All Questions
Tagged with quantum-mechanics quantum-entanglement
1,354 questions
6
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3
answers
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Bell's inequality for angles 120°
In 1964, John Bell first derived the original Bell inequality, $|E(a,b)-E(a,c)|\leq1+E(b,c)$. Here $a,b,c$ are three different possible spin measurement directions, and $E$ is the measured ...
1
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1
answer
70
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What if Delayed Choice Quantum Eraser is actually predicting/affecting which way the idler photons will go?
I understand there is no FTL and retrocausality.
Let's say we have detectors D1 and D2 that have already recorded the following patterns:
Then we send a new photon and the signal photon lands on this ...
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votes
1
answer
75
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Is it possible to know if an entangled particle's state is a superposition or collapsed? [duplicate]
I understand it's not possible to transmit information using entangled particles due to the randomness of the measure results.
But what if the act of measuring itself IS the information?
Let's say ...
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1
vote
1
answer
67
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How are energies conserved when a photon is split into an entangled pair?
Consider a setup in which a single photon is split into an entangled pair and directed towards 2 independent experimental setups (A and B). Both A and B have lenses to detect the polarization of the ...
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4
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2
answers
238
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If two quantum states have the same Schmidt bases at all times, are they equal?
In brief:
if two quantum states can be Schmidt decomposed using the same sets of joint basis at all times, no matter the evolution they go through, are the quantum states equal?
In detail:
Consider ...
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0
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2
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153
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A question about Born's rule in the Many-worlds interpretation
Can somebody explain the idea of self-locating uncertainty when there's a binary choice of eigenstates for an entanglement? I understand the idea that because you are unsure of which branch you are in,...
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3
votes
0
answers
183
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Is there any notion of device independent test for correlation like quantum discord?
A Device independent test is a procedure used to characterise quantum resources with the minimal level of trust. If one wants to test correlations like entanglement in a device-independent way, we get ...
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1
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How to know which states are entangled from a state vector? [closed]
consider the following state vector of three qubits
$$(1/2)|000⟩+(1/2)|011⟩+(1/2)|101⟩+(1/2)|110⟩.$$
how to know which qubits are entangled with respect to their basis states, in other words, how do ...
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1
answer
74
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Can you project on an orthogonal basis for a multipartite quantum system using only local operations and classical communication?
Say Alice possesses one qubit, and Bob two, and that the joint state is $|\psi_{A, B_1, B_2}\rangle = \alpha|n_1\rangle + \beta |n_2\rangle$, where $|n_1\rangle$ and $|n_2\rangle$ are orthonormal ...
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1
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141
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How we know that spin of two entangled photons are not predifined? [duplicate]
If we take two balls that change colours white and black, if we set that change in colours is always opposite one from another, for sure if we take one ball to the end of universe, if that ball will ...
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0
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1
answer
48
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Correlation between Entangled Particles in a Chain Sequence [closed]
Suppose we have two entangled particles, A and B. If we measure particle A and then subsequently entangle particle B with a third particle, C, would the state of particle A influence the combined ...
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2
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1
answer
187
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Quantum Mechanics without Complex Numbers in a multipartite setting
I was fairly convinced that usual QM formalism didn't necessitate the use of complex numbers and that ultimately they're just a matter of convenience and utility rather than anything fundamental. This ...
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1
answer
121
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How can we figure out what fraction of pure states in a Hilbert space are entangled? [duplicate]
The full Hilbert space of a quantum system will generally contain entangled states, and thus when entanglement is lost through decoherence, parts of Hilbert space become inaccessible. Is there a ...
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3
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1
answer
140
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Is there a relation between some kind of distance and the Schmidt basis?
Consider two bipartite quantum states $|\phi\rangle^{AB}$ and $|\psi\rangle^{AB}$ (in a finite dimensional Hilbert space $\mathcal H_A\otimes \mathcal H_B$), such that
$$\| |\phi\rangle\langle\phi|^{...
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1
vote
1
answer
73
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Relative "volume" of entangled vs product states [duplicate]
A system containing $n$ qubits is described by a $2^n-$dimensional Hilbert space. Some of these states can be decomposed as product states, but not all of them. The remaining ones are called entangled ...
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1
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40
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In observing EPR phenomenon, which direction is opposite to the other?
I have a question about the EPR phenomenon of the quantum-mechanics.
When you observe the EPR phenomenon, you separate two spins in the singlet state. Then, you and your fellow independently observe ...
12
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5
answers
2k
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Why quantum entanglement for a non-local object needs explanation?
