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 use of a Universal-NOT gate?

The universal-NOT gate in quantum computing is an operation which maps every point on the Bloch sphere to its antipodal point (see Buzek et al, Phys. Rev. A 60, R2626–R2629). In general, a single ...
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0answers
9 views

Why do we use a vector space for gluons?

One gluon state cannot be added to another since qcd heavily violates superposition. Why do we still use vector spaces to describe them?
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11 views

why is it so successful to start of with a pair potential before quantizing

As soon as we use the quantum theory all orders of correlation functions start to appear if we move from one scale to another. Why was it so successful to start of with a simple pair potential in the ...
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0answers
19 views

What is the difference and/or similarity between multiple universes in inflation and in quantumphysics?

Some theories propose that there are more universes. In one of them it is said that there are parallel universes, due to inflations after the big bang that created them. But in the two-slit ...
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5 views

How to calculate counting rate of two detectors in quantum eraser experiment?

How to calculate the counting rate between two detectors? In their paper this one , they use Glauber Formula. But I don't know this formula and can't find this formula online.
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2answers
159 views
+50

Condition for adiabatic approximation, derivation?

In quantum mechanics it is said that an adiabatic approximation is valid when $$T\gg \frac{\hbar}{\Delta E},$$ where $T$ is the time scale of variation of the Hamiltonian and $\Delta E$ is the typical ...
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0answers
12 views

Transforming to a rotating frame in the x-basis

This is given as the equation obtained after transforming to the rotating frame in the x-basis. I know that the general form of the rotation operator for the spin system is given by: $$ D(\hat ...
1
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0answers
14 views

Deriving Rabi oscillations using the Heisenberg picture of QM

The semiclassical treatment of an simple two level atom in a resonant electromagnetic field is usually done in the Schrodinger/Interaction picture of QM, by assuming that the wavefunction of the atom ...
5
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1answer
66 views

Heisenberg's uncertainty principle derivation in a ring [duplicate]

The standard derivation But now suppose the space is a ring of length $L$, it seems the derivation could work out exactly the same and we get $$\Delta p \Delta x \geq \hbar/2.$$ But since $\Delta x$ ...
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0answers
41 views

Guide for a program that calculate operator equations

Is there any program that calculate operators equations just with having operator commutator relations? For example if $A$ and $B$ are two operators and $$[A,B] = m$$ that $m$ is a number this ...
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1answer
45 views

Eigenvalues, Eigenvectors [on hold]

what is the physical meaning of eigenvalues and eigenvectors? Is there any relation between them and the energy states if there is any reference please provide it
0
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0answers
27 views

Are symmetries of a degenerate ground-state manifold always broken?

If a Hamiltonian has a global symmetry and a degenerate ground state, then in the thermodynamic limit, the ground states $| \psi \rangle$ that are eigenstates of the symmetry operator typically become ...
2
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2answers
69 views

Why the incessant confusion between diffraction and interference? [on hold]

Feynman said, "No one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage, and there is no specific, important physical ...
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2answers
58 views

Is the momentum of a particle both uncertain and, independently, also random?

Is momentum of a particle "random" because it is uncertain, or is it uncertain in addition to being random? Is the uncertainty principle and quantum randomness different names the same physical ...
15
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1answer
1k views

Is the existence of a sole particle in an hypothetical infinite empty space explicitly forbidden by QM?

Suppose the universe is completely empty with one sole particle trapped in it. To simplify, I will only be looking at the one dimensional case. However, all arguments are applicable for three ...
7
votes
2answers
1k views

Why are eigenfunctions which correspond to discrete/continuous eigenvalue spectra guaranteed to be normalizable/non-normalizable?

