qp.transforms.set_decomposition¶

set_decomposition(custom_decomps, dev)[source]¶

Context manager for setting custom decompositions.

Parameters:

custom_decomps (Dict[Union(str, qp.operation.Operation), Callable]) – Custom decompositions to be applied by the device at runtime.
dev (pennylane.devices.LegacyDevice) – A quantum device.

Example

Suppose we would like a custom expansion function that decomposes all CNOTs into CZs. We first define a decomposition function:

def custom_cnot(wires, **_):
    return [
        qp.Hadamard(wires=wires[1]),
        qp.CZ(wires=[wires[0], wires[1]]),
        qp.Hadamard(wires=wires[1])
    ]

This context manager can be used to temporarily change a devices expansion function to one that takes into account the custom decompositions.

dev = qp.device("default.qubit", wires=2)

@qp.qnode(dev)
def circuit():
    qp.CNOT(wires=[0, 1])
    return qp.expval(qp.Z(0))

>>> print(qp.draw(circuit, level="device")())
0: ─╭●─┤  <Z>
1: ─╰X─┤

Now let’s set up a context where the custom decomposition will be applied. To see our change, the circuit is drawn at the device level where the custom decomposition will be applied.

>>> with qp.transforms.set_decomposition({qp.CNOT : custom_cnot}, dev):
...     print(qp.draw(circuit, level="device")())
0: ────╭●────┤  <Z>
1: ──H─╰Z──H─┤

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qp.transforms.set_decomposition¶

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