All Questions
Tagged with quantum-mechanics quantum-entanglement
1,354 questions
0
votes
0
answers
15
views
What is the outcome of Type I SPDC if the pump beam is circularly polarized?
I'm thinking about entangled photon pairs generation, specifically about Type-I SPDC where you use a pair of non-linear crystals such as BBO with their optical axes crossed and then the pump beam is ...
- 35
-6
votes
0
answers
70
views
Where is the raw entanglement data for John Clauser's experiment that won the Nobel prize of 2022? [closed]
Other than the delft experiment (which uses post hoc filtering) there are few experiments which publish the data from bells CHSH experiments.
Can anyone explain to me why I should accept the ...
- 11
1
vote
5
answers
181
views
Entanglement collapse and relative order of events
According to QM (and many confirming experiments) outcomes (e.g. spin) of entangled particles measurement are non-locally correlated (i.e. can’t be pre-configured for such correlations).
It seems that ...
- 93
3
votes
4
answers
80
views
Single particle measurement in entangled states [closed]
There is a system with two particles in a state given by the wave function $F(x_1,x_2)$. What does it mean to make a measurement on one of the particles? This is not defined among the axioms of ...
- 167
1
vote
1
answer
48
views
Decomposing density matrix on non-orthogonal and incomplete set of states
I've recently come across the following conclusion in a quantum optics paper. The paper studies the dissipative dynamics of a two-qubit system and presents the following approximation for the steady-...
- 11
1
vote
3
answers
113
views
Is the spatial spread of the wave function over large distances the rule or the exception in quantum mechanics?
In quantum mechanics, I've read that wave functions for individual particles technically extend over all space, though the probability density tends to decrease with distance. This suggests that a ...
- 501
0
votes
0
answers
45
views
How to maximally entangle two qubits? [duplicate]
I'm looking for a transformation that entangles two qubits $\mid{\psi}_1\rangle = \alpha_1 {\mid}0\rangle + \beta_1 {\mid}1\rangle$ and $\mid{\psi}_2\rangle = \alpha_2 {\mid}0\rangle + \beta_2 {\mid}...
- 1,355
0
votes
3
answers
110
views
Is it possible to affect spin probability of an entangled particle?
Say I have entangled particles A and B. Assuming we are talking about photons, we have 50/% chance of particle A being spin up.
Is it possible to affect the probability of particle A to be spin up ...
- 11
2
votes
1
answer
73
views
Interference pattern with known photon path
I read about the Delayed-choice quantum eraser experiment and came up with an idea. As we know, if we can determine which slit the photon passed through, we cannot observe an interference pattern. But ...
1
vote
1
answer
182
views
Can somebody explain to me one of the Bell experiments?
I can't understand the experiment in this paper.
In this experiment, two electrons at different points $A$ and $B$ are entangled with one photon each. Then, the photons are entangled in point $C$ ...
- 129
0
votes
3
answers
133
views
Understanding how entanglement physically arises in nature
My background is in CS and I have just started to learn Quantum Computing. From what I have understood: Given a set of $N$ qbits that are in some superposition state, can entangle these qbits with ...
2
votes
0
answers
62
views
Is electron correlation in Quantum Chemistry a consequence of many-body entanglement?
Electron correlation is largely defined in Quantum Chemistry as the set of properties that the celebrated Hartree Fock Approximation cannot model accurately. One popular example is the phenomenon ...
- 93
-1
votes
3
answers
173
views
Do quantum entangled particle pairs actually interact? [duplicate]
I believe this question could help simplify the accepted understanding of quantum entanglement for myself and others with little to no real physics background.
So my understanding of one way to create ...
0
votes
1
answer
44
views
Is it possible to detect entanglement by observing only one of the entangled particles?
For example, suppose an entangled electron and anti-electron have been produced in an inertial center-of-mass frame. If we have just a single detector and it observes a positron, then it's probably ...
3
votes
4
answers
297
views
How can non-realism alone explain quantum entanglement?
I’ve seen similar questions on this site but haven’t found a clear answer for this question. For clarity, I’ll define how my layman brain is interpreting locality and realism…
Locality: Information ...
- 33
-1
votes
3
answers
134
views
Another Entanglement Question - Can you tell if the wave function of an entangled particle is collapsed?
Apologies for the additional question on a topic that seems to be queried relatively frequently in this forum -
I was unable to find an explicit answer to this specific question in searching physics ...
0
votes
2
answers
79
views
Are quantum measurements on two different particles always commutative?
If we have some quantum system of two entangled particles -- let's call them $a$ and $b$. Let $A$ and $B$ be some arbitrary observables we can measure on the two particles, respectively.
Is it ...
