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 ...

learn more… | top users | synonyms (4)

4
votes
2answers
64 views

Valence sea quarks parton distribution functions

There's somethin from Thomson (Modern Particle Physics) that I am a little mythed by. Section 8.4.3, eq. 8.3 is given as $$ ...
0
votes
1answer
53 views

Magnetic field induce photons?

So silly question, can a oscillating magnetic field excite electrons around atoms such that they produce photons (In other words can an applied magnetic field increase the energy level of electrons ...
8
votes
4answers
424 views

Is it possible for $\Delta x$ ($\sigma_x$) of any free particle wave packet to be decreasing at any time?

Consider any wave packet describing a free particle (so no potential or other forces acting on it). Then it can be shown that $\Delta p$ does not change in time. However, my question is what happens ...
35
votes
6answers
3k views

Does Heisenberg's uncertainty under time evolution always grow?

Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting ...
1
vote
2answers
259 views

Double slit experiment

I can't understand the relation between Schrödinger's Cat and this amazing experiment of the double slit. It seems like in the double slit we know if we observe the particle the wave function ...
0
votes
0answers
49 views

What knowledge do I need to learn Quantum Physics? [duplicate]

I have a quick question. What prior knowledge do I need to learn and understand quantum physics. For example, what type of math do I need to know, what level of physics, etc.
0
votes
1answer
33 views

How to check if a Hamiltonian is PT symmetric or not?

Consider the Hamiltonian $$H=p^2+ix^3+ix.$$ This paper by Carl M bender claims this is a $PT$ symmetric Hamiltonian. In this he describes $PT$ symmetry as parity $P$, whose effect is to make ...
3
votes
1answer
50 views

WKB Approximation on an linear + harmonic potential

I have a quick question: I have performed the WKB approximation to find the energies of bound states in symmetric potentials (Square, harmonic, ...). To do this I just find the "turning points" by ...
1
vote
1answer
79 views

How is no-conspiracy theory compatible with determinism? [closed]

Bell's theorem states that any physical theory that incorporates local realism and the no-conspiracy assumption cannot reproduce all the predictions of quantum mechanical theory. Hence, we cannot ...
10
votes
1answer
984 views

Can't quantum teleportation be superluminal some percentage of times?

I apologize if this is a really silly question. In the (textbook) quantum teleportation algorithm, in the step right after Alice has measured her system but before she has sent her classical ...
-3
votes
2answers
49 views

What makes the probability distribution of a wavefunction in QM intrinsic? [closed]

I know that the usual interpretation of the wavefunction in QM is that it´s associated with a probability distribution of measurable quantities. Not a deterministic probability (like the probabilities ...
5
votes
2answers
115 views

Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
0
votes
0answers
20 views

Overtone Transition Probability

For an anharmonic potential, like the morse potential, higher order transitions (overtone) with $\Delta n=\pm2,\pm3,..$ are allowed. How do I calculate the probability $P$ for such transitions? My ...
0
votes
1answer
36 views

Rate of the increase of width of a Gaussian wavepacket

So, I'm following the MIT OCW lectures on 8.04 quantum mechanics by Prof. Allan Adams. I have the expression for the probability distribution of a gaussian wavepacket for a free particle situation. No ...
2
votes
3answers
189 views
-4
votes
1answer
53 views

Does quantum uncertainty effect strings? [closed]

If the bases of string theory is that specific vibrations in strings create specific dimensions, how can these vibrations exist within the parameters of quantum uncertainty? Wouldn't the uncertainty ...
46
votes
6answers
5k views

Why does a system try to minimize its total energy?

Why does a system like to minimize its total energy? For example, the total energy of a $H_2$ molecule is smaller than the that of two two isolated hydrogen atoms and that is why two $H$ atoms tries ...
2
votes
1answer
56 views

Expressing eigenstates of $\mathbf{L}^2$ and $L_z$ in terms of the Cartesian eigenstates $|n_x\, n_y\, n_z\rangle$

I want to express the degenerate eigenstates of the three-dimensional isotropic harmonic oscillator written as eigenstates of $\mathbf{L}^2$ and $L_z$, in terms of the Cartesian eigenstates $|n_x\, ...
0
votes
2answers
51 views

Can conducting electrons in a metal be modeled at all as classical particles?

