# This code is part of Qiskit.
# (C) Copyright IBM 2021.
# 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.
"""Exact synthesis of operator evolution via (exponentially expensive) matrix exponentiation."""
from qiskit.circuit.quantumcircuit import QuantumCircuit
from .evolution_synthesis import EvolutionSynthesis
r"""Exact operator evolution via matrix exponentiation and unitary synthesis.
This class synthesis the exponential of operators by calculating their exponentially-sized
matrix representation and using exact matrix exponentiation followed by unitary synthesis
to obtain a circuit. This process is not scalable and serves as comparison or benchmark
for small systems.
[ドキュメント] def synthesize(self, evolution):
from scipy.linalg import expm
# get operators and time to evolve
operators = evolution.operator
time = evolution.time
# construct the evolution circuit
evolution_circuit = QuantumCircuit(operators.num_qubits)
if not isinstance(operators, list):
matrix = operators.to_matrix()
matrix = sum(op.to_matrix() for op in operators)
exp = expm(-1j * time * matrix)