def test_execute_with_pec_with_different_samples(circuit: Circuit, seed):
"""Tests that, on average, the error decreases as the number of samples is
increased.
"""
errors_few_samples = []
errors_more_samples = []
for _ in range(10):
mitigated = execute_with_pec(
circuit,
executor,
decomposition_dict=DECO_DICT,
num_samples=10,
random_state=seed,
)
errors_few_samples.append(abs(mitigated - 1.0))
mitigated = execute_with_pec(
circuit,
executor,
decomposition_dict=DECO_DICT,
num_samples=100,
random_state=seed,
)
errors_more_samples.append(abs(mitigated - 1.0))
assert np.average(errors_more_samples) < np.average(errors_few_samples)
def test_precision_option_in_execute_with_pec(precision: float):
"""Tests that the 'precision' argument is used to deduce num_samples."""
rnd_state = np.random.RandomState(0)
def fake_exec(circuit: Circuit):
"""A fake executor which just samples from a normal distribution."""
return rnd_state.randn()
# For a noiseless circuit we expect num_samples = 1/precision^2:
_, pec_error = execute_with_pec(
oneq_circ,
fake_exec,
NOISELESS_DECO_DICT,
precision=precision,
full_output=True,
)
# The error should scale as precision
assert np.isclose(pec_error / precision, 1.0, atol=0.1)
# If num_samples is given, precision is ignored.
_, pec_error = execute_with_pec(
oneq_circ,
fake_exec,
NOISELESS_DECO_DICT,
precision=precision,
num_samples=1000,
full_output=True,
)
# The error should scale as 1/sqrt(num_samples)
assert not np.isclose(pec_error / precision, 1.0, atol=0.1)
assert np.isclose(pec_error * np.sqrt(1000), 1.0, atol=0.1)
def test_large_sample_size_warning(num_samples: int):
"""Tests whether a warning is raised when PEC sample size
is greater than 10 ** 5
"""
rnd_state = np.random.RandomState(0)
def fake_exec(circuit: Circuit):
"""A fake executor which just samples from a normal distribution."""
return rnd_state.randn()
with warns(LargeSampleWarning,
match=r"The number of PEC samples is very large."):
execute_with_pec(oneq_circ,
fake_exec,
DECO_DICT,
num_samples=num_samples)
def test_execute_with_pec_with_full_output():
"""Tests that the error associated to the PEC value is returned if
the option 'full_output' is set to True.
"""
rnd_state = np.random.RandomState(0)
def fake_exec(circuit: Circuit):
"""A fake executor which just samples from a normal distribution."""
return rnd_state.randn()
_, error_few_samples = execute_with_pec(
oneq_circ, fake_exec, DECO_DICT, num_samples=100, full_output=True
)
_, error_many_samples = execute_with_pec(
oneq_circ, fake_exec, DECO_DICT, num_samples=1000, full_output=True
)
# The error should scale as 1/sqrt(num_samples)
assert np.isclose(error_few_samples * np.sqrt(100), 1.0, atol=0.1)
assert np.isclose(error_many_samples * np.sqrt(1000), 1.0, atol=0.1)
def test_execute_with_pec_one_qubit(circuit: Circuit,
decomposition_dict: DecompositionDict):
"""Tests that execute_with_pec mitigates the error of a noisy
expectation value.
"""
unmitigated = executor(circuit)
mitigated = execute_with_pec(circuit,
executor,
decomposition_dict=decomposition_dict)
error_unmitigated = abs(unmitigated - 1.0)
error_mitigated = abs(mitigated - 1.0)
# For a trivial noiseless decomposition no PEC mitigation should happen
if decomposition_dict == NOISELESS_DECO_DICT:
assert np.isclose(unmitigated, mitigated)
else:
assert error_mitigated < error_unmitigated
assert np.isclose(mitigated, 1.0, atol=0.1)
def test_bad_precision_argument(bad_value: float):
"""Tests that if 'precision' is not within (0, 1] an error is raised."""
with raises(ValueError, match="The value of 'precision' should"):
execute_with_pec(oneq_circ, executor, DECO_DICT, precision=bad_value)