Leverage Terra's circuit library

[mtreinish]

What is the expected behavior?

Since terra 0.13.0 the qiskit.circuit.library path has existed for common circuits that can be used as building blocks as part of larger circuits. Most of the circuits modules in ignis are probably a good fit to live in the terra circuit library (so they are easily used independently of ignis). We should probably start migrating circuits to be in a form that works in the library (some already are like the qv model circuit), and ignis should start consuming the library for circuits where it can.

[ShellyGarion]

Which circuit methods from Terra's circuits library could be used in ignis (except of QV)? Which circuit methods should be moved from ignis to Terra's circuit library? For example, do we think that RB circuits (random Cliffords + inverse gate) should be moved to Terra? Circuits used for characterization?

[mtreinish]

I don't think that there is anything else in the library currently (but I haven't checked exhaustively). But I think we should look at moving most if not all of the circuit generators to use the library over time. So RB circuits, characterization circuits etc all seem like a better fit in the library and we can have ignis use them from there.

[ShellyGarion]

Possible candidates to move from ignis to terra are the entanglement circuits, see the comment in: https://github.com/Qiskit/qiskit-ignis/blob/master/qiskit/ignis/verification/entanglement/init.py