# This code is part of a Qiskit project.
#
# (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
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# 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.
"""Time evolution problem class."""
from __future__ import annotations
from collections.abc import Mapping
from qiskit import QuantumCircuit
from qiskit.circuit import Parameter
from qiskit.quantum_info import Statevector
from qiskit.quantum_info.operators.base_operator import BaseOperator
from ..list_or_dict import ListOrDict
[docs]class TimeEvolutionProblem:
"""Time evolution problem class.
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.
Attributes:
hamiltonian (BaseOperator): The Hamiltonian under which to evolve the system.
initial_state (QuantumCircuit | Statevector | None): The quantum state to be evolved for
methods like Trotterization. For variational time evolutions, where the evolution
happens in an ansatz, this argument is not required.
aux_operators (ListOrDict[BaseOperator] | None): Optional list of auxiliary
operators to be evaluated with the evolved ``initial_state`` and their expectation
values returned.
truncation_threshold (float): Defines a threshold under which values can be assumed to be 0.
Used when ``aux_operators`` is provided.
t_param (Parameter | None): Time parameter in case of a time-dependent Hamiltonian. This
free parameter must be within the ``hamiltonian``.
param_value_map (dict[Parameter, complex] | None): Maps free parameters in the problem to
values. Depending on the algorithm, it might refer to e.g. a Hamiltonian or an initial
state.
"""
def __init__(
self,
hamiltonian: BaseOperator,
time: float,
initial_state: QuantumCircuit | Statevector | None = None,
aux_operators: ListOrDict[BaseOperator] | None = None,
truncation_threshold: float = 1e-12,
t_param: Parameter | None = None,
param_value_map: Mapping[Parameter, complex] | None = None,
):
"""
Args:
hamiltonian: The Hamiltonian under which to evolve the system.
time: Total time of evolution.
initial_state: The quantum state to be evolved for methods like Trotterization.
For variational time evolutions, where the evolution happens in an ansatz,
this argument is not required.
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``.
param_value_map: Maps free parameters in the problem to values. Depending on the
algorithm, it might refer to e.g. a Hamiltonian or an initial state.
Raises:
ValueError: If non-positive time of evolution is provided.
"""
self.t_param = t_param
self.param_value_map = param_value_map
self.hamiltonian = hamiltonian
self.time = time
if isinstance(initial_state, Statevector):
circuit = QuantumCircuit(initial_state.num_qubits)
circuit.prepare_state(initial_state.data)
initial_state = circuit
self.initial_state: QuantumCircuit | None = initial_state
self.aux_operators = aux_operators
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.
"""
self._time = time