Source code for pennylane.transforms.optimization.merge_amplitude_embedding

# Copyright 2018-2021 Xanadu Quantum Technologies Inc.

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"""Transform for merging AmplitudeEmbedding gates in a quantum circuit."""
from pennylane import apply
from pennylane.transforms import qfunc_transform

from pennylane import AmplitudeEmbedding
from pennylane._device import DeviceError
from pennylane.math import kron


[docs]@qfunc_transform def merge_amplitude_embedding(tape): r"""Quantum function transform to combine amplitude embedding templates that act on different qubits. Args: qfunc (function): A quantum function. Returns: function: the transformed quantum function **Example** Consider the following quantum function. .. code-block:: python def qfunc(): qml.CNOT(wires = [0,1]) qml.AmplitudeEmbedding([0,1], wires = 2) qml.AmplitudeEmbedding([0,1], wires = 3) return qml.state() The circuit before compilation will not work because of using two amplitude embedding. Using the transformation we can join the different amplitude embedding into a single one: >>> dev = qml.device('default.qubit', wires=4) >>> optimized_qfunc = qml.transforms.merge_amplitude_embedding(qfunc) >>> optimized_qnode = qml.QNode(optimized_qfunc, dev) >>> print(qml.draw(optimized_qnode, show_matrices=True)()) 0: ─╭●──────────────────────┤ State 1: ─╰X──────────────────────┤ State 2: ─╭AmplitudeEmbedding(M0)─┤ State 3: ─╰AmplitudeEmbedding(M0)─┤ State M0 = [0.+0.j 0.+0.j 0.+0.j 1.+0.j] """ # Make a working copy of the list to traverse list_copy = tape.operations.copy() not_amplitude_embedding = [] visited_wires = set() input_wires, input_vectors = [], [] while len(list_copy) > 0: current_gate = list_copy[0] wires_set = set(current_gate.wires) # Check if the current gate is an AmplitudeEmbedding. if not isinstance(current_gate, AmplitudeEmbedding): not_amplitude_embedding.append(current_gate) list_copy.pop(0) visited_wires = visited_wires.union(wires_set) continue # Check the qubits have not been used. if len(visited_wires.intersection(wires_set)) > 0: raise DeviceError( f"Operation {current_gate.name} cannot be used after other Operation applied in the same qubit " ) input_wires.append(current_gate.wires) input_vectors.append(current_gate.parameters[0]) list_copy.pop(0) visited_wires = visited_wires.union(wires_set) if len(input_wires) > 0: final_wires = input_wires[0] final_vector = input_vectors[0] # Merge all parameters and qubits into a single one. for w, v in zip(input_wires[1:], input_vectors[1:]): final_vector = kron(final_vector, v) final_wires = final_wires + w AmplitudeEmbedding(final_vector, wires=final_wires) for gate in not_amplitude_embedding: apply(gate) # Queue the measurements normally for m in tape.measurements: apply(m)