The stabilizer simulator could have some quantum gates operations improved

[aromanro]

Informations

• Qiskit aer version: Latest development version
• OS: Windows, linux, macosx

What is the current behavior?

Currently some gate operations are done by combining several other gate operations. For example, the swap is done by using three cx operations. There is nothing wrong with that functionally, of course, but instead of going separately with each over all stabilizers & destabilizers, a single loop could apply all such operations. This should increase the speed a little due of cache locality.

What is the expected behavior?

Something like this implementation I've done: https://github.com/aromanro/QCSim/blob/4b2589cb50e2724fbd2da2b18c57001595b3f3f8/QCSim/Clifford.h#L288

Currently aer is doing this:

qiskit-aer/src/simulators/stabilizer/stabilizer_state.hpp

Line 381 in 269c26f

case Gates::swap:

which results in three loops over the stabilizers & destabilizers.

This is only an example, there are many gate operations that could be changed like that.