def test_three_qubit_depolarizing_representation_error():
q0, q1, q2 = LineQubit.range(3)
with pytest.raises(ValueError):
represent_operation_with_global_depolarizing_noise(
Circuit(CCNOT(q0, q1, q2)),
0.05,
)
def test_two_qubit_representation_norm(gate: Gate, noise: float):
qreg = LineQubit.range(2)
optimal_norm = two_qubit_depolarizing_overhead(noise)
norm = represent_operation_with_global_depolarizing_noise(
Circuit(gate(*qreg)), noise,
).norm
assert np.isclose(optimal_norm, norm)
def test_single_qubit_representation_norm(gate: Gate, noise: float):
q = LineQubit(0)
optimal_norm = single_qubit_depolarizing_overhead(noise)
norm = represent_operation_with_global_depolarizing_noise(
Circuit(gate(q)), noise,
).norm
assert np.isclose(optimal_norm, norm)
def test_depolarizing_representation_with_choi(gate: Gate, noise: float):
"""Tests the representation by comparing exact Choi matrices."""
qreg = LineQubit.range(gate.num_qubits())
ideal_choi = _operation_to_choi(gate.on(*qreg))
op_rep = represent_operation_with_global_depolarizing_noise(
Circuit(gate.on(*qreg)), noise,
)
choi_components = []
for noisy_op, coeff in op_rep.basis_expansion.items():
implementable_circ = noisy_op.circuit()
# Apply noise after each sequence.
# NOTE: noise is not applied after each operation.
depolarizing_op = DepolarizingChannel(noise, len(qreg))(*qreg)
implementable_circ.append(depolarizing_op)
sequence_choi = _circuit_to_choi(implementable_circ)
choi_components.append(coeff * sequence_choi)
combination_choi = np.sum(choi_components, axis=0)
assert np.allclose(ideal_choi, combination_choi, atol=10 ** -6)
