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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2answers
78 views

According to many worlds interpretation, to which world will I go?

From my understanding, many worlds interpretation views the actual world (universe) has many branch points. For example, coin flipping may cause two outcomes, but I will experience only on outcome or ...
5
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4answers
590 views

Why do electrons jump between orbitals? [duplicate]

When an electron is excited to higher energy levels, it will jump back to the same level from which it was excited. Why does it develop "sentiment" with that level?
1
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0answers
21 views

Implications for measurement of an initially localized free particle's wavefunction spreading out to infinity?

So, I have been attempting to wrap my head around what happens to a free particle that is initially localized to one spot. It seems that due to their different frequencies, the particle's wavefunction ...
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1answer
38 views

Thomas-Fermi approximation for cold atoms in a 1D harmonic potential

The Time-independent Gross-Pitaevskii equation is $$ \mu{\phi(x)}=\Big(\frac{-\hbar^{2}}{2m}\nabla^{2}+V_{ext}(x)+g|\phi(x)|^{2}\Big)\phi(x) $$ From Thomas-Fermi approximation, $$ ...
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5answers
16k views

How do electrons jump orbitals?

My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals ...
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1answer
22 views

Implication of rotational symmetry on scattering matrix/ scattering cross-section [on hold]

How does the rotational invariance helps simplifying Non-relativistic quantum scattering problems? Is there any any additional information that can be extracted about the scattering amplitude? It ...
0
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0answers
46 views

What does representing position as a function of frequency mean? [on hold]

I am doing an introductory course in quantum physics. A part of the magical paper of Heisenberg says, "For a state characterized by the label $n$, the fundamental frequency $v(n)$, and the ...
0
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0answers
31 views

Can we generate artificial electrostatic energy? [on hold]

Can we generate artificial electrostatic energy for electrostatic attraction?And can it be controlled to get element specific electrostatic attraction?
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1answer
84 views

Is a larger black hole a faster or a slower processor?

For a remote observer, a black hole with mass $M$ has a temperature $T=1/M$. Now I am confused with the problem: A larger black hole can achieve a task faster or slower if it's regarded as a kind ...
12
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0answers
168 views

Has Jaynes's argument against Bell's theorem been debunked?

As a student of theoretical physics I'm well acquainted with the multitude of crackpot ideas attempting to circumvent Bell's theorem regarding local hidden variable theories in quantum physics. ...
2
votes
1answer
194 views

Question on spin-orbit interaction

When you study the spin-orbit interaction in quantum mechanics, even for a simple hydrogen atom, you find only the electric field in the nucleus reference system, while in the electron reference ...
1
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4answers
134 views

Is what statisticians call a “random variable” what physicists call an “observable” in QM? [duplicate]

I read at http://www.statlect.com/fundamentals-of-probability/random-variables that A random variable is a variable whose value depends on the outcome of a probabilistic experiment. Its value is ...
2
votes
2answers
89 views

Higher orders in perturbation theory

I would like to compute an energy level up to many orders in perturbation theory. My difficulty right now is not in the calculation itself but in understanding the algebraic structure of the higher ...
2
votes
4answers
150 views

Regarding the usage of 'classical potentials' in quantum mechanics

I am familiar with basic quantum mechanics and I know that there is no concept of 'force' in quantum mechanics, unlike in classical mechanics. Problems in quantum mechanics are solved by writing down ...
1
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0answers
34 views

Proof that a Hermitian Matrix is not defective?

I am taking an introductory course into Quantum Mechanics. To me to seems pretty simple to prove most properties of Hermitian operators. However, I am stuck at an edge case, proving that if an ...
8
votes
3answers
5k views

Bell's theorem for dummies, how does it work?

I've been reading up on theoretical physics for a few years now and I feel like I am starting to get an understanding of particle physics, at least as much as you can from Wikipedia pages. One thing ...
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0answers
35 views
8
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1answer
205 views

Why does the conjugated $\pi$ bond not violate the Pauli Exclusion Principle?