I have seen computational models that treat the highest energy electrons in a conducting metal as classical particles in a plasma, the ions being held in place with some sort of heuristic ...
2
votes
1answer
33 views

Obtaining wave function from field equation

The Dirac field $\Psi(x)$ satisfies the Dirac equation $$(i\gamma^\mu\partial_\mu-m)\Psi(x)=0$$ When we quantize, each of the four components of the Dirac field becomes an operator that creates or ...
0
votes
0answers
35 views

Rotations acting on quantum states

Suppose I have a free relativistic massive particle described by a state $|p,\sigma\rangle,$, with $p^\mu=(p^0,0,0,p^3)$, so that $P^3|p\rangle=p^3 |p,\sigma\rangle$ and ...
0
votes
0answers
62 views

What does it mean to take a derivative with respect to $\hbar$?

Problem 6.32 of Griffiths Introduction to Quantum Mechanics, 2ed is In part (b), we take a derivative with respect to $\hbar$. Since $\hbar$ is a constant, what does it mean to take a derivative ...
3
votes
2answers
371 views

Why are there gapless excitations in the anti-ferromagnetic Heisenberg model while the true ground state is a singlet?

The true ground state of the anti ferromagnetic quantum Heisenberg Model (nearest neighbor only)is known to be a singlet (I think this is Liebs theorem.) Since a singlet is invariant under rotations, ...
3
votes
2answers
46 views

Introducing a phase, what changes?

This question is related to: Mach-Zehnder interferometer and the Fresnel-Arago laws Let us say we have unpolarised wave taking the form: $$\psi=\psi_0 e^{i(kx-\omega t)+i\phi(t)}$$ Where $\phi$ ...
3
votes
1answer
37 views

Spread of the energy levels and sharp energy eigenvalues of the Schrodinger equation of the H-atom

Solving the Schroedinger equation for the H-atom (or any other system, say a particle in a box, or harmonic oscillator or anything), we obtain the energy eigenvalues are sharp with no spread. However, ...
1
vote
1answer
223 views

What is many-body bound state?

Bound state by definition is a state when particles are bounded together, so then "many-body bound state" would be bound state for a system of many bodies. Then I have several puzzles: is the state ...
1
vote
1answer
111 views

Selection rules with no external field?

According to The physics of quantum mechanics By Binney and Skinner (p284) when no external field is applied, we can have: $$\Delta m=0,\pm 1$$ in any direction. How is this possible considering that ...
5
votes
1answer
131 views

Obtaining the temperature from Bose-Einstein and Fermi-Dirac distribution

Lets say you are given a distribution function $f(p)$ and you want to define a temperature, $T_f$, for this distribution. (I assume $\mu = 0$.) It is then natural to define a temperature the ...
17
votes
4answers
2k views

Same photon or different photon?

Consider a typical optical focusing system: A small light source, then a collimating lens, then a focussing lens, and then a detector (e.g. CCD). Assume that source intensity is so low that only one ...
3
votes
0answers
62 views

A question on the Chern number and the winding number?

Let $\mid \psi(x,y) \rangle$ be a normalized wavefunction living in a $d$-dimensional Hilbert space and depend on two real parameters $(x,y)$ that belong to a closed surface (e.g., $S^2, T^2$, ...). ...
2
votes
0answers
35 views

Is electron phonon interaction important away from fermi surface?

In weak coupling superconductor, the effective electron phonon interaction can be written as $$ H_{eff}=\frac{1}{2}\sum_{q,k_1,k_2,\sigma_1,\sigma_2} V_{k_1,q}C^{\dagger}_{k_1+q,\sigma_1} ...
0
votes
1answer
30 views

Why is the interaction energy of the electrons in an atom positive?

