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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15 views

Resources on estimation of environment model for environemnt induced quantum decoherence

I am curious to see what literature exists about estimation of a quasi-classical environment interacting with a quantum system causing decoherence in system states. There has been in general a lot ...
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27 views

reduced density matrix of multiparticle system

Let the state of a composite system is $|\psi_{i}\rangle$ then the density matrix is defined as, $\rho=\sum P_{i}|\psi_{i}\rangle\langle\psi_{i}|$ Consider a composite system of two particles and its ...
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41 views

Pauli matrices using summation notation?

Is there any way to write the Pauli matrices: ...
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1answer
37 views

What exactly does the expectation value of $x$ mean in quantum mechanics?

When I learn quantum mechanics (by reading Griffith's book Introduction to quantum mechanics 2ed edition (Page 15)), I was confused by the concept of the expectation value of $x$, i.e. $\langle ...
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24 views

Solutions manual for Peres' book 'Quantum Theory: Concepts and Methods'

I'm working through Asher Peres' book 'Quantum Theory: Concepts and Methods,'and finding it immensely useful. I fully Recommend it! But when working on the problems in it I'd like to check my ...
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1answer
48 views

How can energy be negative in a finite square well?

Say if the potential $V(x) < 0$ in the well but the sides or the scattered states its zero potential, anyways How is that the energy in the well is less than zero? Is it because the potential ...
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1answer
59 views

Why aren't $\hat{x}$ and $\hat{p}$ considered functions of time in the expectation value?

In Griffiths Intro to QM (2nd edition), he gives the equation $$ \frac{d}{dt} \langle Q \rangle = \frac{i}{\hbar}\langle [\hat{H},\hat{Q}] \rangle + \left\langle ...
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33 views

Why alpha beta and gamma rays cannot be emitted simultaneously

If alpha beta or gamma rays cannot be emitted simultaneously then what is the basic difference between the composition or nature of substances which emit alpha beta or gamma rays?
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30 views

free energy in the path integral equivalent to the classical 1D Ising model: Shankar

In chapter 21 (eqtn 21.2.90) Shankar gives the free energy (of the PI problem equivalent to the classical 1D Ising model), $$ f=-E_0 = K^* $$ I dont understand how he arrives at this considering in ...
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54 views

Under what condition(s) is a body a wave or a particle? [closed]

I want answer to the above question in Quantum Theory
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1answer
43 views

When uncertainty is calculated in non normalized eigenstates it doesn't give zero. Shouldn't it give zero?

Suppose $\Psi$ is an eigenstate of observable $\text H$ with eigenvalue $E_1$. Then uncertainty in the value of $\text H$,$(\Delta E)^2=\langle E^2\rangle-\langle E\rangle^2$ which gives,$(\Delta ...
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1answer
97 views

Hilbert Schmidt inner product

I am desperately trying to solve the following problem, and would really appreciate help! Suppose $R$ and $Q$ are two quantum systems with the same Hilbert space $\mathcal{H}$ with ...
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27 views

On Rayleigh-Jeans black body distribution derivation

When trying to derive the Rayleigh-Jeans distribution function, all authors say that in k-space each solution of the electromagnetic wave functions(of waves inside a cubic black body) represents an ...
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1answer
67 views

Why is the “expansion postulate” a postulate of quantum mechanics?

I'm currently reading the following set of lecture notes on quantum chemistry, which includes the so-called "expansion postulate" as a fundamental postulate of quantum mechanics: "The eigenfunctions ...
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1answer
57 views

Scattering Theory

In non-relativistic quantum mechanical scattering theory you can derive an expression for the differential scattering cross section under the first order Born approximation as ...
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1answer
76 views

Apparent paradox concerning Heisenberg's uncertainty principle

I have just begun my Introduction to Quantum Mechanics course in my undergrad and I am trying to understand the uncertainty principle on a fundamental level. I think the best way to understand the ...
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0answers
35 views

How to describe spin-orbital coupling in Weyl semi-metal

In three dimensional Weyl semi-metal, the Hamiltonian that describes low excitation quasi-particle is well-know Weyl Hamiltonian: +/- $k\cdot\sigma$. But if I want to add spin-orbital coupling in that ...
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33 views

How to build QM with projective spaces from the beginning?

