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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1answer
14 views

Is there an implicit assumption that each quantum well contains a single electron only?

Is it true that each electron can be represented as a quantum well? I had believed that each energy level was able to contain multiple states and each states were able to hold multiple electrons.
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0answers
10 views

What does it mean for a quantum particle to be trapped in a well of zero potential energy?

In quantum mechanics it is often assumed that inside a well, wire, etc. there is zero potential energy. What does it mean for the inside of the well to have zero potential energy? When potential ...
1
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0answers
17 views

What is the “life time” of a trapped electron?

What does it mean for an electron trapped in a quantum well to have some life time? From the context it sort of times that the electron will move out of this quantum well at some time $\tau$ later. ...
0
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1answer
29 views

Are The Quantum Assumptions of MBT Theory Correct?

I've become very interested in Tom Campbell's MBT Theory (Plenty of YouTube videos). I can't explain it all here because it takes a book (The one he's written). It's based on the virtual reality ...
1
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2answers
24 views

Starter's book on Quantum Mechanics (more general and simple books than full QM textbooks) [duplicate]

This question is a little different from other questions referring to books on QM. I ask you to tell me some books that have QM on a simpler level than that of a full course on QM. Some universities ...
8
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3answers
413 views

Why do lines in atomic spectra have thickness? (Bohr's Model)

Consider the atomic spectrum (absorption) of hydrogen. The Bohr's model postulates that there are only certain fixed orbits allowed in the atom. An atom will only be excited to a higher orbit, if ...
0
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0answers
20 views

Hadamard Gate application help

I need to prove that if you apply Hadamard gates on the input/output before and after a CNOT gate that you get the same answer as flipping the target and control qbits of a CNOT. So for example I'm ...
0
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2answers
42 views

Position space wave function of an electron

In Wikipedia I find the wave function of a free particle to be $$ \Psi(\vec{r},t) = A\,e^{i(\vec{k}\vec{r}-\omega t)}$$ This is is a plane wave moving in the direction of $\vec{k}$ with speed (phase ...
0
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0answers
29 views

Property of helium superfluid [on hold]

I learnt that in helium II every atom would have same wave function and is governed by BE statistics. does that mean all helium II atoms would vibrate in the same way in a field?
1
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0answers
28 views

is there any molecular transition which emits a photon in certain direction

i know molecules having magnetic moment would be aligned in certain direction but do they emit photon in any certain direction when excited? are there any molecules which would emit photon in tthe ...
0
votes
1answer
44 views

Representation of operator in “$a$-representation” [on hold]

I have an operator, $X$ say, which is given by a simple phase-shift of the annihilation operator $a.$ I've been asked to give the matrix of $X$ in the $a$-representation, but I was hoping someone ...
1
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1answer
73 views

Singlet state and it's expectation value

So. We have a singlet sate $$ \dfrac{1}{\sqrt{2}}(\vert\uparrow\downarrow\rangle-\vert\downarrow\uparrow\rangle)$$ And two pauli matrices for z axis - one that acts on 1st spin (lets denote it with ...
3
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1answer
56 views

Entanglement ladder algebra and quantization of entanglement

Usually in QFT, even optical quantum mechanics papers, usually resort to describe n-states in terms of the ladder algebra, plus a parameter for polarization, but the entanglement information is ...
1
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0answers
35 views

Applicability of perturbation theory

Consider some system in some initial state $|k^{(0)}\rangle$. The probability that such a state makes a transition to some other state $|m^{(0)}\rangle$ can be computed to various orders in time ...
0
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0answers
35 views

Fermion commutation relations QFT question

Consider left-handed fermions in two spacetime dimensions $(t,x)$: $\psi_L=\frac{1}{2}(1-\gamma_5)\psi_D$ with $J_0^\epsilon(t,x)=\psi_L^+(x+\epsilon)\psi_L(x-\epsilon)$. (a). Use canonical ...
0
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0answers
27 views

Quartic interacion

I want to change Lagrangian with coupling constant lambda in quartic interaction so that coupling constant will be negative like in unstable vacuum state. This unstable state I want to describe. Can ...
1
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0answers
31 views

Integration measure

Consider the field being decomposed into a orthogonal and completed basis: $\Phi(x) = \sum_n c_n \phi_n(x)$ (or $\Phi(x) = \int dk c_k \phi_k (x)$, if continuous) The notation: $\phi_n(x) = ...
5
votes
1answer
64 views

spooky nonlocal communication, or bad abstract?

