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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16 views

Fermi's theory of beta decay - density of states?

I am following through these MIT OCW notes on Fermi's theory of beta decay. On page 11 (103 as on page) they wrote the expression: $$\rho(p_e)dp_e = dN_e \frac{dN_{\nu}}{dT_\nu}$$ for the density of ...
-4
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0answers
11 views

Find the energy of an x-ray photon which can impact a maximum energy of $50~\mathrm{keV}$ to an electron [on hold]

This is an exercise question from the text book Concepts of Modern Physics by Arthur Beiser. Find the energy of an x-ray photon which can impact a maximum energy of $50~\mathrm{keV}$ to an ...
0
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0answers
15 views

how time is related to gravity? [on hold]

favorite 2 My question is regarding the following Gauged Linear Sigma Model (GLSM) in two dimensions. S=∫d2x(−Dμϕ¯¯¯Dμϕ+D22e′2+D(|ϕ|2−r)).(1) Here Dμϕ=∂μϕ+iQAμϕ, D is an auxiliary field, and e′ is a ...
4
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1answer
41 views

Does angular momentum of hydrogen atom imply motion of electron around the nucleus?

Does the non-zero orbital angular momentum (or z-component of angular momentum) of a stationary state of hydrogen atom imply motion of electron (or at least the probability density $|\Psi|^2$) around ...
0
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3answers
30 views

Invariance of a maximally entangled state under unitary operation $U \otimes U^\dagger$

Apparently the (d-dimensional) maximally entangled state, $|E \rangle = \sum_{i} |ii\rangle /\sqrt{d}$ is invariant under operations of the form $U \otimes U^\dagger$. I want to prove this result, ...
0
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0answers
24 views

Matrix elements for graphene

I study graphene. Now I have to get matrix elements from its wavefunction. My problem is that I've got the wavefunction in exponential form. For instance, I get something like \begin{equation} \...
1
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0answers
20 views

Derivation of expression for Berry curvature

Many texts quote the expression for the Berry curvature for a two-level system, with Hamiltonian $\mathbf{h}(\mathbf{k})=(h_x,h_y,h_z)$ in terms of $\mathbf{k}=(k_x,k_y)$, as something like \begin{...
0
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0answers
16 views

Is there a verified physical balance in the Maxwell source terms derived from QM Wavefunctions [on hold]

In QM one construct the charge and current source distributions for Maxwell equations, seen in standard textbooks on quantum mechanics, so that the external EM field can be calculated. A nice feature ...
0
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0answers
23 views

Is there scattering event if two wave functions overlap in momentum space?

Let's consider two particles, moving, for simplicity, in a 2D plane, represented by their wavefunctions in the form of (when being modulus squared) very very very narrow Gaussians (let's say close to ...
0
votes
1answer
41 views

How do you get quantum Hamilton-Jacobi equation from Schrödinger equation?

I am reading "The undivided universe: an ontological interpretation of quantum theory" and cannot understand this derivation. Schrödinger equation: $$ i\hbar \frac{\partial\psi}{\partial t} = -\frac{\...
3
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0answers
46 views

Switching on a light bulb. Initial EM/electron pulse propagation

TLDR When switching on any electrical device (e.g. a light bulb or a heater), there is an initial wave (pulse) travelling with very high speed (close to the speed of light) and “carrying the ...
0
votes
1answer
82 views

What's the chance that two atoms would swap electrons?

Suppose two atoms are falling away from each other with velocity $v$ each. Suppose they have evenly distributed momentum among their electrons. Suppose one atom swaps an electron with the other atom. ...
2
votes
3answers
84 views

Does electron absorb energy? [on hold]

According to my teacher, an electron is point sized and it does not absorb or release energy. Moreover, my teacher says their orbital absorbs energy rather than the electron. If that is the case, then ...
0
votes
0answers
30 views

Existence of effective Hamiltonian for variational ansatz

I recently saw on Wikipedia that in perturbation theory one can define in a systematic way effective Hamiltonian $\hat{H}_{\rm eff}$ that produces the same kind of states and energies as if one ...
2
votes
1answer
56 views

Calculating the ground state energy in an electron gas (Jellium)

$\renewcommand{\phi}{\varphi} \newcommand{\vec}[1]{\textbf{#1}}$ This is pretty lengthy because I kept having ideas while writing this. Consider an electron gas in a cube of side length $L$, $V=L^...
0
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0answers
24 views

A fundamental theory of superunification [on hold]

So, an year ago I was searching over the Internet about anti gravity (just out of curiosity).. And I stumbled upon this article: http://theoryofsuperunification-leonov.blogspot.bg/2015/01/russia-...
0
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0answers
39 views

Where I can find quantum entanglement, real experimental raw data

For analysis purpose, I am looking for raw data from real entanglement experiment with spin measured at two detectors, at various combinations of angles, but preferably at a single combination of ...
0
votes
1answer
147 views

Universe spawned from the death of a hyper black hole?

