Tagged Questions
6
votes
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 ...
2
votes
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 ...
3
votes
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 ...
3
votes
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% ...
1
vote
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 ...
0
votes
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
votes
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 ...
3
votes
4answers
264 views
Why is quantum entanglement so important?
Entanglement also allows multiple states to be acted on simultaneously, unlike classical bits that can only have one value at a time. Entanglement is a necessary ingredient of any quantum ...
6
votes
1answer
191 views
Why do we want to entangle qubits?
The title is pretty much all I want to ask. Why are qubits entangled? To my knowledge (which isn't that deep) a quantum register can be realized without entangling the qubits.
3
votes
1answer
171 views
System with no entanglement but consuming quantum discord
I have come across an article which talks about quantum discord (Observing the operational significance of discord consumption. M. Gu et al. Nature Physics 8, 671–675 (2012) doi:10.1038/nphys2376), ...
3
votes
2answers
129 views
Understanding a Physics Paper on Quantum Teleportation of Continuous variables
The paper I am trying to understand is here:
http://pra.aps.org/abstract/PRA/v49/i2/p1473_1
The paper describes the quantum teleportation protocol in a general case with continuous dynamical ...
3
votes
0answers
71 views
Concurrence in higher dimensions?
Does anybody know of any calculation of the concurrence for some mixed state other than the qubit-qubit case (which was solved by Wootters)?
3
votes
2answers
193 views
Entanglement measure to classify topological ordered states
I know long-range entanglement is the essence of nontrivial topological ordered states. (Trivial refers to short range entangled and nontrivial refers to long range.) So, entanglement measure at large ...
5
votes
1answer
328 views
Topological Order and Entanglement
I have a question about entanglement in condensed matter physics. It seems that topological order origins from long range entanglement, but what is long range entanglement? It is the same as long ...
2
votes
2answers
313 views
What is the difference between Quantum teleportation and Radio waves?
Quantum teleportation over 143 kilometres using active feed- forward
What is the difference between Quantum teleportation and radio waves?
3
votes
1answer
220 views
Defining entanglement in subspaces of tensor product
I have asked the question in math.stackexchange, but perhaps it should be more relevant here. Hence I am re-posting it with necessary reediting.
Let $\mathcal{H}=\mathbb{C}^n$ be a Hilbert space. A ...
1
vote
2answers
108 views
Can double entanglement preserve correlations?
We have 2 EPR experiments running in parallel, with Alice having one leg of each (a1,a2) and Bob the other leg of each (b1,b2). Thus (a1,b1) are anticorrelated, as are (a2,b2). Thus also (a1,a2) are ...
2
votes
3answers
181 views
Entanglement: Is it possible to prepare and reset probabilities to send information?
I'm pretty certain that the answer to the question in the title is a no, but I don't understand why. I have some basic misunderstanding of quantum processes that I’d like clarified in the form of ...
0
votes
0answers
109 views
State of the entangled particles at the event horizon of black hole
Looking through the article of Samir Mathur http://arxiv.org/abs/0909.1038
he assumes that the entangled particles created at the event horizon have all the state ...
2
votes
0answers
97 views
Separable states of maximum non-classical correlations
Although there is no standard measure of entanglement, the GHZ states
$|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$
are often deemed as maximally entangled states of ...
1
vote
1answer
177 views
What is the difference between quantum cryptography and quantum teleportation?
Generate two entangled photons, send one to a message sender and the other to the intended receiver. Both the sender and the receiver recover the same piece of quantum information from the photons, ...
0
votes
1answer
141 views
Quantum communication
Is it possible to get two atoms to opposite quantum states of one another so when I change the state of first one, the state of the other one changes too? Is it possible to move them to another place ...
7
votes
8answers
616 views
Given entanglement, why is it permissible to consider the quantum state of subsystems?
Quantum entanglement is the norm, is it not? All that exists in reality is the wave function of the whole universe, true? So how come we can blithely talk about the quantum state of subsystems if ...
4
votes
3answers
407 views
Entanglement spectrum
What does it mean by the entanglement spectrum of a quantum system? A brief introduction and a few key references would be appreciated.
1
vote
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 ...
4
votes
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 ...
6
votes
2answers
455 views
Quantum Computing, Qubit Creation/Entanglement
I am currently a high school student researching quantum computing. I was referred to this site by Google and a friend. Currently I am researching the qubit part of quantum computing. My question is ...
1
vote
1answer
76 views
Number of conditions for a two-particle state to be decomposable
Suppose we have a general two-particle state $ \Phi (x_1, x_2 ) = \sum_{n_1,n_2} \phi_{n_1,n_2}(x_1,x_2)|n_1,n_2> $, where $n_1$ can be any of $n$ possible states, and $n_2$ can be any of $m$ ...
11
votes
1answer
80 views
CHSH violation and entanglement of quantum states
How is the violation of the usual CHSH inequality by a quantum state related to the entanglement of that quantum state?
Say we know that exist Hermitian and unitary operators $A_{0}$, $A_{1}$, ...
17
votes
2answers
89 views
What Shannon channel capacity bound is associated to two coupled spins?
The question asked is:
What is the Shannon channel capacity $C$ that is naturally associated to the two-spin quantum Hamiltonian $H = \boldsymbol{L\cdot S}$?
This question arises with a view ...
19
votes
1answer
279 views
State of Matrix Product States
What is a good summary of the results about the correspondence between matrix product states (MPS) or projected entangled pair states (PEPS) and the ground states of local Hamiltonians? Specifically, ...
13
votes
2answers
158 views
A resource theory of quantum discord?
Local Operations and Classical Communication (LOCC) is the classic paradigm for studying entanglement. These are things that are `cheap' and unable to produce entanglement as a resource for a quantum ...
5
votes
3answers
3k views
Quantum entanglement faster than speed of light?
recently i was watching a video on quantum computing where the narrators describes that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster ...
3
votes
1answer
236 views
Constructing a maximally entangled qutrit state from $n$ Bell states
I've read that maximally entangled qubit states are a good "unit" of bipartite entanglement since it is possible to create any other entangled state from them using local operations and classical ...
6
votes
2answers
367 views
Quantum Computing and Animal Navigation
Someone sent me this link to a talk by Prof. Klaus Schulten from the University of Illinois: (my emphasis)
Quantum Computing and Animal Navigation
Quantum computing is all the rage nowadays. ...
1
vote
3answers
275 views
Is it possible to bind an entangled electron to the outer shell of an atom or just a proton?
Say we start with an entangled electron--positron pair and we separate them. I want to take the entangled electron and bind it to a proton or the outer shell of an atom.
Is it possible to do this ...
3
votes
1answer
355 views
Can PEPS explain the holographic principle in quantum gravity?
Condensed matter physicists have shown using quantum information that in many condensed matter systems, entanglement entropy only scales as the area of the boundary, and not the volume. This is the ...
5
votes
3answers
585 views
Conservation of energy in quantum teleportation
Consider the quantum state teleportation protocol of Bennett et. al.
How does one prove that this protocol would never violate the conservation of energy? At the face of it, it doesn't seem to be ...
1
vote
1answer
892 views
What are the benefits of quantum information “teleportation”?
I read occasionally popular science articles and from time to time encounter issues about quantum information teleportation. (this one for example http://www.physorg.com/news193551675.html)
So far I ...
23
votes
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 ...
11
votes
5answers
700 views
Is there such a thing as “Action at a distance”?
What ever happened to "action at a distance" in entangled quantum states, i.e. the Einstein-Rosen-Podolsky (EPR) paradox? I thought they argued that in principle one could communicate faster than ...
