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Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy and the uncertainty principle and is generally used in single body systems. Use the quantum-field-...

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1answer
16 views

Can electrons jump between levels in same shell with constant $L$?

I see many cases where electrons jump from various energy levels of some $L$ value to various levels of other $L$ value. But is there any transition in same $L$ level between its different ...
2
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1answer
56 views

Under what conditions is a wavefunction $\psi(x)$ equal to the probability amplitudes $a(x)$?

For context, consider a general expansion of a wavefunction into continuous eigenstates of position, $\phi(x_m,x)$, multiplied by continuous probability amplitudes, $a(x_m)$ $$\begin{align}\psi(x) &...
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1answer
31 views

Does the $|W\rangle$ state have a stabilizer?

I've been practicing trying to find stabilizer groups for various multi-qubit states $|\psi\rangle$. So far the only method I know is to start with the state $|0\rangle^n$ which is stabilized by the ...
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0answers
28 views

Going from quantum master equation to Fokker-Planck equation for the Wigner function

I am trying to understand how to go from a quantum master equation to a Fokker-Planck equation for the Wigner function. For instance, in this article https://arxiv.org/pdf/quant-ph/0605166.pdf , they ...
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1answer
49 views

What is the interpretation of $|\langle AB\rangle|$? [on hold]

what is the interpretation of $|\langle AB \rangle|$ ? since $|\langle AB \rangle|^2 = \langle AB \rangle [\langle AB \rangle]^\dagger$ , could $|\langle AB \rangle| = \sqrt(|\langle AB \rangle|^2)$ ?...
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0answers
32 views

Meaning of a ladder operator being a scalar or a vector

I was reading an article [1] where the author is deducing the ladder operators for the three-dimensional isotropic harmonic oscillator. He does it two times one considering the said operators to be a ...
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1answer
55 views

Wave-function collapse query

A distant star emits photons towards Earth, where they can be detected and observed, however there is a very dense object (a galaxy) directly between the distant light source and our observation ...
0
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1answer
41 views

Delta function from poles of Green's function

In quantum mechanical scattering theory, we often use Green's functions which contain poles. For example, in Schroedinger quantum mechanics the free Green's function is given by $$ G_0(\vec{p}) = \...
4
votes
1answer
52 views

Quantum mechanics in terms of density operators as the fundamental object?

So I've done a two courses in undergrad quantum mechanics, the first began with wave mechanics and then went on to bras and kets, the second course went more into detail regarding bras, kets, hilbert ...
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0answers
23 views

Expectations value of position [on hold]

I want the complete step by step solution to this problem.
0
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0answers
19 views

Peeking inside Schroedinger's Black Box (not his cat box)

While exploring variations on Shroedinger's Cat, I came up with the following puzzle: Define a Schroedinger's Black Box (SBB) as a volume whose contents have no causal connection to an observer A. ...
0
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0answers
32 views

How to find the small atoms size? [on hold]

How to find atoms size by using lasers. I have curiosity because today,I have found the particle size of lycopodium powder.
0
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1answer
48 views

How close are we to measure Planck time

I know that Plack time is considered a fundamental time unit by some of the physicists. To test this we need to try to falsify it. I want to learn what the smallest time interval we can measure is.
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0answers
49 views

Does a black hole cool off and obey laws of thermal equilibium?

I have read these questions: Kirchhoff law of thermal radiation Why do dark objects radiate thermal electromagnetic energy faster than light objects? And it made me curious. Nothing gets out of a ...
0
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0answers
20 views

Eigenvalues of an operator [migrated]

This is probably a stupid question but I am stuck on this: Deduce the eigenvalues of the operator $A^{\dagger} A$ are positive, where $$A^{\dagger} = -\frac{\text{d}}{\text{d}x} + \tanh(x)$$ ...
1
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1answer
18 views

A Number State of Light through a dielectric

If a number state |1> picks up a factor of $e^{-i\phi}$ on going through a certain medium, what factor will a number state |N> pick up? Will it be $e^{-iN\phi}$ or $e^{-i\phi}$ or something else? And ...
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0answers
28 views

What is quantum synchronization? [on hold]

Can someone provide a clear basic description or reference to how the phenomena of synchronization manifests at the quantum scale? Thanks.
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0answers
26 views

