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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New subatomic particles

In reference to the findings talked about here http://online.wsj.com/articles/two-new-subatomic-particles-found-using-large-hadron-collider-scientists-say-1416409980 and other similar articles ...
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67 views

How can one be 'certain' about anything that has an “Uncertainty Principle” at its core? [closed]

The Uncertainty Principle, which says that more than one aspect of a particle cannot be measured simultaneously, illustrates one of several major differences between quantum physics and classical ...
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33 views

Would a semiconductor shined with monochromatic laser light matching its band-gap have a 100% efficiency if all of the light was absorbed & converted?

The idea of transporting power through laser light is an interesting area of research. Conversions of up to 54% have been reported for long distance transmission. I would assume ...
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1answer
45 views

Why do silicon solar cells only produce ~0.6v when the band gap of silicon is ~1.1v?

I've been researching into this and can't quite figure out where that lost voltage is going. When silicon is excited by a photon within its absorption spectrum, it will always have an internal ...
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49 views

Quantum Entropy-a minimization problem

I came upon this (not homework) problem of minimizing the following expression ...
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1answer
30 views

Spin operator eigenstate in Fock space

I am creating an operator group from representation of spin 1 operators $$J_{x} = \frac{1}{\sqrt{2}}\left(\begin{array}{ccc} 0 & 1 & 0\\ 1 & 0 & 1\\ 0 & 1 & 0 \end{array} ...
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21 views

How is light trajectory affected by the trajectory of environment it passes through?

There's a sci-fi concept of slow light that I find very amazing: Imagine a glass material that has index of refraction $n$ say, $3,000,000,000$ which means: $$v_{glass} = \frac{c_{vacuum}}{n} = ...
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36 views

Density matrix: error with diagonalization claim and fixing it

On page 174 of Townsend's "A Modern Approach to Quantum Mechanics", 2nd edition, it says the following: "For a mixed state, one for which $p_k$ is the probability that a particle is in the state ...
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32 views

kronecker product of representations on SU(2) group [closed]

We know that if we have two irreducible representations, their product is in general reducible : $$T^{\mu}\otimes T^{\nu}(g)=\oplus \sum_{\lambda}c_{\lambda}T^{\lambda} (g)$$ where $c_{\lambda}$ is ...
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20 views

How to generate random symmetric unitary matrices “close” to a given matrix? [migrated]

Note: This question have been asked in Mathematics Stackexchange [click here]. Since random matrix has close relation with some physical problems, I would like to post it here again. Sorry if this ...
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1answer
17 views

Does a photo-excited semiconductor produce a constant voltage output equal to the band gap?

Does the voltage produced by a photo-excited semiconductor always equal the band gap of that semiconductor, or does the voltage vary over a range similar to the photon energies in the emission spectra ...
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1answer
21 views

Electrical Generator [duplicate]

I have seen the generator that produces electricity from the earth's magnetic field demonstrated I have a video if it working It was taken approximately 15 years ago in California
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2answers
57 views

How do we know if distant stars we see by their light are real objects? [closed]

Is there a way to be sure if they are not just light, but real objects?
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3answers
103 views

A misunderstanding regarding infinite square well

Here is a picture of the energy states of infinite potential well. We can see That the first level have a half wavelength which fittes with a full wave of the second level. $$\frac{ \lambda _{1} ...
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54 views

Is quantum uncertainty a function of how matter is distributed in the universe?

As an outcome of his PhD thesis work, Richard Feynman and John Wheeler wrote a series of papers on how the kickback on an electron as it emits a photon can be modeled accurately as the result of an ...
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1answer
26 views

What happens to K.E. in matter antimatter annihilation?

If I have two matter and antimatter particles, say an electron and a positron, each moving towards each other with a certain speed, they annihilate after the collision. Does the energy of the photons ...
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22 views

Can we use combined symmetry to simplify the calculation of algebraic PSGs?

