Quantum entanglement is the phenomenon of two particles depending on each other, once they have interacted, even after becoming physically separated.
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Can a link between photons that don't exist at the same time provide communication with the past?
They have published something about a link between photons that don't exist at the same time. Does this means that it is possible to build a device that will receive messages from itself but these ...
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4answers
128 views
Application of non maximally entangled state
In quantum information and quantum computation, we generally use Bell type states which are maximally entangled. I find that the set of entangled states as interesting objects from a mathematical ...
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1answer
40 views
How do particles become entangled?
A person asked me this and I'm just a lowly physical chemist.
I used a classical analogy (how good or bad is this and how to fix?)
Basically, light has a net angular momentum of zero, insofar as ...
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0answers
39 views
What does the difference in odds for Bell's inequality tell us about quantum mechanics?
Bell's inequality defines a lower bound for agreement/disagreement between entangled particles. When the experiment is conducted it shows lower odds.
What does this tell us? Is it possible that we ...
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0answers
55 views
Entanglement and Black holes
If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole?
If you have billions ...
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0answers
60 views
Quantum entanglement and speed of light $c$
On the topic of quantum entanglement, Wikipedia states:
Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the ...
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1answer
32 views
Name of a state with $d-1$ excitations, distributed uniformly among $n$ qudits
Is there a particular name for a quantum state of the form (up to the normalization):
$$\sum_{i_1+\ldots+i_n = d-1} |i_1\rangle |i_2\rangle \ldots |i_n\rangle$$
or was it studied is some papers?
...
4
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1answer
321 views
A physical understanding of fractionalization
all! Is there a physical understanding of fractionalization in condensed matter physics? The textbook approach is theoretical, not physical. I'm thinking of spin-charge separation for electrons, the ...
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2answers
143 views
Understanding on quantum entanglement
Understanding on quantum entanglement? I am very vague on this topic and would appreciate a detailed explanation on this phenomenon.
Also what are the possible applied uses for quantum entanglement? ...
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1answer
42 views
Entangled photons creating particle pairs
Two gamma ray photons are entangled and travel through space. The first gamma photon interacts with a low frequency photon and creates an electron positron pair. What happens to the other gamma ...
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1answer
107 views
Creating entanglement by measuring in a certain basis
This is one of the problems from Assignment 2 from CS191x at edx.org, so please do not post explicit answers.
We have two qubits in the state |0+⟩ and we want to entangle them by
performing a ...
6
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1answer
177 views
Entangled or unentangled?
I got a little puzzled when thinking about two entangled fermions.
Say that we have a Hilbert space in which we have two fermionic orbitals $a$ and $b$. Then the Hilbert space $H$'s dimension is just ...
6
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4answers
252 views
Interference and which-path information
My understanding is that in a double-slit experiment, quantum interference disappears if which-path information is available. How is available defined? Consider the following experiment:
SPDC is used ...
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0answers
149 views
Quantum Entanglement Versus Inflation in the Early Universe?
Quantum entanglement is one of the most fascinating and mysterious phenomena in nature. It needs no interactions, or any sort of exchange for it to take place. It is possible, not against any rules of ...
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8answers
4k views
Why quantum entanglement is considered to be active link between particles?
From everything I've read about quantum mechanics and quantum entanglement phenomena it's unobvious for me, why quantum entanglement is considered to be active link. I.e. it's stated every time that ...
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3answers
395 views
Does entanglement not immediately contradict the theory of special relativity?
Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that ...
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2answers
98 views
Is it only the spin of a particle that can be entangled with another particles spin?
Is it only the spin of a particle that can be entangled with another particles spin?
Also is there any good physical interpretation of the spin of a particle? because the rotational invariance of ...
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1answer
307 views
EPR-type experiments and faster-than-light communication using interference effects as signaling mechanism
I understand that faster-than-light communication is impossible when making single measurements, because the outcome of each measurement is random. However, shouldn't measurement on one side collapse ...
3
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1answer
82 views
Questions about entanglement from a laymen/quantum hobbyist
Please note I am not a physicist I just read every article I can on it, I understand a good amount on it though. But no maths. (currently trying to learn the maths)
By what means can we as humans ...
