# This code is part of Qiskit.
#
# (C) Copyright IBM 2022.
#
# 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.
"""Translate parameterized gates only, and leave others as they are."""
from __future__ import annotations
from qiskit.circuit import Instruction, ParameterExpression, Qubit, Clbit
from qiskit.converters import circuit_to_dag
from qiskit.dagcircuit import DAGCircuit, DAGOpNode
from qiskit.circuit.equivalence_library import EquivalenceLibrary
from qiskit.exceptions import QiskitError
from qiskit.transpiler import Target
from qiskit.transpiler.basepasses import TransformationPass
from .basis_translator import BasisTranslator
[docs]class TranslateParameterizedGates(TransformationPass):
"""Translate parameterized gates to a supported basis set.
Once a parameterized instruction is found that is not in the ``supported_gates`` list,
the instruction is decomposed one level and the parameterized sub-blocks are recursively
decomposed. The recursion is stopped once all parameterized gates are in ``supported_gates``,
or if a gate has no definition and a translation to the basis is attempted (this might happen
e.g. for the ``UGate`` if it's not in the specified gate list).
Example:
The following, multiply nested circuit::
from qiskit.circuit import QuantumCircuit, ParameterVector
from qiskit.transpiler.passes import TranslateParameterizedGates
x = ParameterVector("x", 4)
block1 = QuantumCircuit(1)
block1.rx(x[0], 0)
sub_block = QuantumCircuit(2)
sub_block.cx(0, 1)
sub_block.rz(x[2], 0)
block2 = QuantumCircuit(2)
block2.ry(x[1], 0)
block2.append(sub_block.to_gate(), [0, 1])
block3 = QuantumCircuit(3)
block3.ccx(0, 1, 2)
circuit = QuantumCircuit(3)
circuit.append(block1.to_gate(), [1])
circuit.append(block2.to_gate(), [0, 1])
circuit.append(block3.to_gate(), [0, 1, 2])
circuit.cry(x[3], 0, 2)
supported_gates = ["rx", "ry", "rz", "cp", "crx", "cry", "crz"]
unrolled = TranslateParameterizedGates(supported_gates)(circuit)
is decomposed to::
┌──────────┐ ┌──────────┐┌─────────────┐
q_0: ┤ Ry(x[1]) ├──■──┤ Rz(x[2]) ├┤0 ├─────■──────
├──────────┤┌─┴─┐└──────────┘│ │ │
q_1: ┤ Rx(x[0]) ├┤ X ├────────────┤1 circuit-92 ├─────┼──────
└──────────┘└───┘ │ │┌────┴─────┐
q_2: ─────────────────────────────┤2 ├┤ Ry(x[3]) ├
└─────────────┘└──────────┘
"""
def __init__(
self,
supported_gates: list[str] | None = None,
equivalence_library: EquivalenceLibrary | None = None,
target: Target | None = None,
) -> None:
"""
Args:
supported_gates: A list of suppported basis gates specified as string. If ``None``,
a ``target`` must be provided.
equivalence_library: The equivalence library to translate the gates. Defaults
to the equivalence library of all Qiskit standard gates.
target: A :class:`.Target` containing the supported operations. If ``None``,
``supported_gates`` must be set. Note that this argument takes precedence over
``supported_gates``, if both are set.
Raises:
ValueError: If neither of ``supported_gates`` and ``target`` are passed.
"""
super().__init__()
# get the default equivalence library, if none has been set
if equivalence_library is None:
from qiskit.circuit.library.standard_gates.equivalence_library import _sel
equivalence_library = _sel
# The target takes precedence over the supported_gates argument. If neither are set,
# raise an error.
if target is not None:
supported_gates = target.operation_names
elif supported_gates is None:
raise ValueError("One of ``supported_gates`` or ``target`` must be specified.")
self._supported_gates = supported_gates
self._target = target
self._translator = BasisTranslator(equivalence_library, supported_gates, target=target)
[docs] def run(self, dag: DAGCircuit) -> DAGCircuit:
"""Run the transpiler pass.
Args:
dag: The DAG circuit in which the parameterized gates should be unrolled.
Returns:
A DAG where the parameterized gates have been unrolled.
Raises:
QiskitError: If the circuit cannot be unrolled.
"""
for node in dag.op_nodes():
# check whether it is parameterized and we need to decompose it
if _is_parameterized(node.op) and not _is_supported(
node, self._supported_gates, self._target
):
definition = node.op.definition
if definition is not None:
# recurse to unroll further parameterized blocks
unrolled = self.run(circuit_to_dag(definition))
else:
# if we hit a base case, try to translate to the specified basis
try:
unrolled = self._translator.run(_instruction_to_dag(node.op))
except Exception as exc:
raise QiskitError("Failed to translate final block.") from exc
# replace with unrolled (or translated) dag
dag.substitute_node_with_dag(node, unrolled)
return dag
def _is_parameterized(op: Instruction) -> bool:
return any(
isinstance(param, ParameterExpression) and len(param.parameters) > 0 for param in op.params
)
def _is_supported(node: DAGOpNode, supported_gates: list[str], target: Target | None) -> bool:
"""Check whether the node is supported.
If the target is provided, check using the target, otherwise the supported_gates are used.
"""
if target is not None:
return target.instruction_supported(node.op.name)
return node.op.name in supported_gates
def _instruction_to_dag(op: Instruction) -> DAGCircuit:
dag = DAGCircuit()
dag.add_qubits([Qubit() for _ in range(op.num_qubits)])
dag.add_qubits([Clbit() for _ in range(op.num_clbits)])
dag.apply_operation_back(op, dag.qubits, dag.clbits)
return dag