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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105 views

Quantum mechanic particle

In non relativistic quantum mechanic, we are dealing with a problem involving a particle in one dimensional space, and it has been given the potential and it reads: ...
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1answer
50 views

Compton Scattering Feynman diagram integral expression

I'm trying to write down the integral expression according to the feynman-rules for this Diagram of an electron with compton scattering and a one-loop correction: ![Compton Scattering][1] ...
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0answers
10 views

Application or Applicability Spin Seebeck Effect

I am looking for any application or study of applicability of the Spin Seebeck Effect. I have not found anything good anywhere so far but maybe someone here knows something? Would appriciate any ...
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9answers
21k views

Why don't electrons crash into the nuclei they “orbit”?

I'm having trouble understanding the simple "planetary" model of the atom that I'm being taught in my basic chemistry course. In particular, I can't see how a negatively charged electron can stay ...
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1answer
106 views

Are Feynman's Six Easy Lectures still relevant today?

I haven't learned anything about modern physics at the university yet, but next year I will, and in the summer before I thought I would read this book, Six easy lectures from Richard Feynman. It was ...
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1answer
100 views

Forward-scattering off a potential well

In his book, James Binney writes the following: My question is what is the meaning of this expansion as $1+T$? I say this because you don't tend to consider the possible "paths" that a particle ...
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1answer
38 views

Particle position and speed [duplicate]

If I understand correctly, particle is something at a point of time, where you can tell it's position, but what if particle is moving, then you can tell it's speed. From what I understand wave is NOT ...
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2answers
90 views

Quantum entanglement and the big bang

Prior to the Big Bang all matter was compressed into a point of high density. Why isn't all matter already entangled?
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2answers
104 views

Two particle operator

Why is the two-particle (fermionic, cause for bosonic operators it is immediately clear that both representations are the same) Hamiltonian given by $$ H = \sum_{a,b,c,d} \langle ab|V|cd \rangle ...
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0answers
4 views

Verdet Constant and optical pumping

While studying Faraday rotation (linear magneto-optic rotation) I came across a fact that faraday rotation can be enhanced. Verdet constant which depends on the wavelength can be enhanced as change in ...
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5answers
412 views

Fermion vs. Bosons and particle vs. wave: is there a link?

I'm puzzled since several years on this basic aspect of quantum mechanics. Quantum theory is supposed to describe particle-wave symmetry of our world. It also describes our universe in term of bosons ...
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0answers
29 views

Delayed choice entanglement swapping: why are Alice & Bob's measurements useless without Victor's?

Here is the article by Ma et al.:http://arxiv.org/abs/1203.4834 I have read many explanations on this site and others that emphasize that Victor's data is needed to make Alice and Bob's usable... ...
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0answers
74 views

Creating an arbitrary state of the quantum simple harmonic oscillator

Suppose $\mathcal{B}=\{|0\rangle, |1\rangle, |2\rangle, ... \}$ is the energy eigen-basis of a quantum simple harmonic oscillator. I want to create the state \begin{equation} |\Psi\rangle = ...
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1answer
70 views

Constructing differential equation from arbitrary Hamiltonian

Suppose I begin with the time-independent Schrodinger equation $$ \left(-\frac{1}{2m}\partial_x^2 + V(x)\right)\psi_n(x) = E_n\psi_n(x), $$ ordinarily we specify the function $V$ and then solve for a ...
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2answers
113 views

Spin zero photons

As I understand it, the reason why there is no Spin 0 Photon is because the polarisation of an EM field lives in two dimension. Hence we only have two basis vectors, yielding two pairs of ladder ...
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1answer
50 views

Mach-Zehnder interferometry wave functions

Consider the set up below: I have read that in the apparatus the wavefunction is given by: $$|\psi \rangle=e^{i\theta}|c \rangle +i |b \rangle$$ where $\theta$ is the phase added by the phase ...
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2answers
54 views

Necessary and sufficient conditions for a function to be the Wigner function of state

For any quantum state defined with a continuous position, the Wigner function is a quasiprobability distribution on phase space. It has many properties, such as that its marginal are probability ...
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0answers
14 views

Creating an arbitrary state of the quantum simple harmonic oscillator [duplicate]

Suppose $\mathcal{B}=\{\lvert 0\rangle, \lvert 1\rangle, \lvert 2\rangle, ... \}$ is the energy eigen-basis of a quantum simple harmonic oscillator. I want to create the state \begin{equation} ...
3
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1answer
207 views

How to write a generic density matrix for multi qubit system?

