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-...

learn more… | top users | synonyms (4)

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
votes
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
vote
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
186 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 ...
0
votes
1answer
23 views

Total spin of many photon thermal state [closed]

I need to find the total spin of a large spin 1/2 ensemble in thermal state: I'm trying to find a formula for $\operatorname{Tr}(S^2 \rho)$ where $\rho=\frac{1}{Z}e^{\beta S_z}$ is the thermal state ...
4
votes
1answer
58 views

Quantum Mechanics: Relate solutions for two dual hamiltonians?

Consider a Hamiltonian in quantum mechanics: $$H_x=-\frac{d^2}{dx^2}+V(x,c)$$ where $x\in\mathbb{R}$ and the potential $V(x,c)$ depends on position $x$ and a continuous parameter $c$. Furthermore, ...
-1
votes
0answers
29 views

Does the Mach-Zender interferometer imply a quantum wave function

If an optical Mach-Zender interferometer that is set up with perfect interference, then at on port no light such be detected, and at the other light will be detected. A common question asked is 'what ...
-1
votes
1answer
48 views

Questions About Quantum Delta Function Potentials [closed]

I didn't think that it would be possible for a wave function to get through the delta function because there is no "leakage" of the wave function through an infinite potential barrier. I can ...
0
votes
1answer
45 views

Can free particle (eg. unbound electron or proton) have angular momentum other than spin?

I am learning about parity of nucleus and (elementary) particles. For example, proton has a intrinsic parity of $+1$. However, a more general term for parity of proton is $(-1)^l$ where $l$ is orbital ...
0
votes
0answers
27 views

4 Photon Entanglement

I know that if you use SPDC (spontaneous parametric down conversion, which is the process in which a photon of a certain energy and frequency is converted into two entangled photons by being passed ...
0
votes
0answers
33 views

Grover's algorithm - how to capture eventual answer?

I don't fully understand what is the output of algorithm: a. Is it "value Y you search exists in your input", or b. Is it "value Y you search sits in location X of input". And another question: "what ...
0
votes
1answer
29 views

Quantum ising/heisenberg model, states representation

I am working with a hamiltonian which looks like this (Heisenberg model) I have made a program which computes this hamiltonian using Pauli matrices (spin 1/2). My working space is then the tensor ...
0
votes
1answer
41 views

How to understand the electric-field operator in quantum optics?

I know the positive field operator $\mathbf{E}^{+}$ is actually an annihilation operator $a$ while the negative field $\mathbf{E}^{-}$ is a creation operator $a^{+}$. I also learned that the ...
0
votes
0answers
25 views

Emptiness of the atom [duplicate]

If the atom is actually 99.99% empty, why can't we just put our hands or things inside them?
1
vote
1answer
26 views

Hamiltonian lattice gauge theory with physically observable local degrees of freedom

In my answer at What, in simplest terms, is gauge invariance?, I mentioned that in certain contexts there can be a "gauge theory" with a local symmetry that leave the Lagrangian/Hamiltonian invariant ...
-1
votes
0answers
10 views

STM Limit of Sample Electric Resitivity

What's the highest level of Electric Resistivity that you can measure with a off-the-shelf STM? I believe Normal Samples have around 1*10⁻⁶ Ohm Centimeters.
0
votes
0answers
27 views

Why doesn't position and momentum commute? [duplicate]

I'm trying to understand the reason for Heisenberg's uncertainty principle which I read is a "fact of nature" rather than an experimental limitation. I found this thread in which the accepted answer ...
1
vote
0answers
34 views

Stoner-Wohlfarth model for ferromagnetism

I'm studing the Stoner-Wohlfarth model for ferromagnatism on the book Ibach-Luth Solid state physics. During the derivation of the Stoner criterion I found this passage (8.43) not so clear for me: ...
14
votes
4answers
679 views

Increasing a potential causes increase in energy levels

Suppose a potential $V(x)$, and suppose a bound particle so the allowed energy levels are discrete. Suppose a second potential $\widetilde{V}(x)$ such that $\widetilde{V}(x) \geq V(x)$ for all $x$ (...
2
votes
2answers
67 views

Does a wave have inertia?

In de Broglie hypothesis, particles have wave nature. The question is does this wave have inertia? If so is it represented in the corresponding wave equation?
2
votes
0answers
43 views

Intuition for why there are quantum beats in $V$-type but not in $\Lambda$-type atoms

When calculating the emitted intensity of an excited $\Lambda$-type or $V$-type atom with a quantized field (instead of a semiclassical approach with only quantized energy levels) one finds that there ...
3
votes
3answers
68 views

Projection operators in quantum mechanics

I'm reading a book on quantum mechanics and a topic in there was not well explained. I couldn't find an answer on the web. Say $\psi(x)$ is a position wave function of a one dimensional free particle,...
3
votes
1answer
51 views

Ehrenfest Theorem and boundary Conditions

In what cases does Ehrenfests Theorem hold? If I look at the wavefunction of electrons in a squared box of length $L$ (with periodic boundary-conditions, $\Psi(0) = \Psi(L)$), then the solution to ...
0
votes
0answers
25 views

Quantum wells probability

Consider a Brownian particle in a potential landscape with potential well of depth $E_1$ and another potential well of depth $E_2$. In equilibium, what is the likelihood of finding the particle in ...
1
vote
2answers
130 views

How exactly does string theory make general relativity and quantum mechanics compatible?

