Quantum Definition and 998 Threads

Hello, I know we have the parity operator for inversion in quantum mechanics and for rotations we have the exponentials of the angular momentum/spin operators. But what if I want to write the operator that represent a reflection for example just switching y to -y, the matrix in real space...

Hello, In Griffiths Intro To Quantum (second edition) example 4.3 page 180 ... Calculating the expectation of <Sx>, equation 4.164. I'm sure I am wrong, but it seems like after using Euler's for the e^i terms there should be 2cos(yB0t)'s terms. I agree the sin's cancel (After using Euler)...

Quantum fields have wave functions that determine a particle position in space. It solves non-locality, double-slit paradox, tunnel effect, etc. What if the wave function is also in time? Won't it solve the breaking of causality at quantum level? (Delayed Choice/Quantum Eraser/Time) Not much...

By the Wigner theorem, symmetries transformations are implemented by operators ##\hat{U}## that are unitary or antiunitary. This is what is written in most books. But I have read somewhere that, to ##\hat{U}## represent a symmetrie, it's necessary that ##\hat{U}^{\dagger} \hat{H} \hat{U} =...

The main role in quantum gravity can be played by the uncertainty principle , where is the gravitational radius, is the radial coordinate, is the Planck length. This uncertainty principle is another form of Heisenberg's uncertainty principle between momentum and coordinate as applied to the...

I have been reviewing potential methods for measuring Quantum Vacuum Fluctuations that I might be able to implement in a home hobbyist environment. Must be room temperature devices. I have seen that there are only a couple of possibilities: The Tunnel FET and the Single Electron Transistor. I...

n is the principal quantum number. l is the angular momentum quantum number. ml is the magnetic quantum number. The possible values of l are 2, 3, and 4. I'm not sure if l can be equal to 4. On the answer key, it shows l = 2, 3.

I am currently studying quantum synchronization. I am reviewing a https://www.researchgate.net/publication/251232415_Quantum_Synchronization_of_Two_Ensembles_of_Atoms which describes quantum synchronization of two ensembles in a cavity. As such, I have a query regarding a cavity physics related...

From here: From here: Peres writes on p.11: And on p.58: Note that Peres says that these issues are not yet fully understood! On p.63, Peres writes: On p.424: And on the next page: The footnote quoted by Peres says: And on p.25, where Peres introduces ensembles, he says (like Gibbs...

Hello, again. My current interest is quantum computation. I've finished Griffiths' QM for the first time. Because it only takes me a month studying the book, I may have study it superficial, so I plan to study it again and complete all the problems after each chapter. Then is this book...

I understand partly what he is saying, but can you discount the measurement effect as a feature of the world? Aren't measurement effects going on all the time between macroscopic and microscopic systems, making it in practice, at times, an indeterministic world? Or is he assuming that...

I am a master student in theoretical physics from Italy and I would like to know more about fields related to "Quantum Information". I've been to some seminars and I think that these fields are very interesting, but I need to understand before applying for a PhD. What should I do?

I'm a student trying to explain quantum superposition without using Schrodinger's cat. Instead, I'm trying to use the principal of wave particle duality to explain how a particle can be in multiple states (and locations) at once before it is observed due to wave properties. However, I'm unsure...

I was reviewing the harmonic oscillator with Sakurai. Using the annihilation and the creation operators ##a## and ##a^{\dagger}##, and the number operator ##N = a^{\dagger}a##, with ##N |n \rangle = n | n \rangle##, he showed that ##a | n \rangle## is an eigenstate of ##N## with eigenvalue ##n -...

Hi all, I am an undergraduate junior majoring in materials science who would like some advice with respect to which courses to take for the fall semester of my senior year. Some background: I am a materials science student and I intend to study spintronics and topological insulators for my...

