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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Uncertainty principle within a neutron star or black hole

Take the time-energy uncertainty relation, $\Delta$$E$$\Delta$$T$$\ge$$\hbar/2$. My question is based on my confusion about the effect this relation may have within the interior of a highly ...
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102 views

Phase added on reflection at a beam splitter?

If we have light of a particular phase that is indecent on a beam splitter, I assume the transmitted beam undergo's no phase change. But I thought that the reflected beam would undergo a phase change ...
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152 views

Why reduced density operator being same is necessary sufficient for no signalling?

Problem Statement : Two parties $A$ ( Alice ) and $B$ ( Bob ) ( in order ) share an entangled pair $\frac{1}{\sqrt{3}}(|00\rangle+|01\rangle +|11\rangle)$. Bob does a measurement in basis $\{ |0\...
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2answers
76 views

Potential step and exponential decay?

Let us say we have a wave going from a region ($x<0$) where the potential is $U_1$ to a region ($x>0$) where the potential is $U_2$. The wave function in the second region takes the form: $$\...
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40 views

Stern-Gerlach experiment need for collimated beam?

In the Stern-Gerlach why do we need a collimated beam? I read somewhere that it was to do with controlling the speed of the particle but I cannot see how collimation whould do this? [Picture ...
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6answers
548 views

Estimating our de Broglie wavelength

This could be a very naive question, but I feel always disturbed by it since I couldn't ever figure out a perfect answer. Why is our de Broglie wavelength (dBw) so tiny and how could we roughly ...
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1answer
148 views

Angular momentum - proof for integer eigenvalues

I am confused about a proof my Quantum Mechanics textbook has left "as an exercise for the reader". So, we've got the angular momentum operator $\hat{L}$. We've also got the generalized angular ...
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326 views

Relation between Wilson approach to renormalization group and 'standard' RG

While studying renormalization and the renonormalization group i felt that there wasn't any completely satisfying physical explanation that would justify those methods and the perfect results they get....
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26 views

Does flux quantization require uniform pair density?

Consider a superconducting circuit with a "box-like 8" geometry like [|] (ie. two square loops which share one side of wire). Here we can have three different currents ($I_1=I_2+I_3$, see H. J. Fink ...
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1answer
93 views

How to see validity of no signalling principles in case of entangled parties?

From what I understood the density operator $\rho$ is a mathematical tool which tells us about the probabilities of getting a particular output after measurement. I have two parties entangled with ...
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1answer
249 views

Complex scaling method for solving resonance states

I am now reading about the complex scaling method for solving resonance states. As far as I understand, the procedure goes like this: Let us take the 1d potential $V(x) = A e^{-x^2} x^2 $ as an ...
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59 views

Quantum Entanglement Particle Properties

I have background in static/dynamic/thermodynamic physic. I am reading on quantum physics and quantum entanglement. Me and some of my colleagues were wondering on the properties that are shared ...
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1answer
52 views

Clarification on inertial mass

I was talking to my friend the other day about the origin of inertia and it pondered both of our brains. I would like to know if the concept of inertia exists at the quantum level? I realize that ...
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3answers
727 views

Is it possible to write the fermionic quantum harmonic oscillator using $P$ and $X$?

The Hamiltonian of the quantum harmonic oscillator is $$\mathcal{H}=\frac{P^2}{2m}+\frac{1}{2}m\omega^2X^2$$ and we can define creation and annihilation operators $$b=\sqrt{\frac{m\omega}{2\hbar}}(X+\...
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1answer
61 views

How far can you propagate something, anything, before it becomes 'background noise'?

An electric field, light, a movement of molecules; anything at all. What is the maximum distance they can go before they are 'noise' to an ideal measurement instrument? So if the distance is infinite,...
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1answer
261 views

Find Eigenstates of a Hamiltonian that lets two spin 1/2 interact but also acts on one of them

I have the following Hamiltonian describing two spin 1/2 systems, represented by the pauli matrices $\sigma_1$ and $\sigma_2$: $H = D \sigma_{1z} + J (\sigma_1 \cdot \sigma_2) $. The two spins are ...
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28 views

How should I interpret degenerate $\pm m_j$ states under the Stark effect?

