Qubits Entanglement: Calculate & Interpret

amgo100
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Homework Statement



Determine which qubits are entangled:

##|\psi\rangle=\frac{1}{2}(|000\rangle+i|010\rangle+i|101\rangle-|111\rangle)##

Homework Equations

The Attempt at a Solution


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My idea was to first calculate the density operator
##\rho = |\psi\rangle \langle\psi|##
and then find the partial trace over the second and the third qubit. Then from Schmidt rank I would know whether the first qubit is entangled with the rest of the system. Then I could repeat the procedure for the other qubits. However the result seams to be 0 and I don't even know how to interpret this result, nor how to find which of the three qubits are entangled.
 
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Can you split the wavefunction into a product?
 
Ok, I've tried separating one of the qubits from the rest to obtain a product state and succeded for the second one (B):
##|\psi\rangle = \frac{1}{2}(|0\rangle_B + i|1\rangle_B)(|00\rangle_{AC} + i|11\rangle_{AC})##,
so it seams that qubit A is entangled with C (the first and the third).

However I'm still left with a question why the method with the partial trace gave me 0. I would expect it to give the same result.
 
amgo100 said:
Ok, I've tried separating one of the qubits from the rest to obtain a product state and succeded for the second one (B):
##|\psi\rangle = \frac{1}{2}(|0\rangle_B + i|1\rangle_B)(|00\rangle_{AC} + i|11\rangle_{AC})##,
so it seams that qubit A is entangled with C (the first and the third).
I agree.

Concerning the other method: Can you show your calculations?
 
To solve this, I first used the units to work out that a= m* a/m, i.e. t=z/λ. This would allow you to determine the time duration within an interval section by section and then add this to the previous ones to obtain the age of the respective layer. However, this would require a constant thickness per year for each interval. However, since this is most likely not the case, my next consideration was that the age must be the integral of a 1/λ(z) function, which I cannot model.
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