I'm referring to this recent paper, "Experimental Proof of Nonlocal Wavefunction Collapse for a Single Particle Using Homodyne Measurements" by Fuwa et al. published in Nature Communications. ...
3
votes
1answer
34 views

Analogies between Fraunhofer diffraction and Josephson junctions

There are several analogies between diffraction patterns and Josephson junctions, especially between a double slit experiment and two Josephson junctions in a superconducting ring (like this): Both ...
1
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1answer
29 views

What is the definition of parity conservation?

I searched quite hard, and am still confused what is the exact definition of parity conservation? For example, we have quantum system with initial state $\Phi_i$, and after decaying it comes to final ...
2
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0answers
53 views

What does it mean “Hawking radiation is in a pure state”?

I'm trying to understand black hole paradox but I'm not sure if I understand what does it mean "Hawking radiation is in a pure state". Does it mean if Hawking radiation is in a mixed state then ...
1
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0answers
23 views

Minimum Uncertainty Wavepackets

I'm reading over some lecture notes on minimum uncertainty wavepackets in quantum mechanics, and I've come across a statement that I'm not entirely convinced by. My take on minimum uncertainty states ...
0
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1answer
34 views

Can we say an atom is ferromagnetic?

Some atoms have nonzero magnetic moments. Does it make sense to say they are ferromagnetic? Or should we say it is paramagnetic?
1
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0answers
46 views

Anomaly for Majorana fermion?

In 4-spacetime dimension, is there U(1) gauge field chiral anomaly associated with Majorana fermion (or I am not sure if it is equivalent, majorana representation)? Besides, I have read from several ...
0
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0answers
56 views

Are the particle-wave duality and the quantum uncertainty principle united? [duplicate]

In a recent paper by Patrick Coles, Jedrzej Kaniewski, and Stephanie Wehner at the Centre for Quantum Technologies at the National University of Singapore, they came to the conclusion that the ...
0
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0answers
31 views

Help a layperson out here [on hold]

Lately I have been at it, from my completely laypersons understanding of QM with what I see si fi wooers simply replacing a God watchmaker with a cosmic Bill Gates in place of this. Help me clear this ...
3
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4answers
217 views

Understanding the Quantum Vacuum State [duplicate]

In terms of the creation and annihilation operators $a_{j}$ and $a_{j}^{\dagger}$ (fermionic or bosonic, doesn't matter): Is the vacuum state $\mid\mathrm{vacuum}\rangle$ exactly the zero vector on ...
0
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0answers
34 views

$n^\text{th}$ operation of creation and annihilation operators on vacuum

My question is similar to the one that has been posted on this link. In particular I would like to express the following expression in the most compact form: ...
0
votes
1answer
27 views

Does a time-varying intensity contribute to the photoelectric effect?

I understand the photoelectric effect demonstrates that electrons are only dislodged from a metal if incident light meets a minimum threshold frequency. I wonder if a varying intensity might also ...
2
votes
2answers
78 views

Binomial expansion of non-commutative operators

I would like to determine the general expansion of $(A+B)^n$, where $[A,B]\neq0$, i.e. A and B are two generally no-commutative operators. How could I express this in terms of summations of the ...
0
votes
1answer
60 views

What exactly is quantum spin? [duplicate]

What is "spin" as it relates to subatomic particles? I've heard that it's similar to angular momentum but I've also heard that's not completely the case.
0
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0answers
23 views

Do all the emitted electron in photoelectric effect have same K.E [duplicate]

we calculate Max K.E of emitted electron.why max?
3
votes
3answers
182 views

Is the Wikipedia version of the Heisenberg equation of motion correct?

