def test_choi_rank_list_kraus():
"""Verify that a list of Kraus operators gives correct Choi rank"""
kraus_1 = np.array([[1, 0], [0, 0]])
kraus_2 = np.array([[1, 0], [0, 0]]).conj().T
kraus_3 = np.array([[0, 1], [0, 0]])
kraus_4 = np.array([[0, 1], [0, 0]]).conj().T
kraus_5 = np.array([[0, 0], [1, 0]])
kraus_6 = np.array([[0, 0], [1, 0]]).conj().T
kraus_7 = np.array([[0, 0], [0, 1]])
kraus_8 = np.array([[0, 0], [0, 1]]).conj().T
kraus_ops = [
[kraus_1, kraus_2],
[kraus_3, kraus_4],
[kraus_5, kraus_6],
[kraus_7, kraus_8],
]
np.testing.assert_equal(choi_rank(kraus_ops), 4)
def test_choi_bad_input():
"""Verify that a bad input (such as a string which still passes
with `numpy.linalg.matrix_rank`) raises an error"""
with pytest.raises(ValueError, match="Not a valid"):
bad_input = 'string'
choi_rank(bad_input)
def test_choi_rank_choi_matrix():
"""Verify Choi matrix of the swap operator map gives correct Choi rank."""
choi_matrix = np.array([[1, 0, 0, 0], [0, 0, 1, 0],
[0, 1, 0, 0], [0, 0, 0, 1]])
np.testing.assert_equal(choi_rank(choi_matrix), 4)