Source code for qiskit_experiments.library.characterization.half_angle

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

"""Half angle characterization."""

from typing import List, Optional, Sequence
import numpy as np

from qiskit import QuantumCircuit
from qiskit.providers import Backend

from qiskit_experiments.framework import BaseExperiment, Options
from qiskit_experiments.curve_analysis.standard_analysis import ErrorAmplificationAnalysis
from qiskit_experiments.curve_analysis import ParameterRepr
from qiskit_experiments.warnings import qubit_deprecate


class HalfAngle(BaseExperiment):
    r"""An experiment class to measure the amount by which sx and x are not parallel.

    # section: overview

        This experiment runs circuits that repeat blocks of :code:`sx - sx - y` gates
        inserted in a Ramsey type experiment, i.e. the full gate sequence is thus
        :code:`Ry(π/2) - [sx - sx - y] ^ n - sx` where :code:`n` is varied.

        .. parsed-literal::

                    ┌─────────┐┌────┐┌────┐┌───┐   ┌────┐┌────┐┌───┐┌────┐ ░ ┌─┐
               q_0: ┤ Ry(π/2) ├┤ sx ├┤ sx ├┤ y ├...┤ sx ├┤ sx ├┤ y ├┤ sx ├─░─┤M├
                    └─────────┘└────┘└────┘└───┘   └────┘└────┘└───┘└────┘ ░ └╥┘
            meas: 1/════════════════════════════...═══════════════════════════╩═
                                                                              0

        This sequence measures angle errors where the axis of the :code:`sx` and :code:`x`
        rotation are not parallel. A similar experiment is described in Ref.~[1] where the
        gate sequence :code:`x - y` is repeated to amplify errors caused by non-orthogonal
        :code:`x` and :code:`y` rotation axes. Such errors can occur due to phase errors.
        For example, the non-linearities in the mixer's skew for :math:`\pi/2` pulses may
        be different from the :math:`\pi` pulse.

    # section: analysis_ref
        :class:`.ErrorAmplificationAnalysis`

    # section: reference
        .. ref_arxiv:: 1 1504.06597
    """

    @classmethod
    def _default_experiment_options(cls) -> Options:
        r"""Default values for the half angle experiment.

        Experiment Options:
            repetitions (List[int]): A list of the number of times that the gate
                sequence :code:`[sx sx y]` is repeated.
        """
        options = super()._default_experiment_options()
        options.repetitions = list(range(15))
        return options

    @classmethod
    def _default_transpile_options(cls) -> Options:
        """Default transpile options.

        The basis gates option should not be changed since it will affect the gates and
        the pulses that are run on the hardware.
        """
        options = super()._default_transpile_options()
        options.basis_gates = ["sx", "rz", "y"]
        options.inst_map = None
        return options

    @qubit_deprecate()
    def __init__(self, physical_qubits: Sequence[int], backend: Optional[Backend] = None):
        """Setup a half angle experiment on the given qubit.

        Args:
            physical_qubits: List containing the qubits on which to run the
                fine amplitude calibration experiment.
            backend: Optional, the backend to run the experiment on.
        """
        analysis = ErrorAmplificationAnalysis()

        default_bounds = analysis.options.bounds
        default_bounds.update({"d_theta": (-np.pi / 2, np.pi / 2)})

        analysis.set_options(
            fixed_parameters={
                "angle_per_gate": np.pi,
                "phase_offset": -np.pi / 2,
                "amp": 1.0,
            },
            result_parameters=[ParameterRepr("d_theta", "d_hac", "rad")],
            normalization=True,
            bounds=default_bounds,
        )

        super().__init__(physical_qubits, analysis=analysis, backend=backend)

    @staticmethod
    def _pre_circuit() -> QuantumCircuit:
        """Return the preparation circuit for the experiment."""
        return QuantumCircuit(1)

    def circuits(self) -> List[QuantumCircuit]:
        """Create the circuits for the half angle calibration experiment."""

        circuits = []

        for repetition in self.experiment_options.repetitions:
            circuit = self._pre_circuit()

            # First ry gate
            circuit.rz(np.pi / 2, 0)
            circuit.sx(0)
            circuit.rz(-np.pi / 2, 0)

            # Error amplifying sequence
            for _ in range(repetition):
                circuit.sx(0)
                circuit.sx(0)
                circuit.y(0)

            circuit.sx(0)
            circuit.measure_all()

            circuit.metadata = {
                "experiment_type": self._type,
                "qubits": self.physical_qubits,
                "xval": repetition,
                "unit": "repetition number",
            }

            circuits.append(circuit)

        return circuits

    def _metadata(self):
        metadata = super()._metadata()
        # Store measurement level and meas return if they have been
        # set for the experiment
        for run_opt in ["meas_level", "meas_return"]:
            if hasattr(self.run_options, run_opt):
                metadata[run_opt] = getattr(self.run_options, run_opt)
        return metadata