In classifying mean-field spin liquids under projective construction, the algebraic projective symmetry group (PSG) approach focus on the mathematical construction of the possible extensions of the ...
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50 views

Do I understand life [closed]

I AM NEW HERE,BUT LOTS OF CONFUSION IN MY MIND, life or Death depends upon time...or other things... on earth A man lives 60 year ,,what about there life at another place of universe where time is ...
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28 views

Finding the expectation value of the annihilation operator with respect to a given state

Using dirac notation we were given a state vector $$|\Psi(t=0)\rangle = A\sum\limits_{q=0}^Q \frac{1}{(q+i)} |\phi_q\rangle$$ Where $\phi$ is part of a complete orthonormal set. I found the ...
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2answers
72 views

why do metals feel cold when electron moves at Fermi velocity?

This might be a very elementary question. Considering that electrons in typical metals have very high Fermi velocity, why is it that when you touch a metal you feel cold? My intuition tells me that ...
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19 views

space representation of a local potential

Why is it that for a local potential $V$: $$\langle x | V | x' \rangle = V(x) \langle x | x' \rangle = V(x) \delta(x - x')$$ I saw this being used in a book but without any explanation. The part with ...
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1answer
47 views

Superposition and simultaneous observation

Trying to understand superposition. Ok, so double slit experiment. The multiple paths the particle simultaneously travels interfere with each other but as it is absorbed, it chooses one "actual" ...
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1answer
67 views

Are there any known physical implementations of quantum gates?

I was wondering if there are any known implementations of a small number of quantum gates that can interact with each other. Certainly we don't have a "complete" set of quantum gates (where ...
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1answer
125 views

Do consciousnesses get “scattered” across the many worlds of the MWI?

According the many worlds-interpretation (MWI) of quantum mechanics, following a decision with possible outcomes $A$ and $B$, with respective probabilities $p_A=P(A)$ and $p_B=P(B)$, a proportion ...
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24 views

Making An Energy Momentum Plot For A Rashba Model (Using Discretization)

I want to make a plot of the Energy versus the Momentum of the Rashba model, using discrete matrices. First Ill show how I did this for the free particle. Subsequently I will show what goes wrong for ...
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2answers
92 views

Bound electrons don't move, right?

I've never been satisfied with the explanation that electrons have a “speed” and move close to the speed of light, thus incurring relativistic effects that make gold pretty and mercury wet. I learned ...
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13 views

Derive allowed transitions in IR spectroscopy [closed]

I have question which I didn't find in the forum yet and hope someone could help me. It's in the field of quantum mechanics, which I know a bit about, but am not a total expert in. I have an ...
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1answer
39 views

Pressure in Harmonic Oscillation

Classical Harmonic oscillator's energy depends on temperature as it equals $k_B$$T/2$. However, quantum harmonic oscillator energy is $(n+1/2)hf$. So, when T=0, quantum predicts motion. I have been ...
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1answer
55 views

Quantum Tunneling

Why is it, that quantum tunneling is only significant between states of nearly equal energy (as claimed here: 'Since tunnelling is significant only between states of nearly equal energy, tunnelling is ...
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49 views

Commutation relation of a operator with Hamiltonian [duplicate]

Given that the eigenvalues of a Hamiltonian operator $H$ are bounded below, will a Hermitian operator $T$ exist such that $[T, H] = i\hbar{\bf 1}$ identity operator?
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1answer
45 views

What is many-body bound state?

Bound state by definition is a state when particles are bounded together, so then "many-body bound state" would be bound state for a system of many bodies. Then I have several puzzles: 1. is the state ...
2
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2answers
42 views

Does an excited state wave function depend on state preparation?

