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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The double slit experiment - methods used to observe single photons prior to striking the target

I can accept that when single photons are used in the double slit experiment that a diffraction pattern results at the target due to their wave property. What I am puzzled about is exactly what ...
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5answers
23k views

Is the universe fundamentally deterministic?

I'm not sure if this is the right place to ask this question. I realise that this maybe a borderline philosophical question at this point in time, therefore feel free to close this question if you ...
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2answers
91 views

Can the vacuum energy be made finite with quantized space

From what I know the reason we have infinite vacuum energy is because according to Quantum Field Theory at every point in space we have something analogous to a harmonic oscillator but since the Zero ...
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2answers
36 views

Is the photon truly not absorbed in Raman scattering?

In reading about Raman Scattering, I was thinking while reading it "okay, incident photo absorbed by molecule, molecule goes to higher energy vibrational state, molecule re-emits photon with either ...
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2answers
494 views

What's an atomic superstate/superposition, and how is it possible?

What's an atomic superstate/superposition, and how is it possible? I understand the basics - being something can be moving and staying still at the same time; the observer changes the behaviour - but ...
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1answer
244 views

Wigner Threshold law in Photodetachment and Photoionization

I am writing this question here because I have a problem in understanding the Wigner Threshold law in Photodetachment and Photoionization. The Wigner Threshold Law is given by: $\sigma$=$E^{L+1/2}$. ...
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1answer
90 views

Evolution of Eigenstates when two spin systems are coupled

I would like to describe the following situation: We have two spin systems: Spin 1 ($S_1$) and Spin 1/2 ($S_2$). Now imagine you somehow change their interaction so that you can fine-tune the ...
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0answers
21 views

Adiabatic Theorem in Terms of Eigenvector Derivatives

The necessary conditions for quantum Adiabatic Theorem validity is usually stated in terms of eigenvalue gaps for parameterized Hermitian matrices, or Hamiltonians. If $H(t)$ is a parameterized ...
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0answers
21 views

Is macroscopic causality an issue in the context of certain quantum experiments?

In order to formulate my question properly I need to explain a few things. Cramer_Herbert Zych_Brukner Reference 1. - John Cramer, Nick Herbert, "An Inquiry into the Possibility of Nonlocal Quantum ...
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0answers
38 views

Relativistic Fermi Golden Rule?

In his slide notes, Georgi mentions: Fermi Golden Rule: $$P_{if}=\frac{2\pi}{\hbar}|M_{if}|^2\rho_f$$ where $\rho_f$ is density of final sates --number of quantum states per unit volume - states in a ...
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0answers
12 views

what is the difference between mictomagnetism and spin glass?

What is the difference between mictomagnetism and spin glasses? I mean what are the distinguishing characteristics of them which makes them separate?
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1answer
148 views

Difference: Fermi wave length vs. phase-breaking length?

I am reading a quantum transport book, where they often mention: phase breaking length and Fermi wavelength. I have looked up and found that: Phase breaking length= length over which electron remains ...
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1answer
46 views

Partial Measurement and the Math Behind it

$\newcommand{\ket}[1]{\left| #1 \right>}$ $\newcommand{bra}[1]{\left< #1 \right|}$ Talking about the partial measurement the professor defines the state $\ket \psi$ to be $$\ket{\psi} = ...
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1answer
98 views

What are phase conventions in angular momentum and rotation calculations?

I work with complicated angular momentum calculations related to atomic physics; nevertheless, I never need to use anything related to a phase convention (apparently because it's taken care of in a ...
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1answer
34 views

How to reconcile active and passive observation in quantum physics?

The two-slit experiment is a classic example of how measurements can affect the behavior of particles. This seems reasonable because, to my knowledge, the measurement is "active" in that it adds ...
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1answer
52 views

When can I swap around the order of operators?

