Pass to decompose multi-control gates before running SABRE

[geexie]

I'm transpiring with SABRE. For performance reason I assume that I should better run SABRE before Unrolling to hardware gates since it's going to be much large circuit. However if my original circuit contains Toffoli gates SABRE reports error. Can I do 2 step unrolling?

1. Unroll multi-control
2. Sabre
3. Unroll to native gate set

[alecandido]

For performance reason I assume that I should better run SABRE before Unrolling to hardware gates since it's going to be much large circuit.

Agreed

However if my original circuit contains Toffoli gates SABRE reports error.

Not sure why. If not documented, that should be investigated (and then either fixed or documented)

Can I do 2 step unrolling?

Well, that's certainly fine. The problem is that I'm not sure there is any transpiler component corresponding to your step 1.
The main problem is that the unrolling function

qibo/src/qibo/transpiler/unroller.py

Lines 125 to 130 in 8a27b9a

	def translate_gate(
	gate,
	native_gates: NativeGates,
	backend=None,
	):
	"""Maps gates to a hardware-native implementation.

requires an instance of

qibo/src/qibo/transpiler/unroller.py

Line 32 in 8a27b9a

class NativeGates(Flag, metaclass=FlagMeta):

which does not allow arbitrary gates to be specified. And not even all those implemented in Qibo.

This is a non-trivial design issue, since we just care about gates being uniquely identified (i.e. they are labels). And their meaning is eventually provided only by the backend.
So, the only ingredients we would need in Qibo are:

• an enumeration of known gates
• possibly user-extensible (with gates which are "unknown" to Qibo - but fine if native, since known to the backend)
• some decompositions associated to known gates

The current structure of gates as individual classes is certainly not optimal for that, and then yields the presence of redundant structures as the NativeGates above.

Solving the entire problem requires deep rewriting (which we already started to think about, i.e. qibo-core), but there may be transitionary solutions possible.

Unfortunately, I believe you will need to provide some code to implement that step 1. But that's certainly something we can discuss :)