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)

8
votes
2answers
438 views

Addition of Angular Momementa in deeply bound situations, proton spin crisis

In Landau and Lipshitz's introductory book on Quanum Mechanics, "Quantum Mechanics Non-Relativistic Theory, Third Edition: Volume 3", chapter XIV (page 433 in the edition on Amazon) is "Addition of ...
3
votes
2answers
496 views

What is Time like Quantum Entanglement?

I came across a New Study at : http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.2565v1.pdf . Which talks about Time like quantum entanglement. What does that mean? Comment added by L.Motl: The same ...
5
votes
1answer
384 views

How to mathematically formulate the Two Slit Experiment in Special Relativity?

How to mathematically formulate the Two Slit Experiment in a Lorentz invariant framework. Is there a paper about this?
6
votes
3answers
1k views

Photon wave packets from distant stars

A distant star like the sun, thousands of light years away, could be so faint that only one photon might arrive per square meter every few hundred seconds. How can we think about such an arriving ...
2
votes
5answers
1k views

Special relativity version of Feynman's “Space-Time Approach to Non-Relativistic Quantum Mechanics”

I'm looking for an article that sets up the framework described by Feynman in Space-Time Approach to Non-Relativistic Quantum Mechanics, but in Special Relativity.
-3
votes
3answers
2k views

What are the main differences between these three quantum theories: QM, QFT & QG? [closed]

What are the main differences between these three quantum theories? Quantum Mechanics (QM), Quantum Field theory (QFT), Quantum Gravity (QG).
4
votes
5answers
524 views

Does decoherence need non-determinism?

Consider standard quantum mechanics, but forget about the collapse of the wavefunction. Instead, use decoherence through interaction with the environment to bring the evolving quantum state into an ...
6
votes
2answers
1k views

What is quantum entanglement?

What is quantum entanglement? Please be pedagogical. Edit: I have updated my background under my profile.
2
votes
1answer
1k views

What are the benefits of quantum information “teleportation”?

I read occasionally popular science articles and from time to time encounter issues about quantum information teleportation. (this one for example http://www.physorg.com/news193551675.html) So far I ...
5
votes
2answers
193 views

Superselection sectors and $p+1$ form potentials in String Theory

we often come across the phrase superselection sector. I have couple of questions from that. First of all, I learned from some references about it (as a overview) and how is it related to ...
2
votes
2answers
373 views

What is the quantum / Berry-Pancharatnam phase for a spin-j state with z-component m?

Quantum phase arises when a spin-j state is sent through a sequence of transitions that return it to its original position. For example with spin-1/2, a state picks up a complex phase of $\pi/4$ when ...
12
votes
2answers
2k views

Can anybody provide a simple example of a quantum computer algorithm?

Does anybody give a good textbook description of a quantum computer algorithm and how its different from an ordinary algorithm?
3
votes
3answers
676 views

Relativistic object impacts the earth

A familiar trope within science-fiction is that of a large relativistic object hitting a planet such as the earth. This is normally an interstellar spacecraft or a kinetic weapon with a mass in the ...
2
votes
2answers
446 views

What is time teleportation?

I read this article about time teleportation. Can someone explain the concept better?
4
votes
2answers
4k views

Zero probability of finding an electron in the nucleus

One and the same electron in a p orbital and taking part in a common π (pi) bond has two lobes visualized as connecting through the nucleus. There is however zero probability of finding an electron at ...
13
votes
4answers
3k views

Is there a maximum possible acceleration?

I'm thinking equivalence principle, possibilities of unbounded space-time curvature, quantum gravity ...
7
votes
3answers
255 views

Basic Spin or Double Cover Experiment

We know that Spin is described with $SU(2)$ and that $SU(2)$ is a double cover of the rotation group $SO(3)$. This suggests a simple thought experiment, to be described below. The question then is in ...
6
votes
2answers
445 views

Is Time Significant in the Double Slit Experiment

When doing the classic double slit experiment is the time between emitting photons significant at all? Say, a single photon is emitted, the scientist waits T seconds, then emits another photon. Are ...
13
votes
6answers
4k views

What is the world's biggest Schrodinger cat?

How big is it by a truly quantum measurement? I am thinking of comparing Science magazines "Breakthrough of the Year" (BYOT) with the Zeilinger buckyball. The BYOT is a piezoelectric mechanical ...
1
vote
4answers
202 views

Cooling via the quantum vacuum?

Suppose you had an isolated cloud of gas at a low temperature in a vacuum with no external sources of radiation (e.g. no CMB). The gas would clearly cool via the emission of low-energy photons. But ...
5
votes
1answer
722 views

Selection Rules in electron spectroscopy

How to derive the selection rules $\Delta L= \pm 1$, $\Delta S=0$ for electron spectroscopy?
4
votes
1answer
345 views

For which irreps can normalized spin vectors be chosen continuously, for all possible spins?

Let $(u_x,u_y,u_z)$ be a unit vector. Then a normalized vector for spin-1/2 in this direction is given by normalizing a column from the pure density matrix: ...
4
votes
3answers
377 views

Why did decoherence start in the first place?

We learn that the quantum wave function $\Psi$ collapses when it interacts with a classic object (measurement). My question is: Why are there classic objects after all, how did it all start? In a ...
4
votes
1answer
262 views

Detecting coherence

Is there a way to know if a particle is acting as a wave or a particle? Alternatively, if an entangled particle was already measured? A - Yes So any experiment over an entangled particle that let ...
37
votes
8answers
6k views

Why quantum entanglement is considered to be active link between particles?

