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

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2021.
#
# 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.

"""Weyl decomposition of two-qubit gates in terms of echoed cross-resonance gates."""

from typing import Tuple

from qiskit.circuit import QuantumRegister
from qiskit.circuit.library.standard_gates import RZXGate, HGate, XGate

from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.exceptions import TranspilerError
from qiskit.transpiler.layout import Layout

from qiskit.dagcircuit import DAGCircuit
from qiskit.converters import circuit_to_dag


[docs]class EchoRZXWeylDecomposition(TransformationPass): """Rewrite two-qubit gates using the Weyl decomposition. This transpiler pass rewrites two-qubit gates in terms of echoed cross-resonance gates according to the Weyl decomposition. A two-qubit gate will be replaced with at most six non-echoed RZXGates. Each pair of RZXGates forms an echoed RZXGate. """ def __init__(self, instruction_schedule_map): """EchoRZXWeylDecomposition pass. Args: instruction_schedule_map (InstructionScheduleMap): the mapping from circuit :class:`~.circuit.Instruction` names and arguments to :class:`.Schedule`\\ s. """ super().__init__() self._inst_map = instruction_schedule_map def _is_native(self, qubit_pair: Tuple) -> bool: """Return the direction of the qubit pair that is native, i.e. with the shortest schedule.""" cx1 = self._inst_map.get("cx", qubit_pair) cx2 = self._inst_map.get("cx", qubit_pair[::-1]) return cx1.duration < cx2.duration @staticmethod def _echo_rzx_dag(theta): """Return the following circuit .. parsed-literal:: ┌───────────────┐┌───┐┌────────────────┐┌───┐ q_0: ┤0 ├┤ X ├┤0 ├┤ X ├ │ Rzx(theta/2) │└───┘│ Rzx(-theta/2) │└───┘ q_1: ┤1 ├─────┤1 ├───── └───────────────┘ └────────────────┘ """ rzx_dag = DAGCircuit() qr = QuantumRegister(2) rzx_dag.add_qreg(qr) rzx_dag.apply_operation_back(RZXGate(theta / 2), [qr[0], qr[1]], []) rzx_dag.apply_operation_back(XGate(), [qr[0]], []) rzx_dag.apply_operation_back(RZXGate(-theta / 2), [qr[0], qr[1]], []) rzx_dag.apply_operation_back(XGate(), [qr[0]], []) return rzx_dag @staticmethod def _reverse_echo_rzx_dag(theta): """Return the following circuit .. parsed-literal:: ┌───┐┌───────────────┐ ┌────────────────┐┌───┐ q_0: ┤ H ├┤1 ├─────┤1 ├┤ H ├───── ├───┤│ Rzx(theta/2) │┌───┐│ Rzx(-theta/2) │├───┤┌───┐ q_1: ┤ H ├┤0 ├┤ X ├┤0 ├┤ X ├┤ H ├ └───┘└───────────────┘└───┘└────────────────┘└───┘└───┘ """ reverse_rzx_dag = DAGCircuit() qr = QuantumRegister(2) reverse_rzx_dag.add_qreg(qr) reverse_rzx_dag.apply_operation_back(HGate(), [qr[0]], []) reverse_rzx_dag.apply_operation_back(HGate(), [qr[1]], []) reverse_rzx_dag.apply_operation_back(RZXGate(theta / 2), [qr[1], qr[0]], []) reverse_rzx_dag.apply_operation_back(XGate(), [qr[1]], []) reverse_rzx_dag.apply_operation_back(RZXGate(-theta / 2), [qr[1], qr[0]], []) reverse_rzx_dag.apply_operation_back(XGate(), [qr[1]], []) reverse_rzx_dag.apply_operation_back(HGate(), [qr[0]], []) reverse_rzx_dag.apply_operation_back(HGate(), [qr[1]], []) return reverse_rzx_dag
[docs] def run(self, dag: DAGCircuit): """Run the EchoRZXWeylDecomposition pass on `dag`. Rewrites two-qubit gates in an arbitrary circuit in terms of echoed cross-resonance gates by computing the Weyl decomposition of the corresponding unitary. Modifies the input dag. Args: dag (DAGCircuit): DAG to rewrite. Returns: DAGCircuit: The modified dag. Raises: TranspilerError: If the circuit cannot be rewritten. """ # pylint: disable=cyclic-import from qiskit.quantum_info import Operator from qiskit.quantum_info.synthesis.two_qubit_decompose import TwoQubitControlledUDecomposer if len(dag.qregs) > 1: raise TranspilerError( "EchoRZXWeylDecomposition expects a single qreg input DAG," f"but input DAG had qregs: {dag.qregs}." ) trivial_layout = Layout.generate_trivial_layout(*dag.qregs.values()) decomposer = TwoQubitControlledUDecomposer(RZXGate) for node in dag.two_qubit_ops(): unitary = Operator(node.op).data dag_weyl = circuit_to_dag(decomposer(unitary)) dag.substitute_node_with_dag(node, dag_weyl) for node in dag.two_qubit_ops(): if node.name == "rzx": control = node.qargs[0] target = node.qargs[1] physical_q0 = trivial_layout[control] physical_q1 = trivial_layout[target] is_native = self._is_native((physical_q0, physical_q1)) theta = node.op.params[0] if is_native: dag.substitute_node_with_dag(node, self._echo_rzx_dag(theta)) else: dag.substitute_node_with_dag(node, self._reverse_echo_rzx_dag(theta)) return dag