def rz_angles_before(self) -> tuple[cirq.TParamVal, cirq.TParamVal]:
        """Returns 2-tuple of phase angles applied to qubits before FSimGate."""
        b0 = (-self.gamma + self.zeta + self.chi) / 2.0
        b1 = (-self.gamma - self.zeta - self.chi) / 2.0
        return b0, b1
Returns 2-tuple of phase angles applied to qubits before FSimGate.
cirq-core/cirq/ops/fsim_gate.py