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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2answers
54 views

Confusion of Schrödinger equation and complex conjugates

I have a similar question that was asked in the following link: (Schrödinger's Equation and its complex conjugate). But I find both the question and answers not specific enough. So let me ...
0
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1answer
88 views

Can we objectively determine whether there is room for miracles in physics? [closed]

I'm not a religious person, but I try to keep an open mind. Most people (80% of the world's population are religious according to a quick Google search) in the world believe in miracles, but that ...
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0answers
36 views

From where should I start studying physics? [closed]

I am Bs Econ Math student and about to finish my degree. I am more interested in mathematics and with the time i have become interested in physics however i have never studied physics. Can anyone ...
3
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1answer
61 views

Stern-Gerlach experiment with Bosons

I'm new to this forum and I'm studying semiconductor physics at the moment. I just wanted to ask a thing about the concept of spin: when it was studied for the first time, in the Stern-Gerlach ...
0
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1answer
19 views

Relation between probability density and transmission probability of a wavefunction?

Problems I did on current densities in elementary quantum mecanics course gives the answer contains transmission coeffecients, I am wondering is there any relation among them.
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1answer
53 views

Measurement on two Qubits

Assuming I have two Qubits, i.e. a four-dim. Hilbert space. In the following, I choose the basis {|11>,|10>,|01>,|00>}. I want to have a look on the non-diagonal part <11|$\rho$|00>. How can I ...
0
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0answers
75 views

Eigenfunctions of translation operator

I had an HW assignment in which we were asked to find the eigenfunctions of the translation operator which is defined as follows: $$\hat{D}(a)=e^{-(i/\hbar)a\hat{P}}$$ where $\hat{P}$ is the momentum ...
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1answer
39 views

Conservation of energy and realm of possibility

The law of conservation of energy states that energy cannot be created or destroyed. Based on this principle, you can safely conclude that any effect resulting from a cause must somehow keep all ...
2
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1answer
42 views

Wavefunction Collapse

I believe my Lecturer and the textbook have contradicted one another. My lecturer gave the example that if the spatial part of the wavefunction of a particle is given by $\psi(x) = c_1\psi_1(x) + ...
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1answer
65 views

What does a zero eigenvalue mean to its eigenstate?

Assume that initial wave function had the form of $\psi(x)= u_1(x) + u_2(x)$ where $u_1$ and $u_2$ are eigenfunctions of $\psi(x)$ to an observable operator $S$. The eigenvalues of $u_1$ and $u_2$ are ...
3
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0answers
87 views

Question about the Dirac equation

Energy and momentum of a particle can be expressed by equation $$E^2=p_1^2c^2+p_2^2c^2+p_3^2c^2+m^2c^4\hspace{40pt}(1)$$ Equation (1) can be divided into $E$ on both sides. We obtain ...
1
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1answer
31 views

Does nuclear fusion of light nuclei occur in fire or boiling water?

At the temperature range of ordinary fire or maybe even ordinary boiling water, is the Coulomb potential between light atomic nuclei occasionally overcome to give way to fusion? Basically, how are ...
5
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1answer
65 views

Butterfly and quantum uncertainty

I'm sorry for the long question. In Brian Greene's book 'The Hidden Reality' he gives a nice illustration of the uncertainty principle. Imagine a butterfly flying around in a room. We would like to ...
3
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1answer
25 views

Spin operator matrix representations in Sx basis

1. The problem statement, all variables and given/known data I want to find the matrix representation of the $\hat{S}_x,\hat{S}_y,\hat{S}_z$ and $\hat{S}^2$ operators in the $S_x$ basis (is it more ...
5
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2answers
111 views

Bell's theorem and fluid-mechanical experiments using droplets: are local hidden-variable theories possible after all?

Recent fluid-mechanical experiments by the groups of Couder in Paris and Bush at MIT, mimic a surprisingly wide range of quantum effects. The essential ingredient of these fluid-mechanical systems is ...
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0answers
63 views

Can't many-worlds interpretation explain wavefunction collapse?

According to the many-worlds interpretation when universe splits in interaction, the observer in each universe measures corresponding pure state thus seeing collapse. Well, it may be an ...
3
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1answer
56 views

Physiological Significance of Superposition

To what extent is the concept of superposition appropriate to physiology? In other words, can organisms "actually" exist in a state of superposition?
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0answers
19 views

I need this to do in an exam but i want also help for the lcao or tight binding method! [closed]

Consider an ideal flat infinite sheet of Graphene. Assume that only nearest neighbour interactions are important and that one $p_z$ orbital per site is sufficient to describe the electronic ...
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1answer
46 views

Sequence of topics for studying quantum theory (Research strategy) [duplicate]

I am trying to learn about the higher level basics of physics. I want to cover up all that is included in particle physics/quantum physics. Now being in high school, I only know partially about ...
1
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1answer
17 views

Difference between Amplitude and Intensity Interferometer?