In conventional treatment of QM, one assumes that (1) physical states are normalized vectors in (rigged) Hilbert spaces and (2) operators correspond to observables, with their eigenvectors denoting ...
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2answers
103 views

Does the uncertainty principle go against chaos theory?

My understanding of the uncertainty principle and quantum physics is that any given object may, without notice or explanation, spontaneously perform an action it previously was unable to do with a ...
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0answers
31 views

What factors affect decoherence times? [closed]

The question say it all. For example is it the mass of the system? The amount of energy? The species of atom? The electric charge?
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39 views

How can we detect particles?

A constant velocity particle (charged or uncharged) can only be detected if its velocity is made to change, e.g. by scattering another particle or radiation off it. If it's velocity remains constant, ...
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1answer
121 views

Kronecker sum or direct sum?

When we write $$H=\sum_k H_k$$ in condensed matter physics, are we using Kronecker sum or direct sum? I think this is direct sum. However, Wikipedia says it is Kronecker sum. Can anyone give some ...
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0answers
24 views

What does it mean to find the stationary states of a free particle in a cubic well? [closed]

Sorry if this is an elementary question but Im not sure what it physically means to find the stationary states of a free particle in a cubic well. If anybody has some insight i'd really appreciate it! ...
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2answers
73 views

Does quantum entangled particle release energy when its “twin” is measured? [closed]

So I was just thinking a bit, and I came up with a couple of questions. As we all know the scenario: We have two quantum entangled particles. Let's call them A and B. We like to measure the state of ...
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2answers
117 views

Annihilating coherent state

Starting facts Annihilation operator $a$ removes one photon from fock state. Coherent states are eigenstates of annihilation operator and they are also superposition of different fock states. This ...
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31 views

Entanglement up to a finite distance

We do not have a theory which predicts the working distance of entanglement, and this distance is usually taken to be infinity. However, up to now, experiments have just rigorously confirmed ...
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1answer
76 views

Beyond usual quantum mechanic description of entanglement, is there any QFT or stringy formalism/explanation of it? [closed]

Currently entanglement is speculated to be one underlying mechanism of emergent spacetime, but what are its foundations?
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1answer
81 views

How do I interpret/make sense of atomic density plots?

For example, this one: I'm familiar with probability density functions, basic quantum mechanics, however, I don't know how to make sense of the chart. Specifically: Are the three numbers in the ...
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1answer
95 views

What force keeps electrons in their orbitals and not collapse into the positively charged nucleus? [duplicate]

I know about quantum mechanical model of an atom and how electrons behave like a standing waves and there isn't any lower level energy available for electrons below ground state energy and energy ...
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1answer
77 views

Does gluons have names?

I was trying to find in some general physics books and using the Internet the answer to my question - does each one of 8 gluons has its own name? For example quarks are named: Up Down Charm Strange ...
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0answers
50 views

Expectation value of the Hamiltonian [closed]

How to calculate expectation value of the Hamiltonian for hydrogen atom? $$\langle H \rangle_{\alpha l} \equiv \frac{\langle \psi_{\alpha l m}|H(r)| \psi_{\alpha l m}\rangle} {\langle \psi_{\alpha l ...
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33 views

Two-Photon Transitions

I'm reading these course notes on two-photon transitions at http://cua.mit.edu/8.421_S06/Chapter9.pdf But I can't understand why it looks like they do not allow for Autler-Townes splitting. In ...
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1answer
64 views

Reduced density matrix

During a course on quantum mechanics we've been talking about density matrices. Now I came across the following exercise. Consider a two spin $\frac{1}{2}$ systems, labeled 1 and 2. Calculate: ...
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34 views

Obtaining an angular distribution from the Klein-Nishina formula

I'm having trouble on how one might obtain an angular distribution from the Klein-Nishina formula for compton scattering of polarised photons, more specifically on how this report is obtaining it. ...
3
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48 views

Simultaneous measurement of non-commuting observables without uncertainty

A pair of non-commuting Observables $\hat{X}$ and $\hat{P}$ does not have a common set of eigenfunctions, i.e., it can not be measured simultaneously. Let us for the sake of simplicity assume that ...
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2answers
159 views

Does relativity violate uncertainty principle?