I am trying to understand Aubry-Andre model. It has the following form $$H=∑_n c^†_nc_{n+1}+H.C.+V∑_n cos(2πβn)c^†_nc_n$$ This reference (at the 3rd page) says that if ##\beta## is irrational (rational) then the period of potential is quasi-periodic incommensurate (periodic commensurate) with...

Hello my dear fellows, how're you doing? I'm trying to learn how to use Quantum Espresso, and in order to do this, I'm trying to simulate a hexagonal boron phosphide primary cell. At the end of the simulation, the structure seems to be fine, but sometimes the distance of the atoms are too short...

This might sound stupid , but I am wondering how exactly could I describe the momentum eigenfunctions of photons? EDIT: to destroy ambiguity, I am searching for a quantum mechanic description of monochromatic light similar to how we represent it classically as: E-> = a->cos(wt+phi)

Can the low temperatures in Space be employed to cool a Quantum computer installed on an operational Space vessel doing away with the need of a super fridge or whatever they use here on Earth? Thank you.

At 12.00h a specific event is being expected in Berlin, whether the wall ist teared down, or not. The sender is in Berlin and wants to send the information about the event to the recipient on the moon. Both sides know about the possibly upcoming event. As the light takes 1 second to the moon...

I would like to know what the implications of this paper are https://arxiv.org/abs/1712.10057. They say " Here we show that, while in nature the complex conjugation needed for time reversal is exponentially improbable, one can design a quantum algorithm that includes complex conjugation and...

Does anybody know what the connection is between Wallis' formula for ##\pi## and quantum mechanics? There was an article about it: https://www.eurekalert.org/pub_releases/2015-11/aiop-ndo110915.php but like all articles for the lay public, all the details were left out. Wallis' formula is...

Can we suppose that a quantum property (like spin, polarisation, velocity, position) becomes a potential, a probability, when we are going to measure it? Can we say that this property does not exist while remaining unmeasured, and that when measured takes on a value that depends on both the...

Hi everyone, I'm a computer scientist (not a physicist), so I will ask a computer scientist's question. In all the descriptions I found of Grover's algorithm, there is an element that is puzzling the computer scientist in me: it seems that you need to tell the Oracle about the position of the...

When we make a symmetrie transformation in a quantum system, the state ##|\psi \rangle## change to ## |\psi' \rangle = U|\psi \rangle##, where ##U## is a unitary or antiunitary operator, and the operator ##A## change to ##A'##. If we require that the expections values of operators don't change...

Let’s say I create two hypothetical quantum entanglement based network devices, A and B, which means communication between A and B is instantaneous. It works like a walkie talkie in that I talk into A and you can hear my voice in B, and vice versa.Now. I take device B with me on a spaceship...

According to this article, written by D-Wave's CEO, the advent of quantum computers will "change the way the world uses energy". However, on a first reading, it sounds like an advertorial that pushes nonsense. I'm no energy scientist (unless you put high energy physics in that category for some...

I understand that downconverted light is not coherent, so that there are essentially many overlapping interference patterns and that coincidence detection filters out one of those patterns. However, could the downconverted light be filtered such that interference can be detected without...

In a https://jila.colorado.edu/thompson/sites/default/files/pdf/PhysRevLett.113.154101_0.pdf on quantum synchronization, they introduce the setup given in the attached 'Fig1.png'. I would like confirm a few concepts regarding this setup. The setup is described in the following way: The general...

I want to know the differences between Newtonian Gravity and Quantum Gravity

I should clarify, I am a linux administrator by trade and I have no physics or scientific background outside of working at a medical institute, So if my ideas are off and seem wild and misguided, please forgive my ignorance, and while you are at it be grateful for a fresh perspective. (joke) So...

Homework Statement Homework Equations I've used: ##mv^2/r## = Centripetal ##q^2/r^2## = Force pulling the electron in A bunch of other ones which I really can't be bothered listing. The Attempt at a Solution I managed to get Part A of the question using pretty simple methods. I set ##mv^2/r...

