diff --git a/docs/technical_docs/vqls.md b/docs/technical_docs/vqls.md
index 4cf66a9..0264a3e 100644
--- a/docs/technical_docs/vqls.md
+++ b/docs/technical_docs/vqls.md
@@ -46,7 +46,7 @@ Systems of linear equations arise naturally in many real-life applications in a
  from qalcore.qiskit.vqls.vqls import VQLS, VQLSLog  
  from qiskit.circuit.library.n_local.real_amplitudes import RealAmplitudes  
  from qiskit_algorithms import optimizers as opt  
- from qiskit import Aer, BasicAer  
+ from qiskit_aer import Aer, BasicAer  
  import numpy as np 
 
  from qiskit.quantum_info import Statevector  
diff --git a/tests/test_hadamard.py b/tests/test_hadamard.py
index a208405..4476c29 100644
--- a/tests/test_hadamard.py
+++ b/tests/test_hadamard.py
@@ -10,9 +10,9 @@
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
 
-import numpy as np
 
-from qiskit.test import QiskitTestCase
+import unittest
+import numpy as np
 
 from qiskit.circuit.library import RealAmplitudes
 from qiskit_algorithms import optimizers as opt
@@ -24,7 +24,7 @@
 from vqls_prototype.hadamard_test.direct_hadamard_test import BatchDirectHadammardTest
 
 
-class TestHadamard(QiskitTestCase):
+class TestHadamard(unittest.TestCase):
     def setUp(self):
         super().setUp()
 
diff --git a/tests/test_hybrid_qst_vqls.py b/tests/test_hybrid_qst_vqls.py
index 0496e62..f1e5357 100644
--- a/tests/test_hybrid_qst_vqls.py
+++ b/tests/test_hybrid_qst_vqls.py
@@ -14,19 +14,16 @@
 
 
 import unittest
-from qiskit.test import QiskitTestCase
 
 import numpy as np
-
-from qiskit import BasicAer
 from qiskit.circuit.library import RealAmplitudes
 
 from qiskit_algorithms.optimizers import COBYLA
-from qiskit.primitives import Estimator, Sampler, BackendEstimator, BackendSampler
+from qiskit.primitives import Estimator, Sampler
 from vqls_prototype import Hybrid_QST_VQLS, VQLSLog
 
 
-class TestHybridQSTVQLS(QiskitTestCase):
+class TestHybridQSTVQLS(unittest.TestCase):
     """Test VQLS"""
 
     def setUp(self):
@@ -36,12 +33,12 @@ def setUp(self):
 
         self.estimators = (
             Estimator(),
-            BackendEstimator(BasicAer.get_backend("qasm_simulator")),
+            # AerEstimator(),
         )
 
         self.samplers = (
             Sampler(),
-            BackendSampler(BasicAer.get_backend("qasm_simulator")),
+            # AerSampler(),
         )
 
         self.log = VQLSLog([], [])
diff --git a/tests/test_qst_vqls.py b/tests/test_qst_vqls.py
index 74bd996..c0f56d1 100644
--- a/tests/test_qst_vqls.py
+++ b/tests/test_qst_vqls.py
@@ -14,19 +14,16 @@
 
 
 import unittest
-from qiskit.test import QiskitTestCase
 
 import numpy as np
-
-from qiskit import BasicAer
 from qiskit.circuit.library import RealAmplitudes
 
 from qiskit_algorithms.optimizers import COBYLA
-from qiskit.primitives import Estimator, Sampler, BackendEstimator, BackendSampler
+from qiskit.primitives import Estimator, Sampler
 from vqls_prototype import QST_VQLS, VQLSLog
 
