def test_choi_to_kraus_fixed_values(choi, expected_kraus):
"""Verifies that cirq.choi_to_kraus gives correct results on a few fixed inputs."""
actual_kraus = cirq.choi_to_kraus(choi)
assert len(actual_kraus) == len(expected_kraus)
for i in (0, 1):
for j in (0, 1):
input_rho = np.zeros((2, 2))
input_rho[i, j] = 1
actual_rho = apply_kraus_operators(actual_kraus, input_rho)
expected_rho = apply_kraus_operators(expected_kraus, input_rho)
assert np.allclose(actual_rho, expected_rho)
def test_choi_to_kraus_action_on_operatorial_basis(choi):
"""Verifies that cirq.choi_to_kraus computes a valid Kraus representation."""
kraus_operators = cirq.choi_to_kraus(choi)
c = np.reshape(choi, (2, 2, 2, 2))
for i in (0, 1):
for j in (0, 1):
input_rho = np.zeros((2, 2))
input_rho[i, j] = 1
actual_rho = apply_kraus_operators(kraus_operators, input_rho)
expected_rho = c[:, i, :, j]
assert np.allclose(actual_rho, expected_rho)
def test_choi_to_kraus_atol():
"""Verifies that insignificant Kraus operators are omitted."""
choi = cirq.kraus_to_choi(cirq.kraus(cirq.phase_damp(1e-6)))
assert len(cirq.choi_to_kraus(choi, atol=1e-2)) == 1
assert len(cirq.choi_to_kraus(choi, atol=1e-4)) == 2
def test_choi_to_kraus_inverse_of_kraus_to_choi(choi):
"""Verifies that cirq.kraus_to_choi(cirq.choi_to_kraus(.)) is identity on Choi matrices."""
kraus = cirq.choi_to_kraus(choi)
recovered_choi = cirq.kraus_to_choi(kraus)
assert np.allclose(recovered_choi, choi)
def test_choi_to_kraus_invalid_input(choi, error):
with pytest.raises(ValueError, match=error):
_ = cirq.choi_to_kraus(choi)
