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Source code for qiskit.transpiler.passes.optimization.commutative_cancellation

# This code is part of Qiskit.
# (C) Copyright IBM 2017, 2019.
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"""Cancel the redundant (self-adjoint) gates through commutation relations."""

from collections import defaultdict
import numpy as np

from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.transpiler.exceptions import TranspilerError
from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.passes.optimization.commutation_analysis import CommutationAnalysis
from qiskit.dagcircuit import DAGCircuit
from qiskit.circuit.library.standard_gates.u1 import U1Gate
from qiskit.circuit.library.standard_gates.rx import RXGate


[docs]class CommutativeCancellation(TransformationPass): """Cancel the redundant (self-adjoint) gates through commutation relations. Pass for cancelling self-inverse gates/rotations. The cancellation utilizes the commutation relations in the circuit. Gates considered include:: H, X, Y, Z, CX, CY, CZ """
[docs] def __init__(self): super().__init__() self.requires.append(CommutationAnalysis())
[docs] def run(self, dag): """Run the CommutativeCancellation pass on `dag`. Args: dag (DAGCircuit): the DAG to be optimized. Returns: DAGCircuit: the optimized DAG. Raises: TranspilerError: when the 1-qubit rotation gates are not found """ # Now the gates supported are hard-coded q_gate_list = ['cx', 'cy', 'cz', 'h', 'y'] # Gate sets to be cancelled cancellation_sets = defaultdict(lambda: []) # Traverse each qubit to generate the cancel dictionaries # Cancel dictionaries: # - For 1-qubit gates the key is (gate_type, qubit_id, commutation_set_id), # the value is the list of gates that share the same gate type, qubit, commutation set. # - For 2qbit gates the key: (gate_type, first_qbit, sec_qbit, first commutation_set_id, # sec_commutation_set_id), the value is the list gates that share the same gate type, # qubits and commutation sets. for wire in dag.wires: wire_name = "{}[{}]".format(str(wire.register.name), str(wire.index)) wire_commutation_set = self.property_set['commutation_set'][wire_name] for com_set_idx, com_set in enumerate(wire_commutation_set): if com_set[0].type in ['in', 'out']: continue for node in com_set: num_qargs = len(node.qargs) if num_qargs == 1 and node.name in q_gate_list: cancellation_sets[(node.name, wire_name, com_set_idx)].append(node) if num_qargs == 1 and node.name in ['z', 'u1', 'rz', 't', 's']: cancellation_sets[('z_rotation', wire_name, com_set_idx)].append(node) if num_qargs == 1 and node.name in ['rx', 'x']: cancellation_sets[('x_rotation', wire_name, com_set_idx)].append(node) # Don't deal with Y rotation, because Y rotation doesn't commute with CNOT, so # it should be dealt with by optimized1qgate pass elif num_qargs == 2 and node.qargs[0] == wire: second_op_name = "{}[{}]".format(str(node.qargs[1].register.name), str(node.qargs[1].index)) q2_key = (node.name, wire_name, second_op_name, com_set_idx, self.property_set['commutation_set'][(node, second_op_name)]) cancellation_sets[q2_key].append(node) for cancel_set_key in cancellation_sets: set_len = len(cancellation_sets[cancel_set_key]) if set_len > 1 and cancel_set_key[0] in q_gate_list: gates_to_cancel = cancellation_sets[cancel_set_key] for c_node in gates_to_cancel[:(set_len // 2) * 2]: dag.remove_op_node(c_node) elif set_len > 1 and cancel_set_key[0] in ['z_rotation', 'x_rotation']: run = cancellation_sets[cancel_set_key] run_qarg = run[0].qargs[0] total_angle = 0.0 # lambda for current_node in run: if (current_node.condition is not None or len(current_node.qargs) != 1 or current_node.qargs[0] != run_qarg): raise TranspilerError("internal error") if current_node.name in ['u1', 'rz', 'rx']: current_angle = float(current_node.op.params[0]) elif current_node.name in ['z', 'x']: current_angle = np.pi elif current_node.name == 't': current_angle = np.pi / 4 elif current_node.name == 's': current_angle = np.pi / 2 # Compose gates total_angle = current_angle + total_angle # Replace the data of the first node in the run if cancel_set_key[0] == 'z_rotation': new_op = U1Gate(total_angle) elif cancel_set_key[0] == 'x_rotation': new_op = RXGate(total_angle) if np.mod(total_angle, (2 * np.pi)) > _CUTOFF_PRECISION: new_qarg = QuantumRegister(1, 'q') new_dag = DAGCircuit() new_dag.add_qreg(new_qarg) new_dag.apply_operation_back(new_op, [new_qarg[0]]) dag.substitute_node_with_dag(run[0], new_dag) # Delete the other nodes in the run for current_node in run[1:]: dag.remove_op_node(current_node) if np.mod(total_angle, (2 * np.pi)) < _CUTOFF_PRECISION: dag.remove_op_node(run[0]) return dag

© Copyright 2020, Qiskit Development Team. Last updated on 2021/03/04.

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