qiskit-aer/test/terra/backends/aer_simulator/test_truncate.py

# -*- coding: utf-8 -*-

# Copyright 2018, IBM.
#
# This source code is licensed under the Apache License, Version 2.0 found in
# the LICENSE.txt file in the root directory of this source tree.

"""
AerSimulator Integration Tests
"""
from ddt import ddt

import qiskit
from qiskit import transpile, QuantumCircuit

from qiskit.providers.fake_provider import GenericBackendV2

from qiskit_aer.noise import NoiseModel
from test.terra.backends.simulator_test_case import SimulatorTestCase, supported_methods

ALL_METHODS = [
    "automatic",
    "stabilizer",
    "statevector",
    "density_matrix",
    "matrix_product_state",
    "extended_stabilizer",
    "tensor_network",
]


@ddt
class TestTruncateQubits(SimulatorTestCase):
    """AerSimulator Qubits Truncate tests."""

    def create_circuit_for_truncate(self):
        circuit = QuantumCircuit(4, 4)
        circuit.u(0.1, 0.1, 0.1, 1)
        circuit.barrier(range(4))
        circuit.x(2)
        circuit.barrier(range(4))
        circuit.x(1)
        circuit.barrier(range(4))
        circuit.x(3)
        circuit.barrier(range(4))
        circuit.u(0.1, 0.1, 0.1, 0)
        circuit.barrier(range(4))
        circuit.measure(0, 0)
        circuit.measure(1, 1)
        return circuit

    def device_backend(self):
        return GenericBackendV2(num_qubits=5)

    def test_truncate_ideal_sparse_circuit(self):
        """Test qubit truncation for large circuit with unused qubits."""
        backend = self.backend()

        # Circuit that uses just 2-qubits
        circuit = QuantumCircuit(50, 2)
        circuit.x(10)
        circuit.x(20)
        circuit.measure(10, 0)
        circuit.measure(20, 1)

        result = backend.run(circuit, shots=1).result()
        metadata = result.results[0].metadata
        self.assertEqual(metadata["num_qubits"], 2, msg="wrong number of truncated qubits.")
        self.assertEqual(
            metadata["active_input_qubits"], [10, 20], msg="incorrect truncated qubits."
        )

    def test_truncate_default(self):
        """Test truncation with noise model option"""
        coupling_map = [  # 10-qubit device
            [0, 1],
            [1, 2],
            [2, 3],
            [3, 4],
            [4, 5],
            [5, 6],
            [6, 7],
            [7, 8],
            [8, 9],
            [9, 0],
        ]
        noise_model = NoiseModel.from_backend(self.device_backend())
        backend = self.backend(noise_model=noise_model)
        circuit = transpile(self.create_circuit_for_truncate(), backend, coupling_map=coupling_map)

        result = backend.run(circuit, shots=1).result()
        metadata = result.results[0].metadata
        self.assertEqual(metadata["num_qubits"], 2)
        self.assertEqual(len(metadata["active_input_qubits"]), 2)

    def test_truncate_non_measured_qubits(self):
        """Test truncation of non-measured uncoupled qubits."""
        noise_model = NoiseModel.from_backend(self.device_backend())
        backend = self.backend(noise_model=noise_model)
        circuit = transpile(self.create_circuit_for_truncate(), backend)

        result = backend.run(circuit, shots=1).result()
        metadata = result.results[0].metadata
        self.assertEqual(metadata["num_qubits"], 2)
        self.assertEqual(metadata["active_input_qubits"], [0, 1])

    def test_truncate_disable_noise(self):
        """Test explicitly disabling truncation with noise model option"""
        coupling_map = [  # 10-qubit device
            [0, 1],
            [1, 2],
            [2, 3],
            [3, 4],
            [4, 5],
            [5, 6],
            [6, 7],
            [7, 8],
            [8, 9],
            [9, 0],
        ]
        noise_model = NoiseModel.from_backend(self.device_backend())
        backend = self.backend(noise_model=noise_model, enable_truncation=False)
        circuit = transpile(self.create_circuit_for_truncate(), backend, coupling_map=coupling_map)

        result = backend.run(circuit, shots=100).result()
        metadata = result.results[0].metadata
        self.assertEqual(metadata["num_qubits"], 10)
        self.assertEqual(metadata["active_input_qubits"], list(range(4)))

    def test_truncate_connected_qubits(self):
        """Test truncation isn't applied to coupled qubits."""
        backend = self.backend()
        circuit = QuantumCircuit(20, 1)
        circuit.h(5)
        circuit.cx(5, 6)
        circuit.cx(6, 2),
        circuit.cx(2, 3)
        circuit.measure(3, 0)
        result = backend.run(circuit, shots=1).result()
        metadata = result.results[0].metadata
        self.assertEqual(metadata["num_qubits"], 4)
        self.assertEqual(metadata["active_input_qubits"], [2, 3, 5, 6])

    def test_delay_measure(self):
        """Test truncation delays measure for measure sampling"""
        backend = self.backend()
        circuit = QuantumCircuit(2, 2)
        circuit.x(0)
        circuit.measure(0, 0)
        circuit.barrier([0, 1])
        circuit.x(1)
        circuit.measure(1, 1)
        shots = 100
        result = backend.run(circuit, shots=shots).result()
        self.assertSuccess(result)
        metadata = result.results[0].metadata
        self.assertIn("measure_sampling", metadata)
        self.assertTrue(metadata["measure_sampling"])