Green's function regularization and delta distribution

I have a free Green's function which is proportional to a $2\times 2$ matrix: $$ G_0 = \frac{1}{E^2-E_k^2}\begin{pmatrix} a & b \\ c & d \end{pmatrix} $$ The total Green's function after ...
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0answers
14 views

A book on quantum dots

I am looking for a good textbook in which theory would be formulated for quantum dots of different sorts both manufactured of a metal and a semiconductor, as well as its interaction with the ...
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0answers
28 views

Number operator and its eigenvectors [duplicate]

So the eigenvalue problem for a Number operator defined in terms of creation and annihilation operators ( $N = a^{\dagger}a$ ) is $$N|n>n|n>$$ If we act with $N$ on $a|n>$ and use ...
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0answers
57 views

Wave-functions in strong gravitational fields?

When I was introduced to quantum mechanics at university, a wave function was described as a function $\Psi: \mathbb{R}^4 \rightarrow \mathbb{C}$, that is space + time. General relativity, meanwhile, ...
1
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1answer
50 views

A particle is in a harmonic oscillator potential. Which are the possible spreads for a simultaneous measurement of the momentum? [on hold]

A particle is in a harmonic oscillator potential, not in the ground state. The position of the particle is known with an rms spread of $1\mathring{\text{A}}$. Which of the following are possible ...
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1answer
41 views

What if we didn't know if particle is observed in double-slit experiment? [duplicate]

The famous double slit experiment shows how light behave like a wave when sensors near one slit are on and recording vs not recording. I didn't find a lot of details, but especially given the case ...
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0answers
88 views

Where is the info of the wavefunction stored at?

I have read these questions: Is the wavefunction a real physical wave or only a mathematical abstraction? The wavefunction gives you the probability description of a particle's position (and other ...
1
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2answers
73 views

Understanding Feynman derivation of probability current density

On page 21-4 of vol. III of The Feynman Lectures on Physics, he derives the formula for the probability current density. Starting with the Schrödinger equation, he presents the time derivative of the ...
2
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1answer
40 views

Holographic Superfluid Space Time and Temperature

I am approaching this from a layman’s perspective and curious about what those more expert in the field have to say about my understanding of Superfluid vacuum theory and the holographic principle and ...
3
votes
1answer
36 views

How is the product $L\cdot S$ between orbital and spin angular momentum operators defined? Do they act on the same or different Hilbert spaces?

For an electron, are the Hilbert spaces for the spin angular momentum and the orbital angular momentum the same or are they different? If they're different, how do we justify the operator $L\cdot S$ ...
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0answers
35 views

How was the expression for $f_1$ derived when $f_1$ and $f_2$ are given? [on hold]

(a) Let $f_1$ and $f_2$ be the total emission powers (thermal radiation plus reflecti[...] respectively. We have $$ f_1 = e_1 + \left( 1-\frac{e_1}{E_1}\right)f_2, \quad f_2 = e_2 + \left( 1- \...
0
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1answer
32 views

Quantum state space constructing operator

If I use British money the amounts I can have are isomorphic to $\mathbb{Z}_{\geq0}$ (in pennies). If I also use Australian money, if I want to think about the amount I have in total, I can use ...
15
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2answers
1k views

What's the significance of the nickel crystal in the Davisson and Germer experiment?

Davisson and Germer, in 1927, conducted an successful experiment to prove the existence of matter waves. What's the meaning of using the nickel crystal? I mean, why didn't they use any other materials?...
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0answers
26 views

Getting the relativistic inner product of Siegel's book

Last time I was discussing with a physicist about quantum field theory and how in the firsts chapters of textbooks it is often regarded that the Klein-Gordon equation does not have a positive definite ...
0
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1answer
50 views

Electromagnetic induction causes electron wave function collapse inside atoms?

Electromagnetic wave interacts with wave function of the electron in metal atoms to become particles? or to keep it simple; moving magnet collapses wave function of electron to make moving electrons?
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0answers
24 views

Angular diameter of a particle outside of the observable universe?

