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 (3)

-3
votes
2answers
53 views

Energy carried by photon not conserved?

In an imaginary frame of reference traveling with a photon, the length of the path traveled is 0. If the length of the path is 0, isn't it similar to say that the photon is either at the source or at ...
1
vote
2answers
103 views

Has a photon or electron ever been observed in a state of superposition?

Has subatomic particles ever been seen in a state of superposition or do we just detect information like qubits about the state of the particle? So is actual matter in superposition or is it just ...
3
votes
1answer
68 views

Two-level system with spontaneous emission

I have been stuck with this elementary problem of two-level system including spontaneous decay. After solving by standard procedure the following pair of equations, when I plot the expressions of the ...
10
votes
1answer
461 views

Interpretations of quantum mechanics

It is well known that there are many interpretations of quantum mechanics. I'm wondering if there is a specific reason why the Copenhagen interpretation is the most popular. Why is it that the ...
1
vote
0answers
54 views

What is the right way to learn quantum physics? [closed]

So I have a question about what i should do with my path to learning quantum physics. I just have no idea where to start or to continue from where I left off. I have been studying quantum mechanics ...
4
votes
1answer
91 views

Why is string theory a two dimensional quantum (conformal) field theory on its worldsheet?

In string theory, we quantize the two dimensional field theory on the string's worldsheet. I have a question about this kind of quantization of string theory: did we have similar theory for point-like ...
3
votes
1answer
73 views

Poles for a particle scattered in a delta potential

I am working on problem a professor gave me to get an idea for the research he does, and have hit a point where I'm having a difficult time seeing where I need to go from where I'm at. I would also ...
1
vote
1answer
49 views

How is a photon/particle measured when passing through one of the slits of the Double Slit Experiment?

It is stated in many popular science videos that one of the reasons that quantum mechanics is so wacky is that if you measure which slit the photon/particle went through on the way, then you no longer ...
1
vote
1answer
63 views

Why do some bound states disappear in a discontinuous way?

Generally, we have the picture that as the parameter (say, the depth of a trap) of a system varies, the bound state gets more and more extended and disappears eventually at some critical parameter ...
0
votes
0answers
24 views

Stochastic process corresponding to Schrödinger evolution

In probability theory, the Fokker-Planck equations governs the trajectory of a sample path of a stochastic process -- say the heat equation in the case of a Wiener process. Consider a Gaussian ...
1
vote
3answers
85 views

Can the distance over time of an electron between two measurements be higher than the speed of light?

So measure an electron, take down it's position $p$. Then measure the electron a second time and take down it's new position $p'$. Note the time between measurements, $t$. What does physics say about ...
0
votes
2answers
115 views

Does processing for a quantum computer take place in other universes?

Apologies in advance if my question seems misinformed. I am a software developer, and neither quantum mechanics nor physics are my specialties. From ...
0
votes
1answer
103 views

Problem in Grandfather paradox

I am very confused about a paradox and a recent research on Quantum particles. I have read an article which states that time travel is possible for quantum particles. If it is possible then why does ...
9
votes
2answers
194 views

Deriving the expectation of $[\hat X,\hat H]$

For a free particle of mass $m$, with Hamiltonian $$\hat{H} = \frac {\hat{P}^2} {2m},$$ where $$\hat{P} = -i \hbar \frac{\partial} {\partial x}.$$ The commutative relation is given by $$[\hat{X}, ...
0
votes
1answer
84 views

Matrix elements of the operator $\hat{x} \hat{p}$ in position and momentum basis

I want to calculate the matrix elements of the operator $\hat{x} \hat{p}$ in momentum and position basis, that is the two quantities ($p,q$ - momenta, $x,y$ - positions): $$\langle p|\hat{x} ...
0
votes
0answers
36 views

A crash course in quantum mechanics [duplicate]

I am shortly due to begin a summer project lasting roughly 6 weeks with the aim of performing some relatively basic calculations in the theory of open quantum systems. However, at this stage in my ...
1
vote
1answer
45 views

Any simple reason why Helium in the ground state is diamagnetic?

I know the electrons are in the spin singlet state, and the spatial part of the wave function is an S-state. But that is not sufficient for it to be diamagnetic.
4
votes
1answer
65 views

Why must these Spinors be normalized?

