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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Einstein's box - unclear about Bohr's retort

I was reading a book on the history of Quantum Mechanics and I got intrigued by the gendankenexperiment proposed by Einstein to Bohr at the 6th Solvay conference in 1930. For context, the thought ...
3
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1answer
456 views

Measuring the magnitude of the magnetic field of a single electron due to its spin

Is it possible to measure the magnitude of the magnetic field of a single electron due to its spin? The electron's intrinsic magnetic field is not dependent upon the amount of energy it has does it? ...
3
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3answers
269 views

Knowing when wavefunction collapses

So I learned that after a measurement of, lets say the position of the wavefunction of a particle is made, if another measurement of the position of the particle is made right away, you should get the ...
9
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3answers
1k views

Is “analog” quantum-computation not useful?

I understand what a qubit-based quantum computer by the current definition is and how they are constructed. I read another thread where someone suggested encoding a computation into a dual-slit ...
7
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7answers
4k views

Eigenvalues of an operator correspond to energy states in quantum mechanics, why?

When finding the discrete energy states of a operator I have been taught to use the time-independent Schrodinger equation which restates the definition of eigenvalues and eigenvectors. What I don’t ...
11
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1answer
4k views

Phase shifts in scattering theory

I have been studying scattering theory in Sakurai's quantum mechanics. The phase shift in scattering theory has been a major conceptual and computational stumbling block for me. How (if at all) does ...
5
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2answers
361 views

Distinguishability in Quantum Ensembles

Inspired by this question: Are these two quantum systems distinguishable? and discussion therein. Given an ensemble of states, the randomness of a measurement outcome can be due to classical reasons ...
26
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11answers
7k views

About the complex nature of the wave function?

1. Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an ...
27
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7answers
1k views

Are these two quantum systems distinguishable?

Suppose Stanford Research Systems starts selling a two-level atom factory. Your grad student pushes a button, and bang, he gets a two level atom. Half the time the atom is produced in the ground ...
4
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3answers
1k views

How to tell if QM is really random?

Given a stream of random binary numbers(*) Is there any way to differentiate if they came from a Truly Random or from a formula/algorithm ? how? if there is no way to decide this, then, I can't find ...
3
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2answers
549 views

Observing the exponential growth of Hilbert space?

One of the weirdest things about quantum mechanics (QM) is the exponential growth of the dimensions of Hilbert space with increasing number of particles. This was already discussed by Born and ...
5
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3answers
3k views

Photon hitting an atom with higher energy than needed to ionize

Suppose we have an atom with several energy levels (e.g. an hydrogen), and it is hit by photons. I know that in order to have the atom change energy levels, the photon must have an energy level ...
1
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5answers
260 views

Does quantum mechanics allow us to formulate causally sufficient conditions for the occurrence of an outcome?

This is a follow-up question to "In QM, why do the probabilities ... add up to 1?". No actual measurement is perfect. While theorists may ignore this, experimenters know well enough that in many runs ...
1
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6answers
732 views

In quantum mechanics, why do the probabilities of the possible outcomes of a measurement add up to 1?

The question assumes the standard formalism with projector-valued measures rather than POVMs. Suppose a measurement has two possible outcomes, and the corresponding probabilities are greater than 0 ...
5
votes
2answers
417 views

What happens when particle-antiparticle pairs annihilate in MWI?

The many-worlds interpretation of quantum physics is built around a configuration space, where the position of a particle is three components of the position of that universe. What happens with ...
8
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7answers
1k views

Why is a classical formalism necessary for quantum mechanics?

This is not a question pertaining to interpretations, after the last one I realized I should not open Pandora's Box ;) For theories to be consistent, they must reduced to known laws in the classical ...
5
votes
1answer
469 views

What's the relevance of Efimov physics?

Is it something unexpected?Why universality in cold atomic gases is important?What researches are looking for?Can this be useful for topological quantum computers? Can we expect a whole myriad of ...
0
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1answer
380 views

Does quantum mechanics prohibit extraterrestrial life? [closed]

There is a known thought experiment, connected to quantum immortality: a duel between physicist and a philosopher. Each turn physicist and philosopher fire at each other with a pistol. The quantum ...
9
votes
2answers
2k views

Perturbation theory with degeneracy even after 1st order

Most textbooks on basic quantum mechanics tell you that when your initial Hamiltonian $H_0$ has degenerate states, then before you can do (time independent) perturbation theory with a perturbation ...
0
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1answer
687 views

Proving Operator identities (Quantum Physics)

How would I go about showing: $$\hat{A}^{\dagger} + \hat{B}^{\dagger} = \left( \hat{A} + \hat{B} \right) ^{\dagger}$$
8
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2answers
19k views

What is in the space between a nucleus of an atom and its electrons?

There is a common analogy about the structure of an atom, such as the nucleus is a fly in the centre of a sports stadium and the electrons are tiny tiny gnats circling the stadium (tip of the hat to ...
7
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1answer
639 views

Question about a Limit of Gaussian Integrals and how it relates to Path Integration (if at all)?

I have come across a limit of Gaussian integrals in the literature and am wondering if this is a well known result. The background for this problem comes from the composition of Brownian motion and ...
5
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1answer
672 views

The Heisenberg limit is not a limit?

This new Best-ever quantum measurement breaks Heisenberg limit PHYSICISTS have made the most accurate quantum measurement yet, breaking a theoretical limit named for Werner Heisenberg. ...
15
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6answers
3k views

Disproof of Bell’s Theorem

The half-page arxiv doc by Joy Christian of Oxford Uni, UK has the Title and Abstract: Disproof of Bell’s Theorem We illustrate an explicit counterexample to Bell’s theorem by constructing a ...
6
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4answers
3k views

Chemical potential

This is something probably very basic but I was led back to this issue while listening to a recent seminar by Allan Adams on holographic superconductors. He seemed very worried to have a theory at ...
7
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1answer
781 views

Recent breakthroughs in quantum computing?

Can anyone explain to me why we have had no major breakthroughs in the theory of quantum computation in the past 15 years? Shor's algorithm set the standard, since then we've had Grover's algorithm ...
2
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3answers
724 views

Causality and Quantum uncertainty [duplicate]

Possible Duplicates: Why quantum entanglement is considered to be active link between particles? Why can't the outcome of a QM measurement be calculated a-priori? Why do some (the majority ...
6
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3answers
303 views

References on the non-compositeness of the known elementary particles

What paper(s) or theory(s) describe or prove that the elementary particles that we have determined today cannot be made up of smaller more fundamental particles?
4
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1answer
492 views

Canonical momentum operators in curvilinear coordinates

What is the quantum canonical momentum operator corresponding to arbitrary canonical position. For example, in Cartesian coordinates ($x^i$), the canonical momentum operator with respect to each $x^i$ ...
3
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3answers
174 views

Are there measurable effects to scaling the action by a constant?

Classically, we obtain the equations of motion by finding a path which has an action that is stationary with respect to small changes in the path. That is the path for which: $\delta S =0$ Scaling ...
4
votes
3answers
775 views

Is contextuality required in quantum mechanics?

I still don't really understand what contextuality means in reference to quantum mechanics. If someone could give a clear definition that would be great. It sounds like it means you can't always ...
14
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5answers
1k views

What combinations of realism, non-locality, and contextuality are ruled out in quantum theory?

Bell's inequality theorem, along with experimental evidence, shows that we cannot have both realism and locality. While I don't fully understand it, Leggett's inequality takes this a step further and ...
3
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1answer
162 views

What are the statistics of three to five bosons?

This should be a very easy question. If you look at the bottom of "Identical Particles" in Wikipedia, you see Table 1, which gives you the two particle statistics for bosons, fermions and ...
27
votes
5answers
2k views

Does Heisenberg's uncertainty under time evolution always grow?

Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting ...
3
votes
2answers
295 views

Web references for Nelson's “Quantum Fluctuations”?

Edward Nelson's book "Quantum Fluctuations" (Princeton UP, 1985) gives an alternative way to introduce trajectories, quite different to the trajectories of de Broglie-Bohm type approaches. I've read ...
4
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3answers
431 views

Young's experiment or why the light can't be described as a particle [closed]

Who hasn't heard about the double-slit experiment? It figures in any book of quantum physics. But there is something no one can explain to me : I understand why the light cannot be described only as a ...
2
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1answer
329 views

3D Minimum uncertainty wavepackets

Based on the 1D case mentioned in Griffiths, I decided to try looking at the features of 3D Gaussian wavefunctions, i.e. (position basis) wavefunctions of the form $\psi(\mathbf{r}) = ...
6
votes
3answers
888 views

Why is tunneling not a classical idea?

There is no tunneling in the case of infinite potential barrier, but there is when we have a finite well. In the classical analog, in the first case we have a particle bouncing between to infinitely ...
2
votes
3answers
749 views

Unstable energy levels

Well, reading about "Raman Effect" I saw that when the electron absorb some energy, with frequency $ \omega_{abs} $, that is different from $ \omega_{n} - \omega_{n-1} \neq \omega_{abs1} $, it go to ...
8
votes
4answers
959 views

By what mechanism do quantum effects become observable in normal life at the macroscopic level?

By what mechanism do quantum effects become observable in normal life at the macroscopic level? For instance, when two molecules "collide" is the momentum a probabilistic event wherein the end state ...
-2
votes
2answers
405 views

Chaos and quantum physics: How many ways can a bonfire burn?

I'm interested in the extent to which quantum physical effects are seen at a macroscopic level. I might get some of the physics wrong, but I think I'll get it close enough that I can ask the ...
3
votes
1answer
649 views

Minimum Uncertainty Wavefunction derivation

Can anyone point me to a reference (preferably either something online or something a small liberal arts school would be likely to have in its library) that goes through a derivation of the minimum ...
1
vote
2answers
249 views

What is the possible potential?

The professor asked us to do this one: "..Determine all potentials $V(r,\theta, \phi)$ for which it is possible for find solutions of the time independent Schrodinger equation which are also ...
18
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7answers
3k views

Why do people still talk about bohmian mechanics/hidden variables [closed]

I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal ...
2
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1answer
267 views

A particular notation about fermions

I am not sure that this notation is specific to supersymmetry theories but I ran into this while studying that. I see people talking of component fields of a chiral superfield as $\phi$ and ...
7
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5answers
1k views

Why isn't the wave equation $\nabla^2 \psi - 1/c^2 \partial_{tt} \psi = (\frac{mc}{\hbar})^2\psi$

Special relativity was well established by the time the schrodinger equation came out. Using the correspondence of classical energy with frequency and momentum with wave number, this is the equation ...
3
votes
1answer
3k views

How to solve this Schrödinger equation?

I am taking an intro level quantum mechanics class. Our textbook gives a problem like this: The deuteron is a nucleus of "heavy hydrogen" consisting of one proton and one neutron. As a simple ...
10
votes
2answers
572 views

Long time deviations from exponential decay in radioactivity

Are there any examples of common substances whose decay is not exponential? We're used to thinking about radioactivity in terms of half-lives. This is a concept that makes sense only for a decay that ...
10
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5answers
769 views

Retrodiction in Quantum Mechanics

To focus this question let us consider first classical mechanics (which is time-symmetric). Given a final condition (and sufficient information) one can calculate the system conditions of an earlier ...
8
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3answers
296 views

References on the physics of anyons

Anyone know some good introductory references on the physics of anyons?