 
-class TestQSTVQLS(QiskitTestCase):
+class TestQSTVQLS(unittest.TestCase):
     """Test VQLS"""
 
     def setUp(self):
@@ -36,12 +33,12 @@ def setUp(self):
 
         self.estimators = (
             Estimator(),
-            BackendEstimator(BasicAer.get_backend("qasm_simulator")),
+            # AerEstimator(),
         )
 
         self.samplers = (
             Sampler(),
-            BackendSampler(BasicAer.get_backend("qasm_simulator")),
+            # AerSampler(),
         )
 
         self.log = VQLSLog([], [])
diff --git a/tests/test_tomography.py b/tests/test_tomography.py
index 5cd146b..d95e7ae 100644
--- a/tests/test_tomography.py
+++ b/tests/test_tomography.py
@@ -10,17 +10,18 @@
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
 
+import unittest
 import numpy as np
-from qiskit.test import QiskitTestCase
 
-from qiskit import Aer
+
+from qiskit_aer import Aer
 from qiskit.circuit.library import RealAmplitudes
 from qiskit.primitives import Sampler
 
 from vqls_prototype.tomography import FullQST, SimulatorQST, HTreeQST, ShadowQST
 
 
-class TestTomography(QiskitTestCase):
+class TestTomography(unittest.TestCase):
     def setUp(self):
         super().setUp()
 
diff --git a/tests/test_vqls.py b/tests/test_vqls.py
index 149ae58..7504159 100644
--- a/tests/test_vqls.py
+++ b/tests/test_vqls.py
@@ -14,15 +14,14 @@
 
 
 import unittest
-from qiskit.test import QiskitTestCase
 
 import numpy as np
 
-from qiskit import BasicAer, QuantumCircuit
+from qiskit import QuantumCircuit
 from qiskit.circuit.library import RealAmplitudes
 
 from qiskit_algorithms.optimizers import ADAM
-from qiskit.primitives import Estimator, Sampler, BackendEstimator, BackendSampler
+from qiskit.primitives import Estimator, Sampler
 from vqls_prototype import VQLS
 
 # 8-11-2023
@@ -30,7 +29,7 @@
 # this test case is skipped for now
 
 
-class TestVQLS(QiskitTestCase):
+class TestVQLS(unittest.TestCase):
     """Test VQLS"""
 
     def setUp(self):
@@ -44,12 +43,12 @@ def setUp(self):
 
         self.estimators = (
             Estimator(),
-            BackendEstimator(BasicAer.get_backend("qasm_simulator")),
+            # AerEstimator(),
         )
 
         self.samplers = (
             Sampler(),
-            BackendSampler(BasicAer.get_backend("qasm_simulator")),
+            # AerSampler(),
         )
 
     def test_numpy_input(self):
diff --git a/vqls_prototype/hadamard_test/hadamard_overlap_test.py b/vqls_prototype/hadamard_test/hadamard_overlap_test.py
index 0d8822c..526f4ff 100644
--- a/vqls_prototype/hadamard_test/hadamard_overlap_test.py
+++ b/vqls_prototype/hadamard_test/hadamard_overlap_test.py
@@ -1,8 +1,6 @@
-from typing import Optional, List, Union
-from qiskit import QuantumCircuit, QuantumRegister, transpile
+from typing import Optional, List
+from qiskit import QuantumCircuit, QuantumRegister
 from qiskit_algorithms.exceptions import AlgorithmError
-from qiskit.opflow import TensoredOp
-from qiskit.quantum_info import SparsePauliOp
 import numpy as np
 import numpy.typing as npt
 
diff --git a/vqls_prototype/hadamard_test/hadamard_test.py b/vqls_prototype/hadamard_test/hadamard_test.py
index 24eb91d..72e629f 100644
--- a/vqls_prototype/hadamard_test/hadamard_test.py
+++ b/vqls_prototype/hadamard_test/hadamard_test.py
@@ -1,9 +1,9 @@
 """Hadammard test."""
 
 from typing import Optional, List, Union
-from qiskit import QuantumCircuit, QuantumRegister, transpile
+from qiskit import QuantumCircuit
 from qiskit_algorithms.exceptions import AlgorithmError
-from qiskit.opflow import TensoredOp
+from qiskit.quantum_info import Operator
 from qiskit.quantum_info import SparsePauliOp
 import numpy as np
 import numpy.typing as npt
@@ -212,7 +212,7 @@ def _build_circuit(
 
         return circuits
 
-    def _build_observable(self) -> List[TensoredOp]:
+    def _build_observable(self) -> List[Operator]:
         """Create the operator to measure |1> on the control qubit.
 
