It is a state where two qubits form an intrinsically linked system.
More precisely, you can see in the figure below the comparison between a system with 2 independent qubits and the one represented by the two entangled qubits.
You can see that two of the 4 possible states are missing.
You can rollover each circle
to discover its characteristics
to discover its characteristics
Mathematically
We saw previously that a combination of states is a tensor product noted as follows:
(a|0> + b|1>) ⊗ (c|0> + d|1>) = ac|00> + ad|01> + bc|10> + bd|11>
Now the mathematical formula representing the entangled pair is:
α|01> + β|10>
It is impossible to note it as (a|0> + b|1>) ⊗ (c|0> + d|1>),
unlike, for example, the non-entangled combination:
α|10> + β|11> which can be written as:
x|1> ⊗ (y|0> + z|1>), with α=x*y and β=x*z
The consequence is that if we separate and move the qubits away, whatever the final distance between them, if we measure one of the qubits ,
"projecting" it onto a value, the other qubit is instantly projected onto the associated value .
We saw previously that a combination of states is a tensor product noted as follows:
(a|0> + b|1>) ⊗ (c|0> + d|1>) = ac|00> + ad|01> + bc|10> + bd|11>
Now the mathematical formula representing the entangled pair is:
α|01> + β|10>
It is impossible to note it as (a|0> + b|1>) ⊗ (c|0> + d|1>),
unlike, for example, the non-entangled combination:
α|10> + β|11> which can be written as:
x|1> ⊗ (y|0> + z|1>), with α=x*y and β=x*z
This notion stems from a debate initiated in 1935 by Einstein, Podolsky and Rosen and called the "EPR paradox".
We will not go into details but at the time it was a "thought experiment": since it has been shown that it is possible to physically achieve an entangled state as has showed Alain Aspect's team in the 1980s.
From entanglement to teleportation
We will detail the teleportation protocol itself very soon.
See you in a few days ...
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