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. Omega0

    Quantum computing: Not for all problems?

    Please note: I am really a beginner in this field. If I write nonsense just let me know, I just gather information. As far as I understood Quantum Computing is super fast but (this is basically my question) not suited to all kinds of engineering questions. As far as I know it should work best...
  2. M

    I Blackbody radiation in quantum mechanics

    Hello! If I place a particle with more energy levels (of the order of kT) in a well defined state, in a thermal bath at temperature T, how will the blackbody radiation affect the internal state of the particle i.e. will the distribution be classical or QM? Basically, if I prepare that particle...
  3. A

    B Is quantum coherence a random event?

    How we should understand the randomness of quantum events in the context of the significant role that they apparently play in our macroscopic world. Using processes as superconductivity, super-fluidity, and in Bose-Einstein Condensates researchers have been able to produce macroscopic quantum...
  4. G

    I Flat arena for quantum gravity?

    In a textbook, which is not in Englisch language unfortunately, I found a passage saying that intrinsic curvature of spacetime is just a specific definition. The alternative definition is that spacetime is flat, whereas clocks and rods have variable lengths - which is just Feynman’s bug...
  5. C

    B How does quantum superposition really work?

    How does putting it potentially inbetween 2 basis states, which U will measure only later, on, do it!? That seems like magic, to me. And yet I accept that it does. Somehow.
  6. C

    I What is the quantum spin of a single electron in an (atomic) orbital?

    What is the quantum spin of the valence electron in the silver atom in the furnace in the Stern-Gerlach experiment? . Up, down, at random, alternating, in a (quantum) superposition (of both), or none? Does it even have/get one until it's measured/observed /needed? . Does the second electron, in...
  7. C

    B Is quantum superposition involved in the Stern-Gerlach experiment?

    This is how I explain it, away, now: Upon entering the magnetic field the silver atom's valence electron's electric field aligns itself at right angle/s to the magnetic field, the quickest/shortest way it can, as they are wont, to do, somehow, and the rest follows, naturally. And if U are...
  8. rpthomps

    I Developing Quantum Expressions using QUBO

    Hi there, I would like some help developing a QUBO expression where a Quantum Annealing approach would find the two ways of summing the 5 numbers {1 2 3 4 5) to 8 by selecting 3 of the numbers. I am basing this off of a dwave.sys video example I found on their site. My initial kick at the can...
  9. siddjain

    A Understanding how quantum annealing solves QUBO problems

    This question is in regards to Dwave's quantum computer which is tailored to solve QUBO problems (minimize $x^T Q x$ where $Q$ is a symmetric matrix and $x$ is $n$ length vector of $0$s and $1$s) using quantum annealing. I would like to understand how it works. The claim is that it does so by...
  10. docnet

    I Discussion about quantum mechanics and spacetime

    Robert Lawrence Kuhn: It seems that special relativity suggests time is like gravity and electromagnetism, not built into the absolute fabric of reality like logic and causation. David J Gross: Yes, time is dynamical. The phenomena are dynamical and are labeled by what we call time. Including...
  11. Roby002

    I Feynman's description of the quantum behaviour of an ammonia molecule

    Hi guys! These days I've been reading Feynman's description of the quantum behaviour of an ammonia molecule. He assumes the N up or down as tuo basis states. He then says there's a little probability that the state UP becomes DOWN and viceversa. But for definition basis states are...
  12. S

    Nobel prize in physics for quantum cryptography?

    Is it likely that this year's Nobel prize could be awarded to the field of quantum cryptography with Charles H Bennet, Gilles Brassard and Artur Ekert as possible nobel laureate candidates?
  13. RUTA

    Insights No Preferred Reference Frame: Quantum Mechanics Interpretations

    Continue reading...
  14. S

    Quantum Open Quantum Systems textbooks with exercises?

    The standard reference for open quantum systems is The Theory of Open Quantum Systems by Breuer and Petruccione, which seems well-written but it lacks exercises, as do all the other textbooks I googled. Does someone have a recommendation for a textbook on open quantum systems with problems to...
  15. Ebi Rogha

    I What does it really mean that photons are quanta of light?

    But then I learned a photon can be split into two or even three photons (red-shifted, energy is conserved), and also photon can lose energy and still be a photon (Raman effect, inelastic scattering). Now, I am not sure what it means when it is said photons are quanta of light (smallest unit of...
  16. llha

    I [Quantum Computing] Quantum Parallelism State Calculation

    Hi, I'm going through Nielsen and Chuang's Quantum Computation and Quantum Information textbook and I don't really understand this part about quantum parallelism: Shouldn't the resulting state be (1/sqrt(2^4)) * (|0, f(0)> + |0, f(1)> + |1, f(1)> + |1, f(0)>), since the resulting state would...
  17. BohmianRealist

    A Bootstrapping quantum Yang-Mills with concrete axioms

    From: https://en.wikipedia.org/wiki/Axiomatic_quantum_field_theory But, that seems like a fairly abstract place to begin the kind of QFT construction that was asked of us by Witten in 2012: At the bottom of that page on axiomatic QFT are the "Euclidean CFT axioms": Are there any examples of...
  18. Ebi Rogha

    I Can a single photon be reflected by a mirror?