These facts are taken for granted in a QM text I read. The purportedly guaranteed non-normalizability of eigenfunctions which correspond to a continuous eigenvalue spectrum is only partly justified by ...
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0answers
21 views

Compton Effect Demonstration using MATLAB

I have recently been taught about Compton Effect and I learnt about the Intensity variation with the wavelength . Now I also know a little bit about MATLAB so I was wondering if I could create plot ...
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0answers
15 views

Evaluating a function with divergent probability outcomes [on hold]

I apologize for any vagueness here but i am trying to learn a general solution for a problem I am working on for fun. Getting the final answer is therefore not my goal but getting unstuck is. Alsi of ...
1
vote
2answers
341 views

Is this definition of orthohelium and parahelium incorrect?

"One electron is presumed to be in the ground state, the 1s state. An electron in an upper state can have spin antiparallel to the ground state electron ($S=0$, singlet state, parahelium) or ...
0
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2answers
14 views

Photoelectric effect and work function

In a photoelectric effect we remove electrons from a metal using high energy photons, the work function is the minimal energy required for this effect. My question is why doesnt the work fucntion ...
0
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1answer
37 views

quantum clone of orthogonal quantum states

I am a little bit confused about the no-cloning theorem for two orthogonal quantum states. In Nielson&Chuang page 24-25, it states that an unknown state $|\phi\rangle$ cannot be copied since ...
0
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1answer
11 views

Does frequency of mechanical vibration of material affect its blackbody radiation spectrum

Can we see the difference in emissivity for instance between the same object vibrating in two different frequencies ?
4
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1answer
142 views

Separating the hamiltonian for a superlattice — is it this easy?

I've been banging my head against a wall trying to figure out what I'm sure is a very simple problem. I want to solve the Kronig Penney model for a superlattice, which is just a normal periodic 1D ...
9
votes
6answers
2k views

Light's inverse square law: Does it require a minimum distance from the source?

Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
4
votes
1answer
228 views

Do the position-momentum uncertainty and time-energy uncertainty really exist in QFT?

It is well known from the Quantum Mechanics(QM) that for a particle, there is a position-momentum uncertainty relation: $$\Delta x\cdot \Delta p\geq \frac{1}{2}\hbar,$$ which bascically can be derived ...
2
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2answers
559 views

Quantum entanglement definition [on hold]

How can we define Quantum entanglement (in QFT)? What are the known mathematical settings and special physical (or logical) conditions of QE applied to Quantum computing?
5
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1answer
55 views

Particle on $S^1$ and $U(1)$-principal bundle

I have a question arisen from a simple QM problem: let consider a boson on $S^1$ minimally coupled with a constant gauge field $A$. Taking the stationary Schrödinger (S) or Klein-Gordon (KG) equation ...
0
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1answer
477 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
2
votes
1answer
47 views

Why is the energy operator special?

Only the energy operator controls the time dependence of a quantum system, but not the others, why is that?
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0answers
19 views

Eigen energy for charged particle in a magnetic field [on hold]

How can I determine the eigen energy for charged particle in a magnetic field?
2
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5answers
1k views

If wavefunction is just a probability function, how does an electron interfere with itself

I have read lots of quantum mechanics books. The chapters that are talking about De Broglie, lots of them name the chapter as "Wave-particle duality" and says: "Electrons are both waves and ...
0
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0answers
31 views

The $T\rightarrow \infty $ limit in quantum field theory

I am new to quantum field theory. Prior to this, I have been using quantum mechanics for a few years. I am reading the book by A. Zee, ''quantum field theory in a nutshell'', 2nd Ed.. On page 18, ...
0
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2answers
1k views

Why 2s state is lower in energy that 2p state in atoms?

The s orbital have higher probability to be closer to the core and feels larger attraction than the p orbital and on average is further away and in addition p has repulsive potentilal l(l+1)h^2/2mr^2. ...
0
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0answers
20 views

Higher $L$ lower energy?

For multi-electron atoms, what is the physical reason behind the fact that a higher total orbital angular momentum, $L$ gives a smaller total energy, $E$?
8
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2answers
388 views

Why was the Stark effect discovered much later than the Zeeman effect?

