def _strat_commutes_from_operation(
v1: Any,
v2: Any,
*,
atol: float,
) -> Union[bool, NotImplementedType, None]:
if not isinstance(v1, ops.Operation) or not isinstance(v2, ops.Operation):
return NotImplemented
if set(v1.qubits).isdisjoint(v2.qubits):
return True
from cirq import circuits
circuit12 = circuits.Circuit(v1, v2)
circuit21 = circuits.Circuit(v2, v1)
# Don't create gigantic matrices.
if np.product(qid_shape_protocol.qid_shape(circuit12)) > 2**10:
return NotImplemented # coverage: ignore
m12 = unitary_protocol.unitary(circuit12, default=None)
m21 = unitary_protocol.unitary(circuit21, default=None)
if m12 is None:
return NotImplemented
return np.allclose(m12, m21, atol=atol)
def pauli_expansion(
val: Any,
*,
default: Union[value.LinearDict[str],
TDefault] = RaiseTypeErrorIfNotProvided,
atol: float = 1e-9,
) -> Union[value.LinearDict[str], TDefault]:
"""Returns coefficients of the expansion of val in the Pauli basis.
Args:
val: The value whose Pauli expansion is to returned.
default: Determines what happens when `val` does not have methods that
allow Pauli expansion to be obtained (see below). If set, the value
is returned in that case. Otherwise, TypeError is raised.
atol: Ignore coefficients whose absolute value is smaller than this.
Returns:
If `val` has a _pauli_expansion_ method, then its result is returned.
Otherwise, if `val` has a small unitary then that unitary is expanded
in the Pauli basis and coefficients are returned. Otherwise, if default
is set to None or other value then default is returned. Otherwise,
TypeError is raised.
Raises:
TypeError: If `val` has none of the methods necessary to obtain its Pauli
expansion and no default value has been provided.
"""
method = getattr(val, '_pauli_expansion_', None)
expansion = NotImplemented if method is None else method()
if expansion is not NotImplemented:
return expansion.clean(atol=atol)
# Don't attempt to derive the pauli expansion if this is a qudit gate
if not all(d == 2 for d in qid_shape_protocol.qid_shape(val, default=())):
if default is RaiseTypeErrorIfNotProvided:
raise TypeError(
f'No Pauli expansion for object {val} of type {type(val)}')
return default
matrix = unitary_protocol.unitary(val, default=None)
if matrix is None:
if default is RaiseTypeErrorIfNotProvided:
raise TypeError(
f'No Pauli expansion for object {val} of type {type(val)}')
return default
num_qubits = matrix.shape[0].bit_length() - 1
basis = operator_spaces.kron_bases(operator_spaces.PAULI_BASIS,
repeat=num_qubits)
expansion = operator_spaces.expand_matrix_in_orthogonal_basis(
matrix, basis)
return expansion.clean(atol=atol)
def _strat_distance_from_unitary(val: Any) -> Optional[float]:
"""Attempts to compute a value's trace_distance_bound from its unitary."""
u = unitary_protocol.unitary(val, default=None)
if u is None:
return NotImplemented
if u.shape == (2, 2):
squared = 1 - (0.5 * abs(u[0][0] + u[1][1]))**2
if squared <= 0:
return 0.0
return squared**0.5
return trace_distance_from_angle_list(np.angle(np.linalg.eigvals(u)))