Issue qiskit-community#367 - Migration from QasmSimulator to qiskit_aer's AerSimulator (qiskit-community#378)

* Migration from QasmSimulator to qiskit_aer's AerSimulator

* eliminate execute from imports (#1)

* remove execute import from faultsampler.py

* remove execute imports from faultenumerator.py

* remove execute import from test_heavy_hex_decoder.py

* remove execute import from test_repetitionmatcher.py

* remove execute import from test_circuitmatcher.py

---------

Co-authored-by: grace-harper <119029214+grace-harper@users.noreply.github.com>

Author: robotastray

src/qiskit_qec/circuits/repetition_code.py

@@ -21,9 +21,9 @@
 import numpy as np
 import rustworkx as rx
 from qiskit import ClassicalRegister, QuantumCircuit, QuantumRegister, transpile
-from qiskit.circuit.library import RZGate, XGate
-from qiskit.transpiler import InstructionDurations, PassManager
-from qiskit.transpiler.passes import DynamicalDecoupling
+from qiskit.circuit.library import XGate, RZGate
+from qiskit.transpiler import PassManager, InstructionDurations
+from qiskit.transpiler.passes import ALAPScheduleAnalysis, PadDynamicalDecoupling
 
 from qiskit_qec.circuits.code_circuit import CodeCircuit
 from qiskit_qec.utils import DecodingGraphEdge, DecodingGraphNode
@@ -1268,7 +1268,6 @@ def check_nodes(self, nodes, ignore_extra_boundary=False, minimal=False):
             # if neutral for maximal, it's neutral
             # otherwise, it is whatever it is for the minimal
             for c in cs:
-
                 neutral = base_neutral
                 num_errors = num_nodes[c]
                 flipped_logicals = flipped_logicals_all[c]
@@ -1379,9 +1378,10 @@ def transpile(self, backend, echo=("X", "X"), echo_num=(2, 0)):
                         qubits = None
                     pm = PassManager(
                         [
-                            DynamicalDecoupling(
+                            ALAPScheduleAnalysis(durations),
+                            PadDynamicalDecoupling(
                                 durations, dd_sequence, qubits=qubits, spacing=spacings[j]
-                            )
+                            ),
                         ]
                     )
                     circuits = pm.run(circuits)

test/code_circuits/test_rep_codes.py

@@ -20,8 +20,9 @@
 import unittest
 from random import choices
 
-from qiskit import Aer, QuantumCircuit, execute
+from qiskit import QuantumCircuit, execute
 from qiskit.providers.fake_provider import FakeJakarta
+from qiskit_aer import Aer, AerSimulator
 from qiskit_aer.noise import NoiseModel
 from qiskit_aer.noise.errors import depolarizing_error
 
@@ -353,7 +354,7 @@ def test_single_error_202s(self):
                                 else:
                                     error_qc.x(code.link_qubit[code.link_index[q]])
                         error_qc.append(gate)
-                    counts = Aer.get_backend("qasm_simulator").run(error_qc).result().get_counts()
+                    counts = AerSimulator().run(error_qc).result().get_counts()
                     for string in counts:
                         # look at only bulk non-conjugate nodes
                         nodes = [
@@ -392,7 +393,7 @@ def test_feedforward(self):
             for gate in qc:
                 test_qc.append(gate)
             test_qcs.append(test_qc)
-        result = Aer.get_backend("qasm_simulator").run(test_qcs).result()
+        result = AerSimulator().run(test_qcs).result()
         # check result strings are correct
         for j in range(2):
             counts = result.get_counts(j)