Let us say I sit on an electron. According to me the electron is at rest. Also, I will know the position of the electron accurately as I can take the electron as the origin. So, I know both position ...
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2answers
25 views

What does an eigenfunction which orthogonal to the general wavefunction mean , does it mean that the probablity of that eigenfunction is zero?

Imagine a wavefunction: $$ \Psi = C_1 \psi_1 + C_2\psi_2 + C_3\psi_3 + C_4\psi_4 $$ where $C_1$, $C_2$, etc are all constants and $\psi_1$, $\psi_2$, etc are eigenfunctions. If it is given that ...
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0answers
43 views

How it is possible that phase velocity of de Broglie wave may exceed velocity of light? [duplicate]

Phase velocity of de broglie wave may exceed the speed of light .Does this violate the relativity theory as we know nothing can overcome speed of light ??
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47 views

inverse problem for specific heat of fermion .. has been solved?

hi given the specific heat is given by an integral equation $$ C(T)=\int_{0}^{\infty}d\nu g(\nu)\frac{u^{2}}{(e^{u\nu}+1)^{2}}\nu^{2}$$ where $ u= \frac{h}{kT}$ my question is is the following ...
2
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1answer
55 views

Many-worlds interpretation (MWI) and conservation of energy [duplicate]

I am not an expert of many-worlds interpretation (MWI), and what I say may be stated incorrectly. In that case i welcome corrections. If the MWI is true and it explains quantum theory and it splits ...
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1answer
26 views

Is the transition electric quadrupole or magnetic dipole?

If a nucleus makes a transition from 0$^+$ ground state to 2$^+$ excited state, then will the transtion have E2 character, or M1? Or partly, both? Should the matrix elements of both E2 and M1 be ...
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0answers
17 views

Where can I find information on gas discharge tube mixes beyond the noble gases?

I have seen plenty of information on the noble gases, and oxygen and nitrogen. I haven't found much on other gases, or mixtures of gases. I don't really know where to look beyond google. I am in ...
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0answers
12 views

Multimode thermal state

A multimode thermal state is defined as: $ \rho=\sum_{\{n_k\}}|\{n_k\}><\{n_k\}|\prod_k\frac{<n_k>^{(n_k)}}{(1+<n_k>)^{n_k+1}} $ Is it also possible to swap the product and the ...
3
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0answers
77 views

Quantum computing with biological matter? [closed]

As a biologist with physics background I wonder whether there is a way to use biological matter to create quantum computers or at least to advance the field somewhat. Usually, my first feeling would ...
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0answers
7 views

type of photoluminescence depending on the FWHM

Depending on the FWHM of CdSe quantum dots, is it possible to estimate the type of dominant photoluminescence in question, as in excitonic luminescence is supposed to have a narrower spread than ...
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1answer
61 views

What's the microscopic and macroscopic effect of wavefunction dispersion?

In Quantum Mechanics (Merzbacher 2nd ed.), problem 2.1 asks us to derive the time evolution of a one-dimensional Gaussian wavefunction (formula given for $t=0$), assuming the velocity is in the $+x$ ...
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0answers
43 views

What type of physicist studies quantum physics the most? [closed]

I want to become a physicist, and I am particularly interested in quantum physics. I know quantum physics has applications in many branches of physics. Condensed matter physicists use it among others. ...
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1answer
35 views

Re-entering superposition

I've realized that I'm somewhat familiar with what happens when an system in a superposition is "measured". But not at all with what happens after. Example: If there is an electron in a ...
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48 views

Operator notation?

I'm starting out with many-body quantum theory, second quantization etc. by reading the book by Bruus and Flensberg. In the first chapter they write; "A given local one-particle operator $T_j$ ... ...