         Returns:
diff --git a/vqls_prototype/matrix_decomposition/matrix_decomposition.py b/vqls_prototype/matrix_decomposition/matrix_decomposition.py
index b3496c4..da0f6f8 100644
--- a/vqls_prototype/matrix_decomposition/matrix_decomposition.py
+++ b/vqls_prototype/matrix_decomposition/matrix_decomposition.py
@@ -1,4 +1,5 @@
 """Methods to decompose a matrix into quantum circuits"""
+
 from itertools import chain, combinations
 from collections import namedtuple
 from itertools import product
diff --git a/vqls_prototype/matrix_decomposition/optimized_matrix_decomposition.py b/vqls_prototype/matrix_decomposition/optimized_matrix_decomposition.py
index c71caff..05dc19d 100644
--- a/vqls_prototype/matrix_decomposition/optimized_matrix_decomposition.py
+++ b/vqls_prototype/matrix_decomposition/optimized_matrix_decomposition.py
@@ -1,4 +1,5 @@
 """Methods to decompose a matrix into quantum circuits"""
+
 import itertools
 from dataclasses import dataclass
 from collections import OrderedDict
diff --git a/vqls_prototype/solver/base_solver.py b/vqls_prototype/solver/base_solver.py
index cbf11e9..fa6289d 100644
--- a/vqls_prototype/solver/base_solver.py
+++ b/vqls_prototype/solver/base_solver.py
@@ -11,7 +11,7 @@
 from qiskit_algorithms.utils.validation import validate_min
 from qiskit.circuit.library.n_local.real_amplitudes import RealAmplitudes
 from qiskit_algorithms.optimizers import Minimizer, Optimizer
-from qiskit.opflow.gradients import GradientBase
+from qiskit_algorithms.gradients import BaseEstimatorGradient
 
 from .variational_linear_solver import (
     VariationalLinearSolver,
@@ -45,7 +45,7 @@ def __init__(
         optimizer: Union[Optimizer, Minimizer],
         sampler: Union[BaseSampler, None],
         initial_point: Union[np.ndarray, None],
-        gradient: Union[GradientBase, Callable, None],
+        gradient: Union[BaseEstimatorGradient, Callable, None],
         max_evals_grouped: int,
     ) -> None:
         r"""
diff --git a/vqls_prototype/solver/hybrid_qst_vqls.py b/vqls_prototype/solver/hybrid_qst_vqls.py
index 4cb01db..ac062eb 100644
--- a/vqls_prototype/solver/hybrid_qst_vqls.py
+++ b/vqls_prototype/solver/hybrid_qst_vqls.py
@@ -10,9 +10,9 @@
 from typing import Optional, Union, List, Callable, Dict, Tuple
 from qiskit_algorithms.optimizers import Minimizer, Optimizer
 import numpy as np
-from qiskit.opflow.gradients import GradientBase
+from qiskit_algorithms.gradients import BaseEstimatorGradient
 from qiskit.primitives import BaseEstimator, BaseSampler
-from qiskit import Aer
+from qiskit_aer import Aer
 from qiskit import QuantumCircuit
 
 from qiskit_algorithms.utils import validate_bounds
@@ -55,7 +55,7 @@ class Hybrid_QST_VQLS(BaseSolver):
             from qalcore.qiskit.vqls.vqls import VQLS, VQLSLog
             from qiskit.circuit.library.n_local.real_amplitudes import RealAmplitudes
             from qiskit_algorithms import optimizers as opt
-            from qiskit import Aer, BasicAer
+            from qiskit_aer import Aer, BasicAer
             import numpy as np
 
