Result of Grover on Qiskit simulator

Question

I have executed this circuit and I don't understand why the result is $|11\rangle$ ?

Thanks you

score 0 · Answer 1 · answered Apr 27 '20 at 15:47

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3 out of 4 states are inverted, that leads to the following situation before you do the Grover Diffusion, which mirror around the red line:

This will bring the all states to zeros, but not $|11\rangle$...

answered Apr 27 '20 at 15:47

draks ...

So, i think it's because the number of solutions is greater than N/2 ? How can I fix it if it's possible ? – julien rodriguez Apr 27 '20 at 17:12
@julienrodriguez what do you expect from the circuit? What are you looking for? Do you know what would happen if the number is exactly N/2? – – draks ... Apr 27 '20 at 19:10
this circuit compute a simple 2-sat formula (not a or not b). I see https://quantumcomputing.stackexchange.com/questions/5318/grover-algorithm-for-more-than-one-element before my ask. – julien rodriguez May 01 '20 at 08:28
@julienrodriguez I'm not sure if this will really help you, since you're dealing with a special case. – draks ... May 01 '20 at 21:57

score 0 · Accepted Answer · answered May 05 '20 at 06:55

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So, I add a "ghost qubit" in the solution space in order to increase N. I fixe the "ghost qubit" to a state (|1> here) and we get #solutions < N/2

answered May 05 '20 at 06:55

julien rodriguez

2 Answers2