Questions tagged [quantum-entanglement]
Quantum entanglement is the mechanism by which quantum correlations between two sub-systems survive even after being physically separated from an interaction region. The correlations could in principle survive without neither time nor space constraint.
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Are von Neumann entropies of complementary but physically distinct subsystems in time-dependent settings identical?
We assume a quantum system AB with subsystems A and B and take the Schmidt decomposition of a state $\vert\psi_{AB}\rangle=\sum_i\lambda_i \vert a_i\rangle\vert b_i\rangle$ defined on the compsite ...
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Is the interference pattern of an entangled particle affected by the measurement of it's pair far enough away to take into account special relativity?
I've been considering a theoretical setup for a quantum experiment where 2 particles are prepared with entangled spin. They are then moved far away from one another where particle B is next to Bob who ...
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Operation on one of the EPR particles [closed]
Sabine Hossenfelder, a science YouTuber, talks about asking the following question to ChatGPT in one of her videos:
If you perform an operation which is not a measurement on one particle in a pair of ...
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What is the fast scrambling conjecture? [duplicate]
What is fast scrambling in context of black hole?
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Why can’t quantum entanglement provide FTL communication? [closed]
The typical explanation for why one can’t use quantum entanglement to communicate is because particle characteristics are unchoosable and random. However, instead of examining the entangled particle ...
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Quantum Entanglement as a Paradox [closed]
Photon splitting, also known as spontaneous parametric down-conversion, is a process where a single high-energy photon can split into two lower-energy entangled photons. This process occurs in a ...
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Does an entangled composite system necessarily imply a nonpure reduced density matrix for a subsystem?
This question is motivated by understanding decoherence processes. Consider a bipartite quantum system $S$ composed of two subsystems, $S_{soi}$ (soi = system of interest) and $S_{env}$ (env = ...
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Mixed-State Density Matrices Versus Physical Ensembles
I am trying to follow a discussion (distinguishing the two sorts of systems mentioned in the title of this question) in Schlossahuer's book, Decoherence: And the Quantum-To-Classical Transition. ...
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Quantum state of two polarization-entangled photons passing an experimental assembly (PBS and polarizing filter)
I'm wondering if anyone can help me understand how the quantum state of two polarization-entangled photons evolve in the following case.
Suppose you have two polarization-entangled photons A and B in ...
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Is a state being unentangled equivalent to statistical independence for all pairs of subsystem observables?
I imagine the answer is yes since, if so, the definition of unentangled is rather non-obvious and yet it gives an operational way to check for statistical independence.
I am working with the standard (...
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Is the set of $k$-extendible states compact?
Let 𝑘 ∈ ℕ
. A state 𝜌_𝐴𝐵 on a bipartite Hilbert space A ⊗ B
is 𝑘-extendible with respect to B if there exists a state 𝜌_(𝐴𝐵_𝑘)
on A ⊗ B^(⊗𝑘), which is invariant under any permutation of the ...
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Quantum modes and annihilation operator construction in a small region
In the note Some Entanglement Properties of Quantum Field Theory, Witten made an arguement:
In the region $U$, given that it is small enough that its causal complement contains another open set $U'$, ...
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Quantum entanglement of the Sachdev-Ye-Kitaev models
I was following the paper https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.245126 on Quantum entanglement of the Sachdev-Ye-Kitaev models. As we know that this is a model of indistinguishable ...
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What happen to entagled Bob particle if Alice particle passes a Stern-Gerlach device? [duplicate]
After sending to spin entangled particles (same value at measure) right and left. What happen if left particle passes SG magnet that align spin up or down. Will the other right particle conserve the ...
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Will General Relativity support "Universe is neither local nor real" in Quantum Gravity Framework?
It has been proven conclusively that universe is not locally real as per quantum theory.
But as per GR, universe is locally real with definite properties irrespective if we observe or not.
Scientists ...
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Have spin-correlation experiments been done on entangled particles other than photons?
I know that Bell experiments on spin correlations have been done with entangled photons, but have spin-correlation experiments ever been done on entangled particles other than photons?
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Could Dark Matter be comprised of gravitational waves entrained in the bulk?
