Trotterization-based Quantum Real Time Evolution

qiskit/algorithms/__init__.py

@@ -106,6 +106,7 @@
 
     RealEvolver
     ImaginaryEvolver
+    TrotterQRTE
     EvolutionResult
     EvolutionProblem
 
@@ -205,8 +206,8 @@
 
 from .algorithm_result import AlgorithmResult
 from .evolvers import EvolutionResult, EvolutionProblem
-from .evolvers.real.real_evolver import RealEvolver
-from .evolvers.imaginary.imaginary_evolver import ImaginaryEvolver
+from .evolvers.real_evolver import RealEvolver
+from .evolvers.imaginary_evolver import ImaginaryEvolver
 from .variational_algorithm import VariationalAlgorithm, VariationalResult
 from .amplitude_amplifiers import Grover, GroverResult, AmplificationProblem, AmplitudeAmplifier
 from .amplitude_estimators import (
@@ -243,6 +244,7 @@
 )
 from .exceptions import AlgorithmError
 from .aux_ops_evaluator import eval_observables
+from .evolvers.trotterization import TrotterQRTE
 
 __all__ = [
     "AlgorithmResult",
@@ -266,6 +268,7 @@
     "NumPyEigensolver",
     "RealEvolver",
     "ImaginaryEvolver",
+    "TrotterQRTE",
     "EvolutionResult",
     "EvolutionProblem",
     "LinearSolverResult",

qiskit/algorithms/evolvers/evolution_problem.py

@@ -23,9 +23,8 @@
 class EvolutionProblem:
     """Evolution problem class.
 
-    This class is the input to time evolution algorithms and contains
-    information on e.g. the total evolution time and under which Hamiltonian
-    the state is evolved.
+    This class is the input to time evolution algorithms and must contain information on the total
+    evolution time, a quantum state to be evolved and under which Hamiltonian the state is evolved.
     """
 
     def __init__(
@@ -34,8 +33,9 @@ def __init__(
         time: float,
         initial_state: Union[StateFn, QuantumCircuit],
         aux_operators: Optional[ListOrDict[OperatorBase]] = None,
+        truncation_threshold: float = 1e-12,
         t_param: Optional[Parameter] = None,
-        hamiltonian_value_dict: Optional[Dict[Parameter, Union[complex]]] = None,
+        hamiltonian_value_dict: Optional[Dict[Parameter, complex]] = None,
     ):
         """
         Args:
@@ -44,15 +44,64 @@ def __init__(
             initial_state: Quantum state to be evolved.
             aux_operators: Optional list of auxiliary operators to be evaluated with the
                 evolved ``initial_state`` and their expectation values returned.
+            truncation_threshold: Defines a threshold under which values can be assumed to be 0.
+                Used when ``aux_operators`` is provided.
             t_param: Time parameter in case of a time-dependent Hamiltonian. This
                 free parameter must be within the ``hamiltonian``.
             hamiltonian_value_dict: If the Hamiltonian contains free parameters, this
                 dictionary maps all these parameters to values.
+
+        Raises:
+            ValueError: If non-positive time of evolution is provided.
         """
 
+        self.t_param = t_param
+        self.hamiltonian_value_dict = hamiltonian_value_dict
         self.hamiltonian = hamiltonian
         self.time = time
         self.initial_state = initial_state
         self.aux_operators = aux_operators
-        self.t_param = t_param
-        self.hamiltonian_value_dict = hamiltonian_value_dict
+        self.truncation_threshold = truncation_threshold
+
+    @property
+    def time(self) -> float:
+        """Returns time."""
+        return self._time
+
+    @time.setter
+    def time(self, time: float) -> None:
+        """
+        Sets time and validates it.
+
+        Raises:
+            ValueError: If time is not positive.
+        """
+        if time <= 0:
+            raise ValueError(f"Evolution time must be > 0 but was {time}.")
+        self._time = time
+
+    def validate_params(self) -> None:
+        """
+        Checks if all parameters present in the Hamiltonian are also present in the dictionary
+        that maps them to values.
+
+        Raises:
+            ValueError: If Hamiltonian parameters cannot be bound with data provided.
+        """
+        if isinstance(self.hamiltonian, OperatorBase):
+            t_param_set = set()
+            if self.t_param is not None:
+                t_param_set.add(self.t_param)
+            hamiltonian_dict_param_set = set()
+            if self.hamiltonian_value_dict is not None:
+                hamiltonian_dict_param_set = hamiltonian_dict_param_set.union(
+                    set(self.hamiltonian_value_dict.keys())
+                )
+            params_set = t_param_set.union(hamiltonian_dict_param_set)
+            hamiltonian_param_set = set(self.hamiltonian.parameters)
+
+            if hamiltonian_param_set != params_set:
+                raise ValueError(
+                    f"Provided parameters {params_set} do not match Hamiltonian parameters "
+                    f"{hamiltonian_param_set}."
+                )

qiskit/algorithms/evolvers/evolution_result.py

@@ -16,7 +16,7 @@
 
 from qiskit import QuantumCircuit
 from qiskit.algorithms.list_or_dict import ListOrDict
-from qiskit.opflow import StateFn
+from qiskit.opflow import StateFn, OperatorBase
 from ..algorithm_result import AlgorithmResult
 
 
@@ -25,7 +25,7 @@ class EvolutionResult(AlgorithmResult):
 
     def __init__(
         self,
-        evolved_state: Union[StateFn, QuantumCircuit],
+        evolved_state: Union[StateFn, QuantumCircuit, OperatorBase],
         aux_ops_evaluated: Optional[ListOrDict[Tuple[complex, complex]]] = None,
     ):
         """

qiskit/algorithms/evolvers/imaginary/imaginary_evolver.py → qiskit/algorithms/evolvers/imaginary_evolver.py

@@ -14,8 +14,8 @@
 
 from abc import ABC, abstractmethod
 
-from ..evolution_problem import EvolutionProblem
-from ..evolution_result import EvolutionResult
+from .evolution_problem import EvolutionProblem
+from .evolution_result import EvolutionResult
 
 
 class ImaginaryEvolver(ABC):

qiskit/algorithms/evolvers/real/real_evolver.py → qiskit/algorithms/evolvers/real_evolver.py

@@ -14,8 +14,8 @@
 
 from abc import ABC, abstractmethod
 
-from ..evolution_problem import EvolutionProblem
-from ..evolution_result import EvolutionResult
+from .evolution_problem import EvolutionProblem
+from .evolution_result import EvolutionResult
 
 
 class RealEvolver(ABC):

qiskit/algorithms/evolvers/real/__init__.py → qiskit/algorithms/evolvers/trotterization/__init__.py

@@ -9,3 +9,13 @@
 # Any modifications or derivative works of this code must retain this
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
+"""This package contains Trotterization-based Quantum Real Time Evolution algorithm.
+It is compliant with the new Quantum Time Evolution Framework and makes use of
+:class:`qiskit.synthesis.evolution.ProductFormula` and
+:class:`~qiskit.circuit.library.PauliEvolutionGate` implementations. """
+
+from qiskit.algorithms.evolvers.trotterization.trotter_qrte import (
+    TrotterQRTE,
+)
+
+__all__ = ["TrotterQRTE"]