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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A quantum particle in a box (with a catch)

I am reading Shankar's Quantum Mechanics and I am looking at the case where there is one particle inside a box, where the potential is zero inside the wall and abruptly goes to infinity outside the ...
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385 views

Is it a total or an explicite time derivative in the Schrödinger equation?

I am always dubious when I need write Schrödinger equation: do I write $\partial / \partial t$ or $d/dt$ ? I suppose it depends on the space in which it is considered. How?
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2k views

What is “Quantum Levitation”?

I just found this video Controlled Quantum Levitation on a WipeOut Track and I'm having a hard time finding the term "Quantum Levitation" used except in reference to the video. What is the proper ...
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158 views

Are energies non-transferable in the Born-Oppenheimer approximation, and when does it apply?

Adiabatic approximation or the Born-Oppenheimer approximation is used whenever the electronic motion is too fast that the electrons effectively see static nuclei and the nuclei, in turn, see an ...
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712 views

What is the symmetry that corresponds to conservation of position?

We know that conserved quantities are associated with certain symmetries. For example conservation of momentum is associated with translational invariance, and conservation of angular momentum is ...
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1answer
754 views

Conjugate Variables and Fourier Transforms in Classical Physics

Let q be a generalized coordinate with a conjugate momentum p and a potential resulting in a periodic motion of q. What is the meaning of the Fourier transform of q(t) over its period? Can this be ...
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601 views

Regularisation of infinite-dimensional determinants

Can a regularisation of the determinant be used to find the eigenvalues of the Hamiltonian in the normal infinite dimensional setting of QM? Edit: I failed to make myself clear. In finite ...
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897 views

Nanorobots. What stops us from producing them yet?

If we can already predicts accuratelly motion on molecular levels, what stops us from developing small robots to, for instance, navigate through our blood vessels looking for cancerous cells and ...
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Kinetic energy of Electron [closed]

I had to find the kinetic energy of electron with wavelength $2$ pm. I used the formula $$ KE = \frac{p^2}{2m} = \frac{h^2}{\lambda^2 2m}$$ which gave me result, $KE = 376.9$ KeV. But the answer ...
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What inspired Schrödinger to derive his equation?

I have almost no background in physics and I had a question related to Schrodinger's Equation. I think, it is not really research level so feel free to close it, but I would request you to kindly ...
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2answers
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Software to simulate and visualize atoms?

Not sure if this is a physics or chemistry question. But if the motion of atoms and it's particles can be described by quantum mechanics, then is there a software that simulate full atoms and it's ...
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7answers
872 views

Which physically acceptable quantum interpretations do not require the existence of any observer at all?

Some interpretations of quantum mechanics — like the Copenhagen interpretation in particular — require the existence of an observer. The role of the observer is a bit mysterious. After ...
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Careers in physics that are related to quantum mechanics or relativity? [closed]

Personally I learned Physics in high-school and found it very interesting, I read up a lot about physics in my free time. Personally I am also a programmer which I think is also good when it comes to ...
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755 views

Why don't quantum effects invalidate the speed of light barrier?

While proving that no matter can reach the speed of light (a fact which I call the kinetic energy barrier), Einstein uses the fact that he can calculate the velocity and position of an electron. ...
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131 views

Identifying fragments when there is a superposition of fragments in quantum Darwinism

In Zurek's theory of quantum Darwinism, information about the pointer states of a system imprint themselves upon fragments of the environment carrying records about the state of the system. ...
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3answers
209 views

What are local electrons in a crystal?

I am reading Pekar's "Research in Electron Theory of Crystals" and I came across a passage I find a bit unclear: The theory developed below takes into account the dielectric polarization of a an ...
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1answer
144 views

What kind of interactions denote 'observation'?

I'm quite perplexed by the notion of 'observation' in regards to the collapse of a particle's probability wave. Does a particle's wave only collapse when it is involved in a strong interaction (such ...
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4answers
790 views

Locality in Quantum Mechanics

We speak of locality or non-locality of an equation in QM, depending on whether it has no differential operators of order higher than two. My question is, how could one tell from looking at the ...
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6answers
350 views

Why quantum states are classified using only conserved quantities?

While studying quantum mechanics from standard textbooks I always felt some conceptual gap that was never mentioned or explained. In what follow I tried to formulate my question, please be patient ...
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2answers
1k views

Can actual quantum effects occur on a macro scale?

I apologize if this question is posted on the wrong portion of the website, but I knew no better place to ask. I've come to see that some effects, such as super-conduction may happen at either ...
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143 views

Consideration of static atomic displacements in electronic structure calculations

I am hoping to discuss some details of electronic structure calculations. I am not an expert on this topic, so please forgive any abuse of terminology. It is my understanding that first principles ...
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3answers
890 views

J.J. Sakurai book on Q.Mech

I just want to ask how recommended is the book on quantum mechanics by J.J. Sakurai. Is it any good as an introductory text? And are there better suggestions (substitutes)? Thanks in advance
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85 views

Relativistic corrections to quantum mechanics of Coloumb potential

Systems of charged particles (such as atomic nuclei and electrons) can be described by nonrelativistic quantum mechanics with the Coloumb interaction potential. A fully relativistic description is ...
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6answers
643 views

Do we really know which slit the photon passed through in Afshar's experiment?

The plain old double slit experiment displays interference when we don't measure which slit the photon passed through, and no interference when it is measured. Let's turn our attention to the case ...
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2answers
244 views

Puzzled by $\mathrm p = -i\hbar \nabla = m \dot{\mathrm r}$?

I'm working on Physics of Atoms and Molecules by Bransden and Joachain. And I've come across the following statement, which I don't understand (p.195, ch. 4.3, "The dipole approximation") ... In ...
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Good book on the history of Quantum Mechanics?