I am a little confused about the usual explanations about quantum entanglement.
In the Schrödinger picture, the state vector evolves in time.
In the Heisenberg picture, the state vector does not ...
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0
answers
25
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Communication via entanglement [duplicate]
For years now i have in my haed a thought experiment for information exchange via quantum entanglement. And i am aware that something must be wrong with it but i can't figure out what it is.
The ...
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1
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2
answers
83
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What are the implications of entanglement swapping for the Pusey-Barrett-Rudolph (PBR) theorem?
The derivation of the PBR theorem makes an assumption that "systems that are prepared independently have independent physical states". However, it is known that it is possible to entangle ...
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1
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128
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Instantaneous transmission of data across arbitrary distances via quantum entanglement [duplicate]
As a forward, I'm no a physicist or a student of it. In fact I'm pretty ordinary. So if I mischarecterize some concepts, bear with me.
So I was reading up on some of the new technologies and then I ...
2
votes
1
answer
77
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Delayed choice quantum eraser setup with no beam splitter?
I know this question has probably been discussed many times before. But, I need a clear answer about this setup, in case there is no beam splitter.
What is going to happen in this situation? My ...
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votes
1
answer
123
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Faster than light communication by entangled photons [duplicate]
Faster than light communication is not possible. If I measure the polarization of an entangled photon and it turns out to be right circularly polarized. In that instant, dont I know that someone ...
5
votes
2
answers
165
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Does entanglement in a quantum physics experiment automatically cancel the interference?
Background: I'm currently doing self-study of quantum physics by following university level quantum physics lectures on YouTube (e.g. the YouTube MIT 8.04 Quantum Physics I, Spring 2013 or Stanford ...
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1
answer
82
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How exactly do triple photon entanglements behave? [closed]
I recently learnt that more than two photons can be entangled.
Are all the three photons are expected to have the same polarized angle due to entanglement?
Does measuring one of the three photons ...
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0
votes
1
answer
57
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Can entanglement cause a chain reaction at distance after measure one particle? [duplicate]
if we have two electrons with their spins entangled like this:
And if we measure the spin on the left electron, then right electron spin also change like this:
So, my question is, do this spin ...
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votes
1
answer
104
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Is there any minimalistic version of superdeterminism theory?
Superdeterminism is one wild conjecture which is an alternative to the standard quantum mechanical interpretation and preserves local realism
Superdeterminism seems to be too much of a stretch. If ...
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1
answer
62
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How non-degenerate photon pair can be entangled?
papers like below describe https://arxiv.org/abs/1305.0986 "A Flexible Source of Non-Degenerate Entangled Photons Based on a Two-Crystal Sagnac Interferometer"
I, somehow, thought that ...
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2
answers
184
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Is the possible Bell's test loophole of entangled particles communicating at a non instantaneous but FTL speed addressed and eliminated? [closed]
TLDR:
There seems to be a loophole in Bell's test that is not addressed or eliminated before we can successfully conclude that it proves that the Universe is unreal and non local. The entangled ...
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2
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98
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Can I perform entanglement swapping on an entangled pair with another 2 pairs simultaneously?
Suppose that I have 3 entangled pairs (a1, a2), (b1, b2), (c1, c2). Can I perform entanglement swapping on (a2, b1) and (b2, c1) simultaneously to get a new entanglement pair (a1, c2)?
The question is ...
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1
answer
247
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How can we be sure Bell's theorem disproves local realism when we are not sure whether the measuring apparatus is in some form of entanglement or not? [duplicate]
Bell's therorem seems to disprove localism because measuring, let's say spin of an entangled electron, seem to communicate the measurement to it's another pair instantaneously.
But isn't another thing ...
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vote
1
answer
60
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When does multi-particle entanglement break? [closed]
Let's say we entangle four electrons based on their spin.
Now, let's say we measure the spin of electron A along the z-axis (up/down), and we observe a spin of 'up'. My understanding is that this ...
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1
answer
77
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Can you provide an example quantum system that violates Bell's inequality? [closed]
I am self-learning QM. I am reading this paper about Bell's theorem https://arxiv.org/pdf/1212.5214.pdf and having difficult to understand the quantum system example in the paper that violates Bell's ...
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0
answers
80
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Entanglement in the Born-Oppenheimer approximation
Consider a scenario where we aim to model an atom as a system consisting of two components: the nucleus and the valence electron.
In this approach, we simulate the behavior of the electron within the ...