The evidence is strong that more massive galaxies have more massive Dark Matter (DM) halos (for example, Qi Guo et al, Monthly Notices of the Royal Astronomical Society, Vol 404 (2010)). Might this ...
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Can a nonlinear evolution be linear at the level of reduced states?
Consider a (possibly unphysical) non-linear transformations of bi-partite quantum states,
$$\mathcal{N} (a A + b B) \neq a \mathcal{N}(A) + b \mathcal{N} (B)$$
for some density matrices $A,B \in \...
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Fermion location and superposition
That a fermion's wave function can extend over space is a perfectly reasonable concept, but why do some physicists also say that the $ \textbf {point particle itself} $ can exist in multiple locations ...
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In quantum mechanics, can we measure anything else than position?
In the basic quantum mechanics lectures, we learn that we can measure any observable. That means mathematically, all Hermitian operators correspond to a physically measurable quantity. In strong ...
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How can two phonons be entangled when the atoms in the crystal are not?
It is my understanding that you can use phonons to make a gaussian packet, which would behave like a quantum particle. I also believe that you can make two such packets and entangle them, that is ...
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In the context of the holographic principle, is the bulk-boundary correspondence due to entanglement?
According to the holographic principle, a "bulk" region of D dimensions corresponds to a "boundary" region of D-1 dimensions. In this context, the laws of physics of the bulk can ...
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Is entanglement the only way to get mixed state that is consistent with the Schrödinger equation?
If we treat our entire system (say an electron and a bunch of atoms) quantum mechanically then all possible interactions will be unitary transformations. Thus any state that I describe will always be ...
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Representation of $d$-dim maximally mixed state in different bases
Consider the maximally entangled state in $d$ dimensions, $|\Psi\rangle:= \frac{1}{\sqrt{d}} \sum_{i=0}^{d-1} |i,i\rangle^{AB}$, where $|i\rangle^{AB} := |i\rangle^{A}\otimes|i\rangle^{B}$ and $\{|i\...
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Does touching something cause quantum entanglement? [closed]
Disclosure: I'm pretty uneducated when it comes to quantum entanglement.
I was aware that there are a few ways for particles to become entangled. Is physical interaction one of them?
I read this ...
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What does entanglement cause between particles? [closed]
I've heard a lot of what quantum entanglement isn't such as it not being able to transfer information especially not faster than the speed of light.
At this point, I want to know what it can do. Why ...
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Entanglement Entropy and Entanglement Negativity for pure/mixed separable/entangled state
My question is how is Entanglement Entropy (EE) and Entanglement Negativity (N) related to the combinations of pure/mixed and separable/entangled states? That is for pure separable (PS), pure ...
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Are the proton and electron quantum entangled in the hydrogen atom
Do the proton and electron share the same wave function when describing a hydrogen atom?
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How does quantum teleportation work without faster than light communication? [duplicate]
So recently I watched a MinutePhysics explanation of quantum teleportation. Recently I have also been asking questions about quantum entanglement, and the answer I am most often getting is faster than ...
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Can electromagnetic wave function be entangled in two photons?
This might be a weird question, but this is what I’m saying.
If we entangle two photons, would it be possible to entangle not a characteristic like spin up or spin down but instead their individual ...
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If you change the state of one entangled particle will it change the other? [duplicate]
I have seen a bunch of duplicates of this question and I’m sorry if this is a true duplicate, but all the other duplicates have super long and complicated answers that I don’t understand.
I just want ...
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Can a particle be entangled with itself?
Suppose I had a single particle with a four-dimensional Hilbert space $\mathcal{H}$ spanned by the states $\{ |1\rangle,|2\rangle,|3\rangle,|4\rangle\}$ and suppose I prepared the particle in the ...
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What is the difference between nonlocality and entanglement?
I'm a bit confused about the difference and relation between (quantum) nonlocality and entanglement.
To give some context about my confusion, I was reading this paper: Brunner, Nicolas, et al. "...
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Infinite stacking of integer quantum Hall systems
Let us consider a (3+1)-dimensional system $\mathcal{H}$ constructed by stacking (2+1)-dimensional integer quantum Hall systems $\mathcal{H}_\text{Hall}$, e.g., $E_8$ bosonic systems (or $\sigma_H=1$ ...
