/
linear_pauli_rotations.py
189 lines (146 loc) · 6.73 KB
/
linear_pauli_rotations.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 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.
"""Linearly-controlled X, Y or Z rotation."""
from typing import Optional
from qiskit.circuit import QuantumRegister, QuantumCircuit
from qiskit.circuit.exceptions import CircuitError
from .functional_pauli_rotations import FunctionalPauliRotations
class LinearPauliRotations(FunctionalPauliRotations):
r"""Linearly-controlled X, Y or Z rotation.
For a register of state qubits :math:`|x\rangle`, a target qubit :math:`|0\rangle` and the
basis ``'Y'`` this circuit acts as:
.. parsed-literal::
q_0: ─────────────────────────■───────── ... ──────────────────────
│
.
│
q_(n-1): ─────────────────────────┼───────── ... ───────────■──────────
┌────────────┐ ┌───────┴───────┐ ┌─────────┴─────────┐
q_n: ─┤ RY(offset) ├──┤ RY(2^0 slope) ├ ... ┤ RY(2^(n-1) slope) ├
└────────────┘ └───────────────┘ └───────────────────┘
This can for example be used to approximate linear functions, with :math:`a =` ``slope``:math:`/2`
and :math:`b =` ``offset``:math:`/2` and the basis ``'Y'``:
.. math::
|x\rangle |0\rangle \mapsto \cos(ax + b)|x\rangle|0\rangle + \sin(ax + b)|x\rangle |1\rangle
Since for small arguments :math:`\sin(x) \approx x` this operator can be used to approximate
linear functions.
"""
def __init__(
self,
num_state_qubits: Optional[int] = None,
slope: float = 1,
offset: float = 0,
basis: str = "Y",
name: str = "LinRot",
) -> None:
r"""Create a new linear rotation circuit.
Args:
num_state_qubits: The number of qubits representing the state :math:`|x\rangle`.
slope: The slope of the controlled rotation.
offset: The offset of the controlled rotation.
basis: The type of Pauli rotation ('X', 'Y', 'Z').
name: The name of the circuit object.
"""
super().__init__(num_state_qubits=num_state_qubits, basis=basis, name=name)
# define internal parameters
self._slope = None
self._offset = None
# store parameters
self.slope = slope
self.offset = offset
@property
def slope(self) -> float:
"""The multiplicative factor in the rotation angle of the controlled rotations.
The rotation angles are ``slope * 2^0``, ``slope * 2^1``, ... , ``slope * 2^(n-1)`` where
``n`` is the number of state qubits.
Returns:
The rotation angle common in all controlled rotations.
"""
return self._slope
@slope.setter
def slope(self, slope: float) -> None:
"""Set the multiplicative factor of the rotation angles.
Args:
The slope of the rotation angles.
"""
if self._slope is None or slope != self._slope:
self._invalidate()
self._slope = slope
@property
def offset(self) -> float:
"""The angle of the single qubit offset rotation on the target qubit.
Before applying the controlled rotations, a single rotation of angle ``offset`` is
applied to the target qubit.
Returns:
The offset angle.
"""
return self._offset
@offset.setter
def offset(self, offset: float) -> None:
"""Set the angle for the offset rotation on the target qubit.
Args:
offset: The offset rotation angle.
"""
if self._offset is None or offset != self._offset:
self._invalidate()
self._offset = offset
def _reset_registers(self, num_state_qubits: Optional[int]) -> None:
"""Set the number of state qubits.
Note that this changes the underlying quantum register, if the number of state qubits
changes.
Args:
num_state_qubits: The new number of qubits.
"""
self.qregs = []
if num_state_qubits:
# set new register of appropriate size
qr_state = QuantumRegister(num_state_qubits, name="state")
qr_target = QuantumRegister(1, name="target")
self.qregs = [qr_state, qr_target]
def _check_configuration(self, raise_on_failure: bool = True) -> bool:
"""Check if the current configuration is valid."""
valid = True
if self.num_state_qubits is None:
valid = False
if raise_on_failure:
raise AttributeError("The number of qubits has not been set.")
if self.num_qubits < self.num_state_qubits + 1:
valid = False
if raise_on_failure:
raise CircuitError(
"Not enough qubits in the circuit, need at least "
"{}.".format(self.num_state_qubits + 1)
)
return valid
def _build(self):
"""If not already built, build the circuit."""
if self._is_built:
return
super()._build()
circuit = QuantumCircuit(*self.qregs, name=self.name)
# build the circuit
qr_state = self.qubits[: self.num_state_qubits]
qr_target = self.qubits[self.num_state_qubits]
if self.basis == "x":
circuit.rx(self.offset, qr_target)
elif self.basis == "y":
circuit.ry(self.offset, qr_target)
else: # 'Z':
circuit.rz(self.offset, qr_target)
for i, q_i in enumerate(qr_state):
if self.basis == "x":
circuit.crx(self.slope * pow(2, i), q_i, qr_target)
elif self.basis == "y":
circuit.cry(self.slope * pow(2, i), q_i, qr_target)
else: # 'Z'
circuit.crz(self.slope * pow(2, i), q_i, qr_target)
self.append(circuit.to_gate(), self.qubits)