qml.commutation_dag¶
-
commutation_dag
(tape)[source]¶ Construct the pairwise-commutation DAG (directed acyclic graph) representation of a quantum circuit.
In the DAG, each node represents a quantum operation, and edges represent non-commutation between two operations.
This transform takes into account that not all operations can be moved next to each other by pairwise commutation.
- Parameters
tape (QNode or QuantumTape or Callable) – The quantum circuit.
- Returns
The transformed circuit as described in
qml.transform
. Executing this circuit will provide the commutation DAG.- Return type
qnode (QNode) or quantum function (Callable) or tuple[List[QuantumTape], function]
Example
>>> dev = qml.device("default.qubit")
@qml.qnode(device=dev) def circuit(x, y, z): qml.RX(x, wires=0) qml.RX(y, wires=0) qml.CNOT(wires=[1, 2]) qml.RY(y, wires=1) qml.Hadamard(wires=2) qml.CRZ(z, wires=[2, 0]) qml.RY(-y, wires=1) return qml.expval(qml.Z(0))
The commutation dag can be returned by using the following code:
>>> dag_fn = commutation_dag(circuit) >>> dag = dag_fn(np.pi / 4, np.pi / 3, np.pi / 2)
Nodes in the commutation DAG can be accessed via the
get_nodes()
method, returning a list of the form(ID, CommutationDAGNode)
:>>> nodes = dag.get_nodes() >>> nodes NodeDataView({0: <pennylane.transforms.commutation_dag.CommutationDAGNode object at 0x7f461c4bb580>, ...}, data='node')
You can also access specific nodes (of type
CommutationDAGNode
) by using theget_node()
method. SeeCommutationDAGNode
for a list of available node attributes.>>> second_node = dag.get_node(2) >>> second_node <pennylane.transforms.commutation_dag.CommutationDAGNode object at 0x136f8c4c0> >>> second_node.op CNOT(wires=[1, 2]) >>> second_node.successors [3, 4, 5, 6] >>> second_node.predecessors []
For more details, see:
Iten, R., Moyard, R., Metger, T., Sutter, D., Woerner, S. “Exact and practical pattern matching for quantum circuit optimization” doi.org/10.1145/3498325