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Please give me a single sentence explaining why faster-than-light morse code through entanglement isn't possible? [closed]
Problem with past explanations is they emphasize the need for random choice of measurement angle, but my understanding is that was only necessary in experiments seeking to remove any possible loop-...
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Does the required cooling energy increase when Quantum computer processors with more and more entangled Qubits are produced?
IBM has succeeded in 2021 in realizing a Quantum computer with 127 entangled Qubits (Processor Eagle). A Quantum computer with 433 entangled Qubits (Processor Osprey) was planned for 2022, and a ...
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Does there exist a ferromagnetic spin system with all ground states entangled?
Is there a lattice Hamiltonian of quantum spins $H_{\rm goal}(\vec{h})= H_{\rm goal}(\vec{0}) - \sum_i \vec{h} \cdot \vec{S}_i$ satisfying the following two conditions as the number of spins $N$ tends ...
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How to distinguish the cause of wavelength and frequency change?
In the theory of relativity, wavelength and frequency will change due to space-time geometry; in quantum mechanics, wavelength and frequency will change due to energy radiation, so how to distinguish ...
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How measure spins along the same axis with relativity
Suppose that a pion decays into an electron and a positron. Now let the particles travel a large distance so that they are lightyears apart. The idea of the EPR paradox is that when you measure their ...
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Interference pattern when the phase difference is 90°
We all know that entangled particles in polarisation will never make an interference pattern, in double slit setup with two orthogonal polarisers on either slits(say one slit with linear polarisers ...
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Quantum entanglement Bell's inequality and Nobel prize [closed]
Just your average layman here, wanting to understand the whole entanglement work for the Nobel prize.
Why can't the entangled pairs have a fixed spin that we don't know? How do experiments prove ...
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How do you calculate the entanglement entropy of a tensor network?
I found that the entanglement entropy can be calculated using the Schmidt coefficients of the state, using
$S = -\sum_i|\alpha_i|^2\log(|\alpha_i|^2)$
In the case of tensor networks, does this simply ...
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How far are we from actual test that gravity is quantum?
As we all know, probing the Planck scale directly is still far beyond our current technologies. But I've heard that proving that in fact gravity is quantum should be much easier and we are not that ...
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What will happen to an entangled pair of photons if one of them is absorbed and remitted by an atom?
Imagine if I have an entangled photon pair in linear polarisation, let them be named photon A and photon B, and if photon A is absorbed by an atom and then re-emitted what would be the state of photon ...
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Why is the phase of the reflected light important in the Hong-Ou-Mandel (HOM) experiment?
Trying to understand the Hong-Ou-Mandel effect (Wikipedia link) I got a bit lost with regards to what the reflection phases mean for the experiment and the kind of beam splitter required.
Instead of ...
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Is it possible to decompose any quantum channel into product channels if allowing negative coefficients?
We know that a separable quantum channel (i.e., a trace-preserving and completely positive map) on a bipartite system $A\otimes B$ is defined as: it can be decomposed to convex superposition of ...
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Proof of Nielsen's theorem (Theorem 12.15) given in Nielsen-Chuang (assumption of invertibility)
Theorem 12.15 of Nielsen and Chuang's 10th anniversary edition is Nielsen's Theorem (1999). In particular, it says,
Theorem 12.15: A bipartite pure state $\mid \psi \rangle$ may be transformed to ...
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How must be the interaction between two systems in order to have entanglement
My question is which characteristics must the interaction between two systems have in order to have entanglement ?
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Why the ground-state energy of S-1/2 Anti-Ferromagnetic Heisenberg Chain is not$-\frac{N}{4}J$
The Hamiltonian of traditional Heisenberg model is
$$\hat H = J\sum_{<i,j>}\vec{S_i}\cdot\vec{S_j}=J\sum_{<i,j>}\left(S_i^zS_j^z+\frac{1}{2}\left(S_i^+S_j^-+S_i^-S_j^+\right)\right)$$
if J ...
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EPR measurement + local unitary operation
Consider an EPR pair $\frac{1}{\sqrt2}\left( |\uparrow \rangle_A \otimes |\downarrow \rangle_B - | \downarrow \rangle_A \otimes | \uparrow \rangle_B \right)$ and the standard conventions (notation) ...
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