All Questions
Tagged with quantum-computer quantum-entanglement
79 questions
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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
1
answer
71
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Equivalence of two entangling operators with respect to local operators
Suppose that $U_1$ and $U_2$ are two (entangling) operators that act on a quantum system consisting of several qubits. Is there any criterion to tell if these two are equivalent up to applying ...
-2
votes
1
answer
147
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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
vote
0
answers
256
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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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1
vote
5
answers
2k
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Mathematical explanation of bra-ket notation in quantum mechanics
$\newcommand{\hp}[1]{\hphantom{#1}}$
We have the entangled state of two pairs of qubits:
$$
|\psi \rangle =\frac{1}{2}|0011\rangle-\frac{1}{2}|0110\rangle-\frac{1}{2}|1001\rangle+\frac{1}{2}|1100\...
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0
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3
answers
822
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Role of entanglement in quantum computing
I'm not a physicist and thus, I'm looking for a simple explanation on the role of entanglement in making quantum computers fast. I got a good analogy of a qubit: a coin tossed in the air can be ...
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0
votes
1
answer
38
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2 qubit entanglement in a QC
To my knowledge, in a Quantum Computer it is possible to obtain any Bell state by applying a Hadamard gate onto a qubit state $|x\rangle$ followed by a CNOT gate onto some target qubit state $|y\...
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1
vote
0
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173
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What exactly is meant by the quality of a qubit?
When looking at a quantum annealer, we can see that D-Wave solutions have produced an annealer with over 5000 qubits whilst other companies that take a quantum gate approach have only managed 127 (IBM)...
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1
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148
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How does CNOT gate work?
In Quantum Computation there is (among others) a so called CNOT gate. Its control input |x> is "driven through", while the other input |y> is converted to some other state, depending ...
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0
votes
1
answer
63
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Displacement gate on an arbitrary quantum state
I am reading this reference. In this article, the author define the Heisenberg-Weyl operators (Eqs. [148] in the reference):
$$X(s)=e^{-is\hat{p}/2} \tag{1},$$
$$Z(t)=e^{it\hat{q}/2} \tag{2},$$
where $...
2
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0
answers
137
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Why does the no-cloning theorem imply the monogamy of entanglement?
I have seen papers where they mentioned that the monogamy of entanglement can be seen as a consequence of the no-cloning theorem. Could somebody sketch this out?
N.B.: I have seen the argument that ...
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1
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0
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44
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What entanglement measures are known to satisfy entanglement monogamy?
As the title says, what entanglement measures are known to satisfy the entanglement monogamy principle?
Im specially interested in those entanglement measures that apply to mixed states.
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0
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0
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178
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Proof: A channel is entanglement breaking if it separates maximally entangled states
I'm working my way through Mark M. Wilde's Quantum Information Theory (2nd edition) and am stuck on a proof regarding entanglement breaking channels (Exercise 4.6.2)
Prove that a channel $\mathcal{N}...
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1
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1
answer
205
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Proof of Uhlmann's theorem (explicit decomposition )
I am having difficulty with Wiki's proof of the Uhlmann's theorem (https://en.wikipedia.org/wiki/Fidelity_of_quantum_states#Proof_with_explicit_decompositions)
The purifications of the states is given ...
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3
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2
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120
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Why does entanglement negativity not satisfy the triangle inequality in the usual sense?
I am a bit puzzled, I’ve read in some places, like the original paper by Vidal, that
$$
\mathcal{N}(\sum_n a_n \rho_n)\leq \sum_n a_n \mathcal{N}(\rho_n)
$$
whenever $a_n \geq 0$ and $\sum_n a_n =1$. ...
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3
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0
answers
116
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How does this quantum circuit work? [closed]
I am getting a bit confused about how to trace through a quantum circuit.
So, for example, if you have the circuit below:
I know that the first gate would split an arbitrary state alpha|0> + beta|...
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0
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0
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110
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What gate combinations create entangled two-qubit states?
I know that in order to make a two qubit entangled state, this quantum circuit is used:
But I was wondering if there are any other gate combinations which also create entangled two quit states.
If ...
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1
vote
1
answer
865
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Bell State Measurement Algorithm
I'm relatively new to quantum computation and am taking a course in it. I was wondering if it is possible to code an algorithm which would be able to take an input of a 2 qubit state and perform a ...