I was doing this question: Using $\left< x \middle| p\right> = \frac{1}{\sqrt{2 \pi \hbar}}e^{ipx/\hbar}$ show that: $$ \left<x \middle| \hat{p} \middle| \psi \right> = -i\hbar ...
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1answer
35 views

Evolution operator in driven harmonic oscillator

The exercise reads: The Hamiltonian of an harmonic oscillator driven by a classical force is $H=H_0+H_1$ with $$H_0=\hbar \omega \left( a^\dagger a+\frac{1}{2} \right) \text{ and } H_1=-i\left( ...
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1answer
407 views

“Hard wall”/ “soft wall”

I have encountered those terms in various places. As I understand it, "soft wall" can correspond to a smooth cutoff of some spacetime, while "hard wall" can be a sharp one, which can be described in ...
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1answer
58 views

Spin commutation relations

For orbital angular momentum defined as $L= r \times p $ we can prove, in quantum mechanics, the commutation relations. Also, we could prove these relationships through the study of rotations ...
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1answer
67 views

Is entanglement a classical phenomena (last attempt)?

This is a reformulation of two previous questions that seem to have been misunderstood, or most likely, I failed to make them clear. I thank all people that answered, even the belligerent ones. Some ...
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1answer
29 views

Correlation between entangled photon polarisation measurement?

From Malus's law we know that if we measure a the polarisation of light with a filter angle $\theta$ to the direction of polarisation then the intensity goes like: $$I=I_0 \cos^2(\theta/2)$$ Firstly ...
30
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5answers
4k views

Why do all the atoms of a radioactive substance not decay at the same time?

Why does the substance decay at a rate which is proportional to the amount of the substance at that moment? As all atoms are in hurry to become a stable atom and as their decay do not depend on any ...
3
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1answer
96 views

Uncertainty relation for non-simultaneous observation

Heisenberg's uncertainty relation in the Robertson-Schroedinger formulation is written as, $$\sigma_A^2 \sigma_B^2 \geq |\frac{1}{2} \langle\{\hat A, \hat B\}\rangle -\langle \hat A\rangle\langle ...
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1answer
74 views

Is entanglement a classical phenomena (2)? [closed]

The answer to this question seems to be yes, because you can simulate it with a classical computer and thus by a local classical theory (rule 110 CA) (see this question). However most people ...
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0answers
39 views

Fourier transform of Coulomb potential in 1D

The Fourier transform of the Coulomb potential $V(r)=\frac{k}{r}$ is typically evaluated by computing the Fourier transform of the Yukawa potential given by $V_{Yukawa}=\frac{ke^{-\epsilon r}}{r}$ and ...
3
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2answers
967 views

Can cellular automata be reconcilied with quantum mechanics?

CAs are deterministic representations of the universe, which, according to the Bell's inequality are not entirely accurate. Cells interact "locally" (only with the closest neighbours), while quantum ...
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1answer
36 views

Finding the average energy from the superposition of state?

If I have two energy eigenstates $\psi_1(x)$ and $\psi_2(x)$ (corresponding to energy $E_1$ and $E_2$ respectively) and we prepare a particle in the superposition of both such that it is described by ...
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1answer
75 views

Doesn't the concept of “hidden variables”, by definition, encompass all possible results? [closed]

While i don't know all the mathematical/experimental specifics i know enough about entanglement/bell's theorem to know the general ideas of what's going on. It's definitely interesting but i'm not ...
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0answers
21 views

Metastable $E=0$ s-wave bound state in a spherical potential well

I am currently dealing with scattering theory. I looked up the scattering on a spherical well potential. $$V(r) = \begin{cases} -V_0 & , r \leq R\\ 0 & ,r > R \end{cases} $$ where ...
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1answer
79 views

Perturbations in arbitrary dimensions

In general is it acceptable to say that if a perturbation is in only one spatial direction then the energy eigenvalue to second order is only changed in that spatial direction? For example 3D ...
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1answer
49 views

Details of the radial Fourier transform pertaining to certain quantum integrals

Consider the integral $$U(t)=\int\frac{d^3p}{(2\pi)^3}e^{-ip^2t/2m}e^{i\vec p\cdot\Delta\vec x}$$ for the free non-relativistic propagator. I'm not quite sure about the gritty details of radial ...
4
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4answers
118 views

Classical and quantum systems [closed]

What are the main differences between a quantum and classical system? How does one can distinguish them?
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0answers
28 views

commutation relation of angular momentum operator in non cartesian coordinates

The angular momentum operator $J$ in quantum mechanics with the commutation relation \begin{equation*} [J_i,J_j]=i\hbar\epsilon_{ijk}J_k \end{equation*} has the structure of a Lie-algebra. It is ...
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3answers
99 views

If two kets are each orthogonal to a third ket, are they also orthogonal to each other?

