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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5
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5answers
135 views

What is the explanation for the interference patterns in MWI?

In Young's double-slit experiment, MWI states that in some "worlds" the particle goes through one slit, and in others it goes through the other. If this is so, why do we get an interference pattern? ...
2
votes
0answers
35 views

Is electron phonon interaction important away from fermi surface?

In weak coupling superconductor, the effective electron phonon interaction can be written as $$ H_{eff}=\frac{1}{2}\sum_{q,k_1,k_2,\sigma_1,\sigma_2} V_{k_1,q}C^{\dagger}_{k_1+q,\sigma_1} ...
0
votes
1answer
30 views

Why is the interaction energy of the electrons in an atom positive?

Consider a simple Hamiltonian for the Helium atom (where $e'^2 = e^2/4\pi \epsilon_0)$: ...
47
votes
6answers
5k views

Why does a system try to minimize its total energy?

Why does a system like to minimize its total energy? For example, the total energy of a $H_2$ molecule is smaller than the that of two two isolated hydrogen atoms and that is why two $H$ atoms tries ...
0
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0answers
64 views

Feynman lecture - bell's theorem, entanglement

My question regards this video: https://www.youtube.com/watch?v=AyejXtZrGb0 Feynman is illustrating entanglement, bell's theorem etc... using correlated boxes. I take the entangled boxes as ...
0
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1answer
44 views

What causes the universe to manifest a given value upon measurement in super-deterministic theory? [closed]

Bell's inequalities show that we have to give up freedom or local realism. If we give up freedom, we have super-determinism, if we give up local realism, we have free-will. In super-deterministic ...
3
votes
0answers
68 views

A question on the Chern number and the winding number?

Let $\mid \psi(x,y) \rangle$ be a normalized wavefunction living in a $d$-dimensional Hilbert space and depend on two real parameters $(x,y)$ that belong to a closed surface (e.g., $S^2, T^2$, ...). ...
0
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0answers
51 views

Can nonrelativistic QM, as used in bound states, be derived from QFT? [duplicate]

Nonrelativistic QM can be applied to bound states like a hydrogen atom. QFT is used for free particles (whatever one means by particles) that shortly interact with each other and are free again after ...
-6
votes
1answer
86 views

If E= hv then E= mc2 then h=mc2/v! [closed]

E= pc (1) = hv (2), p= mc (3) From (1) and (2): c= hv/p (4) We put (4) in (3): p=hv/p.m => p2=hvm (5) If we use E=hv in (5) we will get: E= p2/m (6) We use (3) in (6) we will get: E= mc2 From ...
0
votes
1answer
48 views

Finding similar quantum superposition pairs [closed]

I am not sure if my thinking is correct and I'd like to ask if someone can confirm it, or give explanation, what am I doing wrong. I did task where I was asked to tell if pairs of expressions for ...
0
votes
1answer
49 views

Multiplication of associated probabilities

If a state $\psi $ is in the $ S_{z} $ basis represented by $\mid\psi\rangle = c_{+}\mid z\rangle + c_{-} \mid -z\rangle$ Does the associated probabilities change when I multiply $ \psi $ by $ ...
-4
votes
1answer
60 views

Concerning The Oil Drop Experiment: How does ionizing radiation create the electron(s) that the droplets of oil collect?

Concerning the Oil Drop Experiment: I read, “Ionizing radiation is used to create the electron that the droplets of oil collect. When the air in the apparatus is bombarded by this ionizing radiation ...
-1
votes
1answer
46 views

Implications of weak measurement on entanglement

What are the implications of weak-measurement on entangled particles, and how does that resolve the problem of non-superluminal quantum "communication"? If I understand correctly, entangled particles ...
5
votes
2answers
116 views

Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
1
vote
0answers
32 views

Schrödinger's cat experiment in the context of decoherence

I am trying to visualize in more detail the Schrödinger's cat experiment in the context of decoherence. Please let me know if the description below makes sense or is somehow flawed. If the ...
0
votes
0answers
26 views

Probability density for spinors

I am approaching Relativistic Quantum Mechanics seriously for the first time, going through Bjorken & Drell and doing all the excercises, but I am facing some problems with 3.1. Derive (3.11) ...
2
votes
2answers
142 views

Is my understanding of the delayed choice quantum eraser correct?

