...
  9. billtodd

    I If there ever will be a theory of Quantum Gravity which is testable...

    shouldn't it be a sort of partially GR and partially QM? I mean in a sort of superposition of both theories such that in the specific limit becomes GR and another limit QM, and in the between both regions it's something entirely else, not QM and not GR. Is this possible? I haven't yet done the...
  10. M

    Can Bell's Inequality Be Proven Using Protons, Neutrons, or Other Particles?

    Hello I am MOHD HANZALA I worked on bell's inequality where we measure spin of electron along different basis leading to the bell's inequality . My question is that can we prove bell's inequality through proton or neutron or other particle??
  11. Leandro Bolonini

    I How do quantum fluctuations affect the formation and evolution of structures in the Universe?

    How do quantum fluctuations affect the formation and evolution of structures in the universe on large scales?
  12. flyusx

    What To Project Upon When Doing QM Measurements?

    I have read that if one measures the Hamiltonian and receives a value of h2, then the quantum state will be in ##|h2\rangle##. Finding the probability of a1 is done by projecting ##|a1\rangle## upon ##|h2\rangle## divided by ##\langle h2|h2\rangle##. In other words: $$\frac{|\langle...
  13. S

    I Artificially discretized quantum states - is it a thing?

    Here we have four electron detectors (e.g. electron multipliers) forming positively charged detection regions, with a negative back plate. Mathematically, is it valid to describe this as a measurement with four eigenstates, considering that there are only four possible detection outcomes...
  14. K

    A Rotations on the Bloch sphere

    Hello! I am curious about how different rotations on the Bloch sphere are done in practice. For example, assuming we start in the lower energy state of the z-axis (call it |0>), a resonant rotation on the Bloch sphere by ##\pi/2## around the x-axis will take you to ##\frac{|0>-i|1>}{\sqrt{2}}##...
  15. lambdadandbda

    Zwienbach mastering quantum mechanics exercise 6.2 (time independence of a stationary state)

    I can write $$\psi(x,t_0) =\frac{1}{\sqrt{2}}(e^{\frac{-iE_1}{\hbar}t_0}\psi_1(x) +e^{\frac{-iE_2}{\hbar}t_0}\psi_2(x))$$ for the second coefficient to be -1 i need ## -1=e^{-i\pi}=e^{\frac{-iE_2}{\hbar}t_0} ## so ##t_0=\frac{\pi\hbar}{E_2}## and the above equation becomes $$\psi(x,t_0)...
  16. HighPhy

    I "Wave-particle duality" and double-slit experiment

    Sorry to open a new thread. There are plenty of threads on PF dealing with the issue of "wave-particle duality". Although not unanimously, many agree that the concept of "wave-particle duality" is outdated. Electrons, photons and all of the underlying entities are neither waves nor particles...
  17. Marioweee

    Creating Schrödinger cat states with trapped ions

    I have already solved question number 1 by applying the schrödinger equation obtaining that $$\ket{\psi_2}(t) = \cos(\Omega t)\ket{g} - i \sin (\Omega t)\ket{s}$$ and therefore in ##t=\frac{\pi}{4\Omega}## $$\ket{\psi_2}(t) = \dfrac{1}{\sqrt{2}}(\ket{g} - i \ket{s})$$ I have some doubts...
  18. T

    I Double Check Normalization Condition

    Consider the state ##\ket{\Psi} = \sum_{1 \leq n_{1} \leq n_{2} \leq N} a(n_{1},n_{2})\ket{n_{1},n_{2}}## and suppose $$|a(n_{1},n_{2})| \propto \cosh[(x-1/2)N\ln N]$$ where ##0<x=(n_{1}-n_{2})/N<1##. The claim is that all ##a(n_{1},n_{2})## with ##n_{2}-n_{1} > 1## go to ##0## as...
  19. jzz

    A Is the quantum mechanics explanation for the propagation of light adequate enough to be understood?

