Implements VarQTE algorithm with primitives.

qiskit/algorithms/__init__.py

@@ -124,11 +124,11 @@
    :toctree: ../stubs/
    :nosignatures:
 
-    RealEvolver
-    ImaginaryEvolver
-    TrotterQRTE
-    EvolutionResult
-    EvolutionProblem
+   RealEvolver
+   ImaginaryEvolver
+   TrotterQRTE
+   EvolutionResult
+   EvolutionProblem
 
 
 Time Evolvers
@@ -142,18 +142,31 @@
    :toctree: ../stubs/
    :nosignatures:
 
-    RealTimeEvolver
-    ImaginaryTimeEvolver
-    PVQD
-    PVQDResult
-    TimeEvolutionResult
-    TimeEvolutionProblem
-    SciPyImaginaryEvolver
-    SciPyRealEvolver
+   RealTimeEvolver
+   ImaginaryTimeEvolver
+   TimeEvolutionResult
+   TimeEvolutionProblem
+   PVQD
+   PVQDResult
+   SciPyImaginaryEvolver
+   SciPyRealEvolver
+   VarQITE
+   VarQRTE
+
+
+Variational Quantum Time Evolution
+++++++++++++++++++++++++++++++++++
+
+Classes used by variational quantum time evolution algorithms - VarQITE and VarQRTE.
+
+.. autosummary::
+   :toctree: ../stubs/
+
+   time_evolvers.variational
 
 
 Trotterization-based Quantum Real Time Evolution
-------------------------------------------------
+++++++++++++++++++++++++++++++++++++++++++++++++
 
 Package for primitives-enabled Trotterization-based quantum time evolution algorithm - TrotterQRTE.
 
@@ -308,10 +321,6 @@
 from .evolvers import EvolutionResult, EvolutionProblem
 from .evolvers.real_evolver import RealEvolver
 from .evolvers.imaginary_evolver import ImaginaryEvolver
-from .time_evolvers.imaginary_time_evolver import ImaginaryTimeEvolver
-from .time_evolvers.real_time_evolver import RealTimeEvolver
-from .time_evolvers.time_evolution_problem import TimeEvolutionProblem
-from .time_evolvers.time_evolution_result import TimeEvolutionResult
 from .variational_algorithm import VariationalAlgorithm, VariationalResult
 from .amplitude_amplifiers import Grover, GroverResult, AmplificationProblem, AmplitudeAmplifier
 from .amplitude_estimators import (
@@ -351,8 +360,20 @@
 from .observables_evaluator import estimate_observables
 from .evolvers.trotterization import TrotterQRTE
 
-from .time_evolvers.pvqd import PVQD, PVQDResult
-from .time_evolvers.classical_methods import SciPyRealEvolver, SciPyImaginaryEvolver
+from .time_evolvers import (
+    ImaginaryTimeEvolver,
+    RealTimeEvolver,
+    TimeEvolutionProblem,
+    TimeEvolutionResult,
+    PVQD,
+    PVQDResult,
+    SciPyImaginaryEvolver,
+    SciPyRealEvolver,
+    VarQITE,
+    VarQRTE,
+    VarQTE,
+    VarQTEResult,
+)
 
 __all__ = [
     "AlgorithmJob",
@@ -413,4 +434,8 @@
     "AlgorithmError",
     "eval_observables",
     "estimate_observables",
+    "VarQITE",
+    "VarQRTE",
+    "VarQTE",
+    "VarQTEResult",
 ]

qiskit/algorithms/gradients/base_estimator_gradient.py

@@ -22,7 +22,6 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmJob
 from qiskit.circuit import Parameter, ParameterExpression, QuantumCircuit
 from qiskit.opflow import PauliSumOp
 from qiskit.primitives import BaseEstimator
@@ -40,6 +39,8 @@
     _make_gradient_parameter_values,
 )
 
+from ..algorithm_job import AlgorithmJob
+
 
 class BaseEstimatorGradient(ABC):
     """Base class for an ``EstimatorGradient`` to compute the gradients of the expectation value."""

qiskit/algorithms/gradients/base_qgt.py

@@ -28,7 +28,6 @@
 from qiskit.providers import Options
 from qiskit.transpiler.passes import TranslateParameterizedGates
 
