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)

3
votes
0answers
249 views

Double Slit Experiment with Two Independent Sources

Imagine a variation on the double slit experiment. I'll describe it in 2D using the $x-y$ plane. The $x$-axis is impenetrable other than the two slits, which are positioned at $(-1,0)$ and $(+1,0)$. ...
3
votes
0answers
107 views

What is a covalent bond?

What is a covalent bond, quantum mechanically? How does it hold the two atoms together, and at one point can you qualify the electron as being shated between two atoms, versus feeling attractive ...
3
votes
0answers
521 views

Probability density of Klein-Gordon equation

This may, perhaps, stir some healthy debate; at least I am having some "fun" thinking about it, hopefully I can solicit some outside views too. It is often regarded that the Klein-Gordon equation ...
3
votes
0answers
97 views

Literature on the time reversal operator

Time reversal symmetry seems to be a very useful concept and is mentioned in a good number of papers I recently came across. Most of the time people claim that a certain system or Hamiltonian is time ...
3
votes
0answers
88 views

What are the parameters for Pauli's repulsion pseudo-force?

I have found the following formula for the repulsion potential due to the overlap of the electron clouds arising from Pauli's exclusion principle: $$V = A\exp(-r/\phi)$$ where r is the distance ...
3
votes
0answers
64 views

Physical consequences of non-trivial quantum states homology

The set of quantum states of a finite dimensional system is a complex projective space, whose homology groups are non-trivial http://en.wikipedia.org/wiki/Complex_projective_space#Homology. Has this ...
3
votes
0answers
106 views

Does quantum mechanics require classical measurement apparatus?

I am trying to learn quantum mechanics and I have a question. Landau, in his quantum mechanics book says that it is in principle impossible to formulate basic concepts of quantum mechanics without ...
3
votes
0answers
335 views

Born approximation to Lippmann-Schwinger integral equation

I am having the following problem understanding the Born approximation in the case of the Lippmann-Schwinger equation. This exercise is for something which is entitled "computational physics lab ...
3
votes
0answers
79 views

Can Pauli exclusion be described locally?

Is it possible, in principle, to define the exclusion principle in a "local" sense, as a property of the tangent space at a point, or a single fiber of a spin bundle? Or does it necessitate a global ...
3
votes
0answers
237 views

physical intuition behind quasi-bound state formation in feshbach resonance

In Feshbach resonance, by scattering theory formalism it is found that the resonance in cross-section happens when bound state energy of the closed channel is near to the scattering state energy of ...
3
votes
0answers
62 views

how is feshbach resonance potential term physically produced?

In Feshbach resonance model, a 2*2 potential term with space dependent diagonal and non-diagonal terms is written $\left(\begin{array}{cc} V_{11}(\mathbf{r}) & V_{12}(\mathbf{r})\\ V_{21}(\mathbf{...
3
votes
0answers
62 views

Alternative ways to take particle tracks photographs in a cloud chamber

I know that the most common type of particle tracks photography is in photographic plates, but i'm using a cloud chamber and I would like to know if there are alternative ways to take photographs of ...
3
votes
0answers
140 views

What are the assumptions behind “term symbols”?

In multi-electron atoms, the electronic state of the optically active "subshell" is often expressed in "term symbols" notation. I.e. $^{2S+1}L_J$. This presumes that the system of electrons has ...
3
votes
0answers
305 views

Does natural unit of information and entropy, nat, play special role in the freebit picture?

Please refer this question to understand why I consider the freebit picture important. In short, it is conjectured, that for certain real systems the most complete physical description possible ...
3
votes
0answers
66 views

Thermalising a sub-system of a larger, interacting system

I'm considering a joint system consisting of a spin-1/2 particle (qubit) and a spin-l particle (reference) coupled via a Hamiltonian $H_0$. At a certain point I want to couple the qubit to a bosonic ...
3
votes
0answers
126 views

Geometric quantization AND nuclear physics

Classical mechanics has a natural mathematical setting in symplectic geometry and it may be asked if the same is true for quantum mechanics. Geometric quantization is one formalization of the notion ...
3
votes
0answers
99 views

The nature of the probability distribution for the energy of a photon released via stimulated emission

The vanilla description of stimulated emission (e.g. in the context of an inverted population laser gain medium) says that a photon with some state vector specifying its energy / polarization / ...
3
votes
0answers
109 views