I'm thinking about the Stark effect in Alkalis where fine structure is important (Cs, Rb, etc). The Stark effect doesn't lift the degeneracy of the $\pm m_j$ states. So should I interpret a state ...
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2answers
55 views

How can a correlation be teleported?

I am aware of how a qubit can be teleported from party $A$ to party $B$ if both the parties are entangled. Is there a similar way to teleport a correlation? I googled and found Entanglement ...
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1answer
100 views

Measuring electron spin with multiple Stern–Gerlach apparatus at an angle

To separate the two spins of electron of a particular direction, we use Stern-Gerlach apparatuses to apply a non-uniform Magnetic field. Suppose we have two identical electrons and we know their spin ...
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1k views

What is the difference between general measurement and projective measurement?

Nielsen and Chuang mention in Quantum Computation and Information that there are two kinds of measurement : general and projective ( and also POVM but that's not what I'm worried about ). General ...
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32 views

Creation and annihilation form of hamiltonian to derive a relation between the ac current applied to the crystal and the oscillations of the crystal

in the book "many-particle physics" by G.Mahan in piezoelectric subsection, it uses the second quantization formalism to derive the relation for hamiltonian of the electron-phonon interaction. so ...
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2answers
291 views

Spin, orbital angular momentum and total angular momentum

If I understand correctly, spin is an intrinsic property of particles, which follows the algebra of angular momentum, but has nothing to do with an "orbital angular momentum" in that the particle is ...
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1answer
90 views

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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1answer
70 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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86 views

Relativistic Fermi Golden Rule?

On online slide notes, it is mentioned that: 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 - ...
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256 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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1answer
54 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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2answers
156 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} = \sum_{...
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2answers
241 views

If proton spin emergence from quarks and gluons is mysterious, why is silver atom spin not?

A recent Scientific American article brought up an old issue, which is this: According to quantum chromodynamic models, the emergence of exactly 1/2 unit of spin in a proton (or a neutron, or any ...
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1answer
81 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 \...
2
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1answer
118 views

Evolution operator in driven harmonic oscillator

I have a question about a problem I was set recently. 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^...
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1answer
837 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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2answers
185 views

Is entanglement a classical phenomenon (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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3answers
1k views

Using the uncertainty principle to estimate the ground state energy of hydrogen

I have been reading through this estimate of the ground state energy of hydrogen and others like it. In this one it says it is using the uncertainty principal but then proceeded to use the following: ...
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1answer
85 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 ...
2
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1answer
99 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
246 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 ...
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6answers
551 views

Can quantum entanglement be simulated on a digital computer to any degree of precision?

First principles modelling of physical phenomena has been very successful in physics. The largest limitation is perhaps the fact that many QM problems are NP hard so we would need really powerful ...
4
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1answer
201 views

How to obtain a vector relation for the Rabi frequency?

In this paper by Golovach et al.: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.74.165319 there is the following equation for spin evolution: $$\langle \dot{\bf{S}} \rangle=({\boldsymbol \...
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1answer
154 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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0answers
64 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
56 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 ...
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4answers
356 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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3answers
141 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 \quad\text{and}\...
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2answers
103 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
126 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 ...
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0answers
21 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 $B$: $(D_B^+...
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1answer
126 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?
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456 views

How to guarantee square integrable solutions to time-independent Schrödinger's equation?

Given the time-independent Schrödinger’s equation in one dimension $$H\psi = E\psi$$ what restrictions can we place on V(x) (inside the hamiltonian) and E to guarantee that the solutions won't have ...
4
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1answer
97 views

How can a Step potential exist if potentials are continuous? Quantum Mechanics

I was doing an example which showed step potentials, I then researched it a little and found this on wiki http://en.wikipedia.org/wiki/Solution_of_Schr%C3%B6dinger_equation_for_a_step_potential I don'...