    Ask any informed man on the street for the quantum mechanics explanation of light and his answer would probably be something like this: “Light as it travels from point A to point B is not something real, it exists as an abstract mathematical wave function that exists everywhere and nowhere...
  20. Hennessy

    Help Calculating probability between 2 limits for the ground state

    TL;DR Summary: Looking for help on a Intro to QM Problem Hi All, THIS IS A GRADED PIECE OF WORK AT MY UNIVERSITY PLEASE DO NOT JUST GIVE ME THE ANSWER , I have made this post to see if what i've calculated seems reasonable, it sounds unlikely as 0.4 - 0.5L is in the middle of the well. The...
  21. jedishrfu

    A Gravity Measured with Milligram masses

    https://www.science.org/doi/10.1126/sciadv.adk2949
  22. jedishrfu

    News Google $5M XPRIZE for best uses for Quantum Computers

    Google is looking for practical problems/algorithms that can be solved on quantum computers: https://www.xprize.org/prizes/qc-apps
  23. H

    A Vector field vs. four scalar fields ("QFT and the SM", Schwartz)

    This is the statement in question: But if they were scalar fields, they would not transform at all. How could they contribute differently if they didn't change?
  24. flyusx

    Fourier Transform - Solutions Error?

    This is technically a Fourier transform of a quantum function, but the problem I'm having is solely mathematical. Conducting this integral is relatively straightforward. We can pull the square roots out since they are constants, rewrite the bounds of the integral to be from ##-a## to ##a##...
  25. S

    What is the Role of Energy in Quantum Hybridized Orbitals?

    Hello, I have a few questions about these images that I shared. 1) What does t represent? I am assuming Es is the energy of the atoms before they hybridize, and that t is either the gain or reduction of energy due to the new orbitals that are formed through bonding. Am I way off on this? 2)...
  26. Frabjous

    Quantum Constructing Quantum Mechanics by Duncan

    Anyone read these books and care to share their thoughts? https://www.amazon.com/Constructing-Quantum-Mechanics-Scaffold-1900-1923/dp/0198845472/?tag=pfamazon01-20 https://www.amazon.com/Constructing-Quantum-Mechanics-Arch-1923-1927/dp/0198883900/?tag=pfamazon01-20
  27. jedishrfu

    Never-Repeating Tiles Can Safeguard Quantum Information

    https://www.quantamagazine.org/never-repeating-tiles-can-safeguard-quantum-information-20240223/
  28. jazamm

    I Why is anyone looking for a graviton/force mediator if it's so widely accepted that that gravity is not a force, but physical curvature?

    The Wikipedia article on Quantum Gravity reads: "The observation that all fundamental forces except gravity have one or more known messenger particles leads researchers to believe that at least one must exist for gravity. This hypothetical particle is known as the graviton" To which... yikes...
  29. flyusx

    Quantum Virial Theorem Derivation

    Using the time derivative of an operator, and expanding out, I got to this: $$\frac{d}{dt}\langle\hat{x}\hat{p}\rangle=\frac{i}{\hbar}\left\langle\left[\hat{H},\hat{x}\hat{p}\right]\right\rangle+\left\langle\frac{\partial}{\partial t}\left(\hat{x}\hat{p}\right)\right\rangle$$ Expanding using...
  30. hongseok

    B Is it possible to find the energy level of a hydrogen atom in this way?

  31. AshIsH_0001

    Probabilities out of non-normalizable functions?

    a and b were fairly easy to solve; but the c part which actually demands the probability! How are we suppose to fetch the value if the function can't even be normalized; I tried to make some assumptions like making the system bounded; but I don't think that it's the right way to do so... What...
  32. PhysicsRock

    I Derivation of normal Zeeman-Effect

    I was / am trying to derive the energy shift resulting from the normal Zeeman-Effect by coupling the Hamiltonian to the external field ##\vec{A}##, that carries the information about the field ##\vec{B}## via ##\vec{B} = \nabla \times \vec{A}##. Let ##q = -e## be the charge of the electron and...
  33. U

    I Spin state, base transformation

    how do i write the z spin state using the spin state on x or on y?
  34. jedishrfu

    B Major Math Discoveries in 2023

    Covering: - New Ramsey number bounds - Aperiodic tiling discovery of an Einstein tile - Three Arithmetic Progressions
  35. Morbert

    A The no boundary proposal and quantum gravity

    It is cited here, and here like so: And here [edit] - and here The full quote from the paper I cited: I don't see how this paper is not a paper about the no boundary proposal.
  36. W

    B How are the spins of two entangled photons measured at light speed?

    and how is it known that the two photons are entangled in the first place? I mean before measuring how do you know that you have the correct two photons?
  37. milkism

    Quantum Mechanics I, finding impuls wavefunction.

