Quantum Definition and 999 Threads

According to the uncertainty principle, when we measure a micro-object with a measuring device, we cannot predict what value the device will show. But if we knew exactly the wave function of this device, together with the wave function of the micro-object, could we exactly predict the result of...

Summary:: I’m a beginner trying to get into Quantum Physics, and want some good resources (e.g. books) to get me started. Hi everyone! I’m a beginner trying to get into Quantum Physics, and want some good resources (e.g. books) to get me started. I have a very basic knowledge of physics (10th...

Hi! I want to self study some of quantum mechanics so i need introductory textbook. I've taken courses on linear algebra that covers all "Linear algebra done right" by Sheldon Axler, multivariable calculus, two courses on general physics and the basics of differentials equations. I really like...

Summary:: I'm trying to understand the meaning behind the answer of 2.34... but I haven't taken a quantum class yet so I'm utterly lost. So I took this physics class that's teaching us python and for our final project our teacher assigned random problems to work out, well I got stuck with a...

Hello folks, I am currently studying from Griffiths' Introduction to Quantum Mechanics and I've got a doubt about good quantum numbers that the text has been unable to solve. As I understand it, good quantum numbers are the eigenvalues of the eigenvectors of an operator O that remain...

I am totally confused about the task. Any help will be nice. Thank you so much

If gravity is the affect of time dilation because of the distance from the bottom of an object to the top then wouldn’t that mean that gravity doesn’t exist at the quantum level?

How do we map experimental measurements of quantum fields, such as those seen in accelerators, to the theory's mathematical formalism? When we see images of particle tracks produced in accelerators such as the LHC, I think it's safe to say a measurement (or series of measurements) has been...

I have some questions to this Ansatz and I would really appreciate it if I can get some insight: 1. What is the current status of gate fidelity and what are the current struggles to improve it? 2. Same question but with coherence times. 3. What are the current issues with scalability? 4. Could...

Can you please suggest a good introductory statistical and quantum mechanics book which can be self studied. My math background : I've done multivariate calculus, vector calculus, linear algebra ,some complex analysis all at the usual undergraduate level. The books I've self studied thus far...

This is a surface level question and I don't want to go into detail. Imagine an algorithm which when used with a sensor output gives the statistical moments of a variable in nature (for example mean and standard deviation of a variable). The sensor measures this once in a while (like once in a...

##x## can be discretized as ##x \rightarrow x_k ## such that ##x_{k + 1} = x_k + dx## with a positive integer ##k##. Throughout we may assume that ##dx## is finite, albeit tiny. By applying the Taylor expansion of the wavefunction ##\psi_n(x_{k+1})## and ##\psi_n(x_{k-1})##, we can quickly...

I have some basic questions about mixed states and entanglement. 1. Do mixed states always imply that the states are entangled and vice versa? 2. Can mixed states ever be separable? 3. Does interference have anything to do with entanglement? In terms of Density Matrices, ρ = |ψ><ψ|: 4...

Of course, this question consisted of two parts. In the first part, we needed to calculate the first-order correction. It was easy. In all the books on quantum mechanics I saw, only first-order examples have been solved. So I really do not know how to solve it. Please explain the solution method...

(I am not sure which forum this post belongs to. Hope someone kindly helps me move it to a proper forum.) In papers, for example, here, here, and here, the authors start from the Lagrangian for matters and gravitational fields, then Dirac's constrained canonical quantization is used. They...

Very confused about this article and the experiment it's based on. I'm not very knowledgeable on this, but I'm very confused on what's happening here. It seems extremely weird to me

I'am interested in the notation of the approximation in quantum phase estimation algorithm. In the literature there are different definitions, which I divide into two cases here. Both different in their definition of the ##\delta##. In both cases I start with a quote of the source and show an...

Hi, there. I am interested in quantum gravity. But I am not sure how to find review papers about its recent developments. I tried "quantum gravity" on google scholar. But I could not find a suitable review other than that about loop quantum gravity. I am not sure what are the other approaches to...

Rovelli points to three pieces of existing observational evidence that should guide future quantum gravity research. Bottom line: * abandon Lorentz invariance violating quantum gravity theories, * abandon supergravity and string theory, and * stop working on the anti-deSitter/conformal field...

Please be kind to help.I would be grateful

Could quantum entanglement be used to send faster-than-light communications across vast distances in space, in the distant future? For example, if humans establish permanent colonies on Mars, it would take some time to send communications between Earth and Mars. Could a future technology...

In Nielsen and Chuang p.223 we have the following situation: $$\frac{1}{2^t} \sum\limits_{k,l=0}^{2^t-1} e^{\frac{-2\pi i k l}{2^t}} e^{2 \pi i \varphi k} |l\rangle$$ Which results from applying the inverse quantum Fourier transform to state ##\frac{1}{2^{t/2}} \sum\limits_{k=0}^{2^t-1}...

In HHL algorithm, does the controlled unitary (Hamiltonian simulation part of Quantum phase estimation) depend on Hermitian matrix coefficients and how?

I read about quantum spin a while ago. If it’s not spinning, what is it doing?

I recently started studying some quantum mechanics, so far I have been using online resources(like MIT OCW 8.04/8.05, and Tongs notes I think I have reached a stage where I understand the Schrodinger eqn and can solve it for various potentials(including for the H-atom) but I don't know anything...

If I understand the idea of EPR correctly, the quantum entanglement occurs between two particles for which the total momentum is known (therefore, knowing the momentum of one particle, one can recalculate the other, and this contradicts the uncertainty principle). Then the question arises...