Hi everyone, Could anyone recommend a good QM textbook (undergrad-ish level) or some lecture notes that treat entanglement from the ground-up? Most of the stuff I have seen online on entanglement seem to fly pretty quickly into information-theory or abstract group-theory type stuff, which I am...

Hi all, I have learned the very basics of entanglement (discrete, 2 particle systems) and was hoping that someone can recommend introductory (undergrad-level) material for continuous-variable, 2 particle entanglement. Stuff I have found online so far (like this...

My paper "Classical states, quantum field measurement", arXiv:1709.06711, has been accepted by Physica Scripta, https://doi.org/10.1088/1402-4896/ab0c53. The version as submitted to Physica Scripta on November 4th, 2018 is available as arXiv:1709.06711v5. I believe that anyone who puts some...

In a recent Scientific American article the notions of multi-verse and ugli-verse are examined as dangerous ideas which can stop Physics from looking for deeper truths since they are based in the universe that supports intelligent life. The notion is to extend beyond Everett's Many Worlds...

We need quantum physics for cognitive neuroscience ?

Square law? i raise this question because of recently reading some QM, and realizing that for significantly short periods of time, it becomes hard to detect the mathematical patterns. E.g. in the double slit experiment, the standard pattern doesn’t appear after just a few photons. It takes...

Hi everyone! Sorry for the bad english! So, just a quick doubt... Does things collapse from a wave of probability into a quantum field or is the wave in the quantum field the probabilistic wave itself? An example to make it clearer: Suppose we have an atom, it enters an atom interferometer, it...

Published in the peer reviewed Journal of Applied Mathematics and Physics is the intriguing paper with the following abstract: https://file.scirp.org/Html/11-1721242_88041.htm "Entanglement and the tunnel effect phenomena have been repeatedly observed and are generically accepted under...

A complete description of the thermal interpretation of quantum physics can be found in my just finished papers (for the bare bones, see Section 2.5 of Part II) Foundations of quantum physics I. A critique of the tradition, Foundations of quantum physics II. The thermal interpretation...

On page 59 of Peskin & Schroeder, there's a section on the lorentz transformation of field operators which I've attached. I'm confused about the part towards the end where he does a change of variable on the integration measure; it seems like he's only rewriting the lorentz-invariant integration...

Find the interpretation of QM that best suits your personality. You don't need to think much about quantum interpretations to decide which one is the best for you. Just choose one of the offered answers to a couple of questions on the graph. You don't need to think much about the offered...

Hi, usually, when we talk about quantum quench dynamics we assume situation when Hamiltonian of a system has a sudden change from ##H_0## to ##H_1##. System was initially in the ground state (or more generally - eigenstate) of ##H_0##. The interesting dynamics appears when the commutator...

I've struggled to understand quantum mechanics for many years. I've recently written some notes on the subject that address some of the issues that I've found confusing and that I think might be helpful to others. The moderators on Physics Forums, quite reasonably, won't allow me to publicise...

After learning that QFT describes particles as excitations of underlying fields, I've been trying to gain a more definite understanding of what it means; I came across this paper: https://iopscience.iop.org/article/10.1088/1361-6404/aaa032 Does the author say anything that is misleading? If...

Here we consider a black hole formed by gravitational collapse classically. We also consider a scalar massless Klein-Gordon field propagating on this background. To quantize the field we expand it in appropriate modes. The three sets of modes required are: The incoming modes, appropriate for...

Could someone, in laymen's terms explain to me what stochastic mechanics is?

I was reading a book which had some comments on EPR paper (Einstein, Podolsky, Rosen - 1935) like following: In Newton's physics, when two identical billiard balls hit each other head-on, bouncing off in opposite direction, knowing one ball's position and speed will also indicate other ball's...

Homework Statement Using quantum mechanics, what happens when a photon of light hits glass? Homework Equations Momentum= Mass x velocity The Attempt at a Solution I am not sure of my answer but suffice to say the following: Assuming the collision between the photon particle and those in the...