code: def _layer6(weight, s, r, q, p, set_cnot_wires):
      r"""Implement the sixth layer of the circuit to exponentiate the double-excitation
      operator entering the UCCSD ansatz.
  
      .. math::
  
          \hat{U}_{pqrs}^{(6)}(\theta) = \mathrm{exp} \Big\{ -\frac{i\theta}{8}
          \bigotimes_{b=s+1}^{r-1} \hat{Z}_b \bigotimes_{a=q+1}^{p-1} \hat{Z}_a
          (\hat{X}_s \hat{Y}_r \hat{X}_q \hat{X}_p) \Big\}
  
      Args:
          weight (float): angle :math:`\theta` entering the Z rotation acting on wire ``p``
          s (int): qubit index ``s``
          r (int): qubit index ``r``
          q (int): qubit index ``q``
          p (int): qubit index ``p``
          set_cnot_wires (list[Wires]): list of CNOT wires
  
      Returns:
          list[.Operator]: sequence of operators defined by this function
      """
      # U_1, U_2, U_3, U_4 acting on wires 's', 'r', 'q' and 'p'
      op_list = [
          Hadamard(wires=s),
          RX(-np.pi / 2, wires=r),
          Hadamard(wires=q),
          Hadamard(wires=p),
      ]
  
      # Applying CNOTs
      for cnot_wires in set_cnot_wires:
          op_list.append(CNOT(wires=cnot_wires))
  
      # Z rotation acting on wire 'p'
      op_list.append(RZ(-weight / 8, wires=p))
  
      # Applying CNOTs in reverse order
      for cnot_wires in reversed(set_cnot_wires):
          op_list.append(CNOT(wires=cnot_wires))
  
      # U_1^+, U_2^+, U_3^+, U_4^+ acting on wires 's', 'r', 'q' and 'p'
      op_list.append(Hadamard(wires=s))
      op_list.append(RX(np.pi / 2, wires=r))
      op_list.append(Hadamard(wires=q))
      op_list.append(Hadamard(wires=p))
      return op_list
  
file_path: pennylane/pennylane/templates/subroutines/fermionic_double_excitation.py
imports: import numpy
  import pennylane
  from pennylane.operation import Operation, AnyWires
  from pennylane.ops import RZ, RX, CNOT, Hadamard
label_desc: Use image node_id 6 for calling a global function with example usage: _layer6(weight, s, r, q, p, set_cnot_wires) and returns: op_list