    If the answer is Yes, then I would ask, if the mirror absorbs a portion of the energy of the photon, so the photon should simply stop existing because we cannot have a smaller package of light than a photon. If the answer is No, then I would ask why a beam of light (which is made of a big...
  19. MichPod

    A Does the quantum space of states have countable or uncountable basis?

    It's probably more kind of math question. I consider a wave function of a harmonic oscillator, i.e. a particle in a parabolic well of potential. We know that the Hamiltonian is a Hermitian operator, and so its eigenstates constitute a full basis in the Hilbert space of the wave function states...
  20. Vatsy31

    Admissions Can someone critique my statement of purpose? (Master's Degree in Quantum Engineering)

    I have written and rewritten a lot of times but I need some fresh eyes on my sop. It would be great if someone can help me out. I have less than a week to readjust it and send. My motivation to apply for the Masters Degree in quantum engineering at University of Wurzburg is to...
  21. A

    Philosophical question about Quantum Gravity

    I imagined all possible quantum gravity theories in one set, of which only one is correct, and further divide these theories into testable and non-testable. Question: how do we know if the correct theory is currently testable? If it is testable, then we need to come up with new theories until...
  22. Stal

    Computational Literature suggestions please (Topological Quantum Computers)

    Hi, I will be starting my research in topological QC (based on non abelian anyons following the work of A. Yu. Kitaev). To begin understanding this theory, I need to develop a background in the braiding group used to describe anyons, fault tolerance in quantum computers and probably condensed...
  23. Pipsqueakalchemist

    I Is quantum mechanics imply nature is deterministic or probabilistic?

    So initially I thought quantum mechanics was deterministic in the equations but was probabilistic in measurement. I’m aware of bell’s inequality which rules out hidden variables unless you assume super determinism. But recently I’ve come across something called decoherence and some people have...
  24. edukso

    B Which book is best for learning about quantum entanglement?

    Hello! I would be really thankful if you could recommend me a good book for an introduction to quantum entanglement . Thanks!
  25. sergiokapone

    A Quantum superposition: Is a problem of space-time worldview?

    One of the paradoxical principles in Quantum Physics is the principle of quantum superposition, since in quantum theory we are not really talking about the superposition of waves or oscillations, but about the superposition of states. A classic example demonstrating the phenomenon of quantum...
  26. J

    I How Does Quantum Negativity Vary with Partial Transposes in Bipartite Systems?

    Let as consider a system ##H = A\otimes B## I've been said that quantum negativity, i.e. taking the partial transpose w.r.t A or B and summing the magnitude of the negative eigenvalues obtained, is a measure of how entangled are the parties A and B. First question: Why is it that we do not...
  27. stephen8686

    Courses Quantum Optics, Feeling Overwhelmed and Underprepared

    I am an undergraduate at a fairly well known research university. I have taken undergraduate QM 1, QM 2, and the graduate course on Quantum Optics. I got As in all of them and found them not very difficult. Now I am in a research group researching superradiance. I do not feel like any of my...
  28. VictorMedvil

    How Do You Build A Quantum Computer?

    So I have heard that IBM and Google have constructed Quantum computers, how does one actually construct a Quantum computer? I would like as much detail as possible on the construction of one of these devices and how it works exactly, I wanted to buy a Spin Q Quantum computer and I understand how...
  29. J

    Programming Languages used in Graduate School? (quantum, high energy, and nuclear physics)

    Hello, I have 1 undergrad year left and was wondering what the most used programming languages in grad school are. I still don't know which grad school will accept me so I haven't bothered to ask them directly as my application will be in November when I get my GRE scores. I am Interested in...
  30. T

    I Are there signs that any Quantum Interpretation can be proved or disproved?

    The concept of decoherence seems to be a major progress in quantum mechanics. Has decoherence or any other new finding the potential that a particular interpretation of quantum mechanics will prove correct or incorrect resp. in the foreseeable future?
  31. Twigg

    A Search for CPT violation with protons/antiprotons using quantum logic

    Just wanted to share a cool proposal paper from the BASE collaboration. I found this article dense and the theoretical aspects are way above my pay grade, so please chime in if you think I get anything wrong. For the record, I have no ties to this group and hadn't heard of them before this...
  32. U

    Studying Modern physics after quantum mechanics

    Hello everyone. I am studying physics as a self-study and would like advice on the next topics to study. So far I have been studying: -calculus, linear algebra and basic physics -classical mechanics (from Goldstein's textbook) -classical electrodynamics and special relativity (from Griffiths...
  33. yucheng

    Griffiths Quantum Mechanics Problem 1.18: Characteristic Size of System

    intermolecular distance means distance between particles. So, I imagine a sphere. $$\frac{4}{3} \pi d^3 = \frac{V}{N}$$ However, Griffitfhs pictures a box instead, where $$d^3 = \frac{V}{N}$$ And the difference between both models is a factor of ##(4\pi/3)^{2/5} \approx 1.8##, which is...
  34. K

    I Is this system a superposition?

