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Add circuit generation from set of stabilizers (Qiskit#11483)
* Add stabilizer_to_circuit function * Fix verification test * Mention `stabilizer_to_circuit` in `StabilizerState` documentation * * Add `from_stabilizer_list` function to Stabilizer state * Move to synthesis library and rename accordingly * Add pseudo-random tests * Fix docstrings * doc fixes * Allow any Collection and not just list, fix naming, tests, and docs accordingly. * typo * missed rename * Documentation fixes * fix indent * fix indent 2 * fix indent 3 * Rewrite using `Pauli` instead of string.
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# This code is part of Qiskit. | ||
# | ||
# (C) Copyright IBM 2024. | ||
# | ||
# 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. | ||
""" | ||
Stabilizer to circuit function | ||
""" | ||
from __future__ import annotations | ||
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from collections.abc import Collection | ||
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import numpy as np | ||
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from qiskit.quantum_info import PauliList | ||
from qiskit.exceptions import QiskitError | ||
from qiskit.circuit import QuantumCircuit | ||
from qiskit.quantum_info.operators.symplectic.clifford import Clifford | ||
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def synth_circuit_from_stabilizers( | ||
stabilizers: Collection[str], | ||
allow_redundant: bool = False, | ||
allow_underconstrained: bool = False, | ||
invert: bool = False, | ||
) -> QuantumCircuit: | ||
# pylint: disable=line-too-long | ||
"""Synthesis of a circuit that generates a state stabilized by the stabilziers | ||
using Gaussian elimination with Clifford gates. | ||
If the stabilizers are underconstrained, and `allow_underconstrained` is `True`, | ||
the circuit will output one of the states stabilized by the stabilizers. | ||
Based on stim implementation. | ||
Args: | ||
stabilizers (Collection[str]): list of stabilizer strings | ||
allow_redundant (bool): allow redundant stabilizers (i.e., some stabilizers | ||
can be products of the others) | ||
allow_underconstrained (bool): allow underconstrained set of stabilizers (i.e., | ||
the stabilizers do not specify a unique state) | ||
invert (bool): return inverse circuit | ||
Return: | ||
QuantumCircuit: a circuit that generates a state stabilized by `stabilizers`. | ||
Raises: | ||
QiskitError: if the stabilizers are invalid, do not commute, or contradict each other, | ||
if the list is underconstrained and `allow_underconstrained` is `False`, | ||
or if the list is redundant and `allow_redundant` is `False`. | ||
Reference: | ||
1. https://github.com/quantumlib/Stim/blob/c0dd0b1c8125b2096cd54b6f72884a459e47fe3e/src/stim/stabilizers/conversions.inl#L469 | ||
2. https://quantumcomputing.stackexchange.com/questions/12721/how-to-calculate-destabilizer-group-of-toric-and-other-codes | ||
""" | ||
stabilizer_list = PauliList(stabilizers) | ||
if np.any(stabilizer_list.phase % 2): | ||
raise QiskitError("Some stabilizers have an invalid phase") | ||
if len(stabilizer_list.commutes_with_all(stabilizer_list)) < len(stabilizer_list): | ||
raise QiskitError("Some stabilizers do not commute.") | ||
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num_qubits = stabilizer_list.num_qubits | ||
circuit = QuantumCircuit(num_qubits) | ||
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used = 0 | ||
for i in range(len(stabilizer_list)): | ||
curr_stab = stabilizer_list[i].evolve(Clifford(circuit), frame="s") | ||
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# Find pivot. | ||
pivot = used | ||
while pivot < num_qubits: | ||
if curr_stab[pivot].x or curr_stab[pivot].z: | ||
break | ||
pivot += 1 | ||
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if pivot == num_qubits: | ||
if curr_stab.x.any(): | ||
raise QiskitError( | ||
f"Stabilizer {i} ({stabilizer_list[i]}) anti-commutes with some of " | ||
"the previous stabilizers." | ||
) | ||
if curr_stab.phase == 2: | ||
raise QiskitError( | ||
f"Stabilizer {i} ({stabilizer_list[i]}) contradicts " | ||
"some of the previous stabilizers." | ||
) | ||
if curr_stab.z.any() and not allow_redundant: | ||
raise QiskitError( | ||
f"Stabilizer {i} ({stabilizer_list[i]}) is a product of the others " | ||
"and allow_redundant is False. Add allow_redundant=True " | ||
"to the function call if you want to allow redundant stabilizers." | ||
) | ||
continue | ||
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# Change pivot basis to the Z axis. | ||
if curr_stab[pivot].x: | ||
if curr_stab[pivot].z: | ||
circuit.h(pivot) | ||
circuit.s(pivot) | ||
circuit.h(pivot) | ||
circuit.s(pivot) | ||
circuit.s(pivot) | ||
else: | ||
circuit.h(pivot) | ||
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# Cancel other terms in Pauli string. | ||
for j in range(num_qubits): | ||
if j == pivot or not (curr_stab[j].x or curr_stab[j].z): | ||
continue | ||
p = curr_stab[j].x + curr_stab[j].z * 2 | ||
if p == 1: # X | ||
circuit.h(pivot) | ||
circuit.cx(pivot, j) | ||
circuit.h(pivot) | ||
elif p == 2: # Z | ||
circuit.cx(j, pivot) | ||
elif p == 3: # Y | ||
circuit.h(pivot) | ||
circuit.s(j) | ||
circuit.s(j) | ||
circuit.s(j) | ||
circuit.cx(pivot, j) | ||
circuit.h(pivot) | ||
circuit.s(j) | ||
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# Move pivot to diagonal. | ||
if pivot != used: | ||
circuit.swap(pivot, used) | ||
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# fix sign | ||
curr_stab = stabilizer_list[i].evolve(Clifford(circuit), frame="s") | ||
if curr_stab.phase == 2: | ||
circuit.x(used) | ||
used += 1 | ||
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if used < num_qubits and not allow_underconstrained: | ||
raise QiskitError( | ||
"Stabilizers are underconstrained and allow_underconstrained is False." | ||
" Add allow_underconstrained=True to the function call " | ||
"if you want to allow underconstrained stabilizers." | ||
) | ||
if invert: | ||
return circuit | ||
return circuit.inverse() |
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releasenotes/notes/add-synth-circuit-from-stabilizer-list-4cf9cfa01bbc7ddf.yaml
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--- | ||
features: | ||
- | | ||
Add :func:`qiskit.synthesis.synth_circuit_from_stabilizers` function that, given stabilizers, | ||
returns a circuit that outputs the state stabilized by the stabilizers. | ||
- | | ||
Add :meth:`qiskit.quantum_info.StabilizerState.from_stabilizer_list` method | ||
that generates a stabilizer state from a list of stabilizers:: | ||
from qiskit.quantum_info import StabilizerState | ||
stabilizer_list = ["ZXX", "-XYX", "+ZYY"] | ||
stab = StabilizerState.from_stabilizer_list(stabilizer_list) |
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