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.

View More On Wikipedia.org
Recent contents Top users
  1. jfizzix

    A Is there a quantum uncertainty to the number of atoms in a marble?

    I know precious little about quantum field theory, but want to understand the following. If each Fermion and Boson has its own field.. ..and as an example, the EM field can be in a coherent state, which is a superposition over many photon number states.. .. then can a fermion field, or...
  2. H

    A Overlap of nth QHO excited state and momentum-shifted QHO ground state

    ##\newcommand{\ket}[1]{|#1\rangle}## ##\newcommand{\bra}[1]{\langle#1|}## I have a momentum-shifting operator ##e^{i\Delta p x/\hbar}## acting on the ground state ##\ket{0}## of the QHO, and I want to compute the overlap of this state with the n##^{th}## excited QHO state ##\ket{n}##. Given...
  3. P

    Solutions to schrodinger equation with potential V(x)=V(-x)

    C is just the constant by ##\psi''## My initial attempt was to write out the schrodinger equation in the case that x>0 and x<0, so that $$ \frac {\psi'' (x)} {\psi (x)} = C(E-V(x))$$ and $$ \frac {\psi'' (-x)} {\psi (-x)} = C(E-V(-x))$$ And since V(-x) = V(x) I equated them and...
  4. Bob Walance

    B Quantum computer vs supercomputer performance

    I've been learning about quantum computing for the last year and I can hardly believe what I read and hear. However, assuming that no big technical hurdles get in the way, I do think that the promises will become reality someday. It is becoming a bit clearer to me, but it's a very difficult...
  5. NightHaWk

    Understanding Exponential Terms in Quantum Mechanics Problem

    So I am trying to understand and solve the problem mentioned in the title.I found a solution online: https://physics.bgu.ac.il/COURSES/QuantumMechCohen/ExercisesPool/EXERCISES/ex_9011_sol_Y09.pdf The problem is, I can't understand this step : I relly can't find out how the two expontential...
  6. Physics4Eva

    I Could the Discovery of the Graviton Connect Quantum and Classical Physics?

    W and Z bosons, gluons, and photons are all gauge bosons that have been found. Since the graviton can be connnected to atoms and mass in certain ways, I think that CERN may eventually prove the graviton(if real) through smashing atoms that, supposedly, have a graviton orbiting them. Could...
  7. B

    Electric field of light emitted by atom, given the intensity

    For t < 0 , all I can think of is a qualatative " the field is zero because the intensitity is 0 when the burst of light hasn't been emitted yet " For t >= 0 , I've tried squaring the given E and that let's me say the amplitudes are proportional (with a cos^2 term in the mix) But I feel like...
  8. Greg Bernhardt

    I Quantum Interpretations and Foundations Guidelines

    Cliff Notes Version Quantum Interpretations and Foundations guidelines All PF guidelines applicable to any forum apply here, plus the following. Questions in initial posts of threads may cite unpublished textbooks or pre-publication papers such as ArXiv, subject as always to review of sources...
  9. Greg Bernhardt

    B Guidelines for Quantum Physics Forum

    Brief Description of New Quantum Forum Structure A common topic of discussion regarding quantum mechanics is the foundations of QM as a theory structure and different interpretations of QM. These discussions are of interest to many PF members, but they present some unique challenges since they...
  10. Quantum Alchemy

    B Can entangled particle pairs be measured at the same time?

    Has there been an experiment where 2 particles that are entangled are measured at the same time? If so what was the result? Can any observer occupy the same frame of reference down to an electron? Don't we all exist at different times based on our frame of reference so none of us can share the...
  11. N

    A Conservation of Quantum Information

    I can't seem to wrap my head around the notion of conservation of quantum information. One thing that might help that is if someone can tell me what the associated symmetry is. For example, phase symmetry leads to conservation of electric charge according to Noether's theorem; a fact that...
  12. W

    I Notion of a "clock" in Quantum Mechanics

    Suppose the unitary operator ##e^{-\frac{i}{\hbar}\hat{H}t}## acts on ##|\psi (0) \rangle##, does it make sense for one to think of the time-evolved state as some sort of time-keeping device? If not, why? If so, is such a notion useful? Thanks in advance!
  13. D

    Quantum Quantum Fluctuations & Virtual Bosons for Amateur Physicists

    I am searching for anything on quantum fluctuations and virtual bosons for someone who is a serious but amateur physicist ie. I have completed undergrad physics/math and some graduate level math at university. I am having a hard time finding anything that isn't beyond pop science. Not really...
  14. N

    I Dark Matter and quantum observable

    Are there any research about Dark Matter missing some Hilbert space bases or observable? Are bases or observables like spin, momentum, energy, position the basic quantum ingredients of any matter, what is the apriori explanation?
  15. Amblambert

    Chemistry Quantum Chemistry - Particle in a box

    Here is my attempt at a solution. The thing I am not sure about is the final result of the Shrodinger equation and the n-values that are offered? Did I make a math mistake? Thank you so much for reading through this!
  16. tholepin

    I'm attempting to train a quantum dog (Rusty), suggestions?

