All Questions
33 questions
20
votes
4
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4k
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How is it possible that quantum phenomenons (e.g. superposition) are possible when all quantum particles are being constantly observed?
I don't understand how quantum mechanics (and therefore also quantum computers) can work given that while we work with quantum states, particles that this quantum state consist of cannot be observed, ...
- 333
18
votes
5
answers
8k
views
Is quantum entanglement functionally equivalent to a measurement?
I saw the following talk the other day: http://www.youtube.com/watch?v=dEaecUuEqfc&feature=share
In it, Dr. Ron Garret posits that entanglement isn't really that "special" of a property. He ...
- 211
15
votes
6
answers
3k
views
Entanglement, real or just math? [duplicate]
In quantum entanglement when something acts on one particle the other one reacts also, just in reverse (more or less). From what I've read though, anything acting on either particle will collapse the ...
- 299
12
votes
2
answers
3k
views
Entanglement and simultaneity
According to the special theory of relativity, distant simultaneity depends on the observer's reference frame.
And, according to the quantum theory, in the case of two entangled particles, a measure ...
- 943
7
votes
3
answers
3k
views
What processes cause the collapse of a wavefunction and break entanglement?
This question states that measuring the spin of an entangled particle causes the collapse of the wavefunction and thus the entanglement is broken.
Then this question states that we don't know what ...
- 363
5
votes
2
answers
594
views
Decoherence: faster than light?
The answer to this question suggest that one can solve the measurement problem by decoherence. If I understand it correctly the decoherence appears when the quantum state interacts with the ...
- 741
5
votes
2
answers
278
views
Prepared states and quantum entanglement [duplicate]
Imagine two entangled quantum particles in the singlet state, one held by Alice and the other by Bob. Alice and Bob are both widely separated. Bob measures his spin in some axis and finds it to be ...
- 67
4
votes
6
answers
915
views
Explanation for the EPR-like paradox
I am trying to understand the process of Quantum Entanglement for use in Quantum computers.
The problem I have is this:
Suppose some nuclear process emits an electron-positron pair. Now after ...
- 193
3
votes
1
answer
3k
views
How does the notion of weak measurement resolve Hardy's paradox?
How the notion of weak measurement resolves Hardy's paradox?
- 1,260
3
votes
2
answers
3k
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 ...
- 141
3
votes
1
answer
439
views
Entanglement and the uncertainty principle
Suppose you have two maximally entangled particles. You measure the spin about the x axis of the first and the spin about the y axis of the second. But both spins cannot be known simultaneously, so ...
- 172
3
votes
0
answers
193
views
Uncertainty Principle - measuring momentum on one entangled particle, position on the other
If two entangled particles are sent far apart and then at exactly the same time the position of one, and the momentum of the other, is measured, won't this mean that, because the corresponding values ...
- 123
2
votes
1
answer
1k
views
Quantum Entanglement - Measuring Twice
In the answer here and on the wiki article and many other articles it is mentioned that if one of 2 entangled particles is measured their state collapses according to the Copenhagen interpretation.
...
- 179
2
votes
2
answers
155
views
Current quantum theory does not offer a dynamical mechanism to account for energy transfer in position-measurement, WHY?
In Quantum Mechanics (vol. 1) by Tannoudji et al., there are two pages discussing "perturbation created by a position measurement" (p.278-279). They consider a particle in an infinitely deep potential ...
- 173
2
votes
1
answer
219
views
Quantum non-locality with commuting measurements?
We consider the Bell scenario, in which Alice and Bob share an entangled pure quantum state $\mid \Psi \rangle_{AB}$. Alice gets an input in the set $\{1,2\ldots X\}$ and Bob gets an input in the set ...
- 781
2
votes
0
answers
122
views
Have objective collapse theories been ruled out by recent experiments?
Have objective collapse theories been ruled out by recent experiments, such as the entanglement of macroscopic objects? (vibrating drumheads)
- 31
1
vote
1
answer
875
views
How to understand the measurement on entangled state in the following cases? [closed]
Assuming an EPR pair AB, event MA is a measurement on A.
My questions are:
(1) At MB and MB' (depending on where B is located), if we try to describe the state of B (but not measure B yet), what's ...
