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Fixed Issue 11026: SparsePauliOp.apply_layout should do nothing if given None #11041

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merged 7 commits into from
Nov 16, 2023
Merged

Fixed Issue 11026: SparsePauliOp.apply_layout should do nothing if given None #11041

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44be93c
fixed issue 11026 by adding condition in apply_layout and implemented…
SoranaAurelia Oct 18, 2023
1ade800
fixed formatting
SoranaAurelia Oct 18, 2023
58e0853
Merge branch 'main' into issue_11026_sparse_pauli_op
SoranaAurelia Oct 28, 2023
8bfb176
added expansion of operator if num_qubits is provided and added tests
SoranaAurelia Nov 6, 2023
3c2f8bc
fixed finding
SoranaAurelia Nov 14, 2023
532f156
Merge branch 'main' of qiskit into issue_11026_sparse_pauli_op
SoranaAurelia Nov 14, 2023
493a072
added release note
SoranaAurelia Nov 14, 2023
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8 changes: 6 additions & 2 deletions qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1109,12 +1109,13 @@ def assign_parameters(
return None if inplace else bound

def apply_layout(
self, layout: TranspileLayout | List[int], num_qubits: int | None = None
self, layout: TranspileLayout | List[int] | None, num_qubits: int | None = None
) -> SparsePauliOp:
"""Apply a transpiler layout to this :class:`~.SparsePauliOp`

Args:
layout: Either a :class:`~.TranspileLayout` or a list of integers.
layout: Either a :class:`~.TranspileLayout`, a list of integers or None.
If layout is None, then no action is applied.
num_qubits: The number of qubits to expand the operator to. If not
provided then if ``layout`` is a :class:`~.TranspileLayout` the
number of the transpiler output circuit qubits will be used by
Expand All @@ -1127,6 +1128,9 @@ def apply_layout(
"""
from qiskit.transpiler.layout import TranspileLayout

if layout is None:
return self.copy()

n_qubits = self.num_qubits
if isinstance(layout, TranspileLayout):
n_qubits = len(layout._output_qubit_list)
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6 changes: 6 additions & 0 deletions test/python/quantum_info/operators/symplectic/test_sparse_pauli_op.py
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Expand Up @@ -1088,6 +1088,12 @@ def test_apply_layout_layout_list_and_num_qubits(self):
res = op.apply_layout([4, 0], 5)
self.assertEqual(SparsePauliOp.from_list([("IIIIY", 2), ("IIIIX", 1)]), res)

def test_apply_layout_null_layout(self):
"""Test apply_layout with a null layout"""
op = SparsePauliOp.from_list([("II", 1), ("IZ", 2), ("XI", 3)])
res = op.apply_layout(layout=None, num_qubits=5)
self.assertEqual(op, res)
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This test looks odd to me: it specifically asks for num_qubits=5, but the output operator then asserted to be 2q (by comparison to the input op, which is 2q). Certainly I think that that should be invalid, but it's not clear to me whether it should be an error during SparsePauliOp.apply_layout, or whether that method should do something to expand the operator. I expect it should be an error, but I've opened a discussion in the initial thread: #11026 (comment)



if __name__ == "__main__":
unittest.main()