This tag is for questions about the exact nature of wavefunction collapse.
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4answers
191 views
How do we know that there isn't a classical solution to the measurement problem/Quantum Mechanical uncertainty?
It was mentioned to me that it can be shown that there is no classical explanation for the uncertainty in Quantum Mechanics -- i.e. that there are no hidden workings that we have just not yet seen, ...
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2answers
87 views
Can we measure “wavefunction” of quantum particles?
We know that there is uncertainty principle, so question: can we ever measure wavefunction of particles? I do not think this is possible, but I am not sure. I guess that everything is probabilistic. ...
2
votes
2answers
49 views
Is it possible to determine the state or values of something without measuring it
To give context to this question, I am currently looking into non-locality / hidden variables / Bell's Theorem, EPR / etc.
I've noticed the assertion that the values / state of something when ...
13
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2answers
152 views
Is every quantum measurement reducible to measurements of position and time?
I am currently studying Path Integrals and was unable to resolve the following problem. In the famous book Quantum Mechanics and Path Integrals, written by Feynman and Hibbs, it says (at the beginning ...
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0answers
19 views
Does quantum mechanics depend solely on electromagnetic waves? [duplicate]
I am beginning to learn quantum mechanics. Since determining the position of an object involves probing by electromagnetic waves and since i have read a simple derivation of Heisenberg's uncertainty ...
0
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1answer
119 views
The System and the Measuring Gadget
In Quantum Mechanics the value of an observable results from the interaction between the "system" with the "Measuring gadget".
But when the experimenter[or the technologist concerned] is ...
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3answers
84 views
Observer effect, do this mean literally someone or just any interaction with other matter?
I am a layman and was wondering, the quantum observer effect. The regular notion to laymen seems to be literally "if you look at it", but as I am coming to understand the world I live in better I feel ...
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3answers
512 views
Measuring the spin of a single electron
Is it possible to measure the spin of a single electron? What papers have been published on answering this question? Would the measurement require a super sensitive SQUID, Superconductive Quantum ...
0
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2answers
119 views
Measurement of the energy of an atom using a cold substance
An atom was prepared in a superposition of ground state and excited states.I propose to measure the state by coupling the system to a cold enough substance.
By cold enough I mean $$kT\ll E_1,$$ where ...
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0answers
42 views
Partial Measure Probability
Let be a
$$|\psi\rangle = \dfrac{3}{5\sqrt{2}}|00 \rangle- \dfrac{3i}{5\sqrt{2}}|01 \rangle+ \dfrac{2\sqrt{2}}{5}|10 \rangle - \dfrac{2\sqrt{2} i}{5}|11 \rangle$$
state with two qubits. ...
2
votes
4answers
181 views
Are photons deterministic?
I propose the following scenario:
At $t=0$, a photon is emitted from a star. At $t=n$, said photon is received and interpreted by some detector.
My question is whether or not it is accurate to say ...
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vote
2answers
86 views
Does performing a measurement on a system change its internal energy?
I'm studying Quantum Mechanics in my spare time from a general point of view (no technical details) so some fundamental question came into my mind:
How is it possible to detect a single photon ...
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2answers
76 views
About Heisenberg uncertainty principle [duplicate]
What would happen if someone invented a way to measure both position and momentum precisely? If it is impossible why?
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8answers
503 views
Does the wave function/density state actually exist?
I have been reading with interest the debates here on whether the wave function/density state actually collapses or not, or whether it is subjective Bayesian or objective with actual complex numbered ...
5
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3answers
661 views
Can randomness exist?
Considering every cause has an action, how can anything be random? For something to happen, it must have a cause and through that definition it can't be random.
Considering this why are many quantum ...
4
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6answers
311 views
Why is Heisenberg's uncertainty principle not an experimental error since it is the error created by photons striking on elementary particles?
Why is Heisenberg's uncertainty principle not an experimental error since it is the error created by photons striking on elementary particles?
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5answers
567 views
Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?
