COM-309: Trace is wrong but circuit looks correct

Hi, I implemented the circuit in qiskit and it seems to be correct if I draw it using circuit.draw('mpl'). I computed |0⟩⟨0|⊗I +|1⟩⟨1|⊗U as one matrix in numpy and then converted it into a UnitaryGate, which I then applied to the right qubits. However, I'm getting seemingly random trace estimation results. Does anyone have an idea where I could be going wrong by any chance? This is my result for circuit.draw('mpl'):
Circuit

Thanks in advance for any responses.

Re: Trace is wrong but circuit looks correct

par Khurshed Porus Fitter, mercredi, 20 décembre 2023, 19:49

I believe, if you look at the given circuit diagram again, it will be easy to spot the error :)

Trace is wrong but circuit looks correct

par Dina Khaled Sayed Abdelhadi, mercredi, 20 décembre 2023, 20:13

Hi Daniel,
May be try to increase the number of shots.

Re: Trace is wrong but circuit looks correct

par Dina Khaled Sayed Abdelhadi, jeudi, 21 décembre 2023, 15:01

That is, assuming you do the rest of the computation correctly.
In general, the more shots, the more accurate your estimate is. Try 1 million shots.

Re: Trace is wrong but circuit looks correct

par Daniel Andrzej Polka, jeudi, 21 décembre 2023, 15:42

Thanks! It's okay, I managed to fix it now, everything works