Some Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole a scenario that would help to explain why the cosmos seems ...
1
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3answers
104 views

Finding the Expectation value of harmonic oscillator [on hold]

What is the expectation value for $e^{{\alpha}a^{\dagger}}e^{-\alpha^*{a}}$ of any two states of harmonic oscillator (let say $|n\rangle$ and $|m\rangle$) given below, $$\langle n|e^{{\alpha}a^{\...
-2
votes
2answers
64 views

Can the Copenhagen interpretation and the many-worlds theory be somehow reconciled? [on hold]

Is it possible that, at the moment of observation, a timeline is created where an object is in a state which contrasts its state in the current timeline? Using Schrodinger's cat as an example, let's ...
3
votes
2answers
49 views

Meaning of “Metrically defined” matrix

I got stuck on understanding stuff from Methods of molecular quantum mechanics written by R. McWeeny. The content is: It must be stressed that the representation property embodied in $\mathcal{A} \...
2
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0answers
32 views

Quantum Entanglement Simulation

Suppose there is a digital "quantum entanglement simulator" with a pair generator and two spin detectors, and it Allows to create as many pairs as you want (100 pairs per single click) Allows to ...
0
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2answers
104 views

What is the program of quantum field theory? What is its derivation?

Paraphrasing Griffith's: For some particle of mass m constrained to the x-axis subject to some force $F(x,t)=-∂V/∂x$, the program of classical mechanics is to determine the particle's position at any ...
0
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1answer
52 views

Quantum entanglement of spins

Suppose we have a pair of spins in the state $\left|\Psi\right>=\frac{1}{\sqrt2}(\left|\uparrow\downarrow\right>-\left|\downarrow\uparrow\right>)$. We know that the measurements of the spins ...
6
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0answers
58 views

What's the intuition behind the Choi-Jamiolkowski isomorphism?

What is the intuition behind the Choi-Jamiolkowski isomorphism? It says that with every superoperator $\mathbb{E}$ we can associate a state given by a density matrix $$ J(\mathbb{E}) = (\mathbb{E} \...
14
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1answer
1k views

What are the odds of finding an electron a long way from an atom? As in metres away? [on hold]

Pretty self-explanatory, heard that there is a chance that you might find an electron on the other side of the universe, just wanted to know.
1
vote
1answer
88 views

How to use Heisenberg to explain atom cannot be at rest

In a Dutch national physics exam at the level just before entering university there was a question about a molecule HI: one atom hydrogen plus one atom iodine. Within the molecule, the hydrogen ...
0
votes
1answer
23 views

What is the maximum limit for concurrence for a multiparticle state derived from a symmetric hamiltonian? [on hold]

What is the limit for the Entanglement of a multi particle state? Say I have N spins and a symmetric Hamiltonian. Is it 1 or more? Is there a limit at all? I thought it would be 1, since that value ...
0
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0answers
22 views

Quantum Confinement in Quantum Dots

I have seen it referenced in several places that an electron will behave classically in a bulk material but as the dimension of the material in which the electron exists is limited below the electron'...
0
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1answer
65 views

Approximation of an integral for time dependent quantum Hamiltonian

I want to approximate $\displaystyle\int_{t}^{t+h} dt' H(t')$ in its taylor series, $$H(t)h + \frac{1}{2}\frac{dH(t)}{dt} h^2 + \frac{1}{3!}\frac{d^2H(t)}{dt^2} h^3 + \frac{1}{4!}\frac{d^3H(t)}{dt^3} ...
2
votes
1answer
67 views

Is the use of term Measurement appropriate in quantum physics [on hold]

It may not sound like a physics question, but I think, it is. When we measure spin of an electron in a certain direction, we are actually, setting it up in that direction. That does not sound like ...
0
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0answers
78 views

How does the wave function change upon a boost? [on hold]

I was recently thinking about Lorentz invariance description of a particle. In special relativity is based on the invariance of $$ \text{constant} = c^2t^2 - x^2 - y^2 - z^2$$ I was wondering if ...
0
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0answers
34 views

Why can the y and z-components of spin be measured simultaneously? [duplicate]