From what I understand, the uncertainty principle states that there is a fundamental natural limit to how accurately we can measure velocity and momentum at the same time. It's not a limit on ...
10
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3answers
262 views
Can the path of a charged particle under the influence of a magnetic field be considered piecewise linear?
Ordinarily we consider the path of a charged particle under the influence of a magnetic field to be curved. However, in order for the trajectory of the particle to change, it must emit a photon. ...
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2answers
66 views
Does the unpredictability in the “micro world” means that everything is if we can look at it close enough imperfect?
Does the unpredictability in the "micro world" means that everything is if we can look at it close enough imperfect?
I mean, there is a saying "You will never stand in the same river again" or ...
7
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2answers
589 views
Why is the Heisenberg uncertainty principle stated the way it is?
I spent a long time being confused by the Heisenberg uncertainty principle in my quantum chemistry class.
It is frequently stated that the "position and momentum of a particle cannot be ...
3
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1answer
183 views
In QM, does random data “come from anywhere”? Also, what are the properties of the data?
I have only taken a basic quantum mechanics course (this book, so you know where I'm coming from), but I've been wondering about something.
If we set up a quantum system in a known state and take a ...
9
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2answers
206 views
Is the uncertainty principle just saying something about what an observer can know or is it a fundamental property of nature?
I ask this question because I have read two different quotes on the uncertainty principle that don't seem to match very well. There are similar questions around here but I would like an explanation ...
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6answers
641 views
Measurement problem in the orthodox interpretation
Let's look at the measurement problem in the orthodox interpretation of quantum mechanics as an inconsistency between inner and outer treatment of the measurement apparatus. You can always push your ...
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0answers
29 views
Information conservation during quantum measurement in $\psi$-epistemic interpretations [duplicate]
Possible Duplicate:
Information conservation during quantum measurement
I asked a version of the following quesiton previously on Physics.stackexchange, where it didn't get a lot of ...
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6answers
626 views
What constitutes an observation/measurement in QM?
Fundamental notions of QM have to do with observation, a major example being The Uncertainty Principle.
What is the technical definition of an observation/measurement?
If I look at a QM system, it ...
5
votes
8answers
670 views
Schrodinger's dead cat when the evidence is destroyed
In the classic (and morbid) Schrodinger's Cat thought experiment, we imagine putting a cat into a box with a vial of poison which will be triggered by a quantum detectors. We set up a radioactive ...
2
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1answer
46 views
Unknown quantum state with promise of classical data
I am trying to solve a problem in the measurement and identification of quantum states with a promise as to what states it could be. Here is the problem. Imagine a system that produces qubits in ...
2
votes
6answers
350 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 ...
3
votes
1answer
173 views
If nothing is “objectively real” prior to “measurement”, what exactly is a “measurement”?
If nothing is "objectively real" prior to "measurement", what exactly is a "measurement"?
Is there any "objective" criteria to demarcate a process as being a "measurement" or not? If "measurements" ...
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vote
2answers
127 views
What does the quantum state of a system tell us about itself?
In quantum mechanics, quantum state refers to the state of a quantum
system. A quantum state is given as a vector in a vector space, called
the state vector. The state vector theoretically ...
0
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1answer
63 views
Is the time of collapse of the wave function empirical?
Is the time of the collapse of the wave function empirical?
Suppose there is a very long von Neumann chain of observations of a quantum system. Suppose also practically irreversible decoherence ...
9
votes
1answer
45 views
Accurate quantum state estimation via “Keeping the experimentalist honest”
Bob has a black-box, with the label "V-Wade", which he has been promised prepares a qubit which he would like to know the state of. He asks Alice, who happens also to be an experimental physicist, to ...
0
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1answer
129 views
Who are “we”, and what counts as a “question” in consistent histories?
If the preferred basis in quantum mechanics and/or choice of consistent histories in consistent histories is arbitrary, and can only be determined by the "questions we ask", just who exactly is this ...
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1answer
472 views
Application of Heisenberg's uncertainty principle
I've the following application of Heisenberg's uncertainty principle.