Correct me if I'm wrong, but the reason that quantum mechanics and general relativity are incompatible is because the quantum foam at Planck scales renders space-time discontinuous and doesn't allow ...
2
votes
1answer
75 views

Harmonic oscillator in quantum mechanics

I have brief questions regarding the attachments, which are notes from the book Introduction to Quantum Mechanics by Griffiths which explains the harmonic oscillator case. Any assistance would be ...
1
vote
4answers
119 views

What actually happens when a photon is absorbed by matter?

In my physics courses so far we've only discussed the before and after of a photon being absorbed by matter. But what actually happens here? How does the light "meld" with the atom that it is incident ...
3
votes
0answers
56 views

Commutation Relation between Annihilation & Creation Operators and Ascending & Descending Operators

I am currently working on a QD-Cavity system. After the point Heisenberg Equation of motion is obtained from corresponding Hamiltonian of the system, in order to find the expression for bosonic ...
1
vote
1answer
55 views

Collapse of Wavefunction after space-like Seperated Measurements

Suppose I have a pair of entangled particles, each one goes in a different direction. Now I measure the momentum of one particle and the position of the other at the same time. Because the ...
-1
votes
1answer
51 views

When does a wavefunction get re-created after a collapse? [closed]

Maybe another way of asking this would be, "When is decoherence un-done for a particle?" Example: Consider that we shoot an electron from a gun. Whilst in transit the electron is just a probability ...
0
votes
1answer
20 views

A good book on spectroscopy

I have found out that there are two kinds of books on spectroscopy: chemistry prospective experimental physics prospective I am looking for a book which contains more or less rigorous theoretical ...
0
votes
0answers
45 views

Bandgap calculation in MQW structure

In advance I want to apologize for my bad english. My question is about the calculation of a Bandgap of a multiple structure crystal. In this case: AlGaInAs. Lets assume that the distribution is: Al ...
0
votes
1answer
68 views

Which theoretical models are there between quantum mechanics and cosmology? [closed]

I'm an enthusiast/hobbyist right now and I'm quite curious about the subject of understanding which scales come between the quantum scale (ab initio/first principles) and the macroscopic scale. After ...
-1
votes
1answer
69 views

Feynman path integral interpretation of the Aharonov Bohm effect [closed]

I have recently been reading about the interpretation of the Aharonov-Bohm effect via Feynman's path integral (see viXra:1403.0950). I do not know whether I am missing something, but I do not ...
1
vote
1answer
39 views

π , σ - atomic transitions with respect to a quantization axis

In the absence of a magnetic field, how does one physically (i.e perhaps in a thought expt) access delta_m = 0 or +-1 transitions since (as I understand it) the choice of quantization axis is ...
0
votes
1answer
38 views

What happen if adiabatic evolution fails?

Adiabatic theorem states that: A physical system remains in its instantaneous eigenstate if a given perturbation is acting on it slowly enough and if there is a gap between the eigenvalue and the rest ...
2
votes
1answer
113 views

Why are general wave functions expressed in terms of energy eigenfunctions?

I have read that the eigenfunctions of any hermitian operator can be used as a basis to express any function, but I have only ever really seen the eigenfunctions of the Hamiltonian used. Why is this? ...
4
votes
0answers
50 views

Why isn't there a Time Operator in Quantum Mechanics? [duplicate]

I was wondering about a scenario where you subject a quantum particle to an intense gravitation field. Why can't we apply a sort of time operator to the particle to see how time changes for the ...
1
vote
3answers
46 views

Mean energy of free electrons

My textbook states that the mean energy of free electrons within a solid state is given by $$ E_{av} = \frac{U}{N} = \frac{\int_0^{k_f}D(k)E(k)dk}{\int_0^{k_f}D(k)dk} $$ where $D(k)$ is the density of ...
2
votes
1answer
56 views

non-negative energies

Can someone help me with the following question: given the hamiltonian: $H=\frac{1}{2m}(iP-\hbar f(X))(-iP-\hbar f(X))$ where $f(x)$ an analytic real function. prove that the ...
3
votes
0answers
47 views

How to construct Hermitian(quantum) operator from a physical experiment?

Suppose I want to study a quantum mechanical quantity of a single particle. I have designed an appropriate apparatus, accuracy of which is limited by relevant laws of quantum theory. I have obtained a ...
0
votes
3answers
71 views

de Broglie's relation derivation

While going through de Broglie's relation in my textbook I was stuck by a derivation: Here $$\ E=mc^2 $$ has been applied to photons. That confused me as I thought that mass of photon=0 but a ...
-3
votes
0answers
25 views

Why does the nuclear force become stronger with distance? [duplicate]

Also how factual is the explanation? Is it mostly philosophical like say Many World's 'theory' or is the explanation pretty straight forward with little to no dispute?
4
votes
3answers
318 views

Does the entanglement depend on the basis?

Let's say, we have a composite system $A\otimes B$. We take the basis for $A$ as $|i\rangle,|j\rangle...,$ the basis for $B$ as $|\alpha\rangle,|\beta\rangle....$ Then an entangled state is a state ...
-3
votes
2answers
68 views

In handling two 1/2-spin particles, why is there only one singlet state? [closed]

Why is $\left|\uparrow\uparrow\right\rangle +\left|\downarrow\downarrow\right\rangle$ not discussed, despite having a total spin s = 0?
1
vote
1answer
18 views

Oscillator in Energy Basis Lowering and Raising Operators

On page 205 of Shankar's Intro to Quantum Mechanics, equation 7.4.12 does not make sense to me. I understand why a|e> is an eigenvector and why e-1 is its Eigenvalue, but I don't understand how that ...