Source code for qiskit.chemistry.components.variational_forms.chc
# This code is part of Qiskit.
#
# (C) Copyright IBM 2020.
#
# 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.
""" Compact heuristic ansatz for Chemistry """
from typing import List, Optional, Union
import numpy as np
from qiskit import QuantumRegister, QuantumCircuit
from qiskit.circuit import ParameterVector, Parameter
from qiskit.aqua.components.variational_forms import VariationalForm
from qiskit.aqua.components.initial_states import InitialState
[docs]class CHC(VariationalForm):
""" This trial wavefunction is the Compact Heuristic for Chemistry.
The trial wavefunction is as defined in
Ollitrault Pauline J., Chemical science 11 (2020): 6842-6855. It aims at approximating
the UCC Ansatz for a lower CNOT count.
Note:
It is not particle number conserving and the accuracy of the approximation decreases
with the number of excitations.
"""
[docs] def __init__(self, num_qubits: Optional[int] = None, reps: int = 1, ladder: bool = False,
excitations: Optional[List[List[int]]] = None,
entanglement: Union[str, List[int]] = 'full',
initial_state: Optional[InitialState] = None) -> None:
"""
Args:
num_qubits: number of qubits
reps: number of replica of basic module
ladder: use ladder of CNOTs between to indices in the entangling block
excitations: indices corresponding to the excitations to include in the circuit
entanglement: physical connections between the qubits
initial_state: an initial state object
"""
super().__init__()
self._num_qubits = num_qubits
self._reps = reps
self._excitations = None
self._entangler_map = None
self._initial_state = None
self._ladder = ladder
self._num_parameters = len(excitations) * reps
self._excitations = excitations
self._bounds = [(-np.pi, np.pi)] * self._num_parameters
self._num_qubits = num_qubits
if isinstance(entanglement, str):
self._entangler_map = VariationalForm.get_entangler_map(entanglement, num_qubits)
else:
self._entangler_map = VariationalForm.validate_entangler_map(entanglement, num_qubits)
self._initial_state = initial_state
self._support_parameterized_circuit = True
@property
def num_qubits(self) -> int:
"""Number of qubits of the variational form.
Returns:
int: An integer indicating the number of qubits.
"""
return self._num_qubits
@num_qubits.setter
def num_qubits(self, num_qubits: int) -> None:
"""Set the number of qubits of the variational form.
Args:
num_qubits: An integer indicating the number of qubits.
"""
self._num_qubits = num_qubits
[docs] def construct_circuit(self, parameters: Union[np.ndarray, List[Parameter], ParameterVector],
q: Optional[QuantumRegister] = None) -> QuantumCircuit:
"""
Construct the variational form, given its parameters.
Args:
parameters: circuit parameters
q: Quantum Register for the circuit.
Returns:
QuantumCircuit: a quantum circuit with given `parameters`
Raises:
ValueError: the number of parameters is incorrect.
ValueError: if num_qubits has not been set and is still None
ValueError: only supports single and double excitations at the moment.
"""
if len(parameters) != self._num_parameters:
raise ValueError('The number of parameters has to be {}'.format(self._num_parameters))
if self._num_qubits is None:
raise ValueError('The number of qubits is None and must be set before the circuit '
'can be created.')
if q is None:
q = QuantumRegister(self._num_qubits, name='q')
if self._initial_state is not None:
circuit = self._initial_state.construct_circuit('circuit', q)
else:
circuit = QuantumCircuit(q)
count = 0
for _ in range(self._reps):
for idx in self._excitations:
if len(idx) == 2:
i = idx[0]
r = idx[1]
circuit.p(-parameters[count] / 4 + np.pi / 4, q[i])
circuit.p(-parameters[count] / 4 - np.pi / 4, q[r])
circuit.h(q[i])
circuit.h(q[r])
if self._ladder:
for qubit in range(i, r):
circuit.cx(q[qubit], q[qubit + 1])
else:
circuit.cx(q[i], q[r])
circuit.p(parameters[count], q[r])
if self._ladder:
for qubit in range(r, i, -1):
circuit.cx(q[qubit - 1], q[qubit])
else:
circuit.cx(q[i], q[r])
circuit.h(q[i])
circuit.h(q[r])
circuit.p(-parameters[count] / 4 - np.pi / 4, q[i])
circuit.p(-parameters[count] / 4 + np.pi / 4, q[r])
elif len(idx) == 4:
i = idx[0]
r = idx[1]
j = idx[2]
s = idx[3] # pylint: disable=locally-disabled, invalid-name
circuit.sdg(q[r])
circuit.h(q[i])
circuit.h(q[r])
circuit.h(q[j])
circuit.h(q[s])
if self._ladder:
for qubit in range(i, r):
circuit.cx(q[qubit], q[qubit+1])
circuit.barrier(q[qubit], q[qubit+1])
else:
circuit.cx(q[i], q[r])
circuit.cx(q[r], q[j])
if self._ladder:
for qubit in range(j, s):
circuit.cx(q[qubit], q[qubit+1])
circuit.barrier(q[qubit], q[qubit + 1])
else:
circuit.cx(q[j], q[s])
circuit.p(parameters[count], q[s])
if self._ladder:
for qubit in range(s, j, -1):
circuit.cx(q[qubit-1], q[qubit])
circuit.barrier(q[qubit-1], q[qubit])
else:
circuit.cx(q[j], q[s])
circuit.cx(q[r], q[j])
if self._ladder:
for qubit in range(r, i, -1):
circuit.cx(q[qubit-1], q[qubit])
circuit.barrier(q[qubit - 1], q[qubit])
else:
circuit.cx(q[i], q[r])
circuit.h(q[i])
circuit.h(q[r])
circuit.h(q[j])
circuit.h(q[s])
circuit.p(-parameters[count] / 2 + np.pi / 2, q[i])
circuit.p(-parameters[count] / 2 + np.pi, q[r])
else:
raise ValueError('Limited to single and double excitations, '
'higher order is not implemented')
count += 1
return circuit