# Copyright 2021 Huawei Technologies Co., Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ============================================================================
"""General W State."""
import numpy as np
from mindquantum.core.circuit import Circuit
from mindquantum.core.gates import RY, X
from mindquantum.utils.type_value_check import _check_input_type
[文档]def general_w_state(qubits):
r"""
General W State.
The W State is defined as the equality superposition of bases that only one qubit is in :math:`\left|1\right>`
while others qubits are in :math:`\left|0\right>`. For example, a three qubits W state is defined as:
.. math::
\left|\rm W\right> = (\left|001\right> + \left|010\right> + \left|100\right>)/\sqrt(3)
Here in this API, we can define a W state on any sub hilbert space of any total number qubits.
Note:
Please refer to https://quantumcomputing.stackexchange.com/questions/4350/general-construction-of-w-n-state.
Args:
qubits (list[int]): Qubits you want to apply general W state.
Examples:
>>> from mindquantum.algorithm.library import general_w_state
>>> print(general_w_state(range(3)).get_qs(ket=True))
0.5773502691896257¦001⟩
0.5773502691896258¦010⟩
0.5773502691896257¦100⟩
Returns:
Circuit, circuit that can prepare w state.
"""
_check_input_type('qubits', (list, range), qubits)
circuit = Circuit()
for i in range(len(qubits) - 1):
angle_val = 2 * np.arccos(np.sqrt(1 / (len(qubits) - i)))
if i == 0:
circuit += RY(angle_val).on(qubits[i])
else:
circuit += RY(angle_val).on(qubits[i], qubits[i - 1])
for j in reversed(range(len(qubits) - 1)):
circuit += X.on(qubits[j + 1], qubits[j])
if j == 0:
circuit += X.on(qubits[j])
return circuit