def _hardware_aware_reset(
mapping: ty.Dict[Qubit, int],
circuit: QuantumCircuit,
hardware: IBMQHardwareArchitecture,
) -> ty.Dict[Qubit, int]:
starting_qubit = random.randint(0, hardware.qubit_number - 1)
qubits: ty.List[int] = [starting_qubit]
weights: ty.Dict[int, float] = dict()
while len(qubits) < len(mapping):
# 1. Update the weights
for neighbour in hardware.neighbors(qubits[-1]):
if neighbour not in qubits:
if neighbour not in weights.keys():
weights[neighbour] = 0.5 * (
1 - hardware.get_qubit_readout_error(neighbour))
else:
weights[neighbour] += (
weights.get(neighbour, 0) + 1 -
hardware.get_link_error_rate(qubits[-1], neighbour))
# Find the best weighted qubit
best_weight, best_qubit = 0, None
for qubit, weight in weights.items():
if weight > best_weight:
best_qubit = qubit
best_weight = weight
# Insert it in the qubit list
qubits.append(best_qubit)
del weights[best_qubit]
# Finally, return a mapping with the chosen qubits
return {qubit: idx for qubit, idx in zip(mapping.keys(), qubits)}
def _hardware_aware_expand(
mapping: ty.Dict[Qubit, int],
circuit: QuantumCircuit,
hardware: IBMQHardwareArchitecture,
) -> ty.Dict[Qubit, int]:
qubits = list(mapping.values())
idle_qubits = {mapping[qubit] for qubit in _get_idle_qubits(circuit)}
used_qubits = list(set(qubits) - idle_qubits)
if not idle_qubits:
return _random_shuffle(mapping, circuit, hardware)
# Compute a weight for each qubit.
# A qubit with a lot of links to other qubits in the mapping is good.
# A qubit with bad links is not that good.
weights: ty.List[float] = list()
outside_qubits_weights = dict()
for qubit in used_qubits:
weights.append(0.5 * (1 - hardware.get_qubit_readout_error(qubit)))
for neighbour in hardware.neighbors(qubit):
# Only count the neighbour if it is also in the mapping.
if neighbour in used_qubits:
weights[-1] += 1 - hardware.get_link_error_rate(
qubit, neighbour)
# Else, we keep an eye on the qubits that are not in the mapping because
# we will need the best of them to add it to the mapping.
else:
if neighbour not in outside_qubits_weights.keys():
outside_qubits_weights[neighbour] = 0.5 * (
1 - hardware.get_qubit_readout_error(qubit))
else:
outside_qubits_weights[neighbour] += (
outside_qubits_weights.get(neighbour, 0) + 1 -
hardware.get_link_error_rate(qubit, neighbour))
worst_qubit_index = _argmin(weights)
best_outside_qubit_index = None
best_outside_weight = 0
for neighbour, weight in outside_qubits_weights.items():
if weight > best_outside_weight:
best_outside_qubit_index = neighbour
best_outside_weight = weight
# Now exchange the 2 qubits
inverse_mapping = {v: k for k, v in mapping.items()}
inverse_mapping[worst_qubit_index], inverse_mapping[
best_outside_qubit_index] = (
inverse_mapping[best_outside_qubit_index],
inverse_mapping[worst_qubit_index],
)
return {v: k for k, v in inverse_mapping.items()}