Let's look at the molecule 1,3 butadiene: $CH_2=CH-CH=CH_2$ and number the carbon atoms 1 to 4 from left to right. The bonds between 1 and 2 and between 3 and 4 are double bonds: each ...
3
votes
1answer
41 views

What is a “dynamically generated scale” physically?

A theory like QCD with massless quarks in four dimensions has no explicit mass parameters in its classical Lagrangian. At the quantum level however, instead a mass scale Λ is generated dynamically at ...
2
votes
2answers
173 views

Good resources for learning/reviewing complex time propagator formalism

I studied this at the beginning of my graduate degree but have to review it for my graduate exam. If it's not clear I'm talking about the $\beta = \frac{it}{\hbar} $ turning the integral of your ...
1
vote
1answer
668 views

Where can I find beginner's information about quantum mechanics? [duplicate]

Possible Duplicate: Popular books on QM I hope that this question is suitable for this site. I am interested in reading up on quantum theory so that I can reasonably understand the ...
2
votes
3answers
983 views

J.J. Sakurai book on Q.Mech [closed]

I just want to ask how recommended is the book on quantum mechanics by J.J. Sakurai. Is it any good as an introductory text? And are there better suggestions (substitutes)?
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1answer
43 views

Why does quantum mechanics produce different predictions for Bell test experiments than classical mechanics?

I understand that experimental results from Bell test experiments have shown that measured correlation is a cosine function of the angle between the detectors. What I am struggling to grasp is why ...
3
votes
0answers
57 views

What are fragmented condensates?

It is defined that if more than one eigenvalue of the one-body density matrix are macroscopically occupied the condensate is said to be fragmented. $$ n^{(1)},n^{(2)},...=\mathcal{O}(\mathcal{N}) $$ ...
2
votes
1answer
65 views

Conservation of momentum in infinite square well

This is inspired by Griffiths QM section 2.2, on the infinite square well, which is about how far I've gotten (so, sorry if this is addressed later in the book). For any given starting wavefunction, ...
5
votes
1answer
268 views

Wick's theorem for calculating OPE

I am trying to understand a calculation using Wick's theorem. Let $T(z)$ be the analytic part of a stress-energy tensor, and $\phi(z)$ a free boson field. Now, ...
1
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1answer
110 views

Existence of bound states in 3D Yukawa potential

For a 3D Yukawa potential $$ V(r) = - \lambda { e^{-Mr} \over r}. $$ Bargmann's upper bound can be read as necessary condition for the existence of at least one bound state; we want $N_l>1$ and ...
1
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1answer
51 views

Quantum bases conversion ($S_x$, $S_y$, $S_z$)

As part of several of my homework problems on the subject, I've had to convert between bases, for instance $|+\mathbf{x}\rangle$ in the $S_z$ basis $\left( \frac{1}{\sqrt{2}}\left( |+\mathbf{z}\rangle ...
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1answer
82 views

Galilean relativity in QM

Intro I've been trying to show that the generator of boosts can be written in operator form as can be seen here, as: $$ B = \sum_i m_i x_i(t) - t \sum_i p_i $$ As a reminder the transformation ...
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votes
0answers
58 views

scientific theory [closed]

According to Einstein, any scientific theory should have a mental image like raiding alongside a beam of light, free fall from a tower etc. He said "If a theory doesn't have a mental image that even a ...
1
vote
1answer
112 views

Relationship Between Stopping Voltage and Photocurrent

Online, I found a graph of photocurrent vs. stopping voltage: And I can’t figure out how photocurrent and stopping voltage have such a relationship. Stopping voltage is proportional to maximum KE ...
3
votes
1answer
78 views

Evaluating path integral

I am having some trouble remembering how to evaluate path integrals involving multiple particles. Suppose that I have two interacting particles with Lagrangian $$L= \frac{1}{2}m \dot y^2-\frac{1}{2}m ...
1
vote
0answers
38 views

Black hole evaporation, mass or bit?

Usually when we talk about black hole evaporation, mass or energy is taken as the target and the evaporation time is computed based on mass loss in a given time period. Is there any work to analysis ...
3
votes
1answer
75 views

What makes Bell's original inequality unsuitable for experiments?