I have a gut feeling that this is wrong. By the uncertainty principle where $x,y,z$ are the $x,y,z$ components of spin $$ \sigma_{y}\sigma_{z}\geq \frac{\hbar}{2}\langle x \rangle $$ and it can be ...
1
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0answers
35 views

Are all kinds of energy quantized? [duplicate]

I was reading this answer of David Z about meaning of "Quantum" that this question came in mind: If light is quantized (i.e. is a integer multiples of some unit $\hbar c/k$), are other kinds of ...
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0answers
33 views

Coordinate determines the speed and thus coordinate [on hold]

I have a question about configuration space. You say that coordinate and momentum have one-to-one correspondence in Quantum Mechanics. Imagine that coordinate of a particle is known absolutely in ...
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0answers
69 views

Why isn't CPU made of cesium 133? [on hold]

If this atom can move there and back 9 bilion times per second, then why are we using so poor CPUs?
3
votes
1answer
56 views

Relationship between position and momentum matrix elements

I am going through Faist's Quantum Cascade Lasers book. In the first section of the fourth chapter, he asserts that (in the context of a perturbative analysis of electronic transitions) the ...
3
votes
1answer
49 views

How to make a double slit electron interference as a home experiment? [on hold]

I want to see electron interference making my own experimental equipments. Do you think it is possible? Especially, double slit, how can I have it?
4
votes
2answers
71 views

If orbital shells are just probability functions, why are quantum numbers only ever integers? [on hold]

Quantum numbers are supposed to denote every individual orbital. But if orbital shells are probability functions, then orbitals can't be definite, solid things. So in that case, there can be variation ...
0
votes
1answer
53 views

What is the process of a photon transforming into an electron and positron? [duplicate]

How did they come into existence from a photon? Is it really understood how the process works? Is there even a process or is it just something fundamental?
9
votes
1answer
643 views

Confusion in a trick in solving an energy eigenfunction

Given a non-relativistic energy eigenfunction for a central potential $\left|\Phi \right>$ In solving relativistic hydrogen atom, one of the terms is $$ \left<\Phi\middle|\frac{e^2}{r}\middle|\...
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votes
0answers
49 views

Does “Schroedinger's cat” need entity knowledge to work? [on hold]

I've never studied physics, but am interested in whether this paradox, from an interpretation of quantum mechanics, can still be stated if we don't know anything about unobservable entities. My ...
2
votes
0answers
38 views

When we say particle in a box has quantized energy, is that kinetic or total energy?

In quantum mechanics, it is usually said that energy of the bound (constrained) systems such as particle in a box (infinite potential well) is quantized. It confuses me exactly what type of energy is ...
0
votes
1answer
45 views

What happens with QM particle at constant velocity? [on hold]

In QM particles have wavefunctions that disperse quite fast. The FWHM for gaussian wavepacket increases in time as $\Delta x(t)= \Delta x_0\sqrt{1+(t/\tau)^2} $, $\tau=2m(\Delta x_0)^2/\hbar$ What ...
2
votes
2answers
84 views

Two particles system

Source: this video For a system with two particles (09:30), why is its wave function a product of each particle's wave function? E.g. $$\psi(x_1,x_2)=\psi_a(x_1)\psi_b(x_2)$$ For indistinguishable ...
0
votes
1answer
53 views

When should parameters be replaced while changing basis? [on hold]

I have the following equality: $$a\lvert 00\rangle + b\lvert 11\rangle = a\lvert ++\rangle + b\lvert --\rangle$$ for any $a,b \in C$ that satisfy the normalization condition. For $a = \frac{1}{\...
2
votes
2answers
67 views

Express state as eigenkets

This is very basic but I just suddenly got confused. Any state can be expressed as complete set of eigenkets with discrete eigenvalues: $$|P\rangle = \sum^n c_n |p_n\rangle$$ I understand the above. ...
0
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0answers
32 views

States after measurement

I am learing about quantum mechanics, and I am quite unclear about the the role of measurement and the density operator. Let $\mathcal H$ be a Hilbert space, $\psi(t) \in \mathcal H$, $O$ be a ...
2
votes
1answer
61 views

Proper definition of the Wannier function

I am studying the construction of the Wannier functions for 1D system with periodic boundary conditions and my reasoning seems to be a little bit different from what I can find in textbooks. First ...
7
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0answers
104 views
+50

Zeno effect in quantum gravity?

Given that "the quantum zeno effect can "freeze" the evolution of the system by measuring it frequently enough in its known initial state." Is there any equivalent/similar Zeno effect in quantum ...