RelabelModes

>>> from qiskit.passmanager import MultiStagePassManager
>>> from qiskit.providers.basic_provider import BasicSimulator
>>> from qiskit_fermions.circuit import FermionicCircuit
>>> from qiskit_fermions.circuit.library import InitializeModes
>>> from qiskit_fermions.transpiler import FermionicCircuitToDAG, QuantumDAGToCircuit
>>> from qiskit_fermions.transpiler.passes import (
...     F2QSynthesis, F2QSynthesisPluginManager, RelabelModes, TrivialF2QLayout,
... )
>>>
>>> # blocked occupation: spin-up orbitals 0 and 1 and spin-down orbital 0 are occupied
>>> circ = FermionicCircuit(6)
>>> circ.append(InitializeModes([1, 1, 0, 1, 0, 0]), circ.modes)
>>>
>>> synth_plugins = F2QSynthesisPluginManager()
>>> synth = F2QSynthesis()
>>> synth.methods["InitializeModes"] = synth_plugins.method("InitializeModes", "TrivialOccupation")()
>>>
>>> # map blocked mode order onto the interleaved one
>>> relabel = RelabelModes(permutation=[0, 2, 4, 1, 3, 5])
>>>
>>> pm = MultiStagePassManager(
...     init=FermionicCircuitToDAG(),
...     optimization=relabel,
...     layout=TrivialF2QLayout(),
...     synthesis=synth,
...     output=QuantumDAGToCircuit(),
... )
>>>
>>> qcirc = pm.run(circ)
>>> qcirc.measure_all()
>>>
>>> bit_permutation = qcirc.metadata.get("permutation")
>>> print(bit_permutation)
[0, 2, 4, 1, 3, 5]
>>>
>>> res = BasicSimulator().run(qcirc, shots=1).result()
>>> counts = res.get_counts()
>>> print(counts)  # measured in the interleaved ordering
{'000111': 1}
>>>
>>> # undo the relabeling to recover the counts in the original blocked ordering
>>> post_processed = {
...     "".join(bitstring[~idx] for idx in bit_permutation)[::-1]: count
...     for bitstring, count in counts.items()
... }
>>> print(post_processed)  # recovered in the original blocked ordering
{'001011': 1}