Approximate energy levels for the following potential

Let's have potential $$ U(r) = -U_{0}e^{-\frac{r}{a}}. $$ I need to find energy levels for particles moving in this field (for an arbitrary values of orbital number $l$). This task isn't exactly ...
3
votes
0answers
165 views

Partial waves and the velocity expansion of a scattering cross section

I'm confused about the relation between the velocity expansion of a scattering cross section and the angular momentum (partial wave) expansion. For example, for dark matter annihilation, we write $\...
3
votes
0answers
107 views

The relation between the action of tunneling and the energy

In the semi-classical physics, the probability of the penetration through a barrier is given by $$ p \sim \exp \left( - A_{0} (E) \right), $$ where $A_0$ is the imaginary part of the action and $E$ ...
3
votes
0answers
168 views

Fock Subspaces and Weight Vectors

This is my first time taking a physics course (I'm a mathematics major), so I'm encountering a lot of new things, which I'm kind of expected to know. In particular, how to work with Bosons. I've got ...
3
votes
0answers
125 views

Optimality of product input state in quantum channel

Let $\mathcal N^{A_1\rightarrow B_1}_1,..,\mathcal N^{A_1\rightarrow B_1}_k$ be a set of valid quantum evolutions with equal input and output dimensions. And let the effect of a channel on a system $\...
3
votes
0answers
212 views

Measure energy state of quantum harmonic oscillator

When discussing the quantum mechanical harmonic oscillator we are talking about energy eigenstates. How would one actually measure in which state an harmonic oscillator is in? Could you weigh it and ...
3
votes
0answers
152 views

What does “quantum theory forbids promiscuous entanglements” mean?

The context is this article about black hole firewalls. The phrase appears on page 3. It appears to be saying that only pairs of particles can be entangled, never multiple particles, and that this ...
3
votes
0answers
76 views

Infinite quon statistics/Quantum Boltzmann statistics: models and hamiltonians

I learned long ago that there are some exotic classes of statistics. One of them is calleq $q$-on or quon statistics. It is given by $$a_ia^+_j-qa^+_ja_i=\delta_{ij}$$ Infinite statistics (Quantum ...
3
votes
0answers
289 views

How to set up Schrodinger's equation for an electron (as a charge distribution) under its own electrostatic field

After reading about the hydrogen atom and understanding how Schrodinger's equation explains most part of the atomic spectrum of an hydrogen atom, and also came to know that, it explains most of the ...
3
votes
0answers
448 views

How is the Geometric Phase measured in the experiment?

I had read some papers that have mentioned the geometric phase (Berry phase) can be used to detect the quantum phase transitions in a quantum many-body system. My question is: How is it measured in ...
3
votes
0answers
178 views

Laughlin state unique ground state?

In the FQHE, one typically encounters the statement that the $\nu = 1/3$ Laughlin state is a unique exact ground state of a model Hamiltonian where the Haldane pseudopotentials $V_1 \neq 0$ and $V_m = ...
3
votes
0answers
86 views

Perturbation in Supersymmetric Quantum Mechanics.

To do perturbation analysis of Supersymmetric Quantum Mechanical Hamiltonian, the superpotential is first scaled by a constant $\lambda >> 1$ and then expanded about it's critical point. Finally ...
3
votes
0answers
146 views

Dyson Series Second Order Term Importance vs. Time

Given a time ordered Dyson series expansion of $$H_I=e^{-\frac{i}{\hbar}\sigma_3t}V_0\sin(\omega t)\sigma_1e^{\frac{i}{\hbar}\sigma_3t}$$ $${\cal T}\exp\left[-\frac{i}{\hbar}\int_0^tH_I(t')dt'\...
3
votes
0answers
573 views

Hamiltonian of the surface states of a 3D topological insulator

The surface states of a 3D topological insulator (let's say in the (x-y) plane) are sometimes described by the following Hamiltonian : $$H(k)=\hbar v_F (p_x \sigma_x + p_y \sigma_y)$$ or sometimes by :...
3
votes
0answers
225 views

What is the link between the density matrix and Hestenes' spinors in geometric algebra?

The density matrix (or state matrix) is a generalization of a wave function that is able to describe incoherent superpositions of an N-state system. It is often written as a matrix and observables are ...
3
votes
0answers
311 views

What is the relationship between consistent histories and path integrals?