2
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0
answers
98
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Entanglement measure for a continuous bipartite system
Consider a cavity-spin system and assume we want to quantify the correlation between them. The cavity system can be described using a bosonic mode whereas the spin system requires 2 bosons to describe ...
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2
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100
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Quantum Information Theory: How do I perform entanglement quantification calculations using the Quantum Heisenberg model?
I have been reading Quantum Computation and Quantum Information (10th edition) by Nielsen and Chuang and I am interested in calculating the level of entanglement (with entropy or some other measure I ...
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0
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55
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How efficient are coincidence counting techniques?
Obviously there is a limitation as to how well experimental configurations that depend on coincidence counting can efficiently remove the noise present at any given experiment. This leads me to ...
3
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0
answers
268
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Confusion about the tensor product structure of a multi-fermion Hilbert space
I often see people study entanglement in fermionic systems. The setup is often like this. Suppose we have a 1d lattice of $2L $ sites, which is divided into a left part and a right part, each with $L ...
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1
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55
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Can quantum interference be detected in entangled pairs?
If I had a pair of entangled particles that were both in superposition, and I put one of them through a interference experiment, such as the double slit experiment, would I see an absence of ...
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2
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1
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121
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Why is the GHZ state not rotationally symmetric?
Consider three spin-1/2 systems. Prepare them in the GHZ state:
$|GHZ\rangle=\frac{|+z,+z,+z\rangle + |-z,-z,-z\rangle}{\sqrt{2}}$
Suppose one measures spin along the X axis for all three systems. If ...
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4
answers
366
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Is signal photon independent of idler photon in Delayed Choice Quantum Eraser?
--Diagram from Wikipedia of the experiment of Kim et al. (1999)
Original research paper: A Delayed Choice Quantum Eraser
I want to know whether the landing position of the signal photon (photon that ...
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2
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372
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Quantum Entanglement: Is Non-locality Inherent or Does It Violate Causality? [duplicate]
Dear Physics Stack Exchange community,
I am intrigued by the concept of quantum entanglement and its implications for our understanding of the fundamental nature of reality. I have come across various ...
1
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3
answers
338
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How and what mechanism does govern the failure of visible interference pattern and formation of analytical interference pattern in DCQE experiment?
Preface: This is a follow-up question to the following two questions:
Does simply putting a photon-splitting crystal after a double slit break the interference pattern?
Simplified delayed choice ...
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3
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1
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366
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How do physicist keep entangled particles entangled while moving them/storing them?
Once an entangled particle is measured, it's wave function collapses. From my understanding, any sort of information exchanged to the particles can be considered a mistaken measurement. So how do ...
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2
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227
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What's mechanism of "spooky action at the distance"? [duplicate]
Nobel prize 2022, a local theories of hidden variables are ruled out, Einstein's "spooky action at a distance" seems to be a reality.
Is there ANY explanations of this behavior of quantum ...
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1
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1
answer
111
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Can entanglement allow to predict deterministically results of incompatible measurements?
In my notes regarding entanglement and CHSH inequality it says:
Further, this is the case even for incompatible observables: measurements on one system allow us to predict with certainty the outcomes ...
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1
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148
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What is meant by " a basis is diagonal"?
I am trying to understand Schmidt decomposition. I am stuck in one sentence here. See the example picture.
Here, I can understand everything except the line "For both
HA and HB the Schmidt basis ...
1
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0
answers
46
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What happens when a maximally entangled state passes through a $k$-extendible channel?
In the context of Phys. Rev. A 104, 022401 (arXiv:1803.10710), Figure 3
What happens when a maximally entangled state( not $k$ extendible even for $k=2$) passes through a $k$-extendible channel? We ...
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1
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61
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Can an entangled state in general be created by destructive interference in some subspace?
For instance, if we have a general two-qubit state $$|\psi\rangle=\frac{1}{2}(|0\rangle+e^{i\varphi_a}|1\rangle)\otimes(|0\rangle+e^{i\varphi_b}|1\rangle)=\frac{1}{2}(|00\rangle+e^{i\varphi_b}|01\...
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2
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1
answer
179
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Does spin entanglement imply position entanglement?
My question is whether two electrons can be entangled only with respect to their spins but not with respect to some other observable, such as position.
I initially believed that spin-entanglement ...
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0
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57
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Total spin of Entangled Electrons
If, say, the z-spins of two electrons are maximally entangled (so that their composite state can be given by $|\Psi\rangle = \frac{1}{\sqrt{2}}(|u\rangle|d\rangle + |d\rangle|u\rangle)$, how do you ...
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