Back in 2011, this question asked about the Wikipedia version of the Heisenberg equation of motion for an operator $A$: \begin{equation*} \frac{d}{dt} A(t) = \frac{i}{\hbar} \left[ H, A(t) \right] + ...
1
vote
2answers
103 views
+50

Spin in magnetic field and eigenvalues

We have some arbitrary quantum state, lets say $$\vert\Psi\rangle=\alpha_{1}\vert\uparrow\rangle+\alpha_{2}\vert\downarrow\rangle= \begin{pmatrix} \alpha_{1} \\ \alpha_{2} \\ \end{pmatrix}$$. And ...
-2
votes
1answer
45 views

quantum mechanics, lighting mechanics [on hold]

If we were able to place two square mirrors (each other with exactly the same size) perfectly aligned the one mirror facing the other, at a very very close distance that light could not interfere ...
0
votes
1answer
33 views

Do non-Gaussian states always show negativity in phase space?

According to Hudson’s theorem, any pure quantum state with a positive Wigner function is necessarily a Gaussian state. In cases, in which the existing well-known Hudson theorem immediately tells that ...
0
votes
1answer
51 views

QM: Why is there a minus sign on the Energy operator when using complex conjugate?

I understand how they get the first equation. But I have no idea why there is a minus sign on the second equation: This is from a derivation for the probability density current found here: ...
0
votes
1answer
31 views

Quantum GMT and no-communication theorem [on hold]

Knowing exactly the time is important on many fields of physics. What if we had entangled particle pairs, so that one of the particles is at Greenwich and the other wherever we want, but for fun of it ...
3
votes
0answers
36 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 ...
0
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0answers
33 views

Given the quantum Zeno effect, won't continual observations of a photon stop/slow down light?

The quantum Zeno effect states that continual observations will prevent motion. Therefore, won't continual observations of a photon(s) reduce the speed of light? Is my reasoning flawed?
0
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1answer
28 views

Velocity of electrons during transition to different energy

I was watching a documentary of quantum mechanics (this video). They said something about quantum leap, jumping of electrons from one energy state to other. I want to ask how electrons travel though ...
2
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0answers
21 views

How to calculate the ground states' Berry phases with doubly degeneracy, such as that due to the particle-hole symmetry or time reversal symmetry?

Suppose the ground states of a system are doubly degenerate due to an anti-unitary symmetry $K$, which are $|\psi>$ and $|K\psi>$. If the system is an one-dimensional Fermion system and ...
1
vote
1answer
48 views

What sort of operations can be applied on a Hilbert spaces?

I was reading the paper No Universal Flipper for Quantum States. In this paper they have tried to prove by contradiction that a universal flipping machine cannot exist. By flipping I mean if I have a ...
-1
votes
1answer
43 views

Hawking radiation.time arrow.antigravity [on hold]

Why is a virtual particle of a quantum fluctuation absorbed at the event horizon while the virtual pair is ejected?
1
vote
2answers
72 views

Quantum Harmonic Oscillator and the Classical Limit

We can solve for the stationary states of a quantum harmonic oscillator denoted by $|n\rangle$ with energy eigenvalues $(n+\frac{1}2)\hbar\omega$. However if our system is in a stationary state, the ...
1
vote
1answer
80 views

Is there something wrong with quantizing two times in second quantization?

Second quantization is sometimes considered to be a bad name, because a single quantization is enough. For electrons, we can either start from a many body viewpoint and introduce field operators or we ...
1
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0answers
92 views

Computations for Quantum Vacuum Fluctuations

For quite some time the notion of quantum vacuum fluctuations is bothering me. What exactly is the theoretical origin of this notion? This notion has become quite common in physics and is used to ...
0
votes
1answer
27 views

Green function in non-relativistic quantum mechanics for particles with complicated isotropic spectrum

Let's consider a free particle with some non-trivial isotropic spectrum. What I mean is that Hamiltonian of the particle depends only on the square of the momentum: $$\hat{H}=f(\mathbf{\hat{p}}^2)$$ ...
4
votes
2answers
58 views

photon wave function, double slit, single photon source

There's an old argument by Newton and Wigner, that the photon as a massless particle can't have a position operator and therefore no position space wave function. How does this tie in with the double ...
1
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3answers
140 views

Calculating $\langle x | \hat{x} | p \rangle$ in $p$ basis

I am trying to calculate $\langle x\ |\ \hat{x}\ |\ p\rangle$. I can work in the $x$-basis like so: $$\langle x\ |\ \hat{x}\ |\ p\rangle=\int dx'\langle x\ |\ \hat{x}\ |\ x'\rangle\langle x'\ |\ ...