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 quantum-field-...

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3answers
68 views

What is the Meaning of the Superposition Principle

I am a bit confused as to what the superposition principle actually means. Does it merely mean that you can express any given state as the linear combination of two vectors? If so, isn't that kind of ...
0
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0answers
28 views

Measured Polarization for a Single Photon

I understand that for a given beam of light, it can exist in any number of polarizations. However, I have been told that given a single photon, it can only exist as horizontally or vertically ...
1
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3answers
76 views

Transforming Qubits Into Bits

From what I understand, a qubit exists in a superposition of states and once it has been measured, it must fall into one of the two possible states. Now, I have been told that once a qubit is measured,...
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1answer
34 views

Representation of spin operators in a two electrons system

I've studied that the spin space of an electron is a two-dimensions Hilbert space. A possible representation of this space can be constructed defining: $$\chi_+ = \begin{pmatrix}1 \\ 0 \end{pmatrix} \...
1
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0answers
40 views

Atom-photon interaction

When we describe interaction of atom with EM field, we consider the interaction term in Hamiltonian as follows $$ W(t) = -\frac{e}{2\mu c} (\hat{A} \hat{p} + \hat{p} \hat{A}) + \frac{e^2}{2\mu c^2} \...
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2answers
43 views

Calculating the product state capacity of the quantum depolarizing channel

This is homework, so just let me know if I'm on the right track or where I went wrong, please. So, we are asked to compute the product state capacity $$C_1(T) = \max_{\{p_j,\,\vert \psi_j\rangle\}}\...
2
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2answers
54 views

Quantum Logic Gates

In classical computation, a bit can have the value of either 1 or 0 and one can apply a logic gate to this bit. As far as I understand, in classical computation, no matter what gate is used, the value ...
2
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2answers
48 views

Born's interpretation for momentum operator

Hi I have a basic QM question: Given a state vector $|\psi(t) \rangle$, at some time $t$, we can project this onto the position basis, $\langle \vec{r}| \psi(t) \rangle = \psi(\vec{r},t)$. Then from ...
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1answer
18 views

Inverting squeezing and displacement operators

This question is about inverting the product of squeezing operator and a displacement operator in the following way: I have $D(\alpha)S(\xi)$ and I'd like to turn it into $S(\xi')D(\alpha')$. Where $...
1
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0answers
16 views

Elimination of extra phases in adiabatic formula

Can someone explain to me how the additional phase factor $\gamma_n(t)$ in the adiabatic formula can be eliminated (not just mentioning gauge transformation, but showing why $\gamma_{n}(t)$ can but $\...
1
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1answer
56 views

$\frac{1}{\sqrt{2}}(1 + i)|0\rangle$ on the Bloch sphere

By definition, a quantum state can be expressed as $$|\psi\rangle = a |0\rangle+b |1\rangle.$$ Here, $a, b\in\mathbb{C}$ and $|a|^2 + |b|^2 = 1$. Now, I would like to take $a = \frac{1}{\sqrt{2}}(1 +...
14
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4answers
1k views

Are there more entangled states or non-entangled ones?

I'm trying to understand entanglement in terms of scarcity and abundance. Given an arbitrary vector $v$ representing a pure quantum state of, say, dimension 4, i.e. $v \in \mathcal{H}^{\otimes 4}$, ...
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0answers
26 views

Imaginary part in calculation [closed]

I want to simulate (I use mathematica) a matrix that has imaginary number. Given the matrix, $$A = \begin{pmatrix} e^{2I+3}Sin{(2\Pi t)} & e^{I (\Pi)}Cos{(2\Pi t)} \\ Cos{(2\Pi t)} & -e^{...
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1answer
31 views

What does it mean to say exchange “force” is not really a force?

If I understand it a bit the standard answer for this is: the pushing/holding apart of fermions and the pulling/holding together of bosons is just a result of symmetrization requirement (Griffths' ...
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1answer
43 views

Quantization of energy in semi-infinite well

Consider an electron with total energy $E>V_2$ in a potential with $$V(x)= \begin{cases} \infty & x< 0 \\ V_1 & 0< x< L \\ V_2 & x>L \end{cases} $$ ...
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0answers
22 views

Time-dependent perturbation theory [closed]

In time dependent perturbation theory there is a group of states having energies nearly equal to initial state.what will be time dependence of probability of finding system in any of such state? Plz ...
-1
votes
1answer
24 views