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1answer
90 views
Data For Quantum Entanglement
Is there any publicly accessible data that shows quantum entanglement empirically.
I want to see what these researches are seeing that is showing them that indeed this phenomenon is real.
Also, any ...
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1answer
78 views
What states are satisfying an entropic area law and why do they satisfy it? More specificly why do matrix product states satisfy it?
I am currently reading some papers concerning the question why the density matrix renormalization group (DMRG) method is working well for simulating one dimensional systems and bad for higher ...
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0answers
31 views
Trotter splitting and entanglement entropy
I have heard that a numerical solution to the Schrodinger equation using the Trotter splitting formula for a many-body Hamiltonian can cause an artificial increase in the entanglement entropy. I was ...
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1answer
116 views
Exploiting the Heisenberg Uncertainty Principle as a means to communicate
It seems as though I've come across a rather unusual conclusion that could either simply be a misinterpretation or a contradictory discovery. I seem to have found a way to utilize the Heisenberg ...
4
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1answer
143 views
Can entanglement swapping be performed on already-entangled photons, and if so, can it preserve this entanglement over the swap?
Consider 2 uncorrelated photon pairs (a1,a2), (b1,b2) such that (a1,a2) are entangled, and separately (b1,b2) are entangled. We wish to entangle-swap so as to end up with a new entanglement (a1,b1) by ...
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2answers
85 views
Von Neumann Entropy: varying definitions
I have seen different authors define von Neumann entropy in different ways. In particular, some use the natural logarithm and others log to base 2. What is the reasoning for this? Does it make any ...
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2answers
67 views
Schmidt basis: Entanglement
I do not understand how any state in Hilbert Space $\mathcal{H}=\mathcal{H}_A\otimes\mathcal{H}_B$ of dimension $\text{dim}(\mathcal{H}_A)\times\text{dim}(\mathcal{H}_B)$ can be decomposed in the ...
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1answer
101 views
Does the possibility of large scale entanglement mean 2-Body Problems are also unsolvable?
Experiments are showing that larger and larger objects can be entangled whereby proving that this quantum feature has no upper limit. Assuming this is true, does entangled celestial bodies mean even ...
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1answer
133 views
Coherence, Entanglement, Correlation
Let's deal specifically with a two-level system. I understand that ``coherence'' is due to the off-diagonal elements in the density matrix $\rho(t) = \sum_{i}|\psi_i(t)\rangle p_i\langle\psi_i(t)|$ ...
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0answers
73 views
Impulse travelling faster than light
There have been conducted many experiments in which light impulses traveled faster than light like the one in Princeton in 2000. This phenomenon has something to do with quantum entanglement. Does ...
2
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2answers
170 views
Does the reduced density matrix describes a real mixed state?
Suppose that we have two entangled particles A and B with pure state vector
$|\psi\rangle=a|0\rangle_A |1\rangle_B + b|1\rangle_A |0\rangle_B \hspace{1cm}(1)$
When we take the partial trace over the ...
4
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2answers
143 views
Can the concurrence be calculated in terms of the entanglement of formation?
If I somehow know the entanglement of formation, $E_F$ for two mixed qubits, where
\begin{equation}
E_F = -x \log x - (1-x) \log (1-x),
\end{equation}
where $x = (1+\sqrt{1-\mathcal{C}^2})/2$ and ...
3
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1answer
63 views
mixture of maximally mixed and maximally entangled state
Consider the quantum system $\mathcal{B}(\mathbb{C}^d\otimes\mathbb{C}^d)$ and $|\psi\rangle=\frac{1}{\sqrt{d}}\sum_{i=0}^{d-1}|i,i\rangle$ be the (standard) maximally entangled state. Consider the ...
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112 views
Local explanation of the Aharonov-Bohm effect in terms of force fields
Here is an interesting paper for the Physics SE community: On the role of potentials in the Aharonov-Bohm effect, Lev Vaidman, published in PHYSICAL REVIEW A 86, 040101(R) (2012).
You should check it ...