This is strange. The Zeeman effect involves the magnetic field. The Stark effect involves the electric field. In the course of classical electrodynamics, we get the impression that for many physical ...
1
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1answer
40 views

Writing operator evolution as a quantum dynamical map

In the Heisenberg picture we have the evolution of the operator in time given by: $$A(t)=U^+A(0)U$$ I was looking into the theory of open quantum systems where we introduce the concept of a quantum ...
0
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0answers
10 views

Does the dispertion medium affects Quantum Dots fluorescence efficiency?

I would like to use CdTe Quantum Dots to make a fluorescent coating on a transparent support. There's a link to the material here: ...
0
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0answers
20 views

Why is the energy shift due to a 'sagging' potential negative and independent of box size?

Consider a box of width $L$ and the composed of the following potential $$V(x)=V_0x(x-L), x\in[0,L]$$ and $V(x)=\infty$ elsewhere. Using perturbation theory - with a square box as the similar ...
0
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1answer
64 views

What gives a particle its identity?

A lot of very smart people have stitched together the standard model, and I accept it. I don't understand it, but I assume there should be a mechanism of sorts that gives a particle some fundamental ...
3
votes
1answer
52 views

Relativistic correction to Hydrogen atom - Perturbation theory

Given the relativistic correction $$ H_1' = - \frac{p^4}{8m^3 c^2} $$ to the Hamiltonian (i.e. a perturbation), what does it mean when $[H_1', \mathbf{L}] = 0$? The book I'm reading says this implies ...
0
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1answer
53 views

Can we have $E=0$ in Schrödinger's Equation?

I've read a little bit about zero-energy states, but I just don't get it. I'm just starting to study quantum mechanics and, at least for all the potentials I've seen until now (the most popular ones, ...
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0answers
22 views

Is this state an example of a separable state or an example of an entangled state? [on hold]

The Hong–Ou–Mandel effect also underlies the basic entangling mechanism in linear optical quantum computing, and the two-photon quantum state $\lvert 0,2 \rangle + \lvert 2,0 \rangle$ that leads to ...
0
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0answers
32 views

Why probability of detection by performing unambiguous quantum measurement is less than random guess in mesoscopic quantum regime?

In mesoscopic quantum regime (mean photon number 10000) and non-orthogonal coherent state(number of non-orthogonal coherent state 2000), why probability of detection by performing quantum unambiguous ...
0
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0answers
31 views

How to evaluate $[L^2,x_{j}]$ [on hold]

I want to evaluate the following commutator: $[\vec L²,x_{j}]$ where $\vec L= \vec x\times \vec p$, $(L_{i}=\epsilon_{ijk}x_{j}p_{k})$ and $\vec L²=L_{i}L_{i}$, here is my work so far: ...
0
votes
1answer
16 views

Mach-Zehnder probabilities

Where can I find the computations of probabilities for Mach-Zehnder experiments, say at the undergraduate level? For example I'm thinking of the type of experiments described at the beginning of David ...
7
votes
2answers
462 views

How can we know the state of a quantum system?

One of the postulates of QM states that given a system in a state $|\psi\rangle$ and given an observable $A$ whose eigenstates are $|\phi_i\rangle$, then the state of the system can be expressed as a ...
0
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1answer
45 views

Interpretations and approximations of uncertainty principle

Just a short question regarding an interpretation of the Heisenberg uncertainty principle $$\sigma_x \sigma_p \geq \frac{\hbar}{2}$$. Question: The uncertainty principle is sometimes written as ...
0
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0answers
29 views

Interpretations of uncertanity principle used for approximation

Just a short question regarding an interpretation of the Heisenberg uncertainty principle $\sigma_x \sigma_p \geq \frac{\hbar}{2}$. Question: Why is it also sometimes that $\Delta x$ and $\Delta ...
4
votes
5answers
2k views

Does the observer or the camera collapse the wave function in the double slit experiment?

Ok so if we setup a camera before the slit we will find a single photon and will follow through accordingly, likewise by having a camera setup after the slit, we can retroactivly collapse the wave ...