def taper(self, operator: PauliSumOp) -> OperatorBase:
"""
Taper an operator based on the z2_symmetries info and sector defined by `tapering_values`.
The `tapering_values` will be stored into the resulted operator for a record.
Args:
operator: the to-be-tapered operator.
Returns:
If tapering_values is None: [:class`PauliSumOp`]; otherwise, :class:`PauliSumOp`
Raises:
OpflowError: Z2 symmetries, single qubit pauli and single qubit list cannot be empty
"""
if not self._symmetries or not self._sq_paulis or not self._sq_list:
raise OpflowError(
"Z2 symmetries, single qubit pauli and " "single qubit list cannot be empty."
)
if operator.is_zero():
logger.warning("The operator is empty, return the empty operator directly.")
return operator
for clifford in self.cliffords:
operator = cast(PauliSumOp, clifford @ operator @ clifford)
if self._tapering_values is None:
tapered_ops_list = [
self._taper(operator, list(coeff))
for coeff in itertools.product([1, -1], repeat=len(self._sq_list))
]
tapered_ops: OperatorBase = ListOp(tapered_ops_list)
else:
tapered_ops = self._taper(operator, self._tapering_values)
return tapered_ops
def taper(self, operator: PauliSumOp) -> OperatorBase:
"""
Taper an operator based on the z2_symmetries info and sector defined by `tapering_values`.
The `tapering_values` will be stored into the resulted operator for a record.
Args:
operator: the to-be-tapered operator.
Returns:
If tapering_values is None: [:class`PauliSumOp`]; otherwise, :class:`PauliSumOp`
Raises:
OpflowError: Z2 symmetries, single qubit pauli and single qubit list cannot be empty
"""
if not self._symmetries or not self._sq_paulis or not self._sq_list:
raise OpflowError(
"Z2 symmetries, single qubit pauli and single qubit list cannot be empty."
)
# If the operator is zero then we can skip the following. We still need to taper the
# operator to reduce its size i.e. the number of qubits so for example 0*"IIII" could
# taper to 0*"II" when symmetries remove two qubits.
if not operator.is_zero():
for clifford in self.cliffords:
operator = cast(PauliSumOp, clifford @ operator @ clifford)
if self._tapering_values is None:
tapered_ops_list = [
self._taper(operator, list(coeff))
for coeff in itertools.product([1, -1], repeat=len(self._sq_list))
]
tapered_ops: OperatorBase = ListOp(tapered_ops_list)
else:
tapered_ops = self._taper(operator, self._tapering_values)
return tapered_ops