Apply gate limits automatically

[fretchen]

What is the expected behavior?

For most (every?) gates there is some periodicity involved. The best example are the RLXGate and its cousins. For them it would be great to have automatic modulos applied at some stage, but I am not sure where.

• Ideally it would come directly with the gate as anyone implementing the RLXGate would set the limit to 0 - 2*pi or something similiar.
• It would also leave the user alone with these limits, when it is not absolutely necessary.

However, I am not sure at which stage the transformation should be applied. In the transpiler ? Become a property of each gate ?

[LaurinFischer]

I still do not really see the point why this should be restricted on the Qiskit side at all. This is purely a matter of the backend how it interprets a gate with angles outside of [0, 2Pi] imo. If your backend says that its interpretation is to take a modulo 2Pi, fine, then this can be done on the backend side, no? This is how the standard parametrized gates such as rx work in Qiskit.
Also, depending on the implementations on the backend side, a -Pi/2 rotation might be physically achieved more easily (=shorter or higher fidelity pulse) than an 3*Pi/2 pulse, which, again depends on the backend. Hence I'm not a fan of brute forcing this on the circuit level.

[eggerdj]

We could achieve this with an optional transpiler pass. I don't think we want to wrap into [0, 2 pi] by default. Some experiments could benefit from wrapping around the BlochSphere more than once.