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3answers
229 views
Why can't we use entanglement to defy Heisenberg's Uncertainty Principle?
In principle, it is possible to entangle any property of two particles, including speed and momentum. Surely then, this could be used to defy the Uncertainty Principle, which states that the momentum ...
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2answers
123 views
What properties are entangled in quantum entanglement?
When two particles are entangled, one can measure the properties of one of the particles and instantaneously know the properties of the other. This is because the two particles possess the same ...
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2answers
190 views
Quantum Teleportation Fidelity
I understand that quantum teleportation fidelity is the overlap of the initial quantum state with the teleported quantum state. If the teleportation is perfect, then the fidelity would equal 1 or 100% ...
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7answers
2k views
Quantum Entanglement - What's the big deal?
Bearing in mind I am a layman - with no background in physics - please could someone explain what the "big deal" is with quantum entanglement?
I used to think I understood it - that 2 particles, say ...
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1answer
452 views
Entanglement in time
Quantum entanglement links particles through time, according to this study that received some publicity last year:
New Type Of Entanglement Allows 'Teleportation in Time,' Say Physicists at The ...
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1answer
96 views
Particles entangled after the big bang
Is that true that the big bang caused the quantum entanglement of all the particles of the universe so every particle is entangled to each other particle of the universe?
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4answers
196 views
Does measuring destroy entanglement
Before measuring a quantum particle(photon) it exists in a superposition state, once we observe(measure) it, it settles in one of the possible states(destroying superposition).
For entangled ...
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3answers
65 views
Can two distinct spatially separated many-body systems in the ground state contain entangled particles?
In particular, I am asking if two distinct many-body systems (e.g. system A and system B) separated at some arbitrary distance will necessarily be found to contain entangled particles (such that ...
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0answers
54 views
Equivalence of simple formulations of qubit entanglement
I'm reading some very elementary treatments of quantum computation and am unsure about the correspondence among "definitions" of qubit entanglement.
One definition states that (1) the bits of a ...
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1answer
147 views
Quantum Mechanics proved incorrect. Bohr - Einstein debates concluded?
"Photons act like they go through two paths, even when we know which they took".
Please refer the above link and its conclusion.
I am an Engineer. What I infer from this is :-
This proves ERP.
...
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1answer
94 views
three-particle quantum entanglement
So I know that two particles can be entangled in a quantum way, but is it possible that more than two particles be entangled in a quantum way? Most descriptions provide with two-particles cases, so I ...
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1answer
108 views
Entanglement and conservation
Is the following assertion sufficiently unique to merit a paper? Every absolute conservation law implies a corresponding form of entanglement, not just spin (angular momentum). Linear momentum ...
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1answer
164 views
Quantum circuit, two control not gates
Consider the quantum circuit in the picture below:
We have a Hadamard gate followed by a CNOT gate, this puts the 2nd & 3rd state in the bell state $\beta_{00}=\frac{1}{\sqrt2}(\mid 00\rangle ...
7
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1answer
211 views
Quantum dimension in topological entanglement entropy
In 2D the entanglement entropy of a simply connected region goes like
\begin{align}
S_L \to \alpha L - \gamma + \cdots,
\end{align}
where $\gamma$ is the topological entanglement entropy.
$\gamma$ is ...
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2answers
314 views
When and how did the idea of the tensor product originate in the history quantum mechanics?
At some point in the history of quantum mechanics, it was accepted that a single particle is described by a wavefunction which is a function of the position of the particle $\mathbf{r}$, denoted:
...
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2answers
96 views
Do any entanglement measures for mixed states exist that use only single site correlation functions?
For a pure state $\rho_{AB}$, the entropy of entanglement of subsystem $A$ is
\begin{equation}
S( \rho_A) = -tr (\rho_A \log \rho_A)
\end{equation}
where $\rho_A$ is the reduced density matrix of A. ...
5
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3answers
480 views
Does this Zeilinger group result provide experimental proof of backward-in-time causation?
Does this recent Zeilinger group delayed choice entanglement experiment imply backward-in-time influences?
http://arxiv.org/abs/1203.4834
From the abstract: "This can also be viewed as “quantum ...
