31
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Why are there no clear experiments describing the exact boundary between classical and quantum sizes?
Why are there no clear experiments describing the exact boundary between classical and quantum sizes ?
There are no clear experiments because there is no exact boundary.
Although we think of quantum ...
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26
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What is the quantum mechanical definition of a measurement?
Until we have an accepted solution of the Measurement Problem there is no definitive definition of quantum measurement, since we don't know exactly what happens at measurement.
In the meanwhile, ...
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22
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What are the strongest objections to be made against decoherence as an explanation of "collapse?"
I think most arguments in the literature can be boiled down to the point that decoherence does in no way touch the linearity of the Schrödinger equation, and thus cannot make an "or" from an "and".
...
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20
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What is the difference between classical correlation and quantum correlation?
Correlation is first and foremost a term from statistics. Given a system that consists of two (or more parts), it quantifies how much I can predict about the second system if I have knowledge of the ...
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17
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Would every particle in the universe not have some form of measurement occurring at any given time?
What you describe is the process known as decoherence: any interaction of a quantum system with its environment (e.g. with photons or other particles passing by, and, yes, most likely interacting ...
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16
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Why do particles tend to collapse to *energy*-eigenstates (rather than some other basis)?
But energy eigenstates are just one particular basis for representing quantum states of an electron. Why do particles tend to eigenstates of the hamiltonian,
States don't "tend to" do ...
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15
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Can the collapse of the wave function be modelled as a quantum system on its own?
To model the act of measurement itself as an interaction of the measurement apparatus and the measured system as quantum systems is a perfectly standard thing to do, though you might get disagreements ...
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14
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Why do particles tend to collapse to *energy*-eigenstates (rather than some other basis)?
If a system is undergoing interference and information is copied out of that system that tends to suppress the interference: this process is called decoherence. For macroscopic objects this is usually ...
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13
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What is the quantum mechanical definition of a measurement?
The many-worlds interpretation defines measurement as any physical procedure in which the observer gets entangled with a quantum system. Before the measurement, the universe containing the observer ...
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9
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Pure dephasing $\gamma_\phi$ in a master equation and noise power spectral densities
$\def\ii{{\rm i}}
\def\dd{{\rm d}}
\def\ee{{\rm e}}
$
It turns out that the case of pure dephasing is exactly solvable, and one can obtain nice solutions under certain conditions. In particular, I ...
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What does spontaneous symmetry breaking have to do with decoherence?
I don't think I have anything really new to say here, but saying it again in different words might have some value, so I'll give it a try.
Consider these two seemingly-contradictory statements, both ...
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9
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Why does the electron wavefunction not collapse within atoms at room temperature in gas, liquids or solids due to decoherence?
Welcome to SE -- good question! Decoherence does not mean that there won't be a wavefunction anymore, it just means that if the electron becomes coupled to the surrounding environment, its state will ...
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9
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Why do particles tend to collapse to *energy*-eigenstates (rather than some other basis)?
Sometimes other basis states are interesting. Neutrino flavor eigenstates are not energy eigenstates. So netrinos oscillate, changing from one to the next.
FermiLab's Even Bananas series of video has ...
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9
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Once decohered, is the quantum system always fully transitioned from superposition of states to one definite, 'classical' state?
Short answer: No. Decoherence describes the interaction between a system and its environment. After this interaction, the system and environment will together be in a superposition of different states....
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8
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Decoherence. Does it solve the measurement problem? Is it discontinuous? When does it occur?
You can find a comprehensive review of decoherence and how it fits in the QM interpretation debate in Decoherence, the measurement problem, and interpretations of quantum mechanics (Schlosshauer, 2005)...
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8
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Why are there no clear experiments describing the exact boundary between classical and quantum sizes?
Collapse is supposed to be a process that takes a quantum system in a superposition and somehow selects just one of the states in the superposition:
$$\sum_a\alpha_a|a\rangle\to|a\rangle$$
This ...
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7
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Does uniqueness of the triorthogonal decomposition make quantum measurement objective?
The triorthogonal monomial basis for a Hilbert space decomposed into a triple tensor product is unique, the decomposition of the Hilbert space into such a triple product is not. So the "unique" basis ...
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7
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Are superpositions contagious?
You seem to be trying to play decoherence theory against the measurement problem, but the two are actually orthogonal. QM does not make wrong predictions, but we need to be precise about what a "...
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7
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Is the Copenhagen interpretation still the most widely accepted position?
This is very hard to quantify, particularly because it's hard to define the population that should be under consideration. The best(-known) attempt to do this is reported in the paper
A Snapshot of ...
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7
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Is the Copenhagen interpretation still the most widely accepted position?
It's difficult to answer this question because there seems to be little agreement about what the "Copenhagen interpretation" is.
I don't know a lot about Heisenberg's beliefs, but Bohr's ...
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7
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Relationships between elements in the density matrix
Consider a finite dimensional complex Hilbert space $H$ of dimension $d$ equipped with an inner product denoted by $(\cdot,\cdot)$ and let $\rho$ be a generic density operator, i.e. a positive semi-...
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7
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Can the collapse of the wave function be modelled as a quantum system on its own?
When a quantum system interacts with another system while it is undergoing interference information is copied out of the system that suppresses interference. This effect is called decoherence. Since ...
- 10.2k
6
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Do measurements of time-scales for decoherence disprove some versions of Copenhagen or MWI?
I am not aware of any experimental evidence, so this probably does not qualify as an answer. However I can offer a reference that addresses this question theoretically:
Armen E. Allahverdyan, Roger ...
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6
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Would every particle in the universe not have some form of measurement occurring at any given time?
This topic gave me trouble as well. The fundamental basis for answering it is to look at decoherence.
Basically, any interaction in quantum mechanics yields the expected coherent result that comes ...
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6
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Decoherence: faster than light?
For the record I do not necessarily want to claim that decoherence solves all the subtle interpretational issues that go under the "measurement problem", at least not without some extra ingredient(s) ...
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6
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Is there a classical quantum mechanics?
Quantum mechanics works (as far as we can tell) in all systems (although we still haven't settled on a way to get relativistic gravity to work nicely with quantum mechanics). Quantum mechanics ...
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How do Heisenberg Uncertainty and Quantum Decoherence coexist?
Note In this answer, technical asides are in italics.
There is a false dichotomy in your question, which I think comes from the way quantum mechanics is often presented at a popular science level. The ...
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6
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Why are accessible states taken as eigenstates in statistical physics? Is the resolution via decoherence?
I'll present a complement to AXensen's very good answer.
Statistical physics of quantum systems can be based on the general description of the state of a quantum system in terms of the density ...
5
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Simple question about decoherence
Answer to question 1 is: half-yes, half-no. Answer to question 2 is: you need to think about dynamical behaviour, not just the states.
Decoherence does half the job of solving the measurement problem....
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