I have just begun studying spin and there are two spinors mentioned: The main spinor $\chi $ and the spin-up spin down spinors (eigenspinors) $\chi_+ ,\chi_- $. I learned that the main spinor is a ...
0
votes
0answers
10 views

in an organic semiconductor, what is the average distance travelled by an exciton?

In an organic semiconductor, what is the average distance travelled by an exciton up to recombination? How is this value related to the morfology / structure of the organic semiconductor?
0
votes
0answers
19 views

Why a multilayer OLED is generally more efficient than a single layer OLED?

Could anyone give me a brief explanation why multilayer OLEDS as more efficient than single layer OLEDs? What other advantages exist for multilayer OLEDs over single layer OLEDs?
4
votes
2answers
161 views

Pauli's Exclusion Principle

Can someone tell me how Pauli's Exclusion Principle gives stability to matter? I know two electrons cannot occupy the same energy state so that is why we cannot squeeze bulk matter after a limit and ...
0
votes
0answers
52 views

How classical chaos can be described quantum mechanically?

How can we describe the chaotic properties of classical systems using quantum mechanics when the Schrodinger equation that describes quantum dynamics is linear? How can we use quantum mechanics that ...
5
votes
1answer
133 views

What is the dominant interaction between two neighboring neutrons?

Suppose they are held 10 nm apart. What is the dominant interaction between them? The magnetic dipole interaction or something else?
1
vote
2answers
56 views

Angular momentum for 3D harmonic oscillator in two different bases

I know that the energy eigenstates of the 3D quantum harmonic oscillator can be characterized by three quantum numbers: $$ | n_1,n_2,n_3\rangle$$ or, if solved in the spherical coordinate system: ...
3
votes
1answer
61 views

Schrodinger basis kets with Time-dependent Hamiltonian

I was reading through the proof of the Adiabatic Theorem (in Sakurai) and I realised I'm not quite sure how Schrodinger Basis kets behave when we have a time-dependent Hamiltonian. I know that with a ...
4
votes
1answer
207 views

What interaction is responsible for the 21 cm Hydrogen line transition?

The 21 cm Hydrogen line is from the transition between the hyperfine levels of the ground state of the hydrogen atom. So, what interaction is coupling the hyperfine levels? I suspect that it is not ...
0
votes
2answers
89 views

Determine $p_x$ from $[x,p_x]=i\hbar $ [closed]

With $[x,p_x]=i\hbar $, how to determine the form of the operator $p_x$?
1
vote
2answers
60 views

Why diaphragm in diffraction experiment using electrons is quantum object?

In the book Quantum Mechanics - Volume 1 written by Albert Messiah, page no. 142-143, author says: ...But the diaphragm is a quantum object, just like the electron. Its momentum is not defined to ...
1
vote
0answers
57 views

Can the new results (about photonic time travel) make quantum computers feasible?

New results published about photonic time travel, reference here make quantum computers a reality in the near future? These results seem to indicate that there can be qubits that can exhibit nonlinear ...
2
votes
1answer
134 views

Does the Bohr van Leeuwen Theorem also apply to ferromagnetism?

I know that the Bohr-van Leeuwen theorem shows that there could be not consistent pure classical explanation of dia- and paramagnetism. Does the same theorem also rule out a consistent classical ...
1
vote
0answers
41 views

CPT symmetries for a free Klein-Gordon equation and in minimal coupling

I'm studying for an exam on relativistic quantum mechanics and one of the issues to prepare is about symmetries of Klein-Gordon equation concerning $C$, $P$, $T$ transformations for a free field, and ...
14
votes
4answers
472 views

Density matrix formalism

The density matrix $\hat{\rho}$ is often introduced in textbooks as a mathematical convenience that allows us to describe quantum systems in which there is some level of missing information. ...
2
votes
1answer
91 views

Divergent solution in time-dependent Schrödinger equation

if I transform the time-dependent Schrödinger equation without a potential I get: $$ - \hbar \omega \psi(\omega,x) = \frac{- \hbar^2}{2m} \frac{\partial^2 \psi(\omega,x)}{\partial x^2}$$ The ...
0
votes
0answers
25 views

Computing fine structure of terms in LS coupling,

In order to compute the fine structure of the terms in LS coupling (Russell-Saunders coupling), we must treat the hamiltonian $$H_2 = \sum_{\mbox{open subshells}} \xi(r_i) \vec{l_i}\cdot\vec{s_i}$$ ...
0
votes
0answers
43 views

