[WIP] Add a function to make conditionals twirlable

[TsafrirA]

Related Issues

#27
#29

Summary

This WIP PR adds a function which analyzes conditionals, and (when possible) creates a twirlable form of them for both left\right dressing.

Details and comments

This conditional cannot be twirled:

from qiskit import QuantumCircuit

qc = QuantumCircuit(2,2)
with qc.if_test((qc.clbits[0], 1)) as _else:
    qc.sx(1)
    qc.cx(0, 1)
    qc.h(0)
with _else:
    qc.sx(0)
    qc.x(1)
instr = qc[0]
qc.draw("mpl")

Using the function we can find a twirlable form for left dressing:

from samplomatic.transpiler.passes.analyze_if_else import analyze_if_else_instruction
left_dressing_result, right_dressing_result = analyze_if_else_instruction(instr)

left_dressing = qc.copy_empty_like()
left_dressing.append(left_dressing_result.instr)
for instr in left_dressing_result.additional_1q_ops:
    left_dressing.append(instr)

left_dressing.draw("mpl")

The same should work for right dressing, but there is a bug marked by a TODO in the code.

Some things to think about:

• The inversed operations might not be in the basis set and another transpilation will be needed. Should we add the original pass manager as an input to this function?
• How would something like this fit into the boxing pass manager?

[ihincks]

I think we should put developing conditional support on hold until we've done some refactoring and strategizing to simplify the code base. I'm finding it increasingly difficult to reason about the build process.

[TsafrirA]

@ihincks

I think we should put developing conditional support on hold until we've done some refactoring and strategizing to simplify the code base. I'm finding it increasingly difficult to reason about the build process.

I agree with the general idea, but this particular PR doesn't involve the build process.