def assert_act_on_clifford_tableau_effect_matches_unitary(val: Any) -> None:
"""Checks that act_on with CliffordTableau generates stabilizers that
stabilize the final state vector. Does not work with Operations or Gates
expecting non-qubit Qids."""
# pylint: disable=unused-variable
__tracebackhide__ = True
# pylint: enable=unused-variable
num_qubits_val = protocols.num_qubits(val)
if not protocols.has_unitary(val) or \
protocols.qid_shape(val) != (2,) * num_qubits_val:
return None
qubits = LineQubit.range(protocols.num_qubits(val) * 2)
qubit_map = {qubit: i for i, qubit in enumerate(qubits)}
circuit = Circuit()
for i in range(num_qubits_val):
circuit.append([
common_gates.H(qubits[i]),
common_gates.CNOT(qubits[i], qubits[-i - 1])
])
if hasattr(val, "on"):
circuit.append(val.on(*qubits[:num_qubits_val]))
else:
circuit.append(val.with_qubits(*qubits[:num_qubits_val]))
tableau = _final_clifford_tableau(circuit, qubit_map)
if tableau is None:
return None
state_vector = np.reshape(final_state_vector(circuit, qubit_order=qubits),
protocols.qid_shape(qubits))
assert all(
state_vector_has_stabilizer(state_vector, stab)
for stab in tableau.stabilizers()), (
"act_on clifford tableau is not consistent with "
"final_state_vector simulation.\n\nval: {!r}".format(val))
def xeb_fidelity(
circuit: Circuit,
bitstrings: Sequence[int],
qubit_order: QubitOrderOrList = QubitOrder.DEFAULT,
amplitudes: Optional[Mapping[int, complex]] = None,
estimator: Callable[[int, Sequence[float]],
float] = linear_xeb_fidelity_from_probabilities,
) -> float:
"""Estimates XEB fidelity from one circuit using user-supplied estimator.
Fidelity quantifies the similarity of two quantum states. Here, we estimate
the fidelity between the theoretically predicted output state of circuit and
the state produced in its experimental realization. Note that we don't know
the latter state. Nevertheless, we can estimate the fidelity between the two
states from the knowledge of the bitstrings observed in the experiment.
In order to make the estimate more robust one should average the estimates
over many random circuits. The API supports per-circuit fidelity estimation
to enable users to examine the properties of estimate distribution over
many circuits.
See https://arxiv.org/abs/1608.00263 for more details.
Args:
circuit: Random quantum circuit which has been executed on quantum
processor under test.
bitstrings: Results of terminal all-qubit measurements performed after
each circuit execution as integer array where each integer is
formed from measured qubit values according to `qubit_order` from
most to least significant qubit, i.e. in the order consistent with
`cirq.final_state_vector`.
qubit_order: Qubit order used to construct bitstrings enumerating
qubits starting with the most significant qubit.
amplitudes: Optional mapping from bitstring to output amplitude.
If provided, simulation is skipped. Useful for large circuits
when an offline simulation had already been performed.
estimator: Fidelity estimator to use, see above. Defaults to the
linear XEB fidelity estimator.
Returns:
Estimate of fidelity associated with an experimental realization of
circuit which yielded measurements in bitstrings.
Raises:
ValueError: Circuit is inconsistent with qubit order or one of the
bitstrings is inconsistent with the number of qubits.
"""
dim = np.prod(circuit.qid_shape(), dtype=np.int64)
if isinstance(bitstrings, tuple):
bitstrings = list(bitstrings)
for bitstring in bitstrings:
if not 0 <= bitstring < dim:
raise ValueError(
f'Bitstring {bitstring} could not have been observed '
f'on {len(circuit.qid_shape())} qubits.')
if amplitudes is None:
output_state = final_state_vector(circuit, qubit_order=qubit_order)
output_probabilities = state_vector_to_probabilities(output_state)
bitstring_probabilities = output_probabilities[bitstrings]
else:
bitstring_probabilities = np.abs(
[amplitudes[bitstring] for bitstring in bitstrings])**2
return estimator(dim, bitstring_probabilities)
def assert_all_implemented_act_on_effects_match_unitary(
val: Any,
assert_tableau_implemented: bool = False,
assert_ch_form_implemented: bool = False) -> None:
"""Uses val's effect on final_state_vector to check act_on(val)'s behavior.
Checks that act_on with CliffordTableau or StabilizerStateCHForm behaves
consistently with act_on through final state vector. Does not work with
Operations or Gates expecting non-qubit Qids. If either of the
assert_*_implmented args is true, fails if the corresponding method is not
implemented for the test circuit.
Args:
val: A gate or operation that may be an input to protocols.act_on.
assert_tableau_implemented: asserts that protocols.act_on() works with
val and ActOnCliffordTableauArgs inputs.
assert_ch_form_implemented: asserts that protocols.act_on() works with
val and ActOnStabilizerStateChFormArgs inputs.
"""
# pylint: disable=unused-variable
__tracebackhide__ = True
# pylint: enable=unused-variable
num_qubits_val = protocols.num_qubits(val)
if (protocols.is_parameterized(val) or not protocols.has_unitary(val)
or protocols.qid_shape(val) != (2, ) * num_qubits_val):
if assert_tableau_implemented or assert_ch_form_implemented:
assert False, ("Could not assert if any act_on methods were "
"implemented. Operating on qudits or with a "
"non-unitary or parameterized operation is "
"unsupported.\n\nval: {!r}".format(val))
return None
qubits = LineQubit.range(protocols.num_qubits(val) * 2)
qubit_map = {qubit: i for i, qubit in enumerate(qubits)}
circuit = Circuit()
for i in range(num_qubits_val):
circuit.append([
common_gates.H(qubits[i]),
common_gates.CNOT(qubits[i], qubits[-i - 1])
])
if hasattr(val, "on"):
circuit.append(val.on(*qubits[:num_qubits_val]))
else:
circuit.append(val.with_qubits(*qubits[:num_qubits_val]))
state_vector = np.reshape(final_state_vector(circuit, qubit_order=qubits),
protocols.qid_shape(qubits))
tableau = _final_clifford_tableau(circuit, qubit_map)
if tableau is None:
assert (
not assert_tableau_implemented
), "Failed to generate final tableau for the test circuit.\n\nval: {!r}".format(
val)
else:
assert all(
state_vector_has_stabilizer(state_vector, stab)
for stab in tableau.stabilizers()), (
"act_on clifford tableau is not consistent with "
"final_state_vector simulation.\n\nval: {!r}".format(val))
stabilizer_ch_form = _final_stabilizer_state_ch_form(circuit, qubit_map)
if stabilizer_ch_form is None:
assert not assert_ch_form_implemented, ("Failed to generate final "
"stabilizer state CH form "
"for the test circuit."
"\n\nval: {!r}".format(val))
else:
np.testing.assert_allclose(
np.reshape(stabilizer_ch_form.state_vector(),
protocols.qid_shape(qubits)),
state_vector,
atol=1e-07,
err_msg=
f"stabilizer_ch_form.state_vector disagrees with state_vector for {val!r}",
verbose=True,
)