    I have this following Gaussian wavefunction. I found the constant C to be $$\sqrt{\sqrt{\frac{2 \alpha}{\pi}}}$$. Now they're asking me to find the normalized impuls wavefunction $$\phi(p)$$. I tried to use the fourier transform relation $$\phi (p) = \int e^{-\frac{i ( p x)}{\hbar}} \Psi...
  38. B

    B Entanglement & Superposition Probabilities

    I cannot find a clear answer on the following beginner’s question on some QM fundamentals: Suppose we have two particles, A and B. Let’s say we generated these as (or otherwise entangled them as) an entangled pair with opposite/orthogonal states. Perhaps horizontally and vertically polarized...
  39. cianfa72

    I Understanding Bell Inequality Proof: Explained from a Probability Perspective

    Starting from this link my understanding of Bell inequality proof goes as follows: Suppose we have a model of local pre-determinate hidden variables for QM. This amounts to say QM objects are in pre-determinate given states even if we do not measure it. Locality just means that spacelike...
  40. Wyvyrn

    What is an Intelligent Dilettante?

    Just a guy with huge Curiosity Quotient, in subjects ranging from Astronomy to Quantum Physics, to Geology and Ancient Mythology, Chemistry to Science Fiction & Fantasy, and finally Science in General.
  41. T

    I Understanding Ground State Degeneracy in the Transverse Ising Model

    Hi all, I was wondering if there was a reference/textbook where the degenerate perturbation calculation for the Transverse Ising model was treated fully. I want to better understand how in the weak magnetic field limit, the ground state degeneracy only lifts at N'th order in perturbation theory...
  42. Ben Messer

    Is Sabine Hossenfelder the Key to Unlocking New Theories in Physics?

    Neil deGrasse Tyson has been a great "goto" and respected physicist for me to follow online. I've read Einstein's biography and have been fascinated with the world as theorized by some of the greatest minds and proofs. Recently, I've come across a name I've never known. Admittedly, this is a...
  43. J

    I Question about Photons causing Electron Transitions in Atoms

    An electron requires an "exact" wavelength photon to transition from one level of an atom to another. Yet the wavelength of a photon has a a continuous probability distribution, implying that the point probability of achieving an exact wavelength is zero. One can only talk meaningfully about...
  44. F

    I Photoelectric effect and Saturation Current

    Hello, I understand the photoelectric effect, its importance, and the basic theory. But I have a few questions: 1) One photon "can" free only a single electron, correct? However, it is not certain that if we shine exactly 10 photons (frequency? ##f_0##), that 10 photoelectrons will be free...
  45. P

    I Question about the Photoelectric Effect and the Work Function of a Metal

    By the results of the photoelectric effect experiment, the photoelectric effect does not occur at all if the frequency of the light source is below a certain value. We have the Work Function for a metal. Why when the energy of the photons of the light source is W/2, we don't have the...
  46. M

    How can I solve these GHZ, 3 qubit quantum state problems?

    TL;DR Summary: I have spent all day on these 2 problems but i cannot solve them. Can somebody give me any clue on the solution?
  47. Aramaan

    Physics Physics Graduate planning to do research in photonics

    Hey, I was just contemplating career opportunities after my Undergrad. I am slightly interested in theoretical physics but I can't imagine doing it the rest of my life. My main interests are nano-photonics and quantum technologies and I am planning to do research in these fields. I am not...
  48. Dr Keryn Johnson

    Can Quantum Biology Unlock the Secrets of Regenerative Medicine?

    Hi, I am new here. I expect that most people will find my approach to science interesting because I do not do standard physics. I do SUSY inversion and the He-BEC DE DM model corresponding to a revision of quark charge calculations giving rise to Baryonic symmetry.
  49. H

    Quantum 'Quantum Field Theory for the Gifted Amateur' by Tom Lancaster and Stephen J. Blundell as a self-study textbook?

    I'd like to hear your professional opinion on and experience with using Quantum Field Theory for the Gifted Amateur by Tom Lancaster and Stephen J. Blundell as a self-study textbook. Thank you.
  50. P

    I How does the quantum of action cause indeterminism?

    How and/or why does the existence of the quantum of action (Planck's constant) cause indeterminism?
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