I'm studying shor's algorithm. I implemented in Qiskit and apriori I know that a period is 3 in my example.

However, unless I know about period, how to obtain this period only according to seeing diagram?

This is a circuit diagram.


This is a probability diagram. How to obtain a period from it?



1 Answer 1


With the most probable phase coming out of the phase estimation being 0 (the highest value in the histogram you got), you can't really do much. I suppose you got this from actual hardware, which has more tendency to relax to |0> for each qubit. This is just an artifact coming from the noise in the hardware. I suggest to you to run on noiseless simulator first, and better with more qubits (larger N in the input) so the histogram will be more significant towards the phase estimated from the quantum algorithm. Then, apply (classical) continued-fraction algorithm in the regular procedure to get the order out of the most probable phase extracted from the histogram

  • $\begingroup$ Thank you so much. You are so kind!!:) Have a nice day. $\endgroup$
    – 유도경
    Feb 18, 2020 at 7:12

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