Bell derives the inequality $$|E(\vec{a},\vec{b})-E(\vec{a},\vec{c})|\leq 1+E(\vec{b},\vec{c})$$ in his book Speakable and unspeakable in quantum mechanics. In this derivation he uses the assumption ...
12
votes
3answers
1k views

How to solve bound states of 2D finite rectangular square well?

I want to solve bound states (in fact only base state is needed) of time-independent Schrodinger equation with a 2D finite rectangular square well \begin{equation}V(x,y)=\cases{0,&$ |x|\le a ...
1
vote
1answer
52 views

Quantum physics and determinism [duplicate]

According to classical physics if we know space-time coordinates of every atom in the universe, we can predict the future. But quantum physics introduced probability throwing determinism out of ...
66
votes
10answers
29k 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 ...
1
vote
3answers
71 views

Why is that a question can be answered with several theories? [closed]

This may be silly and I am sorry for that but it is confusing me. My teacher was teaching us about path of electrons around a nucleus. He told us that many theories have been proposed about path of an ...
1
vote
1answer
61 views

Derivative with respect to perturbation in QM

The book "Introduction to Computational Chemistry" by Frank Jensen claims the following (Eq. 10.35): Let $H(\lambda) = H_0 + \lambda V$ be a Hamiltonian parametrized by a perturbation strength of ...
0
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0answers
42 views

Fetter & Walecka's derivation of second quantised canonical Schrodinger equation for fermions

On page 18, before the occupation number variables for states i and j are changed $n_i \rightarrow n'_i = n_i - 1$ and $n_j \rightarrow n'_j = n_j + 1$ respectively, could we not have rewritten eq. ...
-2
votes
0answers
56 views

Entanglement (spooky effect) [closed]

I watched some videos on this subject, and I have seen that a particle may have "spin up" or "spin down" and if one has spin up, the other has spin down when we measure it. My question is: do we ...
-1
votes
0answers
36 views

What's the entanglement of a typical state of multiple qubits?

For a n-qubit system, with n a large number, under free (random) unitary evolution starting from a product state, what's the entanglement distribution of a typical state of the system? Here the ...
0
votes
1answer
69 views

Can quantum mechanical models be used to describe phenomenon on a larger scale? [on hold]

For example: Relativistic effects are only especially prominent when approaching speeds close to that of light. But, one can take into account these effects even at low speeds and still get a correct ...
0
votes
0answers
37 views

What is the meaning of “closure is lost” for a set of kets (or any members of a vector space)?

This is the closure relation in Quantum Mechanics: $$\sum_i |i\rangle \langle i| = 1 $$ which I understand as "the sum of the projections onto the basis vectors leaves the projected vector ...
3
votes
1answer
161 views

How can I simulate a model electronic hole?

Suppose I can solve time-dependent Schrödinger equation for several 1D particles (currently 3). I'd like to see, what an electronic hole is and how it behaves — in a series of numerical experiments. ...
2
votes
1answer
114 views

Can different components of a wavefunction become entangled with different systems?

Imagine a $z$-basis spin Stern Gerlach experiment where a single particle is put through the apparatus. The output is a spin state vector consisting of the sum of the two $z$-spin states. Each spin ...
1
vote
1answer
118 views

Kronecker sum or direct sum?

When we write $$H=\sum_k H_k$$ in condensed matter physics, are we using Kronecker sum or direct sum? I think this is direct sum. However, Wikipedia says it is Kronecker sum. Can anyone give some ...
-1
votes
0answers
21 views

how schwinger process produces electron-positron?

i am not able to understand the mechanism of schwinger process..how it actually produces electron-positron pair. is there any connection with the dirac sea? how to utilize the energy of gamma rays ...
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0answers
32 views

Hamiltonian operator prove [closed]

question : prove that (d/dx) operator is not Hamiltonian operator? quantum mechanics please help me about this
5
votes
1answer
144 views

Delocalization in the square root version of Klein-Gordon equation

In this Wikipedia article a relativistic wave equation is derived using the Hamiltonian $$H=\sqrt{\textbf{p}^2 c^2 + m^2 c^4}$$ Substituting this into the Schrödinger equation gives the square root ...