Consider a simple Hamiltonian for the Helium atom (where $e'^2 = e^2/4\pi \epsilon_0)$: ...
0
votes
1answer
49 views

Multiplication of associated probabilities

If a state $\psi $ is in the $ S_{z} $ basis represented by $\mid\psi\rangle = c_{+}\mid z\rangle + c_{-} \mid -z\rangle$ Does the associated probabilities change when I multiply $ \psi $ by $ ...
3
votes
0answers
133 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 ...
0
votes
0answers
50 views

Can nonrelativistic QM, as used in bound states, be derived from QFT? [duplicate]

Nonrelativistic QM can be applied to bound states like a hydrogen atom. QFT is used for free particles (whatever one means by particles) that shortly interact with each other and are free again after ...
2
votes
1answer
196 views

Perturbation theory in second quantization

I am dealing with electron/phonon interaction in QM. In particular, given the Hamiltonian of a solid, $$H=H_\text{el}+H_\text{ion}+H_\text{el-ion}$$ we have that the el-phonon Hamiltonian is treated ...
0
votes
1answer
48 views

Finding similar quantum superposition pairs [closed]

I am not sure if my thinking is correct and I'd like to ask if someone can confirm it, or give explanation, what am I doing wrong. I did task where I was asked to tell if pairs of expressions for ...
0
votes
0answers
61 views

Feynman lecture - bell's theorem, entanglement

My question regards this video: https://www.youtube.com/watch?v=AyejXtZrGb0 Feynman is illustrating entanglement, bell's theorem etc... using correlated boxes. I take the entangled boxes as ...
0
votes
1answer
44 views

What causes the universe to manifest a given value upon measurement in super-deterministic theory? [closed]

Bell's inequalities show that we have to give up freedom or local realism. If we give up freedom, we have super-determinism, if we give up local realism, we have free-will. In super-deterministic ...
4
votes
2answers
183 views

What events lead to quantum decoherence?

Is there a very specific definition for all types of events where quantum decoherence occurs? Is it merely any event that is "thermodynamically irreversible" and/or "causes entropy to increase"? Is it ...
0
votes
1answer
190 views

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 ...
2
votes
2answers
139 views

Is my understanding of the delayed choice quantum eraser correct?

I'll say in advance that I am by no means an expert on Quantum Mechanics. I understand the basic mathematics of it (Wave function and Schrodinger equation), but did not go deeply into it or study it ...
-6
votes
1answer
84 views

If E= hv then E= mc2 then h=mc2/v! [closed]

E= pc (1) = hv (2), p= mc (3) From (1) and (2): c= hv/p (4) We put (4) in (3): p=hv/p.m => p2=hvm (5) If we use E=hv in (5) we will get: E= p2/m (6) We use (3) in (6) we will get: E= mc2 From ...
9
votes
5answers
3k views

Are there any practical applications of the uncertainty principle

I believe GPS works because of extremely small time differences between the satellites. Because of how small the time differences are, it needs to take into account gravity's effect on time. ...
-4
votes
1answer
59 views

Concerning The Oil Drop Experiment: How does ionizing radiation create the electron(s) that the droplets of oil collect?

Concerning the Oil Drop Experiment: I read, “Ionizing radiation is used to create the electron that the droplets of oil collect. When the air in the apparatus is bombarded by this ionizing radiation ...
1
vote
1answer
138 views

Is there a minimum distance?

I would imagine there is no limit to how small space can get. Is this correct? I am aware of planck's constant, but cannot objects be closer than Planck's constant is short? Perhaps this question is ...
-1
votes
1answer
46 views

Implications of weak measurement on entanglement

What are the implications of weak-measurement on entangled particles, and how does that resolve the problem of non-superluminal quantum "communication"? If I understand correctly, entangled particles ...
1
vote
0answers
29 views

Schrödinger's cat experiment in the context of decoherence

I am trying to visualize in more detail the Schrödinger's cat experiment in the context of decoherence. Please let me know if the description below makes sense or is somehow flawed. If the ...
3
votes
1answer
36 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) ...
0
votes
0answers
26 views

Probability density for spinors

I am approaching Relativistic Quantum Mechanics seriously for the first time, going through Bjorken & Drell and doing all the excercises, but I am facing some problems with 3.1. Derive (3.11) ...