def __rpow__(self, base):
if isinstance(base, (int, float)) and base > 0:
if abs(self.coefficient.real) > 0.0001:
raise NotImplementedError(
'Exponentiated to a non-Hermitian PauliString '
f'<{base}**{self}>. Coefficient must be imaginary.')
half_turns = 2 * math.log(base) * (-self.coefficient.imag /
math.pi)
if len(self) == 1:
q, p = next(iter(self.items()))
gates = {
pauli_gates.X: common_gates.XPowGate,
pauli_gates.Y: common_gates.YPowGate,
pauli_gates.Z: common_gates.ZPowGate,
}
return gates[p](exponent=half_turns, global_shift=-0.5).on(q)
# HACK: Avoid circular dependency.
from cirq.ops import pauli_string_phasor
return pauli_string_phasor.PauliStringPhasor(
PauliString(qubit_pauli_map=self._qubit_pauli_map),
exponent_neg=+half_turns / 4,
exponent_pos=-half_turns / 4)
return NotImplemented
def __pow__(self, power):
if power == 1:
return self
if power == -1:
return PauliString(qubit_pauli_map=self._qubit_pauli_map,
coefficient=self.coefficient**-1)
if isinstance(power, (int, float)):
r, i = cmath.polar(self.coefficient)
if abs(r - 1) > 0.0001:
# Raising non-unitary PauliStrings to a power is not supported.
return NotImplemented
if len(self) == 1:
q, p = next(iter(self.items()))
gates = {
pauli_gates.X: common_gates.XPowGate,
pauli_gates.Y: common_gates.YPowGate,
pauli_gates.Z: common_gates.ZPowGate,
}
return gates[p](exponent=power).on(q)
global_half_turns = power * (i / math.pi)
# HACK: Avoid circular dependency.
from cirq.ops import pauli_string_phasor
return pauli_string_phasor.PauliStringPhasor(
PauliString(qubit_pauli_map=self._qubit_pauli_map),
exponent_neg=global_half_turns + power,
exponent_pos=global_half_turns)
return NotImplemented
def __iter__(self) -> Iterator['cirq.PauliStringPhasor']:
for pauli_string in self._pauli_sum:
theta = pauli_string.coefficient * self._multiplier
theta *= self._exponent / np.pi
if isinstance(theta, complex):
theta = theta.real
yield pauli_string_phasor.PauliStringPhasor(
pauli_string.with_coefficient(1.0), exponent_neg=-theta, exponent_pos=theta
)
def _decompose_(self):
# HACK: Avoid circular dependency.
from cirq.ops import pauli_string_phasor
return pauli_string_phasor.PauliStringPhasor(self)._decompose_()