# Tagged Questions

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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### Electromagnetic wave and quantum mechanics [duplicate]

I'm very new to physics. I studied and read about quantum mechanics and what the assumptions are (wave particle duality, uncertainty principle, observation, wave function collapse, etc.), but I also ...
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### Permutation symmetry - a continuous symmetry?

From quantum mechanics it is known that permutation between identical particles does not change the Hamiltonian. Assuming that the quantum system consists of a very high number of particles such that ...
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### two qubits measurment [closed]

Let $$\text{qubit} = \sqrt{\frac{1}{6}} (i∣00\rangle + ∣10\rangle − 2 ∣11\rangle) \, .$$ I need to calculate the probability for each state while measuring both qubits in the standard basis. I did : ...
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### Difference between scattering amplitude and scattering lenght

I'm studying neutron scattering theory and I noticed that one usually writes the scattered wave as a spherical wave: $$\psi \sim \frac{-b} {r}e^{ikr}$$ where $b$ is known as scattering lenght. From ...
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### Reason for Uncertainty principle

$$\Delta x \Delta p_x \geq \frac{\hbar}{2}$$ I understand what does Heisenberg's uncertainty principle states i.e. it's definition and it has been proven experimentally. But, can anyone please ...
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### Time is what keeps everything from appearing at once [closed]

This is a question about time. In this talk http://ed.ted.com/lessons/einstein-s-brilliant-mistake-entangled-states-chad-orzel Chad Orzel makes the point that if the same quantum experiment is ...
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### Using the double slit experiment to prove or disprove the de Broglie-Bohm pilot wave theory

Probably a dumb question... If you have a double slit experiment with a second experiment (single or double slit) at 90 degrees intersecting the path of the first experiment, would the interference ...
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### Why does circularly polarized light break time-reversal symmetry?

I've encountered some interesting paper on 2D materials where authors use circularly polarized light to break time-reversal symmetry to split energy levels. Here you can find the paper: ...
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### Probability and double slit

if a beam of identical particles at random distances from each other (or exactly 1/2 lambda between each other) travelling with the same v towards a double sllit do not interfere with each others wave ...
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### How should we deal with diagrams which do not conserve particle number in a non-relativistic field theory?

In the last 10 years there has been more and more crossover of techniques from high energy physics being used in AMO and condensed matter scenarios, in particular diagrammatic techniques and related ...
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### Is there a mathematical relationship between Legendre conjugates and Fourier conjugates?

In quantum mechanics, there is an uncertainty principle between conjugate variables, giving rise to complementary descriptions of a quantum system. But the variables are conjugates in two different ...
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### Why does temperature have no uncertainity?

Lets say I have an object A, with temperature $T$ and Hamiltonian $H_{A}$. Now take a thermometer B, with Hamiltonian $H_{B}$. Now when I put the thermometer in contact with A and do a measurement ...
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### Does calculus work on the quantum scale [duplicate]

I have read somewhere that Leibniz championed the idea that the world is continuous as this was needed for his (or maybe Newtons) new invention (or discovery?) of calculus. But if I am not mistaken a ...
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### Is there experimental verification of the s, p, d, f orbital shapes?

Have there been any experiments performed (or proposed) to prove that the shapes of the s,p,d,f orbitals correspond to our spatial reality as opposed to just being a figment of the mathematics that ...
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### Can I apply $E=hf$ to a particle having mass?

I am reading concepts of modern physics (by Arthur Beiser) where he calculates the de Broglie wave velocity. For that he uses the relation $v = fλ$ where $v$, $f$, and $λ$ are velocity (de Broglie ...
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### Does the randomness of QM do much in everyday life? How much? [closed]

My apologies if in its current state this question isn't squarely suited here; I've worked it until it seemed reasonably articulate. Feel free to move it if it'd be better received elsewhere. ...
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### Are photons just electric waves in an electron's frame of reference?

They say that electrons emit photons when they jump to a lower orbit. But the way electrons should see it, there's no any emission, really. There's just rapid change in electric field due to a rapid ...
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### Both Eigenvalues and Operators are “Observables”? [duplicate]

I am having a bit of difficulty wading through the what seems to be multiple usages for Observables in Quantum Mechanics. " Mathematically observables are postulated to be Hermitian operators.. " ...
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### Faster-Than-Light Communication using Entangled Photons

Based on my understanding of the “Double-Slit Quantum Eraser Experiment”, documented here: http://grad.physics.sunysb.edu/~amarch/, it seems that Faster-Than-Light communication is possible. Of ...
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### Why photons reflect off glass?

Why photon reflects and refracts through glass? Some photons pass through glass and some reflects.I know this is due to energy levels of electrons of glass, an incoming photon is unable to excite the ...
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### Why isn't the time-derivative considered an operator in quantum mechanics? [duplicate]

Based on my understanding when doing quantum mechanics we deal with a small set of mathematical objects: namely scalars, kets, bras, and operators. But then in the Schrodinger equation we have this ...
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### Is there a reason why a relativistic quantum theory of a single fermion exists, but of a single scalar not?

When we try to construct the relativistic generalization of non-relativistic time dependent Schroedinger equation, there are at least two possible completions - Klein-Gordon equation and Dirac ...
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### What does it mean to observe? [duplicate]

This is a layman's question. The only thing I know about quantum physics is from casual reading and documentaries. I can imagine electrons being probabilistic waves. Their position is an infinite ...
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### Photon Absorption vs. Photoelectric Effect

USually, photons are absorbed by substances only if their energies coincide with the orbital transitions of that particle. However, in the photoelectric effect, it seems that you can take the energy ...
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### Evolution of a 'state' in the Heisenberg picture

Suppose that we have a Hamiltonian, $\hat{H}$, and an operator $\hat{A}$ which satisfies the Heisenberg equation$^{[a]}$ $$i \frac{d}{dt} \hat{A} = [\hat{A},\hat{H}].$$ Can we create a 'state' by ...
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### Schrodinger equation contains two pieces of information?

I've read that Schrödinger equation contains two pieces of information: about amplitudes and about phases. I know continuity eqn. for probability which is nice expression of former. I wanted to ...
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### Mean squared velocity of a particle moving in a logarithmic potential [closed]

A particle of mass $m$ moves in the logarithmic potential $V(r)= C\ln(ar)$. $C$ and $a$ are constants. What is the mean squared velocity of the particle? Do I have to solve this in ...
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### Find the expression of $j_+$ and $j_-$operators [closed]

I have just started to do exercises about quantum mechanics and I have some difficulties. I have a particle with spin $j=1$ and the Hamiltonian is $H=\gamma(j_xj_y+j_y j_x)$ (where $\gamma$ is a ...
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### Is the connection of two spin-zero projectors with a singlet again a projector?

Let me pose a question that popped up in my research. Consider a square lattice, where each of the lattice sites is associated to 4 spin 1/2 particles. Now let the single-site projector $P_{(1,1)}$ be ...
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### What is the relationship between quantum physics and chaos theory?

I am not a physicist, I am looking for a non-technical explanation. Articles such as this one seem to hint at the fact that "macro reality" regulated by classical mechanics is somehow a pattern ...
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### Width of a 1 dimensional box with same ground state energy as hydrogen atom [closed]

I am trying to find the width $L$ of a one-dimensional box for which the ground state energy of an electron in the box equals the absolute value of the ground state of a hydrogen atom. No ...