As can for example be learned from chapter I.2 of Anthony Zee's Quantum field theory in a nutshell, path integrals can be used to to calculate the amplitude for a system to transition from one state ...
3
votes
0answers
171 views

Spin polarization of decay products

A relativistic moving particle, e.g. muon $\mu^+$, described by its four-momentum vector $p_\mu$, charge $e$ and with a given spin polarization, ${\bf S}=(S_x,S_y,S_z)$, decays into three particles, e....
3
votes
0answers
536 views

Is there any simple quantum model by Gerard 't Hooft which can explain the double slit experiment?

This question is directed to Prof. 't Hooft and anybody who is familiar with his papers. It is a reaction to Prof. 't Hooft's question why nobody is excited about his classical models for quantum ...
3
votes
0answers
64 views

Are there any connections between James–Stein estimator and quantum mechanics?

Very nice statement from wiki: When three or more unrelated parameters are measured, their total MSE can be reduced by using a combined estimator such as the James–Stein estimator; whereas when ...
3
votes
0answers
1k views

Comparison of different ab-initio codes

One may find on the web a lot of different computational packages to perform "ab-initio" calculations of electron structure of the solids. Usually, the documentation is not quite transparent about the ...
3
votes
0answers
87 views

Spectrum of a quantum relativistic “distance squared” operator

This question disusses the same concepts as that question (this time in quantum context). Consider a relativistic system in spacetime dimension $D$. Poincare symmetry yields the conserved charges $M$ (...
3
votes
0answers
315 views

Symmetries of separable potential

For separable potential, say $x^4+y^4$, its symmetry are degenerate. Is that a generic case to every separable potential? I will explain my question: The potential $x^4+y^4$ has $A_1, B_1, A_2, B_2, ...
3
votes
0answers
124 views

How can one trace out polaritonic degrees of freedom?

I have read the paper "Steady state entanglement between hybrid light-matter qubits", arXiv:0711.1830v2. There, writers obtained density operator in matrix form after solving steady state equation (13)...
3
votes
0answers
200 views

Matter-wave interference from free falling cold atoms

and another exam question, this is about current research: Interference of matter waves has been studied using ultra-cold atoms. The phase of a matter wave for free-falling cold-atoms at time $t$ ...
3
votes
0answers
2k views

Energy Levels of 3D Isotropic Harmonic Oscillator (Nuclear Shell Model)

One simple way of detailing the very basic structure of the nuclear shell model involves placing the nucleons in a 3D isotropic oscillator. It's easy to show that the energy eigenvalues are $E = \...
3
votes
0answers
465 views

1D Topological insulator with PT symmetry

Assume I have the Hamiltonian for a 1D topological insulators as: $$H=\sin(P_x) \sigma_x+i \Delta \sigma_{y}+[1-m-\cos(P_x)] \sigma_z $$ where $m$ is the mass term, $P_x$ is the momentum and $\Delta$ ...
2
votes
0answers
32 views

Quantum Entanglement Simulation

Suppose there is a digital "quantum entanglement simulator" with a pair generator and two spin detectors, and it Allows to create as many pairs as you want (100 pairs per single click) Allows to ...
2
votes
0answers
39 views

When we say particle in a box has quantized energy, is that kinetic or total energy?

In quantum mechanics, it is usually said that energy of the bound (constrained) systems such as particle in a box (infinite potential well) is quantized. It confuses me exactly what type of energy is ...
2
votes
0answers
29 views

Degeneracy of energy levels of a particle in a spherical step potential?

I have a particle of mass $m$ and spin $1/2$, in a spherical step potential, $$ V(r) = \begin{cases} 0 & r<a, \\ V_0 & r>a. \end{cases} $$ Now they ask me to find, without solving the ...
2
votes
0answers
44 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 ...
2
votes
0answers
24 views

What is the significance of the assumption of “full energetic degeneracy” in this paper?

I'm reading the new paper "Foundations of statistical mechanics from symmetries of entanglement" (available on arxiv), in which the authors Deffner and Zurek note that the quantum microcanonical state ...
2
votes
0answers
41 views

What are the differences (if any) between the Dyson's series definition and the “in/out” definition of the $S$-matrix

So long, in my QFT courses, I've seen two definitions of the $S$-matrix: The first, more elementary, definition is given in the interaction picture: $$S=\text T \lbrace \exp [-i\intop \text d ^4 x \,...
2
votes
0answers
27 views

Anharmonic quantum oscillator with momentum perturbation

Given the following quantum oscillator for a particle with mass $m$, and perturbation $-\gamma P$ ($\gamma$ is a constant): $$H=\frac{P^2}{2m}+\frac{1}{2}m\omega^2X^2-\gamma P$$ One could find the ...