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 ...

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How is the Breit-Rabi formula derived?

Does anyone know how the Breit-Rabi formula (energy dependence of the hyper-fine splitting in presence of any external magnetic field for alkali atoms when $F=I \pm 1/2$) is derived, or where to find ...
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Applications of the Spectral Theorem to Quantum Mechanics

I'm currently learning some basic functional analysis. Yesterday I arrived at the spectral theorem of self-adjoint operators. I've heard that this theorem has lots of applications in Quantum ...
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Seiberg Witten theory

I'm currently reading the Seiberg-Witten paper on $N=2$ supersymmetric Yang Mills pure gauge theory (i.e. no hypermultiplets). I have the following question: How does one understand that the metric ...
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335 views

Tunneling Rate Constant

I am trying to "decode"/derive an expression for the macroscopic rate constant for the tunneling of protons through a potential energy barrier that I read in a journal article: $$ k_{\rm ...
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Why do electrons occupy the space around nuclei, and not collide with them?

We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
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What makes matter “solid”?

I'm a non-physicist with a basic high-school understanding of physics. I've always wondered what it is that makes things "solid". Why do molecules rebound from each other? There's just a bunch of tiny ...
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466 views

Generalization of spin coherent states for an arbitrary group?

My question is inspired by the analogy of the Berry phase in the spin coherent state representation of a rotator and the Aharonov-Bohm phase of a magnetic monopole (see e.g., Section 1.8.3 in ...
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How to construct the radial component of the momentum operator?

I'm having trouble doing it. I know so far that if we have two Hermitian operators $A$ and $B$ that do not commute, and suppose we wish to find the quantum mechanical Hermitian operator for the ...
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Relation between total orbital angular momentum and symmetry of the wavefunction

My question essentially revolves around multi-electron atoms and spectroscopic terms. I understand the idea that the total wavefunction for Fermions should be antisymmetric. Consider as an example, ...
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369 views

Time evolution of quantum state after an observation

As described in the wikipedia article on wave function collapse, the mathematical formulation of quantum mechanics postulates that wave functions change according to two processes: When not being ...
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730 views

Has quantum entanglement been demonstrated to be able to take place over infinite distances?

In my poor understanding of quantum physics, quantum entanglement means that certain properties of one of two 'entangled' quantum particles can lead to change over infinitely large distances when the ...
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Light waves and Schrödinger probability waves

Ok, bearing in mind that I only have a brief understanding of quantum mechanics (no formal education, only from reading about concepts in books), so I could be way off here, I have a question ...
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What happens if up quarks are replaced by down quarks and down quarks are replaced by up quarks?

I believe the quarks would flip the proton's internal charge, reverse the spin of the proton, transform into another flavor, and then become unconfined and free.
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Can spin be infinite?

Can spin of a particle or a group of particles become infinity? Explain plz. Is there any representation for spins like dot(for $S=0$) and arrow (for $S=1$)? If so what for $S= \infty$?
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Quantum Entanglement: how to generate 2 entangled particles?

I get quantum entanglement but I don't quite get how one would go about generating two complementary particles that are entangled (a photon and its entangled sibling, an electron and its entangled ...
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578 views

How low can an electron go?

Title says it all - recently I encountered a strange homework exercise on de Broglie dual theory with an electron wavelength of few millimeters - which implies the velocity lower than 1 m/s. I ...
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5answers
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What is the Physical Meaning of Commutation of Two Operators?

I understand the mathematics of commutation relations and anti-commutation relations, but what does it physically mean for an observable (self-adjoint operator) to commute with another observable ...
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2answers
966 views

Can quantum communication really replace electromagnetic waves for telecommunication medium in future?

Currently I am planning to get masters degree. So I am thinking about a subject in which I have to get masters degree. Following are my questions to leading physicists.. Which technology is the ...
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Once a quantum partition function is in path integral form, does it contain any operators?

Once a quantum partition function is in path integral form, does it contain any operators? I.e. The quantum partition function is $Z=tr(e^{-\beta H})$ where H is an operator, the Hamiltonian of the ...
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160 views

Bell Tests using position measurement

I don't know about all the details of Bell tests using methods like parametric down conversion, but at least in some versions of the EPR paradox you get two photons moving apart in opposite ...
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What are constraints on a “purity” operator in quantum mechanics?

Consider the normalized state, written in some orthonormal basis as: $$\psi = A |0\rangle + B |1\rangle$$ Let's define a "purity operator" for a basis as any operator whose expectation value gives 1 ...
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Is there a direct physical interpretation for the complex wavefunction?

The Schrodinger equation in non-relativistic quantum mechanics yields the time-evolution of the so-called wavefunction corresponding to the system concerned under the action of the associated ...
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Does Quantum Mechanics assume space and time are continuous?

I was confused when I was listening to a Quantum Mechanics lecture online. Are space and time assumed to be continuous or discrete in Quantum Mechanics? I can see the question is vague, but this is ...
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Bell Test statistics

I have some questions about the statistics of Bell Tests. For convenience I'm going to refer to the test described in this paper: http://arxiv.org/abs/quant-ph/0205171 They show a coincidence rate ...
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181 views

Quick question on the ionization energy and the selection rule

So I am looking through my book and it says ".... the order of the excited states is exactly the same order (3p-4s-3d-4p)". But now I am looking at a question in the book and it says "Is 3d to 4s ...
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Is a 5p to 5s transition possible in a multielectron atom?