Are there any QFT books that use little to no math? If there is a little math that is okay. I don't know much about math. I am looking for good explanations on how it works without math. Any help would be great!

Im trying to obtain regularized (and triangulated) version of Hamiltonian constraint in the LQG. However, one step remains unclear to me. I am starting with the Euclidean Hamiltonian:$$H_E=\frac{2}{\kappa} \int_\Sigma d^3 x N(x)\epsilon^{abc} \text{Tr}(F_{ab},\{A_c,V\}) $$ Now i have to...

"B0 is a static magnetic field (produced by a superconducting magnet) that initially causes the protons in the body to align with the field and precess at the larmor frequency along the z axis . From a mathematical perspective this precession around the B0 axis occurs due to the time evolution...

A lot of people say that Quantum Field theory (QFT) an Quantum Mechanics (QM) are equivalent. Yet, I've found others who dispute these claims. Among the counter-arguments (which I admittedly do not have the expertise to pick apart and check their validity in full) are the following: 1) While QFT...

-1st: Could someone give me some insight on what a ket-state refers to when dealing with a field? To my understand it tells us the probability amplitude of having each excitation at any spacetime point, but I don't know if this is accurate. Also, we solve the free field equation not for this...

Hello , what quantum fields exist in intergalactic space ? What math describes these fields ?

The charge associated with gravitational interactions is the mass. In the Standard Model, charge conjugation is the "flippin" of all kinds of charges (electric, color, etc). So, if we were to, say, incorporate quantum gravity in a beyond the Standard Model theory, what would the full charge...

I recently viewed a PBS "Space time" video The video references two articles of which one is paywalled while the other is not. https://iopscience.iop.org/article/10.1088/1367-2630/abb515/pdf https://www.nature.com/articles/s41586-020-2490-7?proof=tIn the discussion section of the free article...

It came to my attention yesterday this, from my ignorant point of view, amazing paper that describes what it looks as another Theory of Everything: https://arxiv.org/abs/2110.02062 If I didnt understand incorrectly, from first principles / a pre quantum theory (Trace Dynamics, 8D octonionic...

I just finished a new paper, A. Neumaier, Quantum mechanics via quantum tomography, arXiv:2110.05294. (later renamed to) A. Neumaier, Quantum tomography explains quantum mechanics, arXiv:2110.05294. Abstract: Starting from first principles inspired by quantum tomography rather than Born's...

In p.385 of Griffiths QM the vector potential ##\textbf{A} = \frac{\Phi}{2\pi r}\hat{\phi}## is chosen for the region outside a long solenoid. However, couldn't we also have chosen a vector potential that is a multiple of this, namely ##\textbf{A} = \alpha \frac{\Phi}{2\pi r} \hat{\phi}## where...

Homework Statement:: Mathematics to understand Quantum Scattering Theory Relevant Equations:: Suitable math book to understand Quantum Scattering Theory I need to study Scattering theory from Introduction to Quantum Mechanics by David Griffith. But I think I need to study mathematics first...

I am looking for first articles of quantum gravity in the history which before Matyevei. What is earliest articles of quantum gravity and how can ı find them?

Ontology is the easiest and the hardest concept in the field of quantum foundations. It is the easiest because even a child can understand it. When a child asks: "What is the world made of?", she asks about ontology. When you answer: "It's made of atoms" and when she asks "What does the atom...

I have been reading about ontologies in quantum physics recently and I came across Bohmian mechanics. If I understood it correctly BM endorses Particle ontology. Particle ontology claims that point-like particles that move continuously in time are the fundamental building blocks. I know some...

This New Atlas article on Quantum Brilliance describes the development status of a new quantum data processor that can operate at room temperature. They are predicting a useful commercial device in about 5 years. The device is based on nuclear spin in a diamond substrate. The device is very...

Is there a precise definition for the field? That is what I am after, since I am rather annoyed by the fact I currently do not have an unified view of the theory; having a one-liner helps me a lot in better understanding. So far there seems to be a split between an "old" quantum physics, which...

Take a simple case: A system is prepared in state ##\rho_i## at time ##t_0##, and a projective measurement is performed at time ##t_2## with an outcome ##b##. We can retrodict a projective measurement outcome ##a## at time ##t_1## where ##t_0<t_1<t_2##$$p(a|b) =...

for undergraduate students how to explain this?

An axiomatization of classical mechanics such as the one by McKinsey et al. (1) does not contain any reference to humans or experiments, and does not contain the magic (irony!) words of quantum mechanics, i.e. observables and measurements. (1) McKINSEY, J. C. C., et al. “Axiomatic Foundations...

Hello! I see that most experiments applying quantum computing techniques for high precision spectroscopy use a quadrupole trap. I don't know much about the experimental implementation of these kind of traps, so any help (or suggested paper) would be appreciated, but I was wondering how well can...

The s orbital corresponds to l=0 The p orbital corresponds to l=1 For an electron in an sp3 hybridization orbital what is l?

Hello! I read several papers about using quantum information techniques in order to do precision spectroscopy on ions. Usually they trap 2 ions in a quadrupole trap and the 2 ions are coupled through their vibrational motion along the trap axis. However most of these results involve atomic ions...

They say spin up and spin down is correlated at at any distance and that it can’t be explained by basic logic. say I rip a photo in two, shuffle them and put them in two boxes and send them light years away. No matter which box I open, I can’t know which half I have but when I open it the photo...