Is there a proof for this either way? For the normalized kets $\left|a \right\rangle, \left|b\right \rangle, \left|c\right \rangle $ If $$ \left\langle a\middle| b \right\rangle = 0 ...
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17answers
4k views

Quantum mechanics and everyday nature

Is there a phenomenon visible to the naked eye that requires quantum mechanics to be satisfactorily explained? I am looking for a sort of quantic Newtonian apple.
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1answer
41 views

are there known fundamental limits of quantum computer scaling?

Quantum computers provide exponential speedup relative to classical computers. However, it is empirical fact that increasing of number of qubits makes the the computer harder and harder to keep ...
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2answers
69 views

do the planes of electron orbits make an angle?

if we think as the electrons around the atoms classically, then as the two electrons in the first shell (1s) go around the nucleus; do the planes of orbit make an angle with each other (as an average) ...
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1answer
60 views

Why is the ground state energy of a 2DEG higher compared to the 3DEG?

I am reading something about a 2DEG (2-dimensional electrongas model) and can not understand it. My book says the ground state of the 2DEG is higher compared to a 3DEG because the confinement to 2D ...
1
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1answer
75 views

Proof for Negele and Orland equation (2.34)

The equation (2.34) of Negele and Orland has $$\mathcal H_\text{A}(\hat{\mathbf p},\hat{\mathbf x}) = \frac{1}{2m}\left(\hat {\mathbf p} - \frac e c \mathbf A(\hat{\mathbf x})\right)^2.\tag{2.34a}$$ ...
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1answer
147 views

How does an operator transform under time reversal?

We know that a time-reversal operator $T$ can be represented as $$T=UK$$ where $U$ is some unitary operator and $K$ is the complex conjugation operator. Then under time-reversal operation, a quantum ...
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2answers
333 views

Faster than light signals and the price to be paid if we accept them : a very simple protocol

Most physicists currently understand entanglement as transferring information instantaneously, yet not violating causality. Is this really a satisfactory explanation, or should be look for something ...
2
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5answers
385 views

Local EPR-experiments with photons in vacuum?

The principle of non-locality states "that an object is influenced directly only by its immediate surroundings." (Wikipedia) When two entangled particles are measured in an EPR experiment, we ...
9
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5answers
4k views

Chemical potential

This is something probably very basic but I was led back to this issue while listening to a recent seminar by Allan Adams on holographic superconductors. He seemed very worried to have a theory at ...
3
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1answer
63 views

Angular momentum conservation at quantum level

how angular momentum of system is conserved when electron jumps higher energy state to lower energy state and photon is emitted(circularly polarized)? i read somewhere that it is NOT conserved .Why?
2
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0answers
19 views

Does the trial index of typical CHSH experiments constitute a “hidden variable”?

In typical experiments related to the CHSH inequality there are individual detections being made by two separate (analyzer-and-)detector systems, "System $A$: $(D_A^+, D_A^-)$" and "System $B$: ...
5
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0answers
116 views

Is there a specific name for the highest energy state in quantum mechanics?

In quantum mechanics, the lowest energy state is called the ground state. I am wondering if there is a name for the highest energy state? Should I call it the top state, or the ceiling state, or the ...
2
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1answer
82 views

What does it mean “Hawking radiation is in a pure state”?

I'm trying to understand black hole paradox but I'm not sure if I understand what does it mean "Hawking radiation is in a pure state". Does it mean if Hawking radiation is in a mixed state then ...
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2answers
616 views

Double slit experiment alternating holes

If we perform the double slit experiment by shoting photons covering one hole at a time, would we see equally the double slit interference?. That is, the same set up of double slit but fire photons ...
4
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3answers
199 views

Is Interpretation of state vectors and density matrices according to Frequentist or Bayesian interpretation of probability?

I asked a question on math stack exchange what does probability mean. I did not know about Frequentist and Bayesian interpretation of probability previously. So according to which interpretation are ...
3
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1answer
166 views

Has this experiment really demonstrated wave-function collapse?

My question is: why did the following experiment claim that it had demonstrated the wave-function collapse? http://www.nature.com/ncomms/2015/150324/ncomms7665/full/ncomms7665.html I would have no ...