    I'm attempting to train and interact with a quantum dog named Rusty. Any and all suggestions are or aren't appreciated.
  17. BWV

    Google Claims quantum supremacy

    https://www.cnet.com/news/google-reportedly-attains-quantum-supremacy/ Google has reportedly built a quantum computer more powerful than the world's top supercomputers. A Google research paper was temporarily posted online this week, Financial Times reported Friday, and said the quantum...
  18. N

    B Classical physics vs quantum physics

    Is classical physics independent from quantum physics? Or is classical physics an approximation derived from quantum physics? Is it dependent on interpretations? What quantum interpretations support the latter above?
  19. Meruem

    B Quantum Gravity and Special Relativity

    is there a equation that links quantum gravity and special relativity?
  20. nomadreid

    I Quantum states: only vectors?

    Elementary question: Is there ever a case where the solutions for a wave equation turn out not to be a vector (in Hilbert space of infinite complex-valued dimensions, or a restriction to a subspace thereof) , but something else -- say, (higher-order) tensors or bivectors, or some such? My...
  21. Meruem

    B Is quantum entanglement a four dimensional force?

    Why two bodies are related with each other despite the distance between them. It is unbelievable that entanglement exist regardless of any distance. Why on universe are so deeply connected with each other where distance does not play any role for the phenomena?
  22. Bobjoesmith

    I Physical Meaning of a Quantum Field

    Sorry in advance if this question doesn't make sense. Anyway, I am reading a paper about quantum field theory and the Whitman Axioms (http://users.ox.ac.uk/~mert2060/GeomQuant/Wightman-Axioms.pdf), and it describes a field (Ψ) as Ψ:𝑀→𝑉⊗End(𝐷) where 𝑀 is a spacetime manifold, 𝑉 is a vector...
  23. A

    I Classical treatment of quantum eraser?

    The below experimental setup is of the sort one finds frequently discussed in the delayed choice quantum eraser (QE) experiments, such as that of Kim et al. (https://arxiv.org/abs/quant-ph/9903047) I extracted only the essential part I'm wondering about and did not find a satisfying answer in...
  24. A. Neumaier

    B How to teach beginners in quantum theory the POVM concept

    [Edit 23.12.2019: A much extended, polished version of my contributions to this thread can be found in my paper Born's rule and measurement (arXiv:1912.09906).] Well, it is simpler than to introduce in full generality Born's rule. Everything can be motivated and introduced nicely for a qubit...
  25. G

    Implications of communication through quantum entanglement

    I am building an SF universe. While it is very similar to ours, but casual FTL exists. I don't think Lorentz transformations shouldn't work at all, but rather extra dimensions can somehow circumvent them. One kind of FTL is direct communication through entanglement. There can be two version of...
  26. P

    I Solving a quantum harmonic oscillator using quasi momentum

    In the paper below I've seen a new method to solve the quantum harmonic oscillator Introduction to the Spectrum of N=4 SYM and the Quantum Spectral Curve It is done using the concept of quasi momentum defined as $$p = - i \frac{d(\log \psi)}{dx}$$ See pg 7,8 Is this well know? is it discussed...
  27. Danny Boy

    A Correlation functions of quantum Ising model

    I have a single technical question regarding a statement on page 7 of the paper "Dynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence". The paper up until page 7 defines a general correlation function ##\mathcal{G}## of a basic quantum Ising...
  28. L

    A Why do we study quantum spin liquids?

    What kind of research is currently going on in the field of quantum spin liquids and why do we study spin liquids?
  29. K

    Quantum The Philosophy of Quantum Physics by Cord Friebe

    Summary: CordFriebe et al. Has anybody read this book? I am wading through this tome for the second time. Was wondering what others whom might have read it thought. https://www.amazon.com/dp/3319783548/?tag=pfamazon01-20
  30. G

    B Quantum radar and its implications

    https://www.popularmechanics.com/military/a28818232/quantum-radar/ https://www.asiatimes.com/2019/09/article/stealth-killer-quantum-radar-actually-works/?_=3274804 I don't know, whether the above sources are reliable, or not, that is why i ask. "Quantum radars involve pairing photon particles...
  31. G

    I Quantum field theory: an informative approach

    I'm looking for a book that describes the quantum field theory without going deeply in the theory with formulas or complex description of the mathematics under the theory. I know that this theory is really complex and it needs a deep knowledge of quantum physics in order to be understood. But...
  32. Garlic

    I Question about the quantum harmonic oscillator

    Dear PF community, I am back with a question :) The solutions for the quantum harmonic oscillator can be found by solving the Schrödinger's equation with: Hψ = -hbar/2m d²/dx² ψ + ½mω²x² ψ = Eψ Solving the differential equation with ψ=C exp(-αx²/2) gives: -hbar/2m (-α + α²x²)ψ + ½mω²x²ψ = Eψ...
  33. G

    I Delayed-choice quantum eraser experiment

    In the Kim's experiments (see picture below) part of the downwards photons are involved in a quantum eraser and part aren't. In D0 (upward path) we see interference if the entangled photons (downward path) are detected in D1 or D2 and we don't see interference if the entangled photons are...
  34. microsansfil