A lot of books explain the first order and second order coherence correlations for light. They explain the difference between these using interferometers (Michelson and Hanbury-Brown and Twiss (HBT) ...
6
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2answers
64 views

SHO in QM and Klein Gordon field in 1+0D QFT

The SHO in QM with mass $m=1$ has action $$ S[x] = \int dt \frac{1}{2} \dot x^2 + \frac{1}{2}\omega^2 x^2 $$ by integration by parts we see this is the same as 1 dim Klein Gordon QFT action with ...
1
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1answer
38 views

1D Scattering Phase Shift (Finite Well) - Unphysical?

I am calculating the phase shift from a 1-dimensional potential well. This seems extremely simple, but I am just getting so confused by it. Let there be a potential well of depth $V_0$ and spatial ...
-1
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2answers
74 views

If I repeated a quantum measurement, would it be the same? [closed]

I was thinking about the probabilistic nature of quantum mechanics and that if I measured the position of an electron twice in succession, the outcomes would depend on a probability. However, what if ...
1
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1answer
32 views

Isn't there any analog between angular momenta in Classical/Quantum Mechanics, especially for the ground state?

By the ground state, I mean something like the state of the hydrogen atom with the lowest its total energy, where the quantum number $l$ is 0, which means we can't get any orbital angular momentum at ...
3
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0answers
40 views

Why is a particles magnetic moment proportional to its spin?

the magnetic moment of a particles is given by, m=kS, where k is a constant the gyromagnetic ratio but where does this equation come from, is it just from experiments?
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1answer
54 views

Physical reason behind $\langle +,x | \hat S_z |+,x \rangle=0$? [closed]

For a spin half particle we have the following relation: $$\langle +,x | \hat S_z |+,x \rangle=0$$ I have seen this to derive the Pauli matrices and therefore am wondering without knowing anything ...
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0answers
40 views

Galilean transformation of Schrodinger equation and momentum operator

Let $$ \left.\begin{aligned} t'&=t\\x'&=x-vt \end{aligned}\right\} \quad \Longrightarrow\quad \dot{x}'=\dot{x}-v $$ and therefore $p'=p-mv$. If $p'=-i\hbar\nabla' $, then ...
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0answers
29 views

Is it possible to create a double slit experiment that can predict when photons have 'likely' passed through the slits?

This question asked:Is it possible to determine the slit a photon went through in the double slit experiment by measuring its flight time? My question is similar, but doesn't require such detailed ...
1
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1answer
27 views

Taking Measurements of Quantities in QM

I have a quick question relating to Annihilation and Creation operators, and in taking observables in general. Let's say, for instance, that I prepare a particle so that I consider the projection of ...
3
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2answers
95 views
+50

Condition for adibatic approximation, derivation?

In quantum mechanics it is said that an adibatic approximation is valid when: $$T\gt \gt \frac{\hbar}{\Delta E}$$ where $T$ is the time scale of variation of the Hamiltonian and $\Delta E$ is the ...
1
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2answers
36 views

Evaluating double-slit experiment for wave-particle duality

Is it possible that the wave-like behavior of particles in double slit experiments is just an outcome of particle distribution? Can we regard or treat a normal or Gaussian distribution as wave-like? ...
1
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1answer
74 views

How does the uncertainty principle relate to quantum fluctuations?

I found a webpage that just kind of mentions the uncertainty principle lightly but doesn't really go into detail as to why we need it in the first place when considering quantum fluctuations and ...
1
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1answer
43 views

Representation of Symmetry group

Suppose the SE $\boldsymbol{H}\psi=E\psi$ describes a closed system and $G$ is a symmetry group of the system. Then any transformation in $G$ leaves the form of the SE invariant. It seems plausible to ...
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0answers
19 views

Is absorption probality modulated by interferance instanteneous or retarded effect?