- 1,576
1
vote
1
answer
1k
views
What happens to entangled particles when momentum is measured?
In Wikipedia it is mentioned that position and momentum can be entangled as well as spin and polarization etc. I assume etc. is charge etc.
I understand how if you measure spin up on one of a pair you ...
- 2,459
1
vote
2
answers
212
views
If measurement causes entanglement with the observer, is any further measurement possible?
When an observer measures a system, the systems wavefunction collapses and they become entangled. Does this mean that any further measurement by the observer on the system is impossible, as the system ...
1
vote
1
answer
199
views
Trouble understanding the math of the preferred basis problem
I've been trying to understand the preferred-basis problem in QM, specifally in the Everettian intepretation.
To quote an answer to another question which discusses this:
In my opinion, the situation ...
- 2,281
1
vote
1
answer
153
views
What initiates quantum entanglement?
In a previous question, I asked about the measurement problem in quantum mechanics. The sense I got is that the best interpretation we have is the many worlds interpretation, and one of the answers ...
- 768
1
vote
1
answer
115
views
Potential FTL Implications of quantum "weak measurement"?
Physics noob here. I can't find a good answer to this thought experiment that is consistent with general relativity and It's really bothering me. I'm probably missing something huge but just can't ...
user162880
1
vote
4
answers
231
views
Is a macroscopic pair where I observe one of them quantum entanglement?
Of what little I know/understand about quantum entanglement can somebody confirm if the following experiment is a good analogy to quantum entanglement of pair of particles? PS: please don't laugh as ...
1
vote
0
answers
87
views
Are there known paradoxes regarding a detector that was, before use, entangled with a particle it detects?
Is it possible to design a system where a detector is entangled with the particle state it detects (before it is detected), and to create a paradox from this?
Upon observance of a state by the ...
- 390
1
vote
0
answers
88
views
Can two entangled electrons can get disentagled in Nature, withous us making a measurement?
Imagine we have two free, entangled [by their spins, which are in this case non-separable, while $x$ (or $p$) electrons are clearly separable]. In an experimental setup, we can measure (and observe) ...
0
votes
2
answers
273
views
Why do lasers in open air produce 2-slit interference patterns? [closed]
I saw this answer:
Is quantum entanglement functionally equivalent to a measurement?.
I had follow up questions that seem to have been addressed. Here are just a few similar topics:
Why does ...
- 199
0
votes
1
answer
212
views
Quantum Measurement of Entangled Time-Varying Systems
Suppose System A has a dynamic, continuous variable $O_A(t)$, which we wish to measure via a quantum probe. Assume system A has a self-Hmiltonian, $H_{SA}$ so that the evolving wave function of ...
- 887
0
votes
1
answer
73
views
Will the electron interference remain if the photon scattering method doesn't include a photo-detector? Is it an example of quantum entanglement?
It is actually not a question. I am giving a chain of arguments here , I believe at some point I made a mistake. I want the mistake to be pointed out.
/1. The probability of an event in an ideal ...
0
votes
2
answers
213
views
Wave function collapse, EPR paradox and information transfer
For a classical formulation of the EPR paradox, two particles are produced, with total momentum zero and separated by a long distance. So say we measure the momentum of one particle first, and measure ...
- 1,169
-1
votes
1
answer
376
views
Implications of weak measurement on entanglement
What are the implications of weak-measurement on entangled particles, and how does that resolve the problem of non-superluminal quantum "communication"? If I understand correctly, entangled particles ...
- 101
-1
votes
1
answer
132
views
Quantum entanglement and affecting the particles [duplicate]
I am trying to grasp some aspects of the quantum entanglement, but the existing resources (including some of the links here) seem a bit confusing. I am trying to find an answer to the following ...
- 99
-2
votes
2
answers
420
views
Quantum Entanglement - How To Interpret [duplicate]
I have thought about quantum entanglement for some time, and I still don't quite understand the reasoning behind the conclusion that entangled particles somehow can communicate their state to each ...
- 12.4k
-2
votes
2
answers
115
views
In quantum mechanics does the truth/accuracy of a measurement really matter?
Once John Wheeler said "the past has no meaning or existence unless it exist as a record in the present". So, in a experiment of delayed choice entanglement swapping, if we used a faulty detector to ...
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