What magnetic quantum no. Actually represent? [closed]

If azimuthal quantum no. i.e l=3 then magnetic quantum no be -3,-2,-1,0,1,2,3. What does it represent?
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1answer
70 views

What is limitation of Pauli exclusion principle? [closed]

According to Pauli "no two electrons in an atom can have the same values for all the four quantum numbers" but if we take any atom with $n=2$ and its 2nd subshell i.e 2p(that contain 3 orbitals) ...
1
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1answer
62 views

Schrödinger's Equation with multi-part potential

I have this potential $$V(x) = \left\{ \begin{array}{ll} \infty & \mbox{if } x < -a \\ \frac{V_o}{a}x & \mbox{if } -a \leq x \leq a \\ V_o & \mbox{if } x \geq a \ \end{...
4
votes
5answers
108 views

Is it a coincidence that quantum harmonic oscillators and photons have energy quantised as $E=hf$?

I have studied the quantum harmonic oscillator and solved the Schrodinger equation to find the eigen-energies given by $$ E_n = \left(n+\frac{1}{2}\right)\hbar \omega. $$ Which means the energy ...
4
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0answers
49 views

Which charge to use in the Dirac quantization condition?

I have a follow-up question to Dirac magnetic monopoles and quark fractional electric charge quantization, regarding whether the "unit of electric charge" in the Dirac quantization condition should be ...
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0answers
29 views

Entangled particles information transfer

No-communication theorem forbids the transfer of information using entangled particles. But does it implies that information does not pass between the entangled particles themselves? Is there a ...
5
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2answers
112 views

Wouldn't the thermodynamic cost of creating alternate universes make the Many Worlds interpretation implausible?

I was thinking about the many interpretations of quantum physics, and one thing that never made sense to me was the many world's interpretation. Basically at any given moment for which something ...
2
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1answer
82 views

GR says that time and space are aspects of the same thing, yet there is no observable for time in QM

I understand that the topic of a time operator in quantum mechanics has come up more than a few times so forgive me if this is a repeat question but I couldn't find anything specific to my question. ...
2
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2answers
149 views

Eigenvalues of Hermitian operators are real and the dependence/independence of boundary conditions

Without reproducing proofs: Eigenvalues of a Hermitian operator are real (proof does not rely on the boundary conditions). The momentum operator is Hermitian (proof does not rely on the boundary ...
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0answers
49 views

Mathematical method of Physics [closed]

Please any one can tell me how to get lecture of mathematical method of physics complete course online download complete lecture series. Which professor best for this subject please guide me how to ...
0
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0answers
8 views

Is the q-factor equal to infinite for a quantum vibrator at its ground state?

Say, a molecule is vibrating at its ground state forever, where there is no energy loss? Saw a related question here.
3
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4answers
177 views

How would my life be different without quantum entanglement? [closed]

What would happen if for some reason quantum entanglement were suddenly turned off? By "turned off", let's say that every entangled state is immediately replaced with a separable (but still ...
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votes
1answer
50 views

Photon absorbsion through 'quantum foam' [closed]

Over the cosmological distances that the photons travel from distant sources, will 'quantum foam' have an effect on them before they reach us? *Re NASA Science News Dec 31st 2015. The effect on ...
0
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3answers
58 views

Relation between coherent states [closed]

Suppose $\left|\alpha\right\rangle$ and $\left|-\alpha\right\rangle$ be two coherent states. Is there any relation between them or are they completely different coherent states?
0
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0answers
34 views

Expectation value of radius of hydrogen atom [closed]

As an excercise, I have to do the following: The hamiltonian of the hydrogen atom is given. Try to find the radial part $f(r)$ of the wavefunctions by assuming it to be a power series and show that ...
0
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1answer
52 views

What is the capacity of an electron to absorb energy? [closed]

When an electron get excited we find that electron absorbs energy and jumps to the required shell. This means that electron can absorb an infinite amount of energy and can get excited to infinity ...
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0answers
15 views

expectaction value of coordinates on bloch sphere under special time evolution

We consider an example in which the time evolution of a system is given by the following density matrix $\rho(t)=\frac{1}{a_0+c_0}\begin{pmatrix} \eta^2(t)a_0 & \eta(t) b_0\\ \eta(t)b_0^{*} &...
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votes
0answers
18 views

How to get this one qubit evolution operator in Bloch sphere? [closed]

