Quantum Definition and 998 Threads

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...

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...

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...

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...

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...

Continue reading...

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...

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??

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

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...

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...

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}}##...

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)...

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...

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...

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...

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...

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

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

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?

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##...

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)...

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

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

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...

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...

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...

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...

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

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

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.

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?

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...

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...

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...

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.

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...

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...

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...

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...

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...

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?

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...

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.

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.

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

I'm reading the article on the Many Worlds Interpretation in the Stanford Encyclopedia of Philosophy. I'm keeping up well, but this excerpt uses things I'm very unfamiliar with: I guess some characters weren't recognized. It's Section 3.6 here. I'm somewhat familiar with Wigner's Friend, but...

Between the walls of a finite well, the solution to the time independent Schrodinger equation is a combination of sines and cosines. Outside the walls where E - Uo is positive, the solutions are exponential functions. Why?

This is the given circuit: I think to add another Cnot on the right with a1 as control and a0 as target, to set initial states of a0 an a1 both |0⟩, and to measure the a0. If a0=|0⟩ then b0=b1, and vice versa. Is it correct?