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. C

    What is the mechanism behind Quantum Entanglement?

    What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?
  2. D

    I Decoherence and Quantum tunnelling

    A macroscopic object has the order of Avogadro’s number of particles. That’s over 10^23. So the probability of all of them tunneling, at the same time, is on the order of that original small probability, to the 10^23 power. And then on top of that, you have to factor in the chances of it...
  3. H

    A Loop quantum gravity and General relativity

    Hi PFs, I am reading this paper written by carlo Rovelli: https://arxiv.org/abs/1010.1939 there are many things that i fail to understand, but i would like to begin with a simple thing. Rovelli write that: It is locally Lorentz invariant at each vertex, in the sense that the vertex amplitude...
  4. A

    I Quantum computation and entropy

    Quantum gates must be reversible. The usual justification for this is that in QM the time evolution of a system is a unitary operator which, by linear algebra, is reversible (invertible). But I am trying to get a better intuition of this, so I came up with the following explanation: In order to...
  5. J

    I Black hole singularity vs. quantum mechanics

    I'm wondering about some aspects about black holes (BH) and singularities, but since all my questions have to do mostly with quantum mechanics, I placed this thread in here. OK, let's assume there IS a singularity in the middle of a BH. A) Pauli exclusion principle (PEP) says no two fermions...
  6. D

    I Does Heisenberg Have Ontological Commitments to Quantum Theory?

    Heisenberg is regarded as a major figure of the Copenhagen interpretation. In a certain degree, he is influenced by Logical positivism. Despite of that, has he any ontological commitments regarding the Quantum theory? Or, he considers the Quantum theory merely as calculation procedure for...
  7. H

    A In What Space Does Quantum Spin Take Place

    Quantum spin is orientable so it takes place in a space with an even number of dimensions. What is that space? If the space had an odd number of dimensions, then spin in that space wouldn't be orientable. But quantum spin is orientable. We could say that it is Minkowski space, but that space...
  8. M

    Let's build a quantum radio receiver

    Homework Statement:: I would like to write a science fiction story on how alien quantum communication could work and how scientist on Earth build the first "radio" receiver, entangling Quantums over big distances randomly. Relevant Equations...
  9. D

    I "No objective reality" in quantum mechanics?

    As per title and the TL;DR, I'm curious if there could be some truth in these statements of the headlines I had read recently or are they just sensationalist fluff. Personally, I find these statements very hard to believe. In fact, impossible to believe. But I'm not a QM expert, not even an...
  10. Bob Walance

    Insights Quantum Computing for Beginners

    revisions for the attached PDF: May 2023 - Rev4a – Some corrections, and a table of contents added.
  11. J

    I Dimensions of quantum cell automata's state space

    In the paper C. S. Lent and P. D. Tougaw, "A device architecture for computing with quantum dots," in Proceedings of the IEEE, vol. 85, no. 4, pp. 541-557, April 1997, doi: 10.1109/5.573 about quantum dots, it is stated that the basis vectors in the space of quantum states for a single cell...
  12. A. Neumaier

    A Exploring the Limits of Quantum Mechanics: David Wallace's Manuscript (2022)

    David Wallace, The sky is blue, and other reasons quantum mechanics is not underdetermined by evidence, Manuscript (2022). arXiv:2205.00568. From the Abstract: ''I argue that there as yet no empirically successful generalization of'' [Bohmian Mechanics and dynamical-collapse theories like the...
  13. Graham87

    Quantum mechanics - finite square well

    In a) I get that T should be largest where V_0 is least wide, because when V_0 is infinitely wide the particle would be fully reflected. But I don't get how height in b) and energy levels height in c) correlates to T and R. Is it because of their k? I get the opposite answer from the correct...
  14. C

    A Quantum Hall Effect Basics: Topological Insulator & Semi-Metal

    I need them short. I need them so I can understand the basics of topological insulator and semi-metal.
  15. Graham87

    Quantum mechanics - infinite square well problem

    I have solved c), but don’t know how to solve the integral in d. It looks like an integral to get c_n (photo below), but I still can’t figure out what to make of c) in the integral of d). I also thought maybe you can rewrite c) into an initial wave function (photo below) with A,x,a but don’t...
  16. .Scott

    Electron movement in Polyacetylene modeled in quantum device

    Researchers at the Center of Excellence for Quantum Computation and Communication Technology released a study published by Nature describing a quantum device that models the motion of electrons in Polyacetylene. The device is not a general purpose quantum processor, but the methods they used...
  17. E

    B Question about quantum superposition

    All of my speculation is based on my current understanding of quantum physics as an art high school student who just has this as an interest, which is in no way at a quantum physicist's level so I apologize if this question is stupid. Also sorry for my English. Most, if not all of you reading...
  18. D

    I The Casimir effect and Quantum vacuum fluctuations

    The Casimir effect is a small attractive force that acts between two close parallel uncharged conducting plates. That force is caused by quantum vacuum fluctuations of the electromagnetic field. What is the cause of the fluctuations? Or, they are uncaused (random)? At least, what are the...
  19. A

    I The quantum state of the Universe

    The dimension of the space of quantum states of multiple particles grows exponentially as the number of particles increases. I would have expected to more likely find the quantum state of many particles in a strange state (such as an entangled one) but it is not so, why? Why isn't the universe...
  20. F

    Calculators Repositories of Quantum Computing projects?