I was reading the paper device independent outlook on quantum mechanics. Here the author defines a generic two qubit density matrix as $$\rho=\frac{1}{4}(\;I\otimes ...
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2answers
138 views

Interference of overlapping wave functions

I'm a physical layman trying to understand some of the consequences of quantum mechanics. I understand that in the double-slit experiment, where we release individual photons in-phase, the ...
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1answer
71 views

Why are photons bosonic?

I am studying the quantization of the electromagnetic field. My text quantizes by changing amplitudes to ladder operators, by putting in an action and by imposing bosonic commutation relations upon ...
2
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2answers
184 views

When do we see particles to be in a superposition of energy states?

I have two doubts: Exactly when does this happen? and If we are in a superposition of states (lets say E1 and E2) and the particle absorbs a photon, what will happen? If E3-E1 = hf, will it go to E3? ...
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1answer
114 views

Thermionic emission, delayed emission and predissociation

In molecular photodissociation, the thermionic emission, delayed emission and predissociation are the same? Otherwise, what is the difference between them? My question is not about the solids, but I ...
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0answers
28 views

Current density defined by the scattering operator

I have a problem with the definition of the current density. In most literature it is defined as $j^\mu=\frac{i}{2}(S^*\frac{\partial S(A)}{\partial A_\mu(x)})$. I understand that normally we use ...
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1answer
110 views

What is quantum mysticism? [closed]

Most of my questions on stack physics exchange are being commented on as being quantum mystic. The questions I ask are basically related to device independence and how local hidden variable theory ...
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0answers
46 views

Which bipartite entangled states violate the CHSH maximally?

I am reading the device independent outlook on quantum mechanics. Here the author gives a proof that for two qubit system maximally entangled states violate the CHSH inequality maximally that is upto ...
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2answers
248 views

Measurement of the energy of an atom using a cold substance

An atom was prepared in a superposition of ground state and excited states.I propose to measure the state by coupling the system to a cold enough substance. By cold enough I mean $$kT\ll E_1,$$ where ...
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11answers
5k views

QM without complex numbers

I am trying to understand how complex numbers made their way into QM. Can we have a theory of the same physics without complex numbers? If so, is the theory using complex numbers easier?
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30 views

Analogy between a classical discrete system and non classical continous system

Most introduction textbooks about quantum fieldtheory start with a discrete classical harmonic oscillator and then looks at it in the continuous quantized case (quantized field). This leads to the ...
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2answers
67 views

Larmor Precession - What does precession actually means?

Larmor Precession - What does precession actually means? Is it change in the orientation of the axis with which electron revolves around the orbit or what. But, shouldn't the radius of the orbit ...
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2answers
233 views

How is decoherence due to the environment compatible with the Copenhagen interpretation?

Let's say that "decoherence" is that transition from a pure quantum state to a mixed state due to interactions with the environment. (A reasonable definition?) How is that compatible with the ...
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1answer
79 views

Separating the hamiltonian for a superlattice — is it this easy?

I've been banging my head against a wall trying to figure out what I'm sure is a very simple problem. I want to solve the Kronig Penney model for a superlattice, which is just a normal periodic 1D ...
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1answer
106 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
58 views

Deformation parameters of a nucleus

How are the deformation parameters (quadrupole, hexadecapole etc) of a nucleus mathematically related to the reduced transition probabilities $B(El)$ values obtained experimentally?
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32 views

Coherence theory and spatial/temporal coherence

I'm working on a beyond the Standard model (BSM) experiment (on its theoretical side, actually) and I really need to understand better the concepts of spatial and temporal coherence. The rough idea ...
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35 views

How to calculate the eigenenergies of a particle in a triangular billiard?

