From 93e0b16ae363f7c9accfecaf9588c71cbc98f462 Mon Sep 17 00:00:00 2001 From: EG Date: Wed, 5 Jun 2024 13:07:11 +0000 Subject: [PATCH] Fix #6630: sort the qubits in the PauliStrings obtained by iterating on a PauliSum elements --- cirq-core/cirq/ops/linear_combinations.py | 2 +- .../cirq/ops/linear_combinations_test.py | 21 +++++++++++++++++++ 2 files changed, 22 insertions(+), 1 deletion(-) diff --git a/cirq-core/cirq/ops/linear_combinations.py b/cirq-core/cirq/ops/linear_combinations.py index ed223dfe0de..db7c471c2c3 100644 --- a/cirq-core/cirq/ops/linear_combinations.py +++ b/cirq-core/cirq/ops/linear_combinations.py @@ -354,7 +354,7 @@ def _is_linear_dict_of_unit_pauli_string(linear_dict: value.LinearDict[UnitPauli def _pauli_string_from_unit(unit: UnitPauliStringT, coefficient: Union[int, float, complex] = 1): - return PauliString(qubit_pauli_map=dict(unit), coefficient=coefficient) + return PauliString(qubit_pauli_map=dict(sorted(unit)), coefficient=coefficient) @value.value_equality(approximate=True, unhashable=True) diff --git a/cirq-core/cirq/ops/linear_combinations_test.py b/cirq-core/cirq/ops/linear_combinations_test.py index 24dfa0655c9..80a81ca6371 100644 --- a/cirq-core/cirq/ops/linear_combinations_test.py +++ b/cirq-core/cirq/ops/linear_combinations_test.py @@ -1173,6 +1173,27 @@ def test_pauli_sum_pow(): assert psum7copy == psum7 +def test_pauli_sum_consistent_qubit_order(): + for str_1, str_2 in [("XY", "YYZ"), ("YX", "ZYZ")]: + ps_1 = cirq.DensePauliString(str_1).on(q0, q1) + ps_2 = cirq.DensePauliString(str_2).on(q2, q1, q3) + # This is equivalent to ps_2, but with the qubits in ascending order. + # We expected the term of the sum to have the qubits in this order. + str_2_sorted = str_2[1] + str_2[0] + str_2[2] + ps_2_sorted = cirq.DensePauliString(str_2_sorted).on(q1, q2, q3) + + terms = list(cirq.PauliSum() + ps_1 + ps_2) + + assert terms[0].dense(terms[0].qubits) == ps_1.dense(ps_1.qubits) + assert terms[1].dense(terms[1].qubits) == ps_2_sorted.dense( + ps_2_sorted.qubits) + assert str(ps_1), str(terms[0]) + assert str(ps_2_sorted), str(terms[1]) + + assert np.allclose(cirq.unitary(ps_1), cirq.unitary(terms[0])) + assert np.allclose(cirq.unitary(ps_2_sorted), cirq.unitary(terms[1])) + + # Using the entries of table 1 of https://arxiv.org/abs/1804.09130 as golden values. @pytest.mark.parametrize( 'boolean_expr,expected_pauli_sum',