Let say the absorption probability at some atom 1 location is modulated by photo ionized electron wave (ionized from 1) that scatters by neighboring atom 2 and returns to the 1. (Around the absorption ...
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0answers
25 views

Reversibility principle for classical mechanic

I'm studying this colloquium about quantum fluctuation relations for nonlinear thermodynamic, but I'm having a problem. Reading about the principle of micro-reversibility of the dynamic of a system i ...
0
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2answers
72 views

Trace of an observable [closed]

If $X$ and $Y$ are two observables and $\rho$ is a density operator, is it true that for every complex number $z$ the quantity $$ \mathrm{tr}[\rho (X+zY)^*(X+zY)] $$ is non-negative?
5
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1answer
52 views

Holevo Information and Quantum Mutual Information

This question is about the difference between Quantum Mutual Information and Holevo Information of quantum channels. From http://arxiv.org/pdf/1004.2495.pdf equation 7 we know that the sum of quantum ...
3
votes
1answer
47 views

Free electron Gas shortcomings

I am studying surface states and the Rashba effect. A common model I keep coming across is to implement the free electron model. In this model we get the spin orbit interaction Hamiltonian by ...
1
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0answers
40 views

Deriving the correlation function of a system interacting with a bath of harmonic oscillators

I'm working on the book Quantum Effects in Biology by Mohesni et all. My question is however not biology related, it is about a section on quantum master equations in the weak system-bath coupling ...
0
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1answer
43 views

Bell state Orthogonality [closed]

Given the Bell states $|\Psi^+\rangle = \frac{1}{\sqrt{2}}(|H\rangle_1|V\rangle_2-|V\rangle_1|H\rangle_2)$ and $|\Phi^-\rangle = \frac{1}{\sqrt{2}}(|H\rangle_1|H\rangle_2-|V\rangle_1|V\rangle_2)$, I ...
4
votes
1answer
51 views

Non coherence of Fermions and Bosons through $U(1)$

I "know" the textbook answer why we cannot write, $$ |\psi\rangle = a|j=\tfrac{1}{2}\rangle + b|j=1\rangle $$ as "each term in the quantum superposition transforms differently under $U(1)$", $$ ...
1
vote
1answer
39 views

What is $bfr$ in this expression?

I am reading 'Fundamentals of Quantum Mechanics' by Sakir Erokoc and came across this expression in relation to transition probabilities: $$\vec p=e \langle \psi_b |bfr|\psi_a \rangle$$ Which can be ...
5
votes
1answer
67 views

Why are periodic boundary conditions used for the derivation of phonons? [duplicate]

I am currently reading "Quantum Field Theory for the Gifted Amateur". In chapter 2 Phonons are introduced as solutions (in k-space) of a coupled harmonic oscillator. In real space the oscillator is ...
7
votes
3answers
438 views

Interpretation of boundary conditions in time-independent Schrödinger equation

The time-independent Schrödinger equation: $$\ -\frac{\hbar^2}{2m}\frac{d^2\psi}{dx^2} + V\psi = E\psi$$ is second order, so we should expect the solution to have two "degrees of freedom" which can ...
0
votes
0answers
23 views

A book to read that explains the principles of quantum mechanics [duplicate]

I abandoned a formal education in physics in favor for a medicine degree, but I still can't shake my love for physics. However, I only want to read about the principles and ideas, not so much be able ...
3
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1answer
38 views

Generators of a certain symmetry in Quantum Mechanics

In Classical Mechanics to describe symmetries like translations and rotations we use diffeomorphisms on the configuration manifold. In Quantum Mechanics we use unitary operators in state space. We ...
2
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0answers
32 views

Second Order Coherence of NOON State

Given the entangled state $\vert NOON \rangle =\frac{1}{\sqrt{2}}(\vert N,0\rangle + \vert 0,N\rangle)$ how can the second order coherence function at time $\tau$ and 0 be calculated? I know that ...
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0answers
42 views

Extending projection operator to infinite-dimensional case

Hi I have a basic question regarding bra-ket notation. Given that $\{|e_n \rangle \}$ is a discrete orthonormal basis, $$\langle e_m | e_n \rangle = \delta_{mn}$$ then $$\sum_{n}|e_n \rangle \langle ...
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0answers
97 views

Why can we set the coefficient $c_- = 0$ in the solution of the quantum particle on a ring?

In the quantum particle in a ring problem, the general solution for the wavefunction, with $k = R \sqrt{2 m E / \hbar^2}$, $R$ being the ring radius, $c_{+, -}$ being constants, $E$ the energy, and ...
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1answer
83 views

Smallest thing ever measured and quantum mechanic bs [closed]

Is it possible to prove in 2016 that the universe is made up of more discrete units than say an atom or quark? What is the smallest thing we have been able to measure, like not theorize about, but ...