Hey guys, I'm reading my physics book right now and I have a quick question about transitions in multielectron atom. I am posting a picture as well so you can see what I am talking about. How come the ...
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234 views

Uncertainly Principle in orthogonal directions

The Heisenberg Principle states that for each direction, $\Delta x\cdot \Delta p_x \ge \hbar , \Delta y\cdot \Delta p_y \ge \hbar$ and $\Delta z\cdot \Delta p_z \ge \hbar$. But, can anything be said ...
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Charge distribution in positronium

Inspired by this: Electrical neutrality of atoms If I have a wavefunction of the 'reduced mass coordinate' for a hydrogen like atom made from an electron and a positron, what is the spatial charge ...
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What is wrong with the De Broglie–Bohm theory a.k.a “Causal Interpretation” of quantum theory? [duplicate]

Possible Duplicate: Why do people still talk about bohmian mechanics/hidden variables I've heard of De Broglie–Bohm theory a.k.a causal interpretation of quantum theory. The predictions ...
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4answers
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Is it possible to know the exact values of momentum and velocity of a particle simultaneously?

I know that by Heisenberg's Uncertainty Principle that it is not possible to know the exact values of position and momentum of a particle simultaneously, but can we know the exact values of momentum ...
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1answer
411 views

Fourier transform and commutation of functions

The book I am reading takes the unjustified step $$e^{-\frac{i}{\hbar}\vec{p}\cdot\vec{r}}f(\vec{p}) = f(\frac{\hbar}{i}\vec{\nabla})e^{-\frac{i}{\hbar}\vec{p}\cdot\vec{r}}$$ and similarly, he uses ...
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2answers
1k views

Does the wave function need to be zero at the boundaries? [closed]

Recently I had a quiz in my physics class and I feel like the professor made a mistake on the solution for it. Yes, I already have the answer to this question. I am not trying to get people's answers ...
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4answers
721 views

Nature of Photons

Why is it that photons are emitted in bundles? My physics teacher's answer was "it's complicated"...
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179 views

Does the Casimir effect allow to change the lifetime of a radiating atom?

Is it true that a spontaneously light-emitting atom changes its lifetime if it is put between two parallel plates that are so near that they attract each other through the Casimir effect? Thus: does ...
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454 views

Can observations of entangled particles affect their unobserved counterparts?

There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them. Imagine an experiment ...
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1answer
418 views

Expansion of multi-particle state vector as a sum of n-entangled states

Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this: $$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... ...
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Why is the contribution of a path in Feynmans path integral formalism $\sim e^{(i/\hbar)S[x(t)]}$

In Feynman's book "Quantum Mechanics and Path Integrals" Feynman states that the probability $P(b,a)$ to go from point $x_a$ at time $t_a$ to the point $x_b$ at the time $t_b$ is $P(b,a) = ...
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Is energy exchange quantized?

In the photoelectric effect there is a threshold frequency that must be exceeded, to observe any electron emission, I have two questions about this. I) Lower than threshold: What happen with lesser ...
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4answers
890 views

How do I correctly interpret $\rho = \psi_1^* \psi_2$?

Summary: This turned out to be a rather trivial one indeed. As Marek mentioned in the comment, the continuity equation is trivial. And it indeed turns out be so. Godfrey Miller elaborates on this, ...
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1answer
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Open shells in Quantum mechanics of multielectron atoms

This question: How do electron configuration microstates map to term symbols? And the discussion of multielectron effects here: Quantum Computing and Animal Navigation Inspired me to try to understand ...
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3answers
407 views

What is the difference between $|0\rangle $ and $0$?

What is the difference between $|0\rangle $ and $0$ in the context of $$a_- |0\rangle =0~?$$
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2answers
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How do electron configuration microstates map to term symbols?

I am trying to understand energy levels of electron configurations. I visited the NIST web site and discovered that the notation used here are called term symbols. After reading corresponding ...
3
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2answers
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How to measure the spin of a neutral particle?

If a charged particle with charge $q$ and mass $m$ has spin $s \neq 0$ we can measure an intrinsic magnetic moment $\mu = g \frac{q}{2m}\hbar \sqrt{s(s+1)}$. This is how spin was discovered in the ...
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1answer
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Scale set by cosmological constant

Following on Jim Graber's answer to: Can "big rip" rip apart an atomic nucleus? If the cosmological constant is large enough, even the ground state of a hydrogen atom can be affected. So ...
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3answers
347 views

Is it possible to bind an entangled electron to the outer shell of an atom or just a proton?

Say we start with an entangled electron--positron pair and we separate them. I want to take the entangled electron and bind it to a proton or the outer shell of an atom. Is it possible to do this ...
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1answer
207 views

Is the quantum state or information of a particle is all that differentiates it from another particle?

So I have learned in my QM classes that you can't tell one electron from another electron. They are indistinguishable. I also learned that the wavefunction of a particle includes the spacial part and ...
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3answers
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Why electrons behave as a particle and also as a wave?

Why do electrons (and other very small particles) sometimes behave as particles (i.e. when we are not looking at them) where as other times they behave as waves?
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What are the conditions to be satisfied by a theory in order to be a quantum theory?

This is in continuation to my previous question. It is not a duplicate of the previous one. This question arises because of the answers and discussions in that question. Can we call a theory, quantum ...
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Are the basic postulates of QM the only set of postulates that can give rise to a sensible semi-probabilistic physical theory?

Are the basic postulates of QM, such as complex Hilbert space, unitary evolution, Hermitian operator observables, projection hypothesis etc., the unique and only set of postulates that gives rise to a ...
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Does the HUP alone ensure the randomness in QT?

This answer of mine has been strongly criticized on the ground that it is no more than a philosophical blabbering. Well, it may well be. But people seem to be of the opinion that HUP alone does not ...