-from .. import AlgorithmJob
 from .qgt_result import QGTResult
 from .utils import (
     DerivativeType,
@@ -38,6 +37,8 @@
     _make_gradient_parameter_values,
 )
 
+from ..algorithm_job import AlgorithmJob
+
 
 class BaseQGT(ABC):
     r"""Base class to computes the Quantum Geometric Tensor (QGT) given a pure,

qiskit/algorithms/gradients/base_sampler_gradient.py

@@ -21,7 +21,6 @@
 from collections.abc import Sequence
 from copy import copy
 
-from qiskit.algorithms import AlgorithmJob
 from qiskit.circuit import Parameter, ParameterExpression, QuantumCircuit
 from qiskit.primitives import BaseSampler
 from qiskit.primitives.utils import _circuit_key
@@ -36,6 +35,8 @@
     _make_gradient_parameter_values,
 )
 
+from ..algorithm_job import AlgorithmJob
+
 
 class BaseSamplerGradient(ABC):
     """Base class for a ``SamplerGradient`` to compute the gradients of the sampling probability."""

qiskit/algorithms/gradients/finite_diff_estimator_gradient.py

@@ -19,7 +19,6 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.opflow import PauliSumOp
 from qiskit.primitives import BaseEstimator
@@ -29,6 +28,8 @@
 from .base_estimator_gradient import BaseEstimatorGradient
 from .estimator_gradient_result import EstimatorGradientResult
 
+from ..exceptions import AlgorithmError
+
 if sys.version_info >= (3, 8):
     # pylint: disable=no-name-in-module, ungrouped-imports
     from typing import Literal

qiskit/algorithms/gradients/finite_diff_sampler_gradient.py

@@ -20,14 +20,15 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.primitives import BaseSampler
 from qiskit.providers import Options
 
 from .base_sampler_gradient import BaseSamplerGradient
 from .sampler_gradient_result import SamplerGradientResult
 
+from ..exceptions import AlgorithmError
+
 if sys.version_info >= (3, 8):
     # pylint: disable=no-name-in-module, ungrouped-imports
     from typing import Literal

qiskit/algorithms/gradients/lin_comb_estimator_gradient.py

@@ -19,7 +19,6 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.opflow import PauliSumOp
 from qiskit.primitives import BaseEstimator
@@ -31,6 +30,8 @@
 from .estimator_gradient_result import EstimatorGradientResult
 from .utils import DerivativeType, _make_lin_comb_gradient_circuit, _make_lin_comb_observables
 
+from ..exceptions import AlgorithmError
+
 
 class LinCombEstimatorGradient(BaseEstimatorGradient):
     """Compute the gradients of the expectation values.

qiskit/algorithms/gradients/lin_comb_qgt.py

@@ -19,7 +19,6 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.primitives import BaseEstimator
 from qiskit.primitives.utils import _circuit_key
@@ -31,6 +30,8 @@
 from .qgt_result import QGTResult
 from .utils import DerivativeType, _make_lin_comb_qgt_circuit, _make_lin_comb_observables
 
+from ..exceptions import AlgorithmError
+
 
 class LinCombQGT(BaseQGT):
     """Computes the Quantum Geometric Tensor (QGT) given a pure, parameterized quantum state.

qiskit/algorithms/gradients/lin_comb_sampler_gradient.py

@@ -18,7 +18,6 @@
 from collections import defaultdict
 from typing import Sequence
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.primitives import BaseSampler
 from qiskit.primitives.utils import _circuit_key
@@ -28,6 +27,8 @@
 from .sampler_gradient_result import SamplerGradientResult
 from .utils import _make_lin_comb_gradient_circuit
 
+from ..exceptions import AlgorithmError
+
 
 class LinCombSamplerGradient(BaseSamplerGradient):
     """Compute the gradients of the sampling probability.

qiskit/algorithms/gradients/param_shift_estimator_gradient.py

@@ -17,7 +17,6 @@
 
 from typing import Sequence
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.opflow import PauliSumOp
 from qiskit.quantum_info.operators.base_operator import BaseOperator
@@ -26,6 +25,8 @@
 from .estimator_gradient_result import EstimatorGradientResult
 from .utils import _make_param_shift_parameter_values
 