- 779
-1
votes
1
answer
59
views
Are states of entanglement particles defined at creation? [closed]
Are states of entanglement particles defined at their creation?
- 730
-1
votes
3
answers
183
views
Is quantum entanglement independent of measurement timing?
If I have the entangled state
$\vert \uparrow \downarrow \rangle + \vert \downarrow \uparrow\rangle$, and then
measure the spin of one particle and find it to be $\uparrow$, will the spin of the ...
- 730
4
votes
1
answer
100
views
Is the electron pair in an orbital entangled?
In the video "Bird navigation: The Quantum Around You. Ep1", Dr. Andrea Morello seems to imply that the electron pairs in atomic orbitals are entangled and will exhibit properties of ...
- 43
5
votes
1
answer
272
views
Density matrices and locality
I'm having trouble understanding the physical aspect of entangled sub-systems, suppose I have a global entangled state:
\begin{equation}
|\psi\rangle = \frac{1}{\sqrt{2}}\left(|0\rangle_{A} \otimes |1\...
- 562
3
votes
1
answer
119
views
How is quantum entanglement detected experimentally?
What type of detector was used to detect entanglement of different systems, for example, photons?
Are there new detectors being made now?
What technique is used for this detection?
- 119
16
votes
5
answers
2k
views
Electron "clouds" in an atom
I have a very naïve understanding of atomic structure and quantum mechanics. But from what I have heard about the double slit experiment with an electron, we can say that if we shoot photons on the ...
- 8,496
1
vote
1
answer
48
views
Entanglement distance and quantum mechanics length scales
In this answer https://physics.stackexchange.com/a/9253/256311, the author said
Usually, we think of quantum mechanics to govern the microscopic world, involving length scales of under a micrometer, ...
- 21
0
votes
2
answers
82
views
Entangled Photons passing different polarizers
Consider two entangled photons leaving a source. Both are polarized at angle 0. One travels to the left and the other to the right. The one on the left encounters a polarizer at 30 degrees and the one ...
- 19
1
vote
1
answer
143
views
Are states partially ordered in the same way via entanglement and Bell violations?
Recall what a partially ordered set is.
Let $E(\rho)$ be an entanglement measure. Let $B(\rho) \leq 0$ be a Bell inequality. Define the Bell violation measure with respect to $B$ as
$$\tilde{B}(\rho) =...
- 3,295
1
vote
0
answers
65
views
Why can we not experimentally evaluate the expectation value of the CHSH operator after simplifying its expression to check entanglement?
We have the observable corresponding to the CHSH inequality given by,
\begin{align}
\mathcal{\hat{S}} &= \hat{Z}_1 \left(\frac{1}{\sqrt{2}} (-\hat{Z}_2 - \hat{X}_2)\right) + \hat{X}_1 \left(\frac{...
- 131
0
votes
0
answers
48
views
Where to find the Expectation Values of Aspect's and Clauser Experiments [duplicate]
Alain Aspect and John Clauser won the Nobel Prize in Physics for their epxeriments on quantum entanglement. Does anyone know where to find the raw data or at least published calculated expectation ...
-4
votes
1
answer
184
views
Bell's inequality in Claude Cohen-Tannoudji's Quantum Mechanics Volume III
Claude Cohen-Tannoudji et al, Quantum Mechanics Volume III, 2020 edition, Chapter XXI.F-3-b.$\alpha$ (F-7) on p.2210 states
$$\big\langle\hat A(a)\hat B(b) \big\rangle={\cal P_{++}+P_{--}-P_{+-}-P_{-+}...
- 1,060
2
votes
1
answer
202
views
Example of a classical correlation and a quantum correlation
I'm trying to understand the fundamental differences between classical and quantum correlations through examples of a quantum entangled state and a classically correlated state.
I know that this is an ...
- 39
2
votes
1
answer
146
views
What is a physical example of entanglement occurring naturally?
What is a physical example of entanglement occurring naturally? I am looking for an instance that I would see in nature outside the lab. I am looking for this example to be concrete and physical.
I ...
- 1,397
2
votes
0
answers
57
views
Is it possible that a macroscopic object tends to a separable state without the need for objective collapse?
For a multi-particle system, superposition is in some sense equivalent to entanglement; with the Dirac field being treated as classical under second quantization, for example, we could at least argue ...
- 2,587
0
votes
0
answers
40
views
Understanding entanglement [duplicate]
I’m probably missing something obvious. I'm new to physics, so please bear with me. Imagine flipping a perfect coin in a vacuum. The moment we through it up it splits exactly in half, with both halves ...
- 1
-5
votes
1
answer
132
views
Whats wrong with concept of "faster than light" information transfer device? (not about technical implementation, just about theory) [closed]
Yesterday, while lying in bed, an idea came to me, and I don’t understand why it won’t work?