"Angular diameter" and "apparent size" seem to be used interchangeably in cosmology. But if an object is outside of the observable universe, then isn't it no longer "apparent", yet it would still have ...
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2answers
54 views

Can someone explain why this matrix is unitary? [on hold]

I have a matrix $$ \begin{bmatrix} a & b \\ e^{i\theta}b^* & -e^{i\theta}a^* \end{bmatrix} $$ Where $\theta$ is a real number, and $a$ and $b$ are complex number such that $|a|^2 + |...
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2answers
68 views

Force of hydrogen nucleus on an electron

It is known classical mechanics doesn't works to describe atoms mechanics. I'm studying Coulomb's law, i.e: $$F=\frac{k\,q_1q_2}{r_{12}{^2}}$$ that all of you know. I wonder if it is possible to ...
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0answers
23 views

Finding $<x|XP|\psi>$ and $<x|PX|\psi>$ [on hold]

I need to Find $<x|XP|\psi>$ and $<x|PX|\psi>$ I know that $[X,P]=i\hbar$ so $<x|XP-PX|\psi>=i\hbar\psi(x)$ but if I try to open $<x|X \cdot I\cdot P|\psi>$ $=\int^\infty_{-\...
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1answer
28 views

Energy Density of Radiation

What actually does the term energy density u(v,T) denotes? Is it the energy density of cavity radiation or the radiation emitted by blackbody? Is it uniform? While we derive an expression of it , we ...
2
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1answer
80 views

Are *all* quantum states indeterminate if they are outside the observer's light cone?

Is the state of a particle arriving from outside an observer's light cone merely unknown, or is it quantum mechanically indeterminate? I guess the question needs a background in the form of a ...
3
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1answer
72 views

Canonical quantization of time-dependent lagrangians

I have a lagrangian $$ L(x^{a}, \dot{x}^{a}, t), $$ which is non-degenerate, quadratic in the fields, and contains an explicit dependence on the evolution parameter $t$. If $L$ was time-independent,...
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votes
1answer
37 views

Meaning of Eigenvalue and eigenfunction [on hold]

What is the physical meaning of eigenvalue and eigenfunction?
-3
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0answers
53 views

Defense-Related, Affordable Graduate Level Projects [on hold]

What are some graduate level, low cost defense, military, or security related project ideas that would look great on a resume? (Under 2k usd) Assume the project will be assigned to a single ...
-1
votes
1answer
44 views

Vectors needed to find successive states of an electron's movement

Do we need both the position and momentum vectors to know successive states of an electron's movement? Or is one sufficient?
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1answer
59 views

Collapse of the wave function and switching off measurement device before particles hit the wall detector

Would collapsing wave function by measuring/observing and then quickly turning off measurement device cause to uncollapse wave function? so it goes like this : wave--->particle---> wave(hits the wall)...
7
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2answers
672 views

Classical theory fails to explain quantization of motions?

I understand everything written here. But the last point, I cannot get, at all. How does it point towards Quantization of the two motions, since the energy change is not sudden, but gradual? And if ...
0
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0answers
37 views

Derivation of the master equation without using the Markov approximation

In this paper, pg 27, the master equation for reduced density matrix is derived using only two assumptions: 1) the initial total density matrix is unentangled, i.e. tensor product of system and ...
-4
votes
3answers
93 views

How dose the factor $1/2$ in $E=\frac{1}{2} mv^2$ disappear in QM?

How dose the factor $1/2$ in $E=\frac{1}{2} mv^2$ disappear in QM? The TDSE writes: $$ H |\psi \rangle = i\hbar \frac{d}{dt}|\psi \rangle $$ The momentum operator is defined as: $$ \langle x|p|\psi \...
1
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4answers
113 views

Does photon interference violate causality?

Suppose a hydrogen atom jumps down an energy level and emits a photon and that photon later goes through a double slit and gets absorbed by one atom of a screen making it jump up an energy level. ...
1
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1answer
38 views

Strong gravity at the micro level?

I have read this: https://resonance.is/black-holes-elementary-particles-revisiting-pioneering-investigation-particles-may-micro-black-holes/ where it says: For the case of hadrons, it is at least ...
51
votes
10answers
4k views

Quantum made easy: so what *is* quantum mechanics all about? [on hold]

Being a physics grad student, I got used to the weird concepts behind quantum mechanics (used to doesn't mean I fully understand it though). What I mean is that I'm not surprised anymore by the fact ...
1
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1answer
51 views

Using a single harmonic oscillator to implement a quantum gate. Confusion over concept

I'm trying to simulate a quantum gate operation in mathematica using a harmonic oscillator and I have some confusion with how the physical system relates to the theory. This may be a bit long winded ...