Source code for pennylane_orquestra.qiskit_device

# Copyright 2020 Xanadu Quantum Technologies Inc.

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
The Qiskit device class for PennyLane-Orquestra.
"""
import warnings

from pennylane_orquestra.orquestra_device import OrquestraDevice


class QeQiskitDevice(OrquestraDevice):
    """The Orquestra Qiskit device.

    Args:
        wires (int, Iterable[Number, str]]): Number of subsystems represented
            by the device, or iterable that contains unique labels for the
            subsystems as numbers (i.e., ``[-1, 0, 2]``) or strings (``['ancilla',
            'q1', 'q2']``). Default 1 if not specified.
        shots (int or list[int]): Number of circuit evaluations/random samples used to estimate
            expectation values of observables. If ``None``, the device calculates
            probability, expectation values, and variances analytically. If an integer,
            it specifies the number of samples to estimate these quantities.
            If a list of integers is passed, the circuit evaluations are batched over the list of shots.
        backend (str): the name of the Qiskit backend to use supported by
            Orquestra, e.g., ``"qasm_simulator"`` or ``"statevector_simulator"``
    """

    short_name = "orquestra.qiskit"

    qe_component = "qe-qiskit"
    qe_module_name = "qeqiskit.simulator"
    qe_function_name = "QiskitSimulator"

    def __init__(self, wires, shots=10000, backend="qasm_simulator", **kwargs):
        if backend == "qasm_simulator":
            if shots is None:
                warnings.warn(
                    f"The {self.short_name} device cannot be used in analytic "
                    f"mode with the {backend} backend. Setting shots to 10000. "
                    "Results are based on sampling."
                )

                shots = 10000

        # TODO: Remove when the Orquestra supports qiskit>0.18.3 with its Qiskit component
        if backend == "statevector_simulator":
            if shots is not None:
                warnings.warn(
                    f"The {self.short_name} device with the {backend} backend "
                    "always runs with shots=1 due to a malfunction in the "
                    "version of Qiskit used by Orquestra."
                )

        super().__init__(wires, backend=backend, shots=shots, **kwargs)

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