From everything I've read about quantum mechanics and quantum entanglement phenomena it's unobvious for me, why quantum entanglement is considered to be active link. I.e. it's stated every time that ...
2
votes
3answers
848 views

Photon absorption probability for a given molecule in gas phase

So I'm pretty sure I'm approaching this problem in the wrong way and I need some guidance (my first hint is that I think I'm thinking about a quantum mechanical problem too classically) Suppose there ...
-2
votes
2answers
476 views

Can we view quantum fluctuations as a type of quantum power?

(Note: I will let the question stand as is, it has generated a good answer, but the question is too "wishy washy" and needs to be tighter.) We know that the uncertainty principle tells us that the ...
1
vote
2answers
618 views

Can decoherence time be shorter than Planck time?

Decoherence times can be estimated and are inverse functions of mass. Since there are no upper bounds on mass, can decoherence time be shorter than Planck time?
3
votes
2answers
820 views

Why do the formulas for planck's units use h instead of hbar?

On the Answers.com page on Planck length, I see two almost-same formulas for the Planck length that differ only by the use of h and hbar. However, the constants are the same, and my calculator gives ...
7
votes
3answers
1k views

Quantum mechanics of thermal radiation

What are the quantum mechanisms behind the emission and absorption of thermal radiation at and below room temperature? If the relevant quantum state transitions are molecular (stretching, flexing and ...
8
votes
2answers
725 views

Modern and complete references for the $k\cdot p$ method?

I've recently started studying the $k\cdot p$ method for describing electronic bandstructures near the centre of the Brillouin zone and I've been finding it hard to find any pedagogical references on ...
4
votes
2answers
417 views

Virtual photon counting

How to calculate number of exchanged virtual pohotons per unit of time between two electromagnetically interacting objects?
6
votes
3answers
3k views

Properties of the photon: Electric and Magnetic field components

Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions ...
7
votes
2answers
4k views

How does electron move around nucleus?

I need to get a nice picture about how electron moves around nucleus? I find concept of probability and orbitals quite difficult to understand?
7
votes
2answers
573 views

How do electrons interact if one of them had just exited the two slits of the double-slit experiment?

Consider the following experiment: a double-slit set-up for firing electrons one at a time. Let's now add a second electron (orange), which is fired parallel to the first one, but in the opposite ...
5
votes
3answers
1k views

Visualization of proton's wavefunction

Visualizations of hydrogen's wavefunctions / electron orbitals are abound. I could not however locate a visualization of the wavefunction of a proton. The reason I was looking for one is to see ...
4
votes
1answer
582 views

Properties of graph of subatomic particle interactions

Say there was some situation where you have a lot of subatomic particles interacting with each other and decided to draw (say, by joining Feynmann diagrams) those interactions- so that you got some ...
11
votes
5answers
850 views

Double slit experiment near event horizon

What happens if you perform a double slit experiment near an event horizon, if one of the slits is outside, one is inside the event horizon?
9
votes
2answers
462 views

Matrix models and condensed matter physics

I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way ...
7
votes
4answers
9k views

Practical applications for a Bose-Einstein condensate

What are the main practical applications that a Bose-Einstein condensate can have?
4
votes
0answers
1k views

Solution for the Finite 2D Potential Well - Rotational Symmetry [closed]

I was searching for the eigensolutions of the two-dimensional Schrödinger equation $$\mathrm{i}\hbar \partial_t \mid \psi \rangle = \frac{\mathbf{p}^2}{2m_e}\mid \psi \rangle + V \mid \psi ...
8
votes
2answers
590 views

Calculation of the cross section

Why, when we calculate the total cross section, we make the average other initial states and the sum over final states?
12
votes
5answers
2k views

What is the conserved quantity of a scale-invariant universe?

Consider that we have a system described by a wavefunction psi(x). We then make an exact copy of the system, and anything associated with it, (including the inner cogs and gears of the elementary ...
11
votes
3answers
1k views

What's the exact connection between bosonic Fock space and the quantum harmonic oscillator?

Let's suppose I have a Hilbert space $K = L^2(X)$ equipped with a Hamiltonian $H$ such that the Schrödinger equation with respect to $H$ on $K$ describes some boson I'm interested in, and I want to ...
6
votes
3answers
866 views

Pauli exclusion principle and Entangled pairs

It is true for fermions in the same potential that the total wavefunction of two particles must be antisymmetric with respect to exchange of electrons. Which means the spin wavefunction is given by ...
3
votes
3answers
541 views

Time travel and nuclear decay

Reading a previous closed question an interesting variation has come to my mind. Suppose that time travel to the past was possible: I wait for an atom to decay and measure the time, $t_{1a}$ I ...
28
votes
3answers
14k views

Maximum theoretical data density

Our ability to store data on or in physical media continues to grow, with the maximum amount a data you can store in a given volume increasing exponentially from year to year. Storage devices continue ...
7
votes
2answers
2k views

What is the definition of colour (the quantum state)?

I heard somewhere that quarks have a property called 'colour' - what does this mean?
13
votes
5answers
851 views

Is there such a thing as “Action at a distance”?

What ever happened to "action at a distance" in entangled quantum states, i.e. the Einstein-Rosen-Podolsky (EPR) paradox? I thought they argued that in principle one could communicate faster than ...
11
votes
2answers
1k views

Klein–Gordon equation

It is said that Klein-Gordon equation is a relativistic version of the Schrodinger equation. In Schrodinger equation, it is straightforward to include potential energy. But for K-G eqn things seem to ...