Suppose we take the Dirichlet boundary condition, namely the wave function must vanish on the boundary. How about a general n-polygon?
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7answers
3k views

Path integral vs. measure on infinite dimensional space

Coming from a mathematical background, I'm trying to get a handle on the path integral formulation of quantum mechanics. According to Feynman, if you want to figure out the probability amplitude for ...
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2answers
68 views

Using rotation matrix for spin to write x oriented spin in z-spin basis

$\newcommand{\ket}[1]{\left| #1 \right>}$The problem is to write the ket vector for a particle with spin +1/2 along the x axis, in terms of the standard basis vectors $\ket{+1/2}$ and $\ket{-1/2}$ ...
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2answers
45 views

Dirac notation and column representation

$\renewcommand{ket}[1]{|#1\rangle}$ I am facing difficulty in understanding how the right hand side is coming in equation A below In $H$ of dimention 4, the vector $$ \sqrt{\frac{2}{3}} ...
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1answer
15 views

Can we agitate a classical non viscous fluid?

Suppose we have an infinite amount of a non viscous liquid (No boundary). Inside that liquid works a rotating impeller. Can the impeller agitate the liquid at all? The question arise from thinking ...
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1answer
168 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
93 views

Proof for Negele and Orland equation (2.34)

The equation (2.34) of Negele and Orland has $$\mathcal H_\text{A}(\hat{\mathbf p},\hat{\mathbf x}) = \frac{1}{2m}\left(\hat {\mathbf p} - \frac e c \mathbf A(\hat{\mathbf x})\right)^2.\tag{2.34a}$$ ...
3
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0answers
27 views

What determines the spatial variation in phase in a superconductor?

I'm assuming that since a superconductor is in one common wave function, the time evolution is governed by the typical global phase variation: $$ \psi (t) = e^{-\frac{i}{\hbar}E_nt}\psi(0) $$ ...
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2answers
99 views

Why is only one quantity of angular momentum i.e. $L_z$ quantized & not $L_x$ & $L_y$?

This is quoted from Arthur Beiser's Concepts of Modern Physics: Why is only one quantity of $\mathbf{L}$ quantized? The answer is related to the fact that $\mathbf{L}$ can never point in any ...
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1answer
49 views

Heisenberg uncertainty principle applied to large bodies?

Suppose I have a ball of a certain radius inside a box (with the length bigger than the radius) such that the ball fits in the box. The ball has a large mass (1 Kg). Heisenberg uncertainty principle ...
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3answers
52 views

Why can't the angular momentum vector be parallel or anti-parallel to the applied magnetic field?

This is the excerpt from my book, Arthur Beiser's Concepts of Modern Physics: An atom with a certain value of $\displaystyle{m_l}$ will assume the corresponding orientation of its angular ...
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2answers
65 views

Importance of bound states

While solving a potential well problem we get scattering states and bound states (if exist). Number of the bound states we get depends on the potential profile. What I want to ask is, what is the ...
0
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0answers
15 views

Radial excitation and orbital-angular momentum excitation

Sorry. Just want to make sure, but what does radial excitation and orbital-angular excitation mean in the context of bound states? Just higher $n$ and $\ell$ quantum number?
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34 views

Quantum superposition of macroscopic objects [duplicate]

An extract from this article: Extrapolated to the scales of our everyday life quantum theory leads to situations such as the famous example of Schroedinger's cat: the cat is neither dead nor ...
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1answer
52 views

Does spontaneous emission actually emit in a random direction, or is it measured in a random direction?

When an excited state couples to the vacuum, it has an infinite number of directions of the quantized electromagnetic field to couple to. Does it evolve into a superposition of all those directions at ...