             from qiskit.quantum_info import Statevector
@@ -122,7 +122,7 @@ def __init__(
         optimizer: Union[Optimizer, Minimizer],
         sampler: Union[BaseSampler, None],
         initial_point: Optional[Union[np.ndarray, None]] = None,
-        gradient: Optional[Union[GradientBase, Callable, None]] = None,
+        gradient: Optional[Union[BaseEstimatorGradient, Callable, None]] = None,
         max_evals_grouped: Optional[int] = 1,
         options: Optional[Union[Dict, None]] = None,
     ) -> None:
diff --git a/vqls_prototype/solver/qst_vqls.py b/vqls_prototype/solver/qst_vqls.py
index 3e09844..823beb9 100644
--- a/vqls_prototype/solver/qst_vqls.py
+++ b/vqls_prototype/solver/qst_vqls.py
@@ -12,9 +12,9 @@
 
 import numpy as np
 import sparse
-from qiskit.opflow.gradients import GradientBase
+from qiskit_algorithms.gradients import BaseEstimatorGradient
 from qiskit.primitives import BaseEstimator, BaseSampler
-from qiskit import Aer
+from qiskit_aer import Aer
 from qiskit import QuantumCircuit
 from qiskit.quantum_info import SparsePauliOp
 from qiskit_algorithms.utils import validate_bounds
@@ -52,7 +52,7 @@ class QST_VQLS(BaseSolver):
             from qalcore.qiskit.vqls.vqls import VQLS, VQLSLog
             from qiskit.circuit.library.n_local.real_amplitudes import RealAmplitudes
             from qiskit_algorithms import optimizers as opt
-            from qiskit import Aer, BasicAer
+            from qiskit_aer import Aer, BasicAer
             import numpy as np
 
             from qiskit.quantum_info import Statevector
@@ -119,7 +119,7 @@ def __init__(
         optimizer: Union[Optimizer, Minimizer],
         sampler: Union[BaseSampler, None],
         initial_point: Optional[Union[np.ndarray, None]] = None,
-        gradient: Optional[Union[GradientBase, Callable, None]] = None,
+        gradient: Optional[Union[BaseEstimatorGradient, Callable, None]] = None,
         max_evals_grouped: Optional[int] = 1,
         options: Optional[Union[Dict, None]] = None,
     ) -> None:
diff --git a/vqls_prototype/solver/vqls.py b/vqls_prototype/solver/vqls.py
index 1ae0522..c77609d 100644
--- a/vqls_prototype/solver/vqls.py
+++ b/vqls_prototype/solver/vqls.py
@@ -15,7 +15,7 @@
 from qiskit_algorithms.utils import validate_bounds
 from qiskit.quantum_info import Statevector
 from qiskit_algorithms.optimizers import Minimizer, Optimizer
-from qiskit.opflow.gradients import GradientBase
+from qiskit_algorithms.gradients import BaseEstimatorGradient
 
 from .variational_linear_solver import (
     VariationalLinearSolverResult,
@@ -63,7 +63,7 @@ class VQLS(BaseSolver):
             from qalcore.qiskit.vqls.vqls import VQLS, VQLSLog
             from qiskit.circuit.library.n_local.real_amplitudes import RealAmplitudes
             from qiskit_algorithms import optimizers as opt
-            from qiskit import Aer, BasicAer
+            from qiskit_aer import Aer, BasicAer
             import numpy as np
 
             from qiskit.quantum_info import Statevector
@@ -130,7 +130,7 @@ def __init__(
         optimizer: Union[Optimizer, Minimizer],
         sampler: Optional[Union[BaseSampler, None]] = None,
         initial_point: Optional[Union[np.ndarray, None]] = None,
-        gradient: Optional[Union[GradientBase, Callable, None]] = None,
+        gradient: Optional[Union[BaseEstimatorGradient, Callable, None]] = None,
         max_evals_grouped: Optional[int] = 1,
         options: Optional[Union[Dict, None]] = None,
     ) -> None: