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 ...

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What is the correct setting for Kirchhoff's Law of Thermal Emission?

For example, is the setting free space? Is it a surface? etc. So, what is the correct setting of Kirchhoff's Law of Thermal Emission?
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16 views

Why does the interference patterns in delayed choice quantum eraser cancel out? Why/how does it have a phase shift?

Talking about this experiment https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser#The_experiment_of_Kim_et_al._.282000.29 I am assuming that anyone able to answer my question is already ...
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0answers
18 views

Multiple contemporary measures of a photon's state

From quantum mechanics, when you polarize a photon using computational base and you try to measure its state using a diagonal base, you'll get with the 50% of probability $|0\rangle_{{} + {}}$ or ...
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0answers
17 views

Expectation value position of sine wave in infinite square well

I know that the general form of the expectation value for position is $$\langle X\rangle=\int_{-\infty}^{\infty}\psi^*x\psi dx \, ,$$ but my wavefunction is $\sin(n\pi x / a)$ where $a$ is the size of ...
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0answers
13 views

Given Quantum operator matrix [M] solve for matrix [A] such that [M] = e(A) where A is the exponent of e

I have a qunatum mechanical initial wave function of the following form: $$(1/\sqrt2)(|D_0\rangle|C_1\rangle + |D_0\rangle|C_0\rangle)$$ where $$\langle D_0|D_1\rangle = \langle C_0|C_1\rangle = 0$$ ...
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1answer
49 views

$[a,a^{\dagger}]=1$ or $[a,a^{\dagger}]=I$

$[a,a^{\dagger}]=1$ or $[a,a^{\dagger}]=I$? On every book i read $[a,a^{\dagger}]=1$. But doesn't $a$ have infinite dimension? So why does the commutator go to a number which is one dimensional?
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46 views

Why is particle superposition still part of quantum mechanics?

After reading an article on Schrodinger's Cat, it seems that if we take the environment as an observer, that superposition cannot occur because all atomic and subatomic entities would be observed all ...
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21 views

Does an expectation value over only part of a wavefunction have physical meaning?

I understand that from the Born interpretation that $|\Psi(x)|^2$ and $|\Psi(p)|^2$ can be interpreted as the probability density for finding a particle at x or with momentum p respectively and as ...
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1answer
15 views

Fetter & Walecka's derivation of second quantised potential term in many-particle TDSE

For the potential term in the Hamiltonian, I understand that we go through the same process as with the kinetic energy term. On the RHS of the TDSE, we get something like ...
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3answers
34 views

How does commutation between the hamiltonian and angular momentum operator (squared) imply conservation of Angular momentum?

So we are looking at central potentials in QM; The lecturer poses the question, when is $\textbf{L}$ conserved? He then considers the commutator of $\hat{H}$ and $\hat{L^2}$. We have; ...
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22 views

Momentum Operator [on hold]

Hello Community, I'm writing a paper on quantum mechanics and have a question about following formulas and the derivation of them. It's in german but I was told that I have an error somewhere in the ...
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0answers
26 views

Classical Quantum or Relativistic?

An ensemble contains free electrons at 10^3 electrons per m^3 at 10^7 K. What can this ensemble be treated as: a Classical Quantum or Relativistic gas or in some overlapping domain?
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3answers
85 views

How bizarre can the Quantum two slit experiment get?

Note 1: Don't apprehend my question as 'quantum woo'. I do not mean so and hate anyone who does. Note 2: I am just a 14 year old physics enthusiast. Don't expect any background. On to the real ...
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1answer
44 views

Conservation of energy in quantum mechanics

In Griffiths' book Introduction to quantum mechanics (second edition, page 37) it states: The time-independent Schrödinger equation says $$\hat{H} \psi_{n} = E_{n}\psi_{n}$$ so $$\langle H ...
12
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3answers
1k views

Do electrons in an atom always have the same 'direction'?

Perhaps speaking of direction of an electron isn't quite correct. But does QM indicates a kind of way whether all electrons are going e.g. 'clockwise' or not? Of course QM just gives a probability ...
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0answers
11 views

When you make materials smaller is there a trend in the manner light is absorbed or reflected?

For instance if you take gold is shines like yellow, but if you make it smaller I've heared that it absorbes more the smaller frequencies. At a size of 100nm a piece of gold will absorb fe more blue ...
1
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1answer
28 views

What is the correct statement of Kirchhoff's Law of Thermal Emission?

There are various quite different statements in textbooks and other science literature as to Kirchhoff's Law of Thermal Emission. So, what is the correct statement of Kirchhoff's Law of Thermal ...
2
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0answers
38 views

Loss of interference in single-photon Mach–Zehnder interferometer with detector in only one arm

I have read that if you have a Mach–Zehnder interferometer (doing a single-photon experiment) and put a non-destructive detector in only one of the two arms (connected to the first beam splitter), you ...
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0answers
18 views

density of states with changing potential floor

I wish to calculate the density of states for a 1D finite potential well, for the scattering states, meaning $E>0$. I have a potential of the form: $$ V(x)=\begin{cases} -V_0 & |x|<a\\ 0 ...
4
votes
1answer
100 views

Help needed to understand “On the reality of the quantum state”

I am having trouble to understand the reasoning in the following paper, On the reality of the quantum state. MF Pusey, J Barret and T Rudolph. Nature Phys. 8, 475–478 (2012); arXiv:1111.3328. ...
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5answers
87 views

Is QM something that belongs to all relative small particles or only to subatomic particles? [on hold]

For us human beings subatomic particles like elektrons are described by the laws of QM. But imagine their is a very huge giant looking on the universe. For him all the planets and stars are so tiny ...
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0answers
37 views

Are there some explication for the wave function in Quantum Mechanics? [on hold]

I start to learn the Quantum Mechanics and I don't really understand the mechanisme behind the wave function. As what I feel and as I think the world as multivers, 1/ I see wave function like a way ...
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0answers
40 views

Spinor on an eigenstate of $J_z$ [on hold]

The state of a particle with spin 1/2 is described (in the $S_z$ representation) by a spinor $[\Psi]=\left( \begin{array}{c} \phi_+ \\ \phi_- \\ \end{array} \right)$ Its known to be eigenstate of ...
4
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7answers
1k views

How can a product of Bra and Ket be a scalar if they are matrices?

I am trying to teach myself Quantum Mechanics and am currently on Complex Vector Space Arithmetic. According to Wikipedia, product of a Bra and Ket is a scalar (which, I think, means a complex ...
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1answer
47 views

What is the origin of the quantum operators for p and E? [on hold]

It is always stated the quantum operators for p en E are the ones we´re familiair with. But where do these operators come from?
2
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0answers
51 views

What would be the research advances if we discover the gravitational waves? [on hold]

As researchers of LIGO (USA) and VIRGO (France/Italy) say that they have discovered gravitational waves thanks to black hole collision today, what would be, apart of the important confirmation of ...
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1answer
54 views

Physical meaning of weight function in inner product in Quantum Mechanics

When taking the inner product of say two functions in Quantum Mechanics,we include a weight function w(x,y,z) that is usually equal to unity(in my undergraduate introductory QM course anyway). But ...
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0answers
24 views

Restriction to the total angular momentum of two identical particles with spin 1

I've been asked if there is any aditional restriction to obtain the possible values of the total angular momentum J by considering that the 2 particles of spin S=1 are identical. If they are not ...
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0answers
34 views

Proving Probability Current and Momentum relationship

I am trying to show that $\mathbf j = \frac{\hbar}{2mi}\left(\Psi^* \mathbf \nabla \Psi - \Psi \mathbf \nabla \Psi^{*} \right) \,, $ simplifies to $\mathbf j = \frac{\mathbf p}{2m} (|\Psi|^2) $. I ...
2
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0answers
33 views

In what circumstances, can exchange interaction acquire temperature dependence?

Heisenberg exchange interaction (sometimes called as magnetic stiffness?), originating from the Coulomb interaction and the Fermion statistics, is widely used in theories of magnetism. Conventionally, ...
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0answers
20 views

What frequencies is radation being emited in infinite potential well

The problem that I am working on is. Consider an electron in an infinitely deep one-dimensional potential well of width 1nm . This electron is prepared in a state that is an equal linear ...
1
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2answers
99 views

What is the opposite of quantization?