+from ..exceptions import AlgorithmError
+
 
 class ParamShiftEstimatorGradient(BaseEstimatorGradient):
     """

qiskit/algorithms/gradients/param_shift_sampler_gradient.py

@@ -18,13 +18,14 @@
 from collections import defaultdict
 from typing import Sequence
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 
 from .base_sampler_gradient import BaseSamplerGradient
 from .sampler_gradient_result import SamplerGradientResult
 from .utils import _make_param_shift_parameter_values
 
+from ..exceptions import AlgorithmError
+
 
 class ParamShiftSamplerGradient(BaseSamplerGradient):
     """

qiskit/algorithms/gradients/qfi.py

@@ -19,15 +19,16 @@
 from collections.abc import Sequence
 from copy import copy
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.providers import Options
 
-from .. import AlgorithmJob
 from .base_qgt import BaseQGT
 from .lin_comb_estimator_gradient import DerivativeType
 from .qfi_result import QFIResult
 
+from ..algorithm_job import AlgorithmJob
+from ..exceptions import AlgorithmError
+
 
 class QFI(ABC):
     r"""Computes the Quantum Fisher Information (QFI) given a pure,

qiskit/algorithms/gradients/spsa_estimator_gradient.py

@@ -18,7 +18,6 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.opflow import PauliSumOp
 from qiskit.primitives import BaseEstimator
@@ -28,6 +27,8 @@
 from .base_estimator_gradient import BaseEstimatorGradient
 from .estimator_gradient_result import EstimatorGradientResult
 
+from ..exceptions import AlgorithmError
+
 
 class SPSAEstimatorGradient(BaseEstimatorGradient):
     """

qiskit/algorithms/gradients/spsa_sampler_gradient.py

@@ -19,14 +19,15 @@
 
 import numpy as np
 
-from qiskit.algorithms import AlgorithmError
 from qiskit.circuit import Parameter, QuantumCircuit
 from qiskit.primitives import BaseSampler
 from qiskit.providers import Options
 
 from .base_sampler_gradient import BaseSamplerGradient
 from .sampler_gradient_result import SamplerGradientResult
 
+from ..exceptions import AlgorithmError
+
 
 class SPSASamplerGradient(BaseSamplerGradient):
     """

qiskit/algorithms/time_evolvers/__init__.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2022.
+# (C) Copyright IBM 2022, 2023.
 #
 # 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
@@ -12,10 +12,25 @@
 
 """Quantum Time Evolution package."""
 
-from .time_evolution_result import TimeEvolutionResult
+from .imaginary_time_evolver import ImaginaryTimeEvolver
+from .real_time_evolver import RealTimeEvolver
 from .time_evolution_problem import TimeEvolutionProblem
+from .time_evolution_result import TimeEvolutionResult
+from .pvqd import PVQD, PVQDResult
+from .classical_methods import SciPyImaginaryEvolver, SciPyRealEvolver
+from .variational import VarQITE, VarQRTE, VarQTE, VarQTEResult
 
 __all__ = [
-    "TimeEvolutionResult",
+    "ImaginaryTimeEvolver",
+    "RealTimeEvolver",
     "TimeEvolutionProblem",
+    "TimeEvolutionResult",
+    "PVQD",
+    "PVQDResult",
+    "SciPyImaginaryEvolver",
+    "SciPyRealEvolver",
+    "VarQITE",
+    "VarQRTE",
+    "VarQTE",
+    "VarQTEResult",
 ]

qiskit/algorithms/time_evolvers/time_evolution_result.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2021, 2022.
+# (C) Copyright IBM 2021, 2023.
 #
 # 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
@@ -32,7 +32,7 @@ class TimeEvolutionResult(AlgorithmResult):
         observables (ListOrDict[tuple[np.ndarray, np.ndarray]] | None): Optional list of
             observables for which expected on an evolved state are calculated at each timestep.
             These values are in fact lists of tuples formatted as (mean, standard deviation).
-            times (np.array | None): Optional list of times at wich each observable has been evaluated.
+        times (np.array | None): Optional list of times at which each observable has been evaluated.
     """
 
     def __init__(