If a beam of particles in localised in the $x$-direction by a long slit, what is the uncertainty in position?
Firstly, I ...
2
votes
2answers
165 views
Can we determine whether or not a particle is entangled?
Suppose Shaniqua and Tyrone have four pairs, a, b, c, and d, of entangled particles. They take their particles and go very far apart. If Tyrone can determine whether or not a particle is still ...
11
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3answers
131 views
POVMs that do not require enlargement of the Hilbert space
The usual justification for regarding POVMs as fundamental measurements is via Neumark's theorem, i.e., by showing that they can always be realized by a projective measurement in a larger Hilbert ...
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votes
1answer
48 views
Spekkens Toy Model, Internal Comonoids
I have been thinking about Spekkens Toy model in terms of interfaces. The Spekkens paper concerns a physics based on only being able to receive answers to half the number of questions necessary to ...
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1answer
445 views
The measure problem in the anthropic principle
The anthropic principle is based upon Bayesian reasoning applied to the ensemble of universes, or parts thereof, conditioned upon the existence of conscious observers. That still leaves us with the ...
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3answers
238 views
Double slit experiment and indirect measurements
In the classic Young double slit experiment, with slits labeled as "A" and "B" and the detector screen "C", we put a detector with 100% accuracy (no particle can pass through the slit without the ...
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3answers
238 views
Decoherence and collapse
It is said that the decoherence does not solve the problem of measurement and/or the emergence of classicality, can somebody explain it with simple analogies or in a manner accessible to a ...
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2answers
214 views
Why for a spin half particle, possible outcomes of measuring spin projection along any direction are the same?
If one measures the projection of spin of a spin half particle along the x axis one will always get plus or minus half $\hbar$
Measuring it along the y axis one will always get plus or minus half ...
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3answers
257 views
What is the experiment where subatomic particles appear to foresee the future?
I've seen a documentary, whose name I don't remember but I'm curious because it suggests that subatomic particles are able to "foresee the future".
I'll try to describe it here:
Some particles are ...
9
votes
1answer
61 views
Quasiparticles in Bohmian mechanics
My questions are about de Broglie-Bohm "pilot wave" interpretation of quantum mechanics (a.k.a. Bohmian mechanics).
Do quasiparticles have any meaning in Bohmian mechanics, or not? Specifically, is ...
2
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0answers
59 views
How to explain Tsirelson's inequality using extended probabilities?
How to explain Tsirelson's inequality using extended probabilities?
Some people have tried explaining the Bell inequalities using extended probabilities.
For instance, a pair of entangled photons ...
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vote
2answers
192 views
Does every measurement correspond to an eigenstate of an observable?
In the postulates of quantum mechanics, physical observables are described by Hermitian matrices on the state space of a system.
In another of my questions, the measurements of Rydberg-Ritz spectral ...
4
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1answer
84 views
Practical meaning of making a measurement/observation in QM?
When an argument like 'measure the spin along the $x$ axis', 'observe the position of a particle' and so on is made, what is the implied experimental procedure? Since laboratory equipment is ...
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10answers
874 views
What is the difference between a measurement and any other interaction in quantum mechanics?
We've learned that the wave function of a particle collapses when we measure a particle's location. If it is found, it becomes more probable to find it a again in the same area, and if not the ...
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5answers
660 views
Is there a difference between observing a particle and hitting it with another particle?
First, let me state that I'm a lot less experienced with physics than most people here. Quantum mechanics was as far as I got and that was about 9 years ago, with no use in the meantime.
A lot of ...
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1answer
224 views
Controlling the outcome of a quantum measurement through translational entanglement
According to the paper:
A. S. Parkins and H. J. Kimble, Phys. Rev. A 61, 52104 (2000).
http://pra.aps.org/abstract/PRA/v61/i5/e052104
You can entangle position and momenta of two atoms by using ...
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3answers
408 views
Solution to the quantum measurement problem?
What can be a scientific solution to the Q-measurement problem (other than many worlds idea)? Can it be somehow verified through experiment?