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3
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1
answer
442
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How can we "isolate" a qubit
From Wikipedia : In ion quantum computer, if the ions are not properly isolated, noise can result from ions interacting with external electromagnetic fields, which creates random movement and destroys ...
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1
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1
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92
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About universal quantum computation by “quantum wires”?
In this paper: A. Y. Kitaev, "Unpaired Majorana fermions in quantum wires", Phys.-Usp. 44 131 (2001), arXiv:cond-mat/0010440, it says:
Unlimited quantum computation is possible if errors in ...
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3
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2
answers
149
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Is there an unentangled electron pair in the universe?
How can we be sure that there are two electrons in the universe whose spins are uncorrelated (their joint state is the tensor product of their individual projections) but each of them has nonzero ...
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1
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1
answer
71
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Is a qutrit an example of tripartite entanglement? [closed]
Is a qutrit considered to be in a state of tripartite entanglement?
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1
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1
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199
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Confusion regarding bra-ket notation and proof of a ket equation
My question is two-part. First, imagine a bipartite quantum state $|\Phi \rangle_{AB}$, made of $2n$-qubits, shared between Alice and Bob (with $n$-qubits each). Alice performs some unitary operation $...
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2
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2
answers
732
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How to check if a qubit in a circuit is equal to another qubit?
If we have a set of qubits q1 ,q2 and q3 for example,
$$
\vert{q_1}\rangle = a \vert{0}\rangle +b \vert{1}\rangle\\
\vert{q_2}\rangle=\vert{0}\rangle\\
\vert{q_3}\rangle=\vert{0}\rangle
$$
the state ...
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3
votes
1
answer
512
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Applying a rotation on an entangled state
I want to understand an experiment but I am struggling with the (basic) math/braket notation.
In the experiment two ions are entangled and separated into two wells $A$ and $B$. The spin state of the ...
2
votes
0
answers
31
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Quantum computer measurement
Hello Stackexchange physics,
This question is mostly a request for a source of information on quantum measurement and decoherence that is consistent and independent of the particular context.
When I ...
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0
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0
answers
97
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How do entangled states increase computational space for quantum computers compared when only using product states? [duplicate]
My question is:
n-qubit product state.
$$|\psi\rangle=(a_1|0\rangle+a_2|1\rangle)\otimes(b_1|0\rangle+b_2|1\rangle)\otimes \cdots$$
n-qubit Entangled state
$$|\psi\rangle=(a_1|000\cdots000\rangle)+...
2
votes
1
answer
272
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How Do I Calculate the Score of a Bell's Game
I am reading "Quantum Chance" by Nicolas Gisin. I would like to know how to calculate the Bell Game outcome given in the following section of the book.
BACKGROUND
The Bell Game begins with a pair ...
1
vote
1
answer
53
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Is quantum network security an application of quantum entanglement?
If true, does it assume the link between the sending and receiving sides or servers acting on their behalf to be fully optical fiber physical layer or what practical approach is that heading towards?
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1
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0
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191
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What is the definition of genuine entanglement?
I can't seem to find a definition for genuine entanglement but it is being used in an article I'm reading and the references inside but I'm unable to find the precise definition.
One thing I was able ...
1
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0
answers
89
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Can a quantum computing advantage exist in a deterministic universe?
Is a deterministic universe with nonlocal hidden variables incompatible with the quantum superpositioning of states that is required for quantum computing?
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1
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404
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Is quantum entanglement contradictory with Schrödinger's cat?
As I understand, an electron spin is in a superposition state until the spin is observed. Due to the observation, it will either be spin up or spin down.
Due to quantum entanglement, if one electron ...
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1
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66
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Can quantum disentanglement be triggered by time dilation?
The question is really one question that leads to the final one:
Is it possible to realize a qubit that naturally flips between two quantum states on a definite and fixed period without any ongoing ...
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0
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1
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48
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What distinguish a non-interacting two fermions gate from an interacting one?
We start with a Hilbert space consists of two fermions(a and b), which is 4-dimensional. The basis would be $|vec>$,$b^\dagger|vac>$,$a^\dagger|vac>$,$a^\dagger b^\dagger |vac>$.
Denote ...
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1
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0
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75
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What is the simplest circuit on a quantum computer that "proves" superposition/entanglement
I am a Physics Teacher at pre university level.
Tunneling, wavefunctions and uncertainty are on the syllabus on a very vague way. Quantum superposition and entanglement are not but tie in well and I ...
1
vote
0
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50
views
5 qubit quantum error correction property [closed]
Having
$$\eqalign{
|v_0⟩&=|00000⟩+|11000⟩+|01100⟩+|00110⟩+ {}\cr
&\quad |00011⟩+|10001⟩−|10010⟩-|10100⟩− {}\cr
&\quad |01001⟩−|01010⟩−|00101⟩−|11110⟩− {}\cr
&\quad |...
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1
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1
answer
67
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What happens to physical qubits when they decohere during quantum error correction?
Say you have a scaled up system with 98% fidelity so 2% decoheres. These are physical qubits doing error correction on information encoded on logical qubits. 98% of these entangled qubits will be ...
1
vote
1
answer
79
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Superoperator cannot increase relative entropy
So I have to show that a superoperator $\$$ cannot increase relative entropy using the monotonicity of relative entropy:
$$S(\rho_A || \sigma_A) \leq S(\rho_{AB} || \sigma_{AB}).$$
What I have to ...
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3
votes
1
answer
669
views
How to identify whether a quantum state is entangled or separable if you can measure it only in one basis?
Suppose you have two qubits and don't know whether they're in an entangled state $ \frac{1}{\sqrt{2}}\left(|0,0\rangle + |1,1\rangle\right)$ or in an equal mixture of states $ |0,0\rangle $ and $ |1,1\...
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0
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0
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28
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How do I apply no signaling condition for the given Quantum Adder problem
The Unitary transformation for the Imperfect Quantum Adder problem is such:
Both the states belong to two Hilbert Spaces and we are trying to add both states to one system using Ancillary qubit.
I ...
0
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0
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57
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Intuition behind quantum CNOT gate applied to a pair of electrons [duplicate]
I'm looking for some intuition behind how a cNOT gate works. I think I understand the mathematics; but, I'm having trouble imagining how two electrons would interact to produce the predicted result.
...
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3
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1
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104
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Say you run qubit $A = (|0⟩ + |1⟩) / √2$ and qubit $B = |0⟩$ through a CNOT gate. What is the state of qubit $B$ afterwards?
I am new to the weeds of quantum computing and this question is probably pretty elementary.
Say you run qubit A = (|0⟩ + |1⟩) / √2 and qubit B = |0⟩ through a CNOT gate. What is the state of qubit B ...
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2
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204
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Do qubits need to be in superposition to be entangled? [closed]
Do qubits need to be in superposition to be entangled?
Put another way, can qubits be entangled but not in superposition?
2
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1
answer
389
views
Is a mixture of Bell states entangled?
Setup:
I have a two qubit system $\mathbb{C}^2 \otimes \mathbb{C}^2$ an we consider the Bell states
$\newcommand{\ket}[1]{\left|#1\right>}$
$\newcommand{\bra}[1]{\left<#1\right|}$
$\...
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0
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33
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Is the eavesdropper detected by chance in QKD?
So I was starting to familiarise myself with QKD when I came across this video on YouTube breaking down the process (I believe this is the E91 protocol but I could be mistaken) using an animation that ...
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1
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1
answer
136
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Can 2D graph state be represented by branching MERA?
A 2D graph state is a highly entangled state to support general measurement based quantum computation. But its state complexity is relative low. Branching MERA represents also a set of low complexity ...
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3
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0
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468
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Are there any physical realizations of a rebit (a qubit with real coefficients for probability amplitudes of a two-state system)?
While being introduced to the world of quantum computation and qubits, I’ve come across the term rebit, which I understand to mean a two-state quantum system that may be expressed as a real linear ...
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2
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0
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281
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Entanglement fidelity for a single qubit?
So I have been working out problems from the book "Quantum Computing Explained" by David McMahon. On page 166 he defines "Entanglement Fidelity" and says the following:
Consider a density operator for ...
0
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1
answer
1k
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Negative of Quantum Gates and Entangled States
I'm well aware that using this quantum circuit:
$\hskip2in$ $\hskip2in$Quantum circuit used in the generation of EPR pairs.
It is possible to create entangled state of two qubits (EPR pairs), in ...
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3
votes
1
answer
790
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quantum superdense coding -How many qubits are needed?
This is an extract from Wikipedia about superdense coding:
"In quantum information theory, superdense coding is a quantum communication protocol to transmit two classical bits of information (i.e., ...
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