    A Bohmian mechanics for instrumentalists and quantum measurement

    Hi, I'm reading Demystifier's article about an interpretation of quantum mechanics. One concept that seems important for this interpretation is that of what is perceptible by us human beings compared to what is not (non-perceptible). Demystifier says: A perception by a naked eye is direct, a...
  35. E

    A Applying General Lorentz Boost to Multipartite Quantum State

    I would like to apply a General Lorentz Boost to some Multi-partite Quantum State. I have read several papers (like this) on the theory of boosting quantum states, but I have a hard time applying this theory to concrete examples. Let us take a ##|\Phi^+\rangle## Bell State as an example, and...
  36. HaZe-

    Quantum physics (blackbody radiation)

  37. B

    Where is a particle most likely to be? (Griffiths Quantum Mechanics)

    The wave function described seems impossible. Wave functions have to be differentiable at all points, right? Otherwise they don't represent a physically realizable state. The wave function in the example isn't differentiable at x=A, the maximum point. Also, for problem (c), I know it's visually...
  38. P

    A Can Work Be Defined for a Quantum System with a Time-Dependent Hamiltonian?

    I have a Hamiltonian ##H_{\lambda(t)}##, where ##\lambda (t)## characterizes a time dependent path in parameter space. The parameter is changed in finite time from ##\lambda (t_i)## to ##\lambda(t_f)## . At ##t = t_i## the system is in the intial state ##|\Psi>##. What is the work done on the...
  39. Ampulla

    B What causes quantum uncertainty?

    What causes quantum uncertainty? My friend who's working for Apknite says that detectors are not the cause of wave collapse, because you are measuring something that isn't remaining in the same state.
  40. M

    I Quantum Correlations without Many Worlds or Determinism

    I'm trying to understand the comment by bhobba below from another thread. A related followup from RUTA is provided for reference. After reviewing these I still don't understand. If I think in terms of a single-world (not Everette) and assume Alice and Bob are free to adjust their SG...
  41. H

    A Quantum Mechanics: Exploring Symmetry and Continuation

    Does quantum mechanics follow causality, phase transition, critical point, symmetry, asymmetry, order, disorder, continuation, discontinuation, limitation, without limitation, convergence, divergence, similarity, hierarchical structure, singularity, plurality?
  42. Baibhab Bose

    Infinitesimal Perturbation in a potential well

    If I calculate ## <\psi^0|\epsilon|\psi^0>## and ## <\psi^0|-\epsilon|\psi^0>## separately and then add, the correction seems to be 0 since ##\epsilon## is a constant perturbation term. SO how should I approach this? And how the Δ is relevant in this calculation?
  43. A

    Quantum numbers of a system of particles

    Hello everybody! I have a problem with this exercise when I have to find the possible angular momentum. Since ##\rho^0 \rho^0## are two identical bosons, their wave function must be symmetric under exchange. $$(exchange)\psi_{\rho\rho} = (exchange) \psi_{space} \psi_{isospin} \psi_{spin} =...
  44. cromata

    Quantum Quantum information recommendation

    I am 3rd year physics student (actually I have just finished it). I have good knowledge on basics of quantum mechanics: I had 1 semester of Introduction to Quantum Physics and then 2 semesters of Quantum Physics. Our literature were Griffiths (Introduction to Quantum Mechanics) and ''Gennaro...
  45. M

    A Gravitational dressing in quantum field theory

    In quantum field theory, a dressed particle is a particle ("bare particle") considered in combination with certain secondary effects that it produces (e.g. the virtual pair creation involved in vacuum polarization). The dressed states are regarded as more physical, hence closer to reality. Axel...
  46. H

    I How to be sure we have found all magnetic quantum numbers?

    The book uses ladder operators ##L_+## and ##L_-## to find the eigenvalues ##m## of ##L_z##. By first deducing that these operators raise or lower the eigenvalue by ##\hbar##, and then deducing that the lowest eigenvalue is the negative of the highest eigenvalue ##l##, it proves that ##m = -l...
  47. M

    I Why does quantum mechanics believe that gravity is a field?

    According to general relativity, gravity is simply the side-effect of bending the geometry of space-time. As a thought experiment imagine a 3D image being projected from a 2D hologram - the distance between the actual 2D pixels in the 2D plane always remains constant, yet depending on the shape...
  48. K

    B IB Physics Extended Essay - Quantum Levitation

    I've decided to focus my essay on quantum locking: including superconductors (YBCO), the Meissner Effect. I have access to the materials needed to experiment with this topic (materials from quantumlevitation.com). Could anyone help me formulate an appropriate research question for my Extended...
  49. D

    Courses Graduate Quantum as an Undergrad

    Hello, I'm considering taking the graduate level quantum mechanics course offered at my university (based on Sakurai/Shankar). I am currently reading Sakurai's QM, and mostly understand the topics (I'm currently reading the theory of angular momentum). There have been some steps where I still...
  50. Solomei

    B Quantum microphone and phonons

    https://phys.org/news/2019-07-physicists-particles-quantum-microphone.html Are phonons fundamental for advanced levitation technology?
Back
Top