Different results in circuit generated by Qiskit and the corresponding unitary

When using the simulator ascella I get different results for a circuit containing an unique Hadamard gate generated by the QiskitConverter and a circuit generated by the unitary representation of the Hadamard gate. In the circuit generated by the QiskitConverter I get exactly what I would expect in a simulation: the counts are divided into |01> and |10>. On the other hand, the simulations using the Hadamard unitary have a few counts going to |11>. I cannot understand why such a different result occurs with a same input circuit. Is there a different parametrization on the circuit generated by QiskitConverter?


When you’re simulating a Hadamard gate from a converted Qiskit QuantumCircuit, from a Perceval BS.H component or directly from the Hadamard unitary martix (in a pcvl.Unitary component), you should obtain the same results. Could you provide me with a small script to reproduce your issue?

Also, by default sim:ascella is a noisy simulator, meaning that some simulated photons will be distinguishable, leading to a non-zero probability of obtaining a |1,1> output. It’s possible to ask it to perform a perfect simulation, if that’s what you require. You can let me know.

Best wishes,