    Hello. I need to code a project (solution of a typical problem or approaches to new one) of quantum computation and I want to study any solved project in order to understand the algorithms and how to run the script in a real quantum computer or simulator. Where can I found some repositories of...
  21. D

    I Quantum interpretation and classical-quantum distinction

    Are/were there any quantum interpretation according to which quantum mechanics COMPLETELY cease to apply at the macroscopic scale? If YES, please name it. I am interested to learn about such interpretation, even if it is inadequate and not widely supported. Of course, the big question remains...
  22. Admiralibr123

    Physics Quantum Computing masters with Theoretical physics background

    I want to do a masters related to quantum computing from a physics background and my criteria for the place is: 1. A quantum computing group with experimental realizations and industrial ties. 2. A strong theoretical physics department with research in fundamental physics 3. A good chance of...
  23. S

    A Why do we need a quantum correction for black hole entropy?

    Hey to all,... It is now generally believed that information is preserved in black-hole evaporation. This means that the predictions of quantum mechanics are correct whereas Hawking's original argument that relied on general relativity must be corrected. However, views differ as to how...
  24. G

    Admissions Do I have a chance at doing a physics Ph.D. in quantum ML?

    I graduated with Physics and Applied math degrees ~4 years ago with a really low gpa ~2.7 with research experience on CMS. I then completed a B.S. in Electrical Engineering last year with a 3.7 and a MS in Artificial Intelligence with a 4.0. Over the past 4 years I've been working as a...
  25. P

    Quantum exam practice, operators and eigenstates

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  26. gremory

    A S-Matrix in Quantum Field Theory

    Hello, i need help with the S-matrix. From what i understand, with the S-matrix i would be able to compute the scattering amplitude of some processes, is that correct? If so, how would i be able to do that if i have some field ##\phi(x,t)## in hands? Is that possible?
  27. VictorMedvil

    I How Do You Break Quantum Entanglement Bonds?

    I was doing some research into quantum entanglement but it is never well described how you break the bonds once they are formed does anyone have any expertise in this area on how to break quantum entanglement bonds? The best that I can understand is the bond is broken when interaction with the...
  28. Faizan Samad

    I Why does doping make resonating valence bonds (singlet pairs) mobile?

    I know in RVB theory that neighbouring Copper atoms form singlet pairs via the superexchange "force". Upon doping with holes, these neutral singlet RVB pairs become mobile and charged and are able to superconduct. I know that the resonating valence bonds are in the copper 3d(x^2-y^2) orbital and...
  29. gremory

    A Power series in quantum mechanics

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  30. Lynch101

    B Statistical Independence in Quantum Mechanics

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  31. Thelamon

    Mechanical engineer and scientific researcher.

    Hi, I'm Dutch, not any kind of Quark ;-) (so excuse me for any bad English) and I'm very curious about "how the universe works". Cosmology/astrophysics and modern physics (quantum, relativity). I find it all mighty intersting. Actually all physics and also how it's all developed and "evolved"...
  32. ThiagoMNobrega

    I Blender Particle Photon Simulation (interesting results w soft bodies)

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  33. arjit

    Mathematica Simulating the quantum Zeno effect using Mathematica

    I'm trying to simulate the quantum Zeno effect using Mathematica and I need to apply von Neumann and projection operator on to same density matrix and in a loop one by one, it's basically switching between two evolutions in time., so I need help on how to do it.
  34. S

    A 1D Quantum Well - Different width "naming" gives different result ?

    Greetings everyone, Exactly as the title says. I am reaching to something strange and I do not know what I am missing. It must be something obvious... case 1: -L/2 to L/2 After taking the Schrodinger equation and considering potential equal to zero inside we reach at this...
  35. ThiagoMNobrega

    B Wave function won't collapse under a microscope?