Can anyone recommend a good book on the history of Quantum Mechanics, preferably one that is technical and not afraid to explain the maths (I did a degree in Physics many years ago) and also that ...
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304 views

Mass of the particle and gravitational field

Which mass of the particle is the source of gravitational field? If we define mass as a pole of the propagator, and calculate loop corrections to the pole we get infinities. Now the way we get rid of ...
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347 views

The Lorentz Transformations in the Micro-World

Two particles[or micro-observers] A and B are in relative uniform motion wrt each other in the x-x’ direction. The “observer” A decides to deduce[or interpret] the Lorentz Transformations wrt to B. ...
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155 views

Do interaction-free measurements require a physical collapse or splitting in order to be truly interaction free?

Interaction-free quantum experiments like Renninger's experiment or the Elitzur-Vaidman bomb tester are often taken to be examples of interaction-free measurements of a system. Unfortunately, such ...
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Variation of delayed choice quantum eraser

Let me base the discussion on the pictorial description of the delayed choice quantum eraser experiment on wikipedia. First suppose that we do precisely the same thing with the lower parts of the ...
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8answers
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What exactly is the 'observer' in physics and/or quantum mechanics? [duplicate]

Possible Duplicate: nature of an observer For instance, in the double slit experiment, what is exactly defined as an observer? I remember from somewhere, light is also an observer?
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1answer
117 views

Cross sections and renormalization scheme

Can the result on cross section of some process be dependent on the renormalization scheme used?
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3k views

Deterministic quantum mechanics

I came across a very recent paper by Gerard 't Hooft The abstract says: It is often claimed that the collapse of the wave function and Born's rule to interpret the square of the norm as a ...
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3answers
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What exactly is a quantum of light?

I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a photon as a quantum of light, which it further explains as some kind of a wave-packet. What ...
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136 views

How do you properly analyze decoherence when the system-environment interaction is strong?

The standard decoherence analyses work something like this. Split the universe into a system and its environment, and split the Hamiltonian as the sum of the system Hamiltonian, environment ...
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What does a unitary transformation mean in the context of an evolution equation?

Let be the unitary evolution operator of a quantum system be $U(t)=\exp(itH)$ for $t >0$. Then what is the meaning of the equation $$\det\bigl(I-U(t)e^{itE}\bigr)=0$$ where $E$ is a real ...
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0answers
202 views

Semiclassical approximation for the exponential sum (partition function)

For any real and positive $s$ and in the sense of semiclassical approximation, is this valid? $ \sum_{n}exp(-sE_{n})\sim \iint_{C}dxdpe^{-s(p^{2}+V(x))}$ valid for every $s$ Here simply both the sum ...
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10answers
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Does the Pauli exclusion principle instantaneously affect distant electrons?

According to Brian Cox in his A night with the Stars lecture$^1$, the Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the ...
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2answers
789 views

Assumptions in Heisenberg's 1925 paper

I am not entirely clear as to what were the bases for Heisenberg's assumptions in his 1925 paper. He claims that one cannot consider relations between quantities that are unobservable "in principle", ...
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Index Manipulation and Angular Momentum Commutator Relations

I have been trying for hours and cannot figure it out. I am not asking anyone to do it for me, but to understand how to proceed. We have the relations $$[L_i,p_j] ~=~ i\hbar\; \epsilon_{ijk}p_k,$$ ...
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5answers
887 views

Observable: possible outcome of measurement vs (linear) transformation

One of the postulates of quantum mechanics is that every physical observable corresponds to a Hermitian operator $H$, that the possible outcomes of the measurements are eigenvalues of the operator, ...
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396 views

Is energy conserved in decay of hydrogen atom in superposed state?

This looks like a paradox. Let's say we have an hydrogen atom. Superposition of states could be possible for electrons. But if an electron is in a superposition, I guess it could decay into a lower ...
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443 views

Physical interpretation of Wheeler - Dewitt equation

What is the mainstream ( if there is one ) interpretation of the Wheeler - Dewitt equation $\hat{H}\Psi =0$ ?
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4answers
542 views

Atom Theory vs Quantum Physics

This never really occurred to me until now, so maybe it does not categorize as a really important question, but, according to Quantum Mechanics, anything that is not observed exists as a probability ...
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2answers
253 views

Reconstruction of information stored in an evaporating black hole from the emission spectrum?

For simple setups, where the radiation field deviates not too far from thermodynamic equilibrium (< 10 %), corrections to the Planckian thermal emission spectrum can be calculated (and measured) ...
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Can you magnetize iron with a hammer?

We know that a piece of ferromagnet, such as iron, can be magnetized by putting in a strong magnetic field to get domains parallel to the field grow. I also remember from pop. culture and MacGyver ...
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2answers
248 views

Can the Heisenberg interpretation or path integrals apply to open quantum systems?

It has been claimed by some people that Schrödinger's picture is more misleading compared to the Heisenberg principle or path integrals, and that we would be better off abandoning the ...
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The implication of anti-commutation relations in quantum mechanics

All the textbooks I saw are very clear about the implications of commutating operators in quantum mechanics. However, much less is said about anti-commutation relations. Does it have a general ...
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8answers
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Why do quantum physical properties come in pairs?

Why do quantum physical properties come in pairs, governed by the uncertainty principle (that is, position and momentum?) Why not in groups of three, four, etc.?
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812 views

“Completeness” of eigenvectors in a complete, commuting set

This question was originally the one below dashed line. Now after further discussions, it has boiled down to this question: Is the following construction possible? Suppose we have a 3 dimensional ket ...