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Migrate to Qiskit Nature v0.5 #3

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Migrate to Qiskit Nature v0.5 #3

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0fb71a8
Migrate HeisenbergModel to Qiskit Nature v0.5
towynlin Feb 14, 2023
ab1ec8e
Migrate the notebook to Qiskit Nature v0.5
towynlin Feb 14, 2023
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83 changes: 11 additions & 72 deletions heisenberg_model.py
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Original file line number Diff line number Diff line change
@@ -1,69 +1,14 @@
# Modifed from the Ising model found here: https://qiskit.org/documentation/nature/_modules/qiskit_nature/problems/second_quantization/lattice/models/ising_model.html#IsingModel

"""The Heisenberg model"""
import logging
import numpy as np

from fractions import Fraction
from typing import Optional

from qiskit_nature.operators.second_quantization import SpinOp
from qiskit_nature.problems.second_quantization.lattice.lattices import Lattice
from qiskit_nature.problems.second_quantization.lattice.models.lattice_model import LatticeModel
from qiskit_nature.second_q.operators import SpinOp
from qiskit_nature.second_q.hamiltonians.ising_model import IsingModel

class HeisenbergModel(LatticeModel):
class HeisenbergModel(IsingModel):
"""The Heisenberg model."""

def coupling_matrix(self) -> np.ndarray:
"""Return the coupling matrix."""
return self.interaction_matrix()


@classmethod
def uniform_parameters(
cls,
lattice: Lattice,
uniform_interaction: complex,
uniform_onsite_potential: complex,
) -> "HeisenbergModel":
"""Set a uniform interaction parameter and on-site potential over the input lattice.

Args:
lattice: Lattice on which the model is defined.
uniform_interaction: The interaction parameter.
uniform_onsite_potential: The on-site potential.

Returns:
The Lattice model with uniform parameters.
"""
return cls(
cls._generate_lattice_from_uniform_parameters(
lattice, uniform_interaction, uniform_onsite_potential
)
)


@classmethod
def from_parameters(
cls,
interaction_matrix: np.ndarray,
) -> "HeisenbergModel":
"""Return the Hamiltonian of the Lattice model
from the given interaction matrix and on-site interaction.

Args:
interaction_matrix: A real or complex valued square matrix.

Returns:
LatticeModel: The Lattice model generated from the given interaction
matrix and on-site interaction.

Raises:
ValueError: If the interaction matrix is not square matrix, it is invalid.
"""
return cls(cls._generate_lattice_from_parameters(interaction_matrix))


def second_q_ops(self, display_format: Optional[str] = None) -> SpinOp:
def second_q_op(self) -> SpinOp:
"""Return the Hamiltonian of the Heisenberg model in terms of `SpinOp`.

Args:
Expand All @@ -72,25 +17,19 @@ def second_q_ops(self, display_format: Optional[str] = None) -> SpinOp:
Returns:
SpinOp: The Hamiltonian of the Heisenberg model.
"""
if display_format is not None:
logger.warning(
"Spin operators do not support display-format. Provided display-format "
"parameter will be ignored."
)
ham = []
ham = {}
weighted_edge_list = self._lattice.weighted_edge_list
register_length = self._lattice.num_nodes
# kinetic terms
for node_a, node_b, weight in weighted_edge_list:
if node_a == node_b:
index = node_a
ham.append((f"X_{index}", weight))
ham[f"X_{index}"] = weight

else:
index_left = node_a
index_right = node_b
coupling_parameter = weight
ham.append((f"X_{index_left} X_{index_right}", coupling_parameter))
ham.append((f"Y_{index_left} Y_{index_right}", coupling_parameter))
ham.append((f"Z_{index_left} Z_{index_right}", coupling_parameter))
return SpinOp(ham, spin=Fraction(1, 2), register_length=register_length)
ham[f"X_{index_left} X_{index_right}"] = coupling_parameter
ham[f"Y_{index_left} Y_{index_right}"] = coupling_parameter
ham[f"Z_{index_left} Z_{index_right}"] = coupling_parameter
return SpinOp(ham, spin=Fraction(1, 2), num_spins=self.register_length)
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