    So what am I doing wrong here? I can clearly observe it, I'm nearly sure I can tell which particles are going throw each slit if I used another laser too. My suspicion is that the electrical current of the photon detector that uses germanium or silicon to detect the particles are influencing the...
  36. M

    Quantum Tunneling to an infinite wall

    I have the equations for all three regions but usually for region 3, which is Ce^ikx+De-ikx, the C term would be zero since there is no reflection, but with the infinite wall would it reflect? Would the whole wavefunction go to zero like when working with the infinite square wall? I'm stuck on...
  37. Jamister

    A Homodyne detection quantum state tomography

    In balanced homodyne detection, it is claimed that one can do state tomography. I understand most of the derivation except one part. Here is a figure describing homodyne detection. the operator that is being measured is $$ R=N_{1}-N_{2}=a^{\dagger} b+b^{\dagger} a $$. taking the mode b to be...
  38. tworitdash

    A Quantum weak measurement parameter estimation vs Classical Estimation

    I am not an expert in quantum theory. I want to carry out some parameter estimation on a set of data I have. I have a model for the data with the parameter(s) of interest as variable(s). The data available is sporadic, meaning non-statistical or techniques involving no prior knowledge on the...
  39. G

    I Conventional description of the matter wave

    I have been working on a relatively simple problem. Just take a quantum wave function for which a physical requirement is that an arbitrary displacement of x or an arbitrary shift of t should not alter the character of the wave, and I want to find the state function solution. A possible guess...
  40. bbbl67

    B Is gravitized quanta the solution rather than quantum gravity?

    Usually we hear about people working on a theory of quantum gravity, in order to avoid the singularity in the center of a black hole for example. But what if it's the other way around to some extent as well? What if it's gravity keeping quantum objects from doing their greatest reality-defying...
  41. J

    Preparing for a Quantum Computation Course: Superconducting Qubits

    Summary:: Looking for articles/books to prepare myself for the course: Quantum computation with superconducting qubits Hello everyone. I am about to take a course in Quantum computation with superconducting qubits and I am searching for material to prepare it. I took a first course on that...
  42. P

    A Position basis in Quantum Mechanics

    Can I conceive a countable position basis in Quantum Mechanics? How can I talk about the position basis in the separable Hilbert space?
  43. ubergewehr273

    I Capping layer in semiconductor quantum dot fabrication

    Hi everyone, I've been studying about semiconductor heterostructures and in particular quantum dots. I was wondering, why is there a need to have a "capping" layer above the layer where the quantum dots are formed within a sample? Thanks in advance!
  44. T

    I want to learn about Quantum Computing

    I want to learn about Quantum Computing (QC). I am familiar with Quantum Mechanics. So far I have found two types of literature: (1.) Introductions to QC for the layman, and (2) Literature for people who are already knowledgeable about the field. Can someone recommend a mid-level source along...
  45. D

    Is the Bohr Model Defined by Equating Coulomb and Centripetal Forces?

    So for this question I just want to make sure that 1. Bohr model is that F_coulomb = F_centripetal? and then get w(r) is called determind? 2. for (b) calculate the frequency, should I use Rydberg formula or what?
  46. mohamed_a

    I Classical analogy approach to quantum mechanics

    I have read about several approcahes to bypass some classical restrictions to quantum facts such as the electron being in a torus-like shape to avoid ,the greater than speed of light, rotation paradox . Could you recommend websites , sources or books that give good classical analogy to quantum...
  47. A

    A A good quantum number for Cnv symmetry?

    Hello, I was wondering if it was possible to define good quantum numbers in solid state physics or chemistry when systems posses a discrete cylindrical symmetry Cnv. I know that in terms of angular momentum, L and L_z will be good quantum numbers for spherical symmetry, then only L_z is a good...
  48. K

    I Particle on a sphere problem in quantum mechanics and its solution

    To solve a particle on a sphere problem in quantum mechanics we get the below equation :##\left[\frac{1}{\sin \theta} \frac{d}{d \theta}\left(\sin \theta \frac{d}{d \theta}\right)-\frac{m^{2}}{\sin ^{2} \theta}\right] \Theta(\theta)=-A \Theta(\theta) ## To solve this differential equation, we...
  49. Mr_Allod

    Edge States in Integer Quantum Hall Effect (IQHE)

    Hello there, I am having trouble understanding what parts b-d of the question are asking. By solving the Schrodinger equation I got the following for the Landau Level energies: $$E_{n,k} = \hbar \omega_H(n+\frac 12)+\frac {\hbar^2k^2}{2m}\frac{\omega^2}{\omega_H^2}$$ Where ##\omega_H =...
  50. Tan Tixuan

    I Classical field in quantum field theory?

    In quantum field theory, we have the following expansion on a scalar field (I follow the convention of Schwarz's book) $$\phi(\vec{x},t)=\int d^3 p \frac{a_p exp(-ip_\mu x^\mu)+a_p^{\dagger}exp(ip_\mu x^\mu)}{(2\pi)^3 \sqrt{2\omega_p}} \quad p^{\mu}=(\omega_p,\vec{p})$$ With commutation relation...
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