I'll say in advance that I am by no means an expert on Quantum Mechanics. I understand the basic mathematics of it (Wave function and Schrodinger equation), but did not go deeply into it or study it ...
0
votes
0answers
64 views

Usage of Complex Numbers in Quantum Mechanics [duplicate]

In Griffiths 2nd Edition Quantum Mechanics page 148, it says when describing the eigenfunction to a part of the central potential problem as $$\mathrm e^{i m \phi}$$ "In electrodynamics we would ...
1
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0answers
53 views

Proof for fluctuations in vacuum

I'm not a physicist. My understanding of Heisenberg's uncertainty principle and its proof (that is given by an imaginary microscope) is that for example: at a specified time determining the exact ...
2
votes
0answers
61 views

Gauge transformations for Schrödinger equation [closed]

I want to prove the Schrödinger equation is invariant under the gauge transformations \begin{align*} \mathbf{A} & \rightarrow \mathbf{A}' + \mathbf{\nabla} \chi \\ \phi & \rightarrow \phi' - ...
-2
votes
1answer
45 views

Do we have rest mass according to quantum physics? [closed]

I know wave must be in motion and resonant waves are actually in motion. So I don't understand what is a rest mass of a particle. If a particle is just a wave in a particular field, it should be ...
-3
votes
1answer
75 views

Are one photon at-a-time experiments regarded as the Quantum versions of Classical experiments? [closed]

Is it a correct distinction to regard classical experiments conducted one photon at-a-time as the quantum version of the experiments? For instance, if we take Young's original double-slit, and convert ...
0
votes
1answer
72 views

Why does the equality $\int \mathbf{r}\times \nabla f d\nu=0$ holds? [closed]

My question comes from Problem 4. Classical laws for angular motion of Practical Quantum Mechanics. And the Prob.4 is that, To show that the classical relation between angular momentum ...
0
votes
1answer
42 views

Does Heisenberg's uncertainty hold for any two quantum measurements?

Heisenberg's uncertainty principle is most commonly expressed in terms of the uncertainty in measurement of position and momentum of a particle, $$\Delta x\Delta p \geq \hbar$$and uncertainty in ...
12
votes
2answers
1k views

Unfamiliar Notation in Sakurai

In chapter 5 section 9 of Sakurai, 2nd edition, he uses some notation that I am unfamiliar with. This may be suited for Math.se but I figured it could be peculiar physicist notation. Anyways it is ...
3
votes
0answers
61 views

how are the infinitesimal generators of translation related to the lagrangian?

In studying analytical mechanics (or it's quantum analog), one will come across statements such as: $$f(x^{i}+\delta x^{i})=f(x^{i})+\delta f(x^{i})=f(x^{i})+\frac{\partial f(x^{i})}{\delta ...
-1
votes
1answer
32 views

Given that we know the exact position of an electron orbiting a proton what is the PDF of its energy?

Given a known amount of energy we can plot a PDF of where an electron orbiting a proton should be. Can we reverse this? If we know the exact position of an electron orbiting a proton what is the PDF ...
0
votes
0answers
14 views

Why probability of detection of optimum unambiguous discrimination between linearly independent symmetric states is less than random guess? [duplicate]

Considering the analysis and result of this paper, http://arxiv.org/pdf/quant-ph/9807023v1.pdf, I have used equation (3.15) and (4.3) to calculate the optimum probability of success for mean photon ...
0
votes
1answer
29 views

Conformational Analysis of Ethane and Butane

How does a condensed matter theorist explain conformations of Ethane and Butane using tools from Quantum field theory? If they don't how do they calculate energy differences and predict differences ...
0
votes
1answer
53 views

Does the Observer Effect define quantum behavior regardless of conscious observation?

I read the Wikipedia article about the Observer effect and I was a bit confused by the wording of the introductory section. Does the method of observation collapse the wave function (or define the ...
3
votes
0answers
33 views

In path integral of multiply connected manifold, how to prove the partial amplitudes are linear independent? [closed]

In path integral of multiply connected manifold $X$, $$K(b,t_b;a,t_a)=\sum_{\alpha\in \pi_{1}}\chi(\alpha)K^{\alpha}(b,t_b;a,t_a)$$ where $K^\alpha$ is called partial amplitude, $\alpha$ denotes the ...
0
votes
0answers
13 views

Simple deduction of differential cross section from total cross section

In Povh's book "Particles and Nuclei" we read the following: I simply cannot wrap my head around what happened from eq. 5.20 to 5.22. How did he deduce that the cross section for the scattering into ...
0
votes
0answers
18 views

Precession or projection?