I can't find have to get matrix equation (13) in this paper: http://arxiv.org/abs/1401.2495 if any body knows how he has derived this matrix please share it in details.
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votes
2answers
55 views

Possiblity for particle to be carried by a wave such as a photon or electromagnetic wave/waves in general for means of transportation/travel? [closed]

I am wondering whether it is possible for a photon/EM wave to carry a very small particle like an elementary particle or smaller on it like a highway carries a car traveling on the highway or an ocean ...
2
votes
0answers
106 views

Linear combination of eigenstates problem [closed]

Let's say that we have a system such that $$\Psi(x,0)=\frac{\sqrt3}{2}\phi_1(x)+\frac12\phi_2(x)$$ where both $\phi(x)$ are eigenfunctions of the Hamiltonian operator. I want to find $\Psi (x,t)$ ...
5
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0answers
63 views

What happens to a radar signal when it meets with a superconductor? [duplicate]

A radar system has a transmitter that emits radio waves called a radar signal, consisting of electromagnetic radiation. What happens when it meets with a strong superconductor, considering the fact ...
0
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0answers
20 views

Heuristic derivation of Schrodinger equation [duplicate]

Is there a heuristic derivation of Schrodinger equation beginning with concepts from classical physics? When I say classical I mean something at the level of an engineer.
4
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0answers
62 views

Landau quantization: degeneracy of first level

In some books the degeneracy of one Landau level in a two-dimensional gas of free electrons is calculated in the following way: Note: The electron spin is not considered. Number of states of a free ...
-4
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0answers
26 views

Need an answer for a simple question, how does an electron propel itself? [closed]

The thing is that even with all these math tricks going on an crazy theories poping up solving mysteries of the universe, I don't seem to find the answer why electrons move, the question might be a ...
3
votes
2answers
105 views

Does a wave function describe the motion of electrons or atoms?

I took the course of quantum mechanics a while ago. I do not quite remember all the detail on how to derive the wave function for hydrogen but I still remember the general picture. I think the text ...
4
votes
2answers
122 views

By what logic does one come to support a certain interpretation of quantum mechanics?

I have been on Wikipedia reading up on the various interpretations of quantum mechanics. I am entering my final semester as an undergraduate and have taken a QM course, so I am familiar with the basic ...
0
votes
2answers
70 views

Bogoliubov transformation is not unitary transformation, correct?

To diagonalize quadratic term in the antiferromagnet Heisenberg model, we may introduce the Bogoliubov transformation:$a_k=u_k\alpha_k+v_k\beta_k^\dagger$, $b_k^\dagger=v_k\alpha_k+u_k\beta_k^\...
3
votes
1answer
41 views

Distributive property of the time-ordering symbol

Most derivations of the LSZ reduction formula, e.g. Srednicki (equations 5.13, 5.14, 5.15), Schwartz (equations 6.17, 6.18, 6.19), Wikipedia use a property of the time-ordering symbol that looks like ...
0
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0answers
26 views

How to define quantum chaos?

I was told that quantum chaos is just a system whose Hamiltonian's classical version shows chaotic behavior. However, I just wondering what happens when one eigenstate of this Hamiltonian evolves? ...
1
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0answers
24 views

Demonstration that $H\star f(x,p)$ is equal to $Ef(x,p)$ for the time-independent Wigner function [closed]

I am attempting to understand why $H(x,p)\star f(x,p)=Ef(x,p)$, where $H(x,p)$ is the Hamiltonian, $\star=e^{\frac{i\hbar}{2}\left(\overleftarrow{\partial_x}\overrightarrow{\partial_p}-\overleftarrow{\...
0
votes
1answer
185 views

Experiment that demonstrates the wave-particle duality of electrons

EDIT : You're about to read the first iteration of my question which is flawed. Please go to the end to see an illustration of what I meant to say. The phenomenon I was talking about is called ...
2
votes
2answers
74 views

What happens to Pauli's argument (that says that there is no time operator) when applied to $X$ operator for some simple systems?

An argument by Pauli is usually referred to in the literature when it is stated that there cannot be a time operator in quantum mechanics. This argument can be found as a footnote to P63 of W. Pauli, ...
3
votes
1answer
42 views

Using Dyson formula in Schrodinger picture

From Time-ordering and Dyson series and what I learnt, Dyson formula is used in the situation of interaction picture: $$i\frac{dU_I}{dt} = H_{I}(t)U_I$$ where $H_I(t)$ is interaction Hamiltonian ...