Custom fake backend stopped working after 0.23 #9592
Description
Environment
- Qiskit Terra version: 0.24.0.dev0+e016f9c
- Python version: 3.9
What is happening?
The following script creates a custom fake backend and transpiles a QV for it:
import rustworkx as rx
from qiskit.transpiler import Target, InstructionProperties
from qiskit.providers.backend import BackendV2
from qiskit.circuit.library import UGate, ECRGate
from qiskit.circuit import Parameter
from qiskit.circuit.controlflow import IfElseOp
class FakeBackend(BackendV2):
def __init__(self):
super().__init__()
graph = rx.generators.path_graph(3)
num_qubits = len(graph)
self._target = Target("Fake backend", num_qubits=num_qubits)
self._target.add_instruction(UGate(Parameter("theta"), Parameter("phi"), Parameter("lam")),
{(qarg,): None for qarg in range(num_qubits)})
self._target.add_instruction(IfElseOp, name="if_else")
self._target.add_instruction(
ECRGate(),
{edge: InstructionProperties() for edge in graph.edge_list()},
)
@property
def target(self):
return self._target
@property
def max_circuits(self):
...
@classmethod
def _default_options(cls):
...
def run(self, circuit, **kwargs):
...
backend = FakeBackend()
from qiskit.circuit.library import QuantumVolume
from qiskit.compiler import transpile
qc = QuantumVolume(3, depth=5, seed=12345678942).decompose()
print(transpile(qc, backend=backend))It works fine in terra 0.23.*, but in current main fails like this:
Traceback (most recent call last):
File "/<redacted>/qiskit-terra/bug_IfElseOp.py", line 47, in <module>
print(transpile(qc, backend=backend))
File "/<redacted>/qiskit-terra/qiskit/compiler/transpiler.py", line 381, in transpile
_serial_transpile_circuit(
File "/<redacted>/qiskit-terra/qiskit/compiler/transpiler.py", line 474, in _serial_transpile_circuit
result = pass_manager.run(circuit, callback=callback, output_name=output_name)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 528, in run
return super().run(circuits, output_name, callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 228, in run
return self._run_single_circuit(circuits, output_name, callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 283, in _run_single_circuit
result = running_passmanager.run(circuit, output_name=output_name, callback=callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 125, in run
dag = self._do_pass(pass_, dag, passset.options)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 173, in _do_pass
dag = self._run_this_pass(pass_, dag)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 202, in _run_this_pass
new_dag = pass_.run(dag)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 428, in run
return self._run_main_loop(
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 469, in _run_main_loop
synth_dag = method.run(unitary, **kwargs)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 713, in run
decomposers2q = self._decomposer_2q_from_target(
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 635, in _decomposer_2q_from_target
supercontrolled_basis = {
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 636, in <dictcomp>
k: v for k, v in available_2q_basis.items() if is_supercontrolled(v)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 627, in is_supercontrolled
kak = TwoQubitWeylDecomposition(Operator(gate).data)
File "/<redacted>/qiskit-terra/qiskit/quantum_info/operators/operator.py", line 99, in __init__
raise QiskitError("Invalid input data format for Operator")
qiskit.exceptions.QiskitError: 'Invalid input data format for Operator'
How can we reproduce the issue?
Run the code script.
What should happen?
it should work as it was in 0.23.*
Any suggestions?
No idea. Notice the following:
If you remove self._target.add_instruction(IfElseOp, name="if_else") ( in line 19) also works in 0.23.* and in main fails like this:
Traceback (most recent call last):
File "/<redacted>/qiskit-terra/bug_IfElseOp.py", line 47, in <module>
print(transpile(qc, backend=backend))
File "/<redacted>/qiskit-terra/qiskit/compiler/transpiler.py", line 381, in transpile
_serial_transpile_circuit(
File "/<redacted>/qiskit-terra/qiskit/compiler/transpiler.py", line 474, in _serial_transpile_circuit
result = pass_manager.run(circuit, callback=callback, output_name=output_name)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 528, in run
return super().run(circuits, output_name, callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 228, in run
return self._run_single_circuit(circuits, output_name, callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passmanager.py", line 283, in _run_single_circuit
result = running_passmanager.run(circuit, output_name=output_name, callback=callback)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 125, in run
dag = self._do_pass(pass_, dag, passset.options)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 173, in _do_pass
dag = self._run_this_pass(pass_, dag)
File "/<redacted>/qiskit-terra/qiskit/transpiler/runningpassmanager.py", line 202, in _run_this_pass
new_dag = pass_.run(dag)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 428, in run
return self._run_main_loop(
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 469, in _run_main_loop
synth_dag = method.run(unitary, **kwargs)
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 713, in run
decomposers2q = self._decomposer_2q_from_target(
File "/<redacted>/qiskit-terra/qiskit/transpiler/passes/synthesis/unitary_synthesis.py", line 639, in _decomposer_2q_from_target
basis_2q_fidelity = 1 - getattr(available_2q_props[basis_2q], "error", 0.0)
TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'
If you decompose again in line 46 (qc = QuantumVolume(...).decompose().decompose() it works in main.
So, it seems like a problem in unitary_synthesis, which got a recent update in #9175