A spin of 1/2 in a magnetic field is known to rotate around the direction of the field. But then it is also stated that it must be projected spin up or down. Is this simultaneous or happens after ...
0
votes
0answers
22 views

Interesting question regarding stimulated emission

why is outgoing photon emitted during stimulated emission in phase with the incoming photon? I can't see why this is so because the two photons may be out of phase yet conserving momentum and energy. ...
1
vote
0answers
52 views

Uncertainty Principle with the corresponding operators

Why does the corresponding operator do not commute if there is uncertainty related to two observables A and B that states $\Delta A\,\Delta B > 0 $ ?
0
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1answer
31 views

Difficulty in understanding amplitude probability calculation

I am trying to understand methodology of amplitude probability. I know, that when I have amplitude $ langle x \vert y \rangle$ the amplitude is: \begin{equation} \lvert \langle x \vert y \rangle ...
0
votes
1answer
32 views

Find unitary for given rotations on Bloch sphere

I want to characterize a unitary by given rotations on the Bloch sphere. I know, that when I send in the State $|\Psi\rangle =\begin{pmatrix}1\\0 \end{pmatrix}$, I get the state ...
1
vote
1answer
57 views

Measurements in quantum mechanics

Why does measurement change things? I read that measurement changes things because we have to bounce photons off an object to 'see' it and that changes its position, momentum etc... But on the other ...
3
votes
1answer
51 views

WKB Approximation on an linear + harmonic potential

I have a quick question: I have performed the WKB approximation to find the energies of bound states in symmetric potentials (Square, harmonic, ...). To do this I just find the "turning points" by ...
1
vote
2answers
59 views

Interference experiment and entanglement with apparatus

Consider a single photon in a Mach-Zehnder interferometer. Considering the photon only, the output state is the sum over both paths $$\vert 1 \rangle + \vert 2 \rangle=\vert \psi \rangle + ...
0
votes
0answers
55 views

Finding $\psi(0)$ using Schrodinger equation with potential $U(x) = q\delta(x)$

I am having some trouble answering the following question in my "Advanced Quantum Mechanics" course: Using the integral equation: $$\psi(x) = Ae^{ikx} + Be^{-ikx} - ...
5
votes
1answer
131 views

Obtaining the temperature from Bose-Einstein and Fermi-Dirac distribution

Lets say you are given a distribution function $f(p)$ and you want to define a temperature, $T_f$, for this distribution. (I assume $\mu = 0$.) It is then natural to define a temperature the ...
-1
votes
0answers
46 views

Concerning The Oil Drop Experiment and Photon Absorption

Concerning The Oil Drop Experiment and Photon Absorption What would happen if you emit photons into the droplets, the molecule(s)? Is it possible for the photons to be absorbed by the droplet? I ...
0
votes
0answers
44 views

Gaining intuition over Hamiltonian for qubit systems

A typical Hamiltonian for a two state system with some driving field can be written as $$H=J(t)\sigma_z+h\sigma_x$$ This represents a qubit system driven along a single axis. On the other hand we ...
-3
votes
0answers
77 views

Does electron spin? [duplicate]

Spin quantum number I was reading above article on spin quantum number. It says Uhlenbeck, Goudsmit, and Kronig introduced the idea of the self-rotation of the electron, which would naturally ...
0
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0answers
34 views

Heisenberg equation of motion for angular momentum operator

I am working on problem 5, from chapter 3 of Sakurai's Modern Quantum Mechanics. The problem has the following Hamiltonian: $$ H = \frac{1}{2}\left ...
0
votes
1answer
52 views

What is the accuracy when firing an electron at a target?

Consider firing an electron at a target. Let the target be at a distance $d$ and the electron be travelling at a non-relativistic speed $v$. How can we estimate the maximum possible accuracy ...
0
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0answers
28 views

The electronic wave function

Is it correct to say that the wave description of the probability of finding the electron some where in space as specified by the wave function is concluded or supposed because, in the double slit ...
0
votes
1answer
42 views

Alternatives to scattering experiments

Scattering experiments have been a fruitful and efficient way to determine the particles that exist in nature and how they interact. What are some of the other experimental techniques used to ...
0
votes
1answer
57 views

What is the upper limit of objects behaving as a wave-particle?

Photons, electrons are quantum particles to which the wave-particle duality apply. protons are heavier quantum objects and posses quantum tunneling which is a wave character. What is the upper limit ...