place_wire_cuts(graph: networkx.classes.multidigraph.MultiDiGraph, cut_edges: Sequence[Tuple[pennylane.operation.Operation, pennylane.operation.Operation, Any]])networkx.classes.multidigraph.MultiDiGraph[source]

Inserts a WireCut node for each provided cut edge into a circuit graph.

  • graph (nx.MultiDiGraph) – The original (tape-converted) graph to be cut.

  • cut_edges (Sequence[Tuple[Operation, Operation, Any]]) – List of MultiDiGraph edges to be replaced with a WireCut node. Each 3-tuple represents the source node, the target node, and the wire key of the (multi)edge.


Copy of the input graph with WireCut nodes inserted.

Return type



Consider the following 2-wire circuit with one CNOT gate connecting the wires:

with qml.tape.QuantumTape() as tape:
    qml.RX(0.432, wires=0)
    qml.RY(0.543, wires="a")
    qml.CNOT(wires=[0, "a"])
>>> print(qml.drawer.tape_text(tape))
 0: ──RX(0.432)──╭●──┤ ⟨Z⟩
 a: ──RY(0.543)──╰X──┤

If we know we want to place a WireCut node between nodes RY(0.543, wires=["a"]) and CNOT(wires=[0, 'a']) after the tape is constructed, we can first find the edge in the graph:

>>> graph = qml.transforms.qcut.tape_to_graph(tape)
>>> op0, op1 = tape.operations[1], tape.operations[2]
>>> cut_edges = [e for e in graph.edges if e[0] is op0 and e[1] is op1]
>>> cut_edges
[(RY(0.543, wires=['a']), CNOT(wires=[0, 'a']), 0)]

Then feed it to this function for placement:

>>> cut_graph = qml.transforms.qcut.place_wire_cuts(graph=graph, cut_edges=cut_edges)
>>> cut_graph
<networkx.classes.multidigraph.MultiDiGraph at 0x7f7251ac1220>

And visualize the cut by converting back to a tape:

>>> print(qml.transforms.qcut.graph_to_tape(cut_graph).draw())
 0: ──RX(0.432)──────╭●──┤ ⟨Z⟩
 a: ──RY(0.543)──//──╰X──┤