Finite potential well, parity of solutions

I'm working through some problems for a QM exam and I've realised I don't really understand the concept of parity of solutions. I'm looking at a simple finite potential well problem: $$V(x)=0, \quad ...
2
votes
0answers
32 views

WKB approximation in two dimensions

Does anybody know how to implement the WKB approximation for the two-dimensional Schrodinger equation with a harmonic oscillator potential: $\frac{1}{2}\Biggl[-\biggl(\frac{\partial^2}{\partial ...
1
vote
2answers
58 views

Significance of mc/h constant in Klein-Gordon equaiton

The are several ways, in which one can write the Klein-Gordon equation, the most straightforward being probably the following: $$ \hbar^2 \partial_t^2 \psi(x) = (\hbar^2 c^2 \Delta + m^2c^4) \psi(x) ...
4
votes
2answers
94 views

Algebra, commutators and test functions

I am trying to make sense out of the algebra of the generators of the conformal group and I am running into some issues regarding how to calculate commutators. For instance, for translations of a ...
3
votes
1answer
98 views

What's wrong with this experiment showing that either FTL communication is possible or complementarity doesn't hold?

The assumptions are: Alice and Bob have perfectly synchronized clocks Alice and Bob have successfully exchanged a pair of entangled photons The idea is simply to have Alice and Bob perform the ...
1
vote
0answers
49 views

Can quantum weirdness be explained by waves in space? [closed]

Looking at the reflections of the Sun off a wavy lake the Sun appears located in many places at once and jumps positions instantly and randomly. Might quantum weirdness simply be a particle's ...
0
votes
1answer
80 views

Initial condition for Fourier transformed Schrödinger equation

I asked in this thread Time-dependet Schrödinger equation how to solve the Time-dependent Schrödinger equation. One of JamalS' recommendations was the Fourier transform, which is why I want to quote ...
10
votes
4answers
352 views

Applying an operator to a function vs. a (ket) vector

I have a question regarding the effect of quantum mechanical operators. The definition that I'm familiar with says that an operator $A$ acts on a vector from a Hilbert space, $|\psi\rangle$, and the ...
5
votes
1answer
41 views

Vacuums and free space

Do physicists use the terms "vacuum," "quantum vacuum," and "free space" synonymously? For example, I have read that based on conservation arguments, the spontaneous splitting of a photon into an ...
1
vote
1answer
24 views

Expectation value and Dispersion of an Operator

Suppose we have an operator $Q$ with eigenvalue $q$. Expectation value is $\langle Q \rangle$ and dispersion $D(Q) = \sqrt{\langle \left( Q - \langle Q \rangle \right)^2 \rangle} $. I want to find ...
15
votes
4answers
2k views

Why do we need high energy to explore small dimensions?

I am taking a quantum physics class, and for the life of me, I can not remember why we would need a vast amount of energy to understand the microscopic universe.
3
votes
1answer
34 views

Probability of measuring momentum [closed]

Suppose we have this wavefunction: $$ \psi = A \left( cos(kx) + cos (2kx) \right) $$ I have to find the possible results of measurement of momentum and their probabilities. Attempt For a momentum ...
3
votes
1answer
56 views

Is the ferromagnetism of iron understood completely?

In Feynman's lecture notes, he said that it is not (at his time). How is the situation today? Can first-principle calculation accounts the ferromagnetism of iron quantitatively now?
5
votes
2answers
251 views

Time-dependent Schrödinger equation with $V=V(x,t)$

I was wondering about the following: If you have the time-dependent Schrödinger equation such that $$i \hbar \frac{\partial\psi(x,t)}{\partial t} = - \frac{\hbar^2}{2m} ...
2
votes
1answer
86 views

How is the time independent potential term a solution of Schrodinger equation

Consider a time-independent potential: $V(x)$. Then, it is usually stated that $$ \Psi(x,t)=\rho(x)\exp{\left(-\frac{i}{\hbar}Et\right)} $$ is the general form of a solution of the Schrodinger ...
0
votes
0answers
14 views

Why photoelectron imaging is a 'complete' measurement?

In many articles and books, it says that photoelectron imaging gives a 'complete' information. What is mean by 'complete' measurement or a 'complete' information? Through photoelectron imaging ...