qp.transforms.remove_barrier

remove_barrier(tape)

Quantum transform to remove Barrier gates.

Parameters:

tape (QNode or QuantumTape or Callable) – A quantum circuit.

Returns:

The transformed circuit as described in qp.transform.

Return type:

qnode (QNode) or quantum function (Callable) or tuple[List[.QuantumTape], function]

Example

The transform can be applied on QNode directly.

@remove_barrier
@qp.qnode(qp.device('default.qubit'))
def circuit(x, y):
    qp.Hadamard(wires=0)
    qp.Hadamard(wires=1)
    qp.Barrier(wires=[0,1])
    qp.X(0)
    return qp.expval(qp.Z(0))

The barrier is then removed before execution.

Usage Details

Consider the following quantum function:

def qfunc(x, y):
    qp.Hadamard(wires=0)
    qp.Hadamard(wires=1)
    qp.Barrier(wires=[0,1])
    qp.X(0)
    return qp.expval(qp.Z(0))

The circuit before optimization:

>>> dev = qp.device('default.qubit')
>>> qnode = qp.QNode(qfunc, dev)
>>> print(qp.draw(qnode)(1, 2))
0: ──H─╭||──X─┤  <Z>
1: ──H─╰||────┤

We can remove the Barrier by running the remove_barrier transform:

>>> optimized_qfunc = remove_barrier(qfunc)
>>> optimized_qnode = qp.QNode(optimized_qfunc, dev)
>>> print(qp.draw(optimized_qnode)(1, 2))
0: ──H──X─┤  <Z>
1: ──H────┤

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