Consider a quantum system with a ground state and many excited states (e.g. an atom). If the system is in an excited state, to what extent does its wave function depend on the method of state ...
6
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2answers
163 views

How can we differentiate between matter and antimatter? [duplicate]

For instance if there was a galaxy, assume it to be made up of antimatter (isolated from other "normal" galaxies), how would we, or rather, would we be able to distinguish if it was made up of matter ...
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1answer
48 views

Photon and Wave

There are some aspects of light that can be easily demonstrated by using the concept of wave. However I really want to know what it would be like in term of photon point of view. So I have some ...
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1answer
43 views

Koopman Von Neumann state vs Quantum state

Is it correct to think that a state in Hilbert space represents the "most we can know" about a system? Is therefore a state in KvN Hilbert space the same as a state in the usual quantum Hilbert space, ...
2
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1answer
39 views

Everyone calls Electromagnetic Induced Transparencyan interference phenomenon, but is it also an interference phenomenon in classical systems?

Electromagnetically induced transparency is a hot topic in physics. However I'm curious about its mechanics in physics. Physicists think that it's a phenomenon of interference from transition of two ...
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39 views

Wave function of N electrons in a superconductor

Assuming that the wave function consisting of $N$ electrons is $\Psi_{N}(\bf{r_1,r_2,\cdots r_N)}$ then in the presence of a magnetic field ($\bf{B}=\nabla \times A$), how do I show that the current ...
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15 views

Many body quantum rotors

I'm stuck on a particular problem about quantum rotors. Suppose we have $N$ such rotors and they are connected to a thermal reservoir of temperature $T$. Neglecting any center of mass motion, I'm ...
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2answers
108 views

Why is time evolution of wavefunctions non-trivial?

(Note: This post focuses on a single simple example, however I'm asking about the error in general in my logic). Consider the infinite potential well "particle in a box" system described by ...
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1answer
59 views

Scalable tool (engine) for simulating the universe

Does there exist a large scale scalable tool (engine) for simulating the universe that incorporates both quantum mechanics and cosmology, i.e. micro & macro scales? (It would be best if this tool ...
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2answers
90 views

What is the physical interpretation of a field operator

So far in our lecture we defined creation operators $a^{\dagger}_{n}$ in the following way, that we said: Somebody got you a antisymmetric or symmetric N- particle state and now $a^{\dagger}_{n}$ ...
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1answer
58 views

Energy as charge with respect to time translations in QM

Consider a non relativistic quantum mechanical system with Hamiltonian $\mathcal{H}$, and denote the states by $\psi \equiv \psi(t) \equiv | \psi(t) \rangle$. From the Schrödinger equation we know ...
5
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2answers
102 views

Ground state of Spherical symmetric potential always have $\ell=0$?

I was given a problem where I have a spherically symmetric potential (the exact form is not relevant to this question, I think - but anyway is it 0 for $r\in[a,b]$ and $\infty$ everywhere else) and I ...
1
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1answer
71 views

What is the smallest length scale ever measured?

And, by the way, what is, or are, the measured values?
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1answer
30 views

How do discretize a finite crystal?

I am trying to find a general method to discretize a finite crystal system. How I have been discretizing systems so far (using Wannier functions): When you have an infinite crystal, you may apply ...
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1answer
46 views

Where did I go wrong in ket vector in quantum mechanics? [closed]

Consider a system of total angular momentum j = 1. The operator jx is given by: What are the possible values when measuring jx? My attempt: The eigenvalues after calculation are -1, 0, 1. Now I ...
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0answers
43 views

Phase and group velocity of a soliton? [closed]

How do I find the phase velocity and group velocity of a soliton with a $\operatorname{sech}$ (hyperbolic secant) envelope?
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1answer
21 views

Filled molecular orbitals: Avoidance vs Mixing

I am trying to figure out if the mixing of two filled orbitals requires some additional activation energy and, if it does, if there is some orbital avoidance area where the filled orbitals will not ...
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12 views

Crystal in Magnetic Field

When you have a 2D crystal in a uniform perpendicular magnetic field, you can use the Peierls substitution to convert one tight-binding before-magnetic-field-band into a $q$-bands under the influence ...
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3answers
91 views

Fock space and occupation number

I have troubles to understand the concept of a Fock space. We defined it as a direct sum of the 0-particle, single particle, two particle etc. Hilbert space. Unfortunately, I am not sure if I ...