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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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 ...
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0answers
13 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 ...
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0answers
16 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 ...
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1answer
19 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?
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29 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 ...
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25 views

Particle-Wave Duality and the Quantum Uncertainty Principle United?

In a pretty recent research 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 ...
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28 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 ...
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4answers
198 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 ...
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29 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: ...
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1answer
26 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
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2answers
74 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 ...
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1answer
57 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.
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22 views

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

we calculate Max K.E of emitted electron.why max?
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2answers
130 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[ A(t) ,H \right] + ...
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2answers
65 views

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 ...
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1answer
44 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 ...
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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 ...
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1answer
49 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: ...
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1answer
30 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
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0answers
31 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 ...
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31 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?
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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
20 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 ...
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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 ...
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1answer
42 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?
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2answers
71 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 ...
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1answer
79 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 ...
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88 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 ...
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1answer
26 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
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2answers
55 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 ...
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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'\ |\ ...
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0answers
16 views

CSCO and Hamiltonian

Is there a relationship between the Hamiltonian and the number of observables needed in a CSCO to fully describe a quantum system? I am thinking that a new observable is needed each time there is a ...
4
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2answers
243 views

Entanglement of Mixed Quantum State

As per Wikipedia: Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot ...
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0answers
34 views

Transition probability of a two level quantum system [on hold]

Please I want somebody to a help with a download of the paper "L. D. Landau, Physik Z. Sowjetunion 2, 46 (1932)".
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36 views

Superfluids (meaning, properties)

I am curious as to what a superfluid is? I have seen videos that say that they have zero viscosity, and I know that it means that there is no friction between the layers of the fluid. But what is its ...
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44 views

Quantum particles hopping in spacetime

Quantum mechanics assumes a non-empty vacuum. There can be created pairs of particles for a short time. Suppose that there are Special vacuum fluctuations that arise from unsteady particle Motion, ...
3
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1answer
149 views

Do some of the laws of Thermodynamics break down in Quantum Mechanics?

I do not know if this is a stupid question as i am not an expert in thermodynamics and certainly no expert in QM. So,we know that the laws of thermodynamics are laws based on statistics.thus require ...
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1answer
37 views

Energy Conservation in Quantum System?

Let us assume, 2 same mass atoms are moving towards each other at equal velocity and they are in course to crash into each other - so what would happen when they do crash into each other? If we use ...
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0answers
21 views

When observing the electrons in the double slit experiment, does the light still appear as if it were a wave?

In the quantum double slit experiment it is said that observing the electrons causes them to appear as particles. Does this observation which causes the electrons to "transform" into particles also ...
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1answer
51 views

Calculating L^2 operator in spherical coordinates [on hold]

I found this development for the calculation of angular momentum L^2 operator in spherical coordinates. The image attached shows the latest step of this. I cannot figure out the algebra between these ...
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0answers
31 views

What are momentum, configuration and coordinate spaces? [closed]

What is a momentum space, a coordinate space and a configuration space? Are they in classical or quantum mechanics or both? What are their similarities and differences and when, where and how are they ...
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1answer
107 views

Double slit experiment where the “particle” is a macroscopic capsule with people inside

I understand that the double slit experiment (i.e. the creation of interference pattern) holds also when the "particle" is not just a single particle but any item, experimentally proven even for a C60 ...
2
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1answer
44 views

Probability current in scattering problems

This is a section from Wikipedia: In regions where a step potential or potential barrier occurs, the probability current is related to the transmission and reflection coefficients, respectively ...
1
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1answer
41 views

Total angular momentum operator

How do the eigenfunctions of the total angular momentum operator analytically look like? I mean the operator is given by $J = L+S$ so the eigenfunctions have to be tensor-product states, right? Can ...
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0answers
30 views

Why doesn't a quantum pairwise Hamiltonian couple states in which more than one interaction occurs?

This question is about the standard quantum mechanical pairwise interaction Hamiltonian. I'll phrase it in terms of an example using Rydberg atoms, but you could just as well imagine spins (for ...
11
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4answers
1k views

Entanglement, real or just math?

I'm new here, actually this is my first question so I'll just get to it. In quantum entanglement when something acts on one particle the other one reacts also, just in reverse (more or less). From ...
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2answers
67 views

Why isn't the Time-Independent Schrödinger Equation an equation of motion?

I thought an equation of motion was something where you are given a Lagrangian and, using the Euler-Lagrange equation, you then find the equations of motion for that system. Same basic idea for the ...
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0answers
40 views

Why did the universe have a low entropy at the big bang?

Sean Carroll, in his book "From Eternity to Here", asks the following question. Why did the universe have a low entropy at the big bang? in John Cramer version of the Wheeler - Feynman absorber ...
3
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2answers
70 views

Slowing down the double slit experiment

Towards the end of the following video https://www.youtube.com/watch?v=GzbKb59my3U the double slit experiment is executed with 'single' photons and it is shown how the interference pattern emerges as ...
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1answer
50 views

Requirements prior to Quantum Mechanics [duplicate]

What are the requirements in physics and mathematics that somebody must have in order to start learning Quantum Mechanics by himself?