Is the opposite of quantization just taking the limit $h \rightarrow 0$ ? Or are there more steps involved (maybe related to bosons and fermions?)? How would one call the the opposite of quantization? ...
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1answer
139 views

Do I need to consider the spin of electrons when they are in infinite potential well

This is the problem I have And this is one of my books tell me what should I do And my question is: Do I need to consider spin in this case?(that is, I don't think the book is right...) I found ...
1
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0answers
33 views

Normalizing ket vectors

So I've run in to a bit of a notation problem on my coursework I have a vector, |A> expressed in the orthogonal basis |1> and |2> |A> = |1> + i |2> I need to convert it into bra form to normalize ...
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0answers
36 views

De-broglie wavelength [on hold]

The de-broglie wavelength of an electron emitted from the ground state of an H-atom after the absorption of a photon equals 1/2 of the de-broglie wavelength when it is in orbit. The energy of the ...
0
votes
2answers
50 views

Is the video “How to Reveal Subatomic Particles at Home”'s explanation of its experiment misleading?

https://www.youtube.com/watch?v=wN_DMMQEhfQ The video asserts that along the path of an electron or muon, a trail of condensation will appear. But from what I understand, if an electron or muon (both ...
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0answers
53 views

Undergraduate Physics Senior Research Topic (Theory/Mathematical Physics Based) [on hold]

This is most likely a question for those who have experience/knowledge of theoretical/mathematical physics at the graduate level and can provide recommendations following my criteria. Here is some ...
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0answers
24 views

ferromagnetic and Curie temperature. Energy question

Is energy absorb and release back when a ferromagnetic material heats and cools passing through the Curie temperature?
1
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1answer
102 views

How can space and time occur spontaneously? [on hold]

In the book: "A universe from nothing" by the theoretical physicist Lawrence Krauss he mentions that space and time can occur spontaneously. Unfortunately he does not explain how. So my question is, ...
0
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0answers
52 views

On the Pauli Principle

Consider a quantum mechanical system as shown-say a piece of metallic conductor in the shape of a long, thin bar.(Must it be a single crystal to be considered a "system"?). Now focus on two free ...
1
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0answers
28 views

Does a set of eigenvalues in QM correspond to a random variable in statistics? [duplicate]

In quantum mechanics the possible outcomes of a measurement of a quantity corresponding to a linear hermitian operator $A$ are only the eigenvalues $a_i$ of $A$ (see e.g. ...
3
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0answers
39 views

Decoherence and interpretations

With quantum decoherence, are there still any "gaps" in our knowledge of quantum mechanics that hint (either in terms of the physics, philosophy, or otherwise) at the need for further interpretation? ...
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1answer
37 views

Orbital angular momentum eigenstates in the $|\mathbf{r}\rangle$ representation

Consider the orbital angular momentum operators $L^2$ and $L_z$. In the $|\mathbf{r}\rangle$ representation using spherical coordinates those operators actions are given by ...
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0answers
18 views

P-N Junction - (Depletion Region) [duplicate]

Will i have simple q ,,, Why the electron in N Type don't go to the Formed Positive Ions ?
1
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0answers
40 views

Entanglement in laser beams [on hold]

Recent experiments in entanglement of two laser beams using OPOs indicates higher level of entanglement. But laser beams are nothing more than group of photons. How are the photons inside the two ...
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0answers
23 views

Measurement without collapse

Does anybody have a reference for Cini's model of Quantum Measurement theory. I have a background of Quantum Mechanics (Ballentine level). Also I don't have access to Cini's paper.
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0answers
20 views

To which extent is the treatment of nuclear multipole radiation by the means of a classical electromagnetic field valid?

In the treatment of nuclear multipole radiation, for example in the context of nuclear gamma decay, it is standard, at least at the elementary level, to formalize the electromagnetic radiation as a ...
1
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1answer
31 views

Is the relation c=νλ valid only for Electromagnetic waves?

What is the validity of the relation $c = \nu\lambda$? More specifically, is this equation valid only for Electromagnetic waves? I read this statement in a book, which says: de Broglie waves are ...
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0answers
17 views

Simple Harmonic Osillator [on hold]

For simple harmonic oscillator, calculate a. The energy b. The mean position c. The mean momentum square d. Standard deviation of position e. Standard deviation of momentum f. Cheek uncertainty ...
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0answers
18 views

flux quantization in quantum hall effect

Why is it that in the quantum Hall effect (integer or fractional) the number of flux quanta penetrating the surface is integer? I can see how the flux quantum arises if you calculate the degeneracy of ...