Setup:
1.1) Two infinite stores of entangled pairs of photons, each connected to a double-slit device.
1.2)...
-4
votes
1
answer
90
views
Transmitting Data faster than the speed of light using entangled particles [duplicate]
If we have a pair of super-asymmetrical entangled particles, and move them a light year away so that they retain their quantum entanglement, and we set a clockwise spin (or vertical polarization) as 0 ...
- 11
-1
votes
1
answer
122
views
Why can quantum entanglement not use temporal encoding to transmit information? [closed]
It's common knowledge that quantum entanglement can't be used to transmit information; however, I'm struggling to understand why an encoding based on time intervals in which measurements are made ...
- 505
2
votes
2
answers
162
views
Simple examples of computing the quantum discord
I'm looking for a relatively simple, nontrivial example of computing quantum discord (if such an example exists). Could anyone provide such an example?
- 201
8
votes
0
answers
136
views
Time evolution keeps a certain product state always a product state. Is there a time-independent factorizable evolution for this state?
I am typically thinking of quantum spin chains in the following of some length $L$. I am OK without any locality in the assumptions on $H$.
I have a product state $|\psi\rangle$ and a potentially very ...
- 2,382
0
votes
2
answers
149
views
Quantum entanglement from different frames of reference and the conservation laws
From my understand, if the wave function of a particle in entanglement collapses by being observed, the other particle's wave function also collapse immediately.
My questions are:
Is it possible to ...
- 105
0
votes
1
answer
84
views
Rotation of Entangled States $(R \otimes R)|\phi\rangle = e^{i\delta}|\phi\rangle$
Maximally entangled states are said to be rotational invariant should a rotation be applied to both particles. That is (for some rotation operator $R$):
$$(R \otimes R)|\phi\rangle = e^{i\delta}|\phi\...
0
votes
1
answer
53
views
Seperable Quantum States
Some similar questions have been ask before, but I still don't really get the definition of seperable states in quantum mechanics.
Consider a bell state of a two qubit system.
\begin{align}
\left|\Psi\...
- 527
0
votes
1
answer
39
views
What's the relationship between wavefunction (anti-)symmetrization and entanglement? [duplicate]
Wavefunction symmetrization for bosons, or antisymmetrization for fermions, renders the wavefunction no longer a simple tensor product, i.e. it is no longer separable. This is the same thing that ...
- 2,587
-2
votes
1
answer
57
views
Is two degree quantum entanglement possible? And by two degree of entanglement I mean one in space and other in time? [closed]
Whenever we try to entangle two particles, the entanglement lasts for a very short period. If we observe our present universe we can see that all the matters present in our universe are finely ...
0
votes
2
answers
72
views
States of entangled particles after no/partial/full measurement
I'm getting contradictory information from the internet concerning entangled particles, measurement, and state knowledge that I'm hoping can be cleared up with a simple setup.
Say we have a source of ...
1
vote
0
answers
108
views
What is the appropriate 'Page Value' for entanglement entropy in a symmetry sector, say for example with a $U(1)$ symmetry?
Don Page derived the formula for the average entropy of a subsystem of a quantum system (assumed to be in a pure state), if the system is partitioned into two subsystems of dimensions $m$ and $n$, ...
- 43
1
vote
2
answers
91
views
How to measure the direction of circular polarization of single photons?
I just watched this video about the 2022 Nobel prize in physics which mentions the experiments that have been conducted to test Bell's inequality. In the video, they also described the experiment by ...
- 300
0
votes
2
answers
166
views
How can the quantum state of one particle depend on the other in entanglement without non-locality? [duplicate]
There are many different interpretations of quantum mechanics. Some posit determinism and non-local influences between particles. Others do not, such as in the Copenhagen interpretation.
My question ...
user401242
-1
votes
1
answer
101
views
If particles do not have definite properties before measurement in entanglement, what are they? [closed]
It is said that in quantum entanglement, a photon does not have definite properties before measurement. I have two questions.
Is this true for all interpretations of quantum mechanics?
what does it ...
4
votes
3
answers
437
views
Was Einstein "spooky action at a distance" about entanglement or about wave function collapse?
I've been watching Sabine's videos and this is my understanding:
There is no "spooky action at a distance" based simply on entanglement. Entanglement is a correlation. There is no ...
- 49
4
votes
3
answers
362
views
Is maximal entanglement basis independent?
Is there a basis such that if we measure the bell state $\dfrac{|00\rangle+|11\rangle}{\sqrt2}$ the results might not be correlated at all (or at least not maximally)?
For example $\dfrac{|00\rangle+|...
- 109