    Suppose a blind man builds a machine that paints three apples with three colors, either red, blue or green. Once the machine has done this, are the three apples in the following superposition: or is the wavefunction just one of It feels like because the man is blind, the apples should be in...
  35. Strilanc

    I [video] Simulating a delayed choice quantum eraser in an online drag-d

    This is a follow-up video I made to a previous one on common misconceptions about the experiment. I'm interested in people's opinions here about how close the simulated experiment is to the real thing (e.g. there have to be some compromises due to the simulator not having free space propagation...
  36. Orenshved

    What's needed to use quantum entanglement for FTL data transfer?

    Hey all, I need help with the book I'm currently writing. What would it take (even theoretically) to use quantum entanglement for FTL data transfer? From what I understand, the state of entangled particles can not be changed without breaking the entanglement. Do you think this would ever be...
  37. A

    B Time travel in the quantum world

    hi users, I'm a new member of the forum. My question is about time travel in the quantum world. I am aware of the enormous limitations, but my topic is about individual particles and their ability to travel through time, is that possible for them? My question comes from a speech by an important...
  38. J

    A Do we really need the Hilbert space for Quantum Mechanics?

    Let's play this game, let's assume the infinite Hilbert Space, the operators and all the modern machinery introduced by Von Neuman were not allowed. How would be the formalism? Thanks
  39. G

    B What Math do I need to learn best for Classical and Quantum Physics?

    I am a 14 year old who is very interested in Physics, especially astrophysics, but I don’t know exactly which math I should study in order to learn more in depth of the field. What is the best thing to learn?
  40. A

    I What part of physics describes what happens just outside of an electron?

    Coulomb's law for three dimensional space is an empirical law that describes the forces between two stationary point charges and is defined as: \vec{F}=\frac{K q_1 q_2 (\vec{r}_1-\vec{r}_2)}{|\vec{r}_1-\vec{r}_2|^3} From Coulomb's law, the magnitude and direction of an electric field produced by...
  41. R

    Working on my scientific script on quantum physics (sources for the Casmir effect)

    Summary:: Any good english or german sources for Casimir effect, quantum fluctuations or zero point energy Hello, fellow quantum physicists I am currently writing a detailed physics script for my quantum physics project and I wanted to ask if you know some good internet sources on the theme of...
  42. G

    B Quantify Quantum Eraser Experiment

    I'm trying to grasp a quantum eraser experiment as described in a book I read. It helps me to put numbers to things, so my goal is to calculate the amount (intensity) of the light that demonstrates interference. The author describes a double slit quantum eraser experiment using polarized light...
  43. heslaheim

    I Some questions in "Introduction to quantum mechanics"

    A certain field has a singularity at the origin, and the divergence of its curl is zero at any point outside the origin, but surface integral of the curl is not zero in the area of any closed surface containing the origin. So how should the Stokes theorem related to this field be expressed at...
  44. AlexTab

    Finding the Ratio of Particles in a Three-Level Quantum System

    Summary:: Find the ratio of the number of particles on the upper level to the total number in the system. Consider an isolated system of ##N \gg 1## weakly interacting, distinct particles. Each particle can be in one of three states, with energies ##- \varepsilon_0##, ##0## and...
  45. M

    B Description of isolated macroscopic systems in quantum mechanics

    If we prepare a macroscopic system (something like Shrodinger's cat) in a known quantum-mechanical state and we let it evolve for a very long time completely isolated, for what I understand the position of all it's particles will become more and more spread in space. But if the evolution of the...
  46. Orenshved

    Sci-fi writer in need of futuristic Quantum Physics ideas

    Summary:: Looking for ideas for my book about future QP applications. Hey everyone, I'm writing a sci-fi thriller set 25 years in the future, where my main character and his team are trying to stop an artificial superintelligence that is operating on the world's most powerful quantum...
  47. RockSteadyUK

    I Quantum entanglement. -- Spin up, spin down, isn't it the same?

    If I were viewing the Earth from high above the North pole, I would notice it spinning in an anti clockwise direction BUT when viewed from the South pole it would be spinning in a clockwise direction. If I were high above the equator oriented in a "North up" position I would observe the globe...
  48. J

    I Quantum Negativity & 4-Partite Entanglement of GHZ State

    When I computes the negativity (with the partial transpose) of the density matrix corresponding to the GHZ I obtain zero, no matter what is the partition I choose. I've read somewhere that this is because GHZ's distillable entanglement is zero, which I don't really understand because I haven't...
  49. J

    B Does the Higgs Boson really have 0 spin?

    Does the Higgs Boson really have 0 spin or is the spin between 0 and 1/2 x (1.054 571 817... x 10-34 J s)?
  50. T

    I Quantum Astronomy - well sort-of

    It is a proposed method for relaying the light from multiple telescope, long baseline, interferometers. Some proposed hardware has passed the initial proof-of-concept stage. https://www.scientificamerican.com/